k' M K \ * \ * ) Division of Agricultural Sciences UNIVERSITY OF CALIFORNIA FURROW IRRIGATION James C. Marr CALIFORNIA AGRICULTURAL Experiment Station MANUAL 37 Price $ 2 .00 November, 1967 The Author: James C. Marr is Irrigation Specialist, Experiment Station (retired) at Davis. THIS MANUAL is one of a series published by the University of California College of Agri- culture and sold for a charge which is based upon returning only a portion of the production cost. By this means it is possible to make available publications which, due to relatively high cost of production, or limited audience, would otherwise be beyond the scope of the College publishing program. FURROW IRRIGATION The different irrigation methods are shown in this schematic tree representing the three principal forms of irrigation in the American West. The smallest main branch stands for the limited practice of subsurface irrigation (6, 10, 14, 34); and the larger branch for sprink- lers (31, 36). The upper main trunk represents surface irrigation (29), with two large branches — flood (3, 22) and furrow (28) irrigation. This manual deals specifically with furrow irrigation. Its first section discusses the principles of furrow irrigation, and will be useful for those who want to irrigate as simply and economically as possible, but also for those who want to conserve water because of scarcity, high cost, or their concern with the needs of the future. The second through the sixth sections discuss the main systems of furrow irri- gation and their differing uses. LIBRARY UNIVERSITY OF CALIFORNIA DAVIS CONTENTS Page I. Irrigation Factors 1 Soil 1 Erosion 10 Irrigation Water 11 Cropping 12 Fertilizer Application 13 Pest Control 13 Economics 13 Systems 15 II. Flat Land Furrow Systems 19 Factors Affecting Use 19 Construction and Maintenance 19 Headland Facilities 21 Surface Drainage 30 III. Corrugation Systems 31 Factors Affecting Use 31 Construction and Maintenance 34 Headland Facilities 36 Surface Drainage 38 IV. Contour Furrow Systems 39 Factors Affecting Use 39 Furrow Design and Construction 39 Headland Facilities 40 Cropping 42 Surface Drainage 42 V. Furrows of Miscellaneous Shapes 43 Long, Sloping Side Uses 43 Broad Base Furrow Uses 44 VI. Furrows of Miscellaneous Arrangements 47 Crops 47 Small Irrigation Streams 50 Reduction of Furrow Slope 51 Increase of Furrow Water Intake 52 Appendix A : Conversion Tables 52 Appendix B: Capacity Tables and Charts for Headland Facilities 54 Vppendix C: Design of Systems for Re-Use of Irrigation Tailwaler 61 Vppendix I): Methods of Determining the Number and Cost of Sj phon ( Outlets Needed 62 Selected Bibliography 64 FURROW IRRIGATION I IRRIGATION FACTORS To develop a suitable furrow irrigation system, knowledge of field characteristcs and of the water delivery systems is necessary. This section discusses the following factors: • Soil conditions — water intake rate, movement of water within the soil, useful water-holding capacity, and salinity. • Erosion factors — furrow slopes, gullying, and earth slides. • Water delivery — size and availability of irrigation stream. • Cropping — relationship between type of crop and irriga- tion system. • Fertilizer application through irrigation. • Pest control through irrigation. • Economic considerations — cost comparison of irrigation systems. • Furrow-irrigation systems — principal features and uses. SOIL Water intake rate (WIR) When water is applied to the surface of most soils it sinks relatively fast at first (initial WIR) and at a slower steadier rate after an hour or so (final or basic WIR). For satis- factory furrow irrigation, the WIR of different soils varies from excessive to insufficient. Within the beneficial range it may be the principal factor that determines the best type, shape and length of furrow, and rate of water appli- cation. Determination of WIR, although you must allow for some uncertainties, will prove of great advantage for ob- taining and maintaining a satisfactory irrigation efficiency. A consistent wide difference in WIR from one portion of a farm to another may warrant a division into separate fields for irrigation. The basic WIR of a soil properly in- cluded in such a single field usually must encompass a range of values, which are predominantly high, moder- ately high, moderately low, or low. The suggested allow- able limits for these ranges are : 1" to 3"/hr, y 2 " to l"/hr, X /4" to Vo'Vhr, and %"/*»* or less. FURROW IRRIGATION The WIR will indicate the proper furrow length to pro- vide an effiricnt and uniform water application. Furrows that are too long will increase earth-moving costs; furrows that are too short will increase costs of field operations. After determining the appropriate WIR range, select the furrow lengths suitable for the lower limit of the range i ] 2" hr in the V2" to l"/hr range). Adjustments in fur- row length can be made by appropriate placement of head dil( lies. Quite often compaction and salt-induced change in WIR (1,9) will call for adjustments in furrow length. In some cases it may be desirable for a period of years to keep the field free of permanent structures which might complicate needed adjustments. RECOMMENDED FURROW LENGTHS FOR INITIAL LAYOUTS ON SLIGHT SLOPES BASED ON WIR OF SOIL Basic WIR inches per hour Probable soil texture Maximum furrow length High- 1 to 3 . Sandy, Clay, Sand Clay Loam Loam, Silt Loam Clay, Clay Loam, Silty Clay loam Clay feet 660 Medium High: 1/2 to 1... Medium Low: 1/2 to 1/4. . 1,320 2,640 2,640 The table above suggests the maximum length of fur- rows for each of the four proposed WIR ranges, and do not apply to furrow slopes of more than 0.5 per cent. The steeper the slope the smaller must be the furrow stream to prevent soil erosion, and often the smaller the furrow stream the shorter must be the furrow to obtain equal dis- tribution of water throughout its length. Furrow irrigation is not ordinarily recommended for soils having a basic WIR more than 3"/hour, or less than VJi/'/hour. At rates above 3"/hour, it is difficult to avoid excessive water loss by deep percolation in the upper end. However, this upper limit would be raised for unusual situ- ations where extremely short furrows and relatively large furrow streams are used, as on some small vegetable or berry farms. The low WIR limit is reached when it becomes impos- sible to put water into a soil fast enough to the depths where il is needed to sustain plant growth. In reeommend- ing tin- extremely low basic WIR of % "/hour, much importance is attached to the high initial WIR of most tight soils. Such snik usually crack as they dry and thus pros ide quick passage of water from furrows to the vicinity of the planl root-. 'I his feature coupled with the practh e of frequent irrigation can sustain crop growth. It i- possible to correct an unfavorably low WIR con- dition. A plow sole m . i \ he eliminated b\ subsoiling, pref- erably with a winged blade. \ relatively thin substrate of irrevi i ible cemented material, that is close enough to the surfaci to be reached, usually can be broken up perma- nently and economical!) I>\ blasting or subsoiling. A drj Cylinder infiltrometer installation. sample of the tight layer may be shattered or pulverized, soaked in water and redried to determine whether it will remain shattered. Continued use of high-calcium or mag- nesium irrigation waters may improve the permeability of tight clay soils (1) . Extreme WIR irregularity, which renders it impossible to isolate soils that differ in this respect, makes the practice of furrow irrigation difficult. The use of a cylinder or ring infiltrometer (photo above) is recommended for making WIR measurements (12). It consists of a cylinder about 1%' long made of 14 or 16 gage sheet metal, set in an upright position and driven tightly into the soil 4" or more. Make measurements while furrow water surrounds the infiltrometer. Partially fill the cylinder with water and measure the distance to its level from the edge of the container. Repeat the measure- ment at regular intervals, starting with 15 minutes during the first hour and then hourly until the loss of water be- comes constant or nearly so. Repeat the test at several loca- tions. See the graph on page 3 for examples of infiltration rates. According to these two curves, soil texture was a good indication of WIR, but this may not always be true. Some soils may appear porous that actually are tight, and seem- ingly tight soils occasionally are quite porous (9) . Movement of water within the soil After water enters the soil it may move rapidly or slowly in any direction, or it may accumulate at some level depend- ing upon the physical character of the soil at various depths. Knowledge about water movement in your soil will help you determine how to furrow irrigate so water will reach the roots of the planted crop without wasting il below the root /one. and without raising the water table so that waterlogging or salt accumulation will occur. IRRIGATION FACTORS - 2 - 1 r-£^rf K Cloy '' < t 30 60 90 Minutes 120 ISO Infiltration rates for two soils. The WIR of the sandy loam starts at about 2.7"/hr and becomes nearly constant, at l"/hr, after about 90 minutes. The initial WIR of the clay soil decreases rapidly from almost 2"/hr to close to zero within 30 minutes. The best way to explore a soil in depth is by excavation. Usually a pit exposure supplemented by a number of bor- ings will serve the purpose. After an irrigation, open a trench across several furrows to observe the wetting pattern of the water. Probing with a properly blunt-ended steel rod, or sampling the soil with a core-recovering auger or tube can give the same information. Your findings will cor- respond more or less to one of the twelve soil-profile situ- ations listed in the chart on pages 4r-6. The chart shows that soil texture as well as subsoil irregularity have im- portant effects on water movement within the soil following furrow irrigation. Soil water reservoir The capacity of soil to store and release water for plant use is similar to the filling and emptying of a natural lake. The capacity of soil to hold water depends upon the size and number of voids, just like the capacity of a lake de- pends on its pool and bank storage. The space can be filled with water in only one way: The first foot of depth must be filled to capacity before storage in the second foot can be started — the soil is filling from the top downward and the lake from the bottom up. After the water is stored, only part of it can be readily removed. In the lake, the remain- der is held at the sides and the bottom. Likewise, only part of the moisture stored in a soil is readily available for plant use. The remainder, which differs from soil to soil, cannot be drawn upon fast enough by plants to keep them growing. Hence we have the soil-moisture terms: • Field Capacity (FC), the total volume of water a soil will hold against the pull of gravity. •Readily Available Moisture (RAM), the part that keeps plants alive and growing. • Permanent Wilting Percentage (PWP), the part re- maining in the soil when plants wilt permanently. People engaged in scientific soil-moisture research differ about how these values should be interpreted (7, 11, 42). In irrigation practice it is safe to assume, at least, that soil moisture is minimal at PWP. Hence the greatest soil mois- ture deficiency that may be expected ordinarily occurs when the RAM is exhausted. The list below gives a general idea how large and varied the RMA is in different California soils for which the in- formation is available: Soil READILY AVAILABLE WATER PER FOOT OF SOIL Inches Aiken clay loam 0.71 Botella silty clay loam 2.09 Bale gravelly loam 1.90 Capay clay 2.01 Columbia sandy loam 1.12 Columbia silt loam 1.75 Corning gravelly loam 1.88 Delano sandy loam 0.88 Diamond Springs loam 2.66 Dublin clay adobe 1.79 Farwell silty loam 1.93 Fresno sand 1 .35 Greenfield coarse sandy loam 0.87 Hanford fine sandy loam 1.12 Holland sandy loam 1.94 Lockwood gravelly loam 2.59 Madera loam 2.57 Metz clay loam 2.34 Oakley fine sand 0.67 Redding gravelly sand loam 1.52 San Joaquin loam 0.67 Tehama loam 1.55 Tehama clay loam 1.53 Yolo clay 2.43 Yolo fine sandy loam 1.23 Yolo silt loam 1.75 Zamora clay loam 1.76 If all or part of the RAM in the soil water reservoir is used by a crop, and an irrigation has supplied a much greater amount, the excess is wasted to the field, and drain- age troubles may develop. Reasons for such a waste usually lie in a field irrigation system that uses furrows that are so long and furrow streams that are so small that the waste is necessary to reach all parts of the field with the required amount of water. Also, water may be allowed to waste un- necessarily from the lower ends of the furrows. To deter- FURROW IRRIGATION The next three pages show the effect of twelve soil profiles on furrow irrigation. Log of Soil to 6 ft. Depth Profile Description Furrow Wetting Pattern Remarks '•'.' ■.'•■ Deep, extremely permeable sand or peat. V T Y Insufficient lateral move- ment of moisture to make furrow irrigation feasible. Deep, permeable sandy clay or loam. Final WIR 1/2" to 3 7hr. Suitable for furrow irrigation but may require special water application technique where the final WIR exceeds 1 "/hr. Y 1 Deep clay or loom with permeability decreasing gradually with depth-Final WIR 1/4 "to 1 "/hr. Ideal for furrow irrigation. r-rv-r^-T Abrupt change (interface) from slowly permeable top soil to extremely permeable subsoi I. More water may be stored in this soil than might be expected. Interface delays downward movement of moisture and increases to some extent the storage of water for plant use. IRRIGATION FACTORS Log of Soil to 6 ft. Depth Profile Description Furrow Wetting Pattern Remarks Potentially saline loam or clay top soil with permanent water table within 6 to 8 of surface and poor sub- surface drainage. Original position of permanent water table. Unsuitable for continuous furrow irrigation of row crops. Artificial drainage may be a solution. Rise of water table due to irrigation. yys yy& + f ~" j j> Less than 3 or 4' of potentially saline loam or clay soil with permanent water table a few inches beneath it in poorly drained sand or gravel stratum. Exceedingly hazardous to furrow irrigate. Slight rise in water table may cause consentration of harmful salts at ground surface. Original position of permanent water table. Rise of water table due to irrigation. Exceedingly tight, deep soil (WIR l/10"to 1/4" /hr. Insufficient water penetra- tion for successful irrigation except possibly when con- tinuously flooded for rice growing. Initial water intake through soil cracks is sufficient for crop requirements. Shrinkage cracks make possible deep wetting of the soil. FURROW IRRIGATION Log of Soil to 6 ft. Depth Profile Description Furrow Wetting Pattern Remarks Same except soil cracks or rodent burrows provide channels into the subsoil. Water stored in soil may be less than might be expected Furrow streams waste into subsoil. Top soil left totally or partially dry. This condition can make surface irrigation futile. Same except inter- face due to presence of sand or gravel lens or cavity. Whole or portions of crop row may be insufficiently watered. Destruction of interface by deep subsoiling may remedy the trouble. vjzsa, r f Permeable potentially saline top soil over tight subsoil. No subsurface drainage. Nonirrigable (except by continuous flooding for rice growing) unless sub- surface drainage can be provided. Same except that slope provides drainage. Frequently satisfactory for furrow irrigation. IRRIGATION FACTORS mine furrow-irrigation performance, the length of furrow and the irrigation practice can be evaluated by any trained technician who has access to the necessary equipment and laboratory facilities (8, 33). A simpler procedure, sufficient for practical purposes, to determine how furrow systems should be designed and operated, contain the following four steps: (1) Determine the RAM deficiency with a cylinder infil- trometer immediately before the customary time of irrigation. (2) Make a reasonable allowance for unavoidable waste of water during irrigation. (3) Compute the depth of water applied during irriga- tion. (4) Adjust, if necessary, the length of furrow and size of furrow stream to make the water applied (step 3) equal to that found to be required (steps 1 and 2) . Step 1. The RAM of the soil reservoir is made up of two components — the depth of soil occupied by the roots of the planted crop, and the RAM of the soil to that depth. Hence, if a root zone extends to a depth of 6' and the aver- age RAM per foot of soil amounts to l 1 /^" depth of water, the soil reservoir would have a RAM of 9" depth of water. Technicians determine the effective depth of plant root- ing by noting the extreme depth from which the plants ex- tract moisture from the soil (7) . This depth is different in each crop. For example, it can be assumed to be 6' for field corn unless normal root development is impaired by hard or impervious strata, a water table, a concentration of injurious salts, or other barrier. The following list shows the depth to which mature crops will exhaust the RAM in deep, permeable, well drained soils under average condi- tions: Crop Depth Feet Alfalfa 10 to 15 Almonds 6 to 9 Apricots 6 to 9 Artichokes 4% Asparagus 10 Beans (dry) 3V 2 Beans ( green ) 3 Beans ( lima ) 4 Beets (sugar ) 5 to 6 Beets (table) 3 Broccoli 2 Cabbage 2 Cantaloupes 4 to 6 Carrots 3 Cauliflower 2 Celery 2* Chard 3 Cherries 6 to 9 Citrus 4 to 6 Corn ( sweet ) 3 Corn (field ) 6 Crop (cont'd) Depth Cotton 4 Cucumber 3V2 Eggplant 3 Figs 5 Grain and Flax 4 Grapes 8 Ladino clover and grass mix 2 Lettuce 1% Melons 5 Milo 6 Mustard 3% Olives 6 to 9 Onions 1 Parsnips 4 Peas 3y 2 Peaches 6 to 9 Pears 6 to 9 Prunes 6 to 9 Peppers 3 Potatoes ( Irish ) 3 Potatoes (sweet) 4 to 6 Pumpkins 6 Radishes 1% Spinach 2 Squash (summer) 3 Sudan grass - 6+ Tomatoes 6 to 10 Turnips 3 Strawberries 3 to 4 Walnuts 12 to 18 Watermelons 6 * A major portion of the roots of the celery plant are in the first foot. Often, after irrigation has become routine in a field, situations occur where only a part of the RAM is regularly exhausted at the time of irrigation. In such cases, water application can be reduced. To find out when this may be done, a procedure for determining RAM deficiency is needed. Laboratory instruments and techniques may be used but simpler methods ordinarily are sufficient. A trial and error method is recommended for this pur- pose. Apply water at different depths in cylinder infiltrome- ters, followed twenty-four hours or so later by probing or sampling inside each cylinder to determine the depth in the soil reached by the water. Install infiltrometers at a place in the field where crop stand and condition are average and probe with a tool such as pictured on page 8. The water depths selected for trial runs may range from the RAM of the soil-water reservoir to about half that amount. Use irri- gation to a depth that wets the soil to the depth of rooting. The probing tool will indicate to you a change of resistance when it is forced beyond the depth of water penetration. The soil tube is used to obtain soil for moisture content appraisal. The table on page 9 shows how to judge from the soil samples the depth where moisture change occurs. This test procedure applies to all soils and can be carried out without experience in judging moisture content of soil. Irrigation on individual farms usually follows a regular FURROW IRRIGATION Hand tools for sampling or probing soils, a — probe; b — auger; t — Veihmeyer tube; d — basket-type. schedule so that determination of soil moisture deficiency before an irrigation seldom needs repeating. Step 2. Having noted the depth of water required to recharge the -oil-water reservoir, you need to know how near!) il is possible or practical to furrow irrigate ade- quately with that depth of water. Two situations tend to require an additional depth. The soil can be too porous to allow the lower end of a field to he irrigated adequately without loss of water by deep percolation at the upper end. Or. use of a stream larger than needed to satisfy the furrow WIR to continue running (after it reaches the lower end of the furrow) may cause some water to be lost by runoff or ponding and deep percolation. This runoff, or prolonged ponding can be prevented by collecting and returning the excess water to the head of the field as prescribed in Step 4. Also, where the furrow slopes are uniform and slight, runoff and ponding can usually be prevented by carefully regulating the furrow streams. Otherwise, and particularly so where the furrows are short and steep or irregular in length, it becomes less practical to irrigate efficiently. In such cases the loss of water may amount to 20 per cent or more. Where the WIR of the soil is %"/hr or less, the water loss by its unequal distribution along a furrow is small, or it can be easily made so by the procedure described in Step 4. However, the high WIR range soils (1" to 3"/hr) may require up to 10 per cent more water to take care of deep percolation losses even though all reasonable efforts are made to prevent them. Hence under most adverse conditions the difficult-to- prevent loss of water from both causes can amount to at least 30 per cent. On the other hand, under the most ideal conditions it can be negligible. Step. 3. After you determined the total depth of water required, you must know how much ordinarily is applied to tell you if some is wasted and that changes in irrigation layout and practice are needed. If the water is pumped, as is done on about half the irrigated land in California, the flow rate will be known from pump tests that regularly are made by electric power companies. Otherwise most irriga- tion water is measured when delivered (37). The various units of measure are converted to depths of water applica- tion almost exactly by the formulas on the bottom of this page. Step 4. The two main procedures of preventing any flood damage or water wastage discovered in steps 1 to 3 are: A — Reduce to a minimum, by furrow shortening and initial use of maximum size unit stream, the difference in depth of water penetration in the upper and lower reaches \\ ater m< asured in - hours used . , , ., . . , ,. , = acre-inches per acre, or depth in inches applied l.)0 ■ number of acres acre-inches per acre, or depth in inches applied — acre-inches per acre, or depth in inches applied Watei measured in statute miner's inches: Number of miner's inches hours used 10 number of acres W atei M t< i I in southi rn California miner's inches: Nnmbei u[ MiiiM i s inches • hours used 50 numbei of acres IRRIGATION FACTORS HOW TO DETERMINE DEPTH OF WATER PENETRATION AFTER IRRIGATION Soil condition Depth at which sample drawn Moisture content Test and finding Deep, well drained soil of any texture At and above the depth of water penetration Field capacity When soil sample is squeezed in hand no free water appears on soil, but wet outline of ball is left on palm. This soil condition should extend to the depth of plant rooting. Same Below the depth of water penetration Generally below to well- below field capacity When soil sample is squeezed in hand no wet outline of ball is left on palm. Where water is not lost by deep percolation during irrigation and rainfall is nominal, this condition of soil moisture prevails at all times below the depth of crop rooting. Water table, within the normal root zone of the planted crop At and below a water table Saturated Free water appears on the soil when soil sample is squeezed, kneaded, puddled or bounced on hand. This above-field capacity condition may be desirable as an extra source of water for plant use, but usually is harmful if sufficient to last for more than a day or so. of furrows. B — Minimize ponding or runoff from the lower ends of furrows by reducing sufficiently the size of the fur- row stream after it reaches the lower end of the field, or permit it to continue and arrange to re-use the water. By following these two procedures, any depth of water can be applied uniformly simply by allowing the final furrow stream to run for the required length of time. More specifi- cally, Step 4 is carried out as follows: A — The length of furrow is checked and shortened, if necessary, as follows: The largest stream that can be used without flooding the crop rows or eroding the soil is turned into a furrow and allowed to flow to the end of the run. Its rate of advance is noted as shown in the graph below and the point or section where it begins to change materi- ally is considered the end of the furrow that can be irri- gated with satisfactory uniformity. In general, the size of the stream that can be used and the length of furrow found to be satisfactory will be such that the water will reach the end of the run in about one-fourth of the time required to adequately wet the soil. The test-run result can be markedly affected by a temporary loosened condition of the soil because of an initial plowing or subsoiling and/or cultiva- tion during the early stages of crop growth. Such cases may call for two test runs and two lengths of furrow — one for use temporarily while the soil is loose, and a longer one finally for the undisturbed soil condition. Temporary use of reduced length of furrow generally requires extra procedures. To conserve planting space and reduce the expense of cultivation and ditch cleaning, it is usually desirable to open the extra head ditches for irriga- tion and close them for cultivations. Because furrows of unequal length require much additional time for starting, regulating, and stopping the unit streams, they should all be kept of one length within a field; to this end, the fields should possibly be divided into halves, thirds, quarters, etc. This, of course, cannot be done where the topography or property lines require the use of furrows of unequal length. B — The unit stream cut-back practice aims at reducing the initial furrow stream at a time and in an amount that will leave water standing in the furrow from end to end through the remainder of the irrigation without causing tailwater. This demands close attention by the irrigator to BY USING TWO 660 FURROW LENGTHS BY USE OF 1320 FURROW LENGTH 1200 r- LU LU 1000 U_ 1 X 800 r- o 600 2- LU -J 400 ^ o on 200 en 3 1 2 3 4 5 6 7 8 9 10 11 12 13 TIME REQUIRED FOR WATER TO ADVANCE ALONG FURROW -HRS. An example of how furrow shortening may improve the uniformity of water application. FURROW IRRIGATION make his efforts as effective as possible. Furrow-stream control devices are essential. If the progress of the furrow streams cannot be watched from the head ditch and the field is large, roadways and transportation may be neces- sary to make possible quick inspections at both ends of the furrows. Two irrigators may be required — one at the head ditch to regulate the furrow streams and the other at the far end of the furrows to signal when the sizes of the unit streams must be reduced. Cutting back the furrow streams may not be possible because sometimes qualified irrigators are scarce; or be- cause the maximum size unit stream that can be used in some furrow systems on steep slopes (see table on page 11) is too small. The second plan for overcoming surface runoff problems, i.e., arrange to recover and re-use the water (15) is gener- ally possible but usually requires additional investment and an annual operation expense. The essential features usually include: a surface drain or ditch with terminal basin or sump for collecting and storing the excess water; pump installation with sufficient capacity to handle the sump inflow; and pipeline for conveying the pumped water to the point of re-use. This plan has been widely adopted in California because of the desire to save water and the need for a solution to the irrigation labor problem. The quality of the runoff water has been checked on numerous occa- sions and has been found to be unimpaired. Such layouts are commonly termed "tailwater re-use systems." Sug- gestions for their design and construction appear in Appen- dix C. A third plan for disposing of the tailwater problem and achieving high irrigation efficiency is theoretically possible, but has proven difficult in practice. It consists of grading a land surface in the direction of irrigation to a diminish- ing slope from head ditch to waste ditch. The multiple slope arrangement is supposed to eliminate the difference in water-intake opportunity caused by running water on an even slope from the upper to the lower ends of fields. Rapid drainage of the upper and sufficient ponding of the lower furrow reaches because of their respective slopes is counted on to offset the normal water-intake difference. But the re- sults are never known until the layout is completed and in ij-c which makes the venture a gamble. Fortunately, the other procedures for obtaining high water-application effi- ciency Still can he applied successfully, though with added difficulty, to those diminishing-slope layouts that turn out to be failure^. Salinity Where row-crop irrigation is practiced under saline and alkaline conditions, the lateral movement of the soil mois- ture coupled with surface evaporation causes sail concen- tration in the ridges or beds between furrows which may be harmful i" the planted crop. Two types of this problem <>' < hi One covers extreme conditions thai make successful in i ible unless the subsurface is adequately drained and the harmful salts removed from the soil (16) . The other is a borderline condition in which the salts are harmful only during seed germination and emergence of the planted crop. If this early salt effect can be prevented the crop may be expected to mature without further diffi- culty. This usually is accomplished in three ways. A special furrow and ridge or bed shaping makes the salt move to the peak of the ridges during irrigation and leaves planting strips next to the water in the furrows that are essentially salt free (4) . Another way is to plant in the relatively salt- free bottoms of the furrows following a preirrigation. The third way consists of preirrigation by the furrow method; removal of the ridges by scraping or floating; and seeding the crop in the firm moist, relatively salt-free soil along the middle of the reduced ridges. EROSION Land slope, a factor in surface drainage and water appli- cation efficiency, also may affect soil erosion. Erosion may take place in three different ways. It can occur in furrows that are too steep for the stream of water they are made to carry. It can result from gullying brought about by stream breakthrough from higher to lower fur- rows, one after another, on hillsides where the furrow slope is less than the land slope. It also can take the form of earth slides where the soil on steep hillsides tends to slip when wet. Either rainfall or irrigation can cause eroding. Furrow slope The severity of erosion that takes place in furrows during an irrigation depends on furrow slope and stream size and, to a lesser degree, on the soil and soil conditions (20, 28) . Where irrigation water must flow directly down steep slopes, it is recommended to run sufficiently tiny streams of water in correspondingly small compacted furrows (see photo, page 16, top) so erosion is minimized regardless of soil type Where the furrows are as large as can be allowed for and their slopes are slight, (see "Flat-Land Furrows," photo on page 15) streams up to 50 gpm (gallons per minute) will cause practically no erosion regardless of soil type. Minor adjustments in stream size may be necessary on account of the soil, but are so small and uncertain that it is best to leave them to the responsibility of the irrigator. It is possible to keep erosion under control on increas- ingly steep slopes by correspondingly decreasing the size of the furrow streams. Erosion that is becoming serious is revealed by the color of the water and the changing shape of the furrow near the inlet end during an irrigation. To establish nonerosive furrow streams, the following rule of thumb can he offered: The largesl stream that can be used in a furrow of sufficient capacity without causing serious erosion is found by divid- ing the number 10 by the furrow slope expressed in per cent (equivalent to feet fall ill 100 feet length of furrow), or LO IRRIGATION FACTORS 10 per cent slope = gpm (gallons per minute) The table below shows for a number of critical cases the results obtained by this rule of thumb and evaluates them according to observed performances during furrow irrigation of the suitable type. Gullying Gullying brought about by furrow-stream breakthrough from higher to lower furrow normally can occur only where the land slope exceeds considerably the furrow slope. This situation is confined almost entirely to hillside irrigation by the contour-furrow method (photo, page 16, bottom). The breakthrough may be the result of overtopping of the ridges by furrow streams of excessive size; or failure of the soil to confine unit streams of furrow-capacity size. The soils that are subject to failure are those that crack deeply (as, for instance, clays) ; those that tend to slide when saturated with water (some sands and silts) ; and those weakened by rodent infestation. It is unsafe to practice contour-fur- row irrigation where any of these soil conditions are prob- able. Overtopping of excessively large furrow streams is usu- ally caused by unbridled runoff from rainfall. Gullying through overtopping can be overcome by proper design and use of the irrigation system, as indicated in the graph on page 12. Earth slides Possible earth-slide trouble is indicated on otherwise smooth hillsides by scars left by old soil slippages on soil saturated by rainfall to a slick, more or less impervious substrata. The only safeguard against furthering this action is to leave such areas undisturbed by cultivation and irriga- tion. IRRIGATION WATER Delivery schedule Irrigation water, in addition to wetting the soil and pos- sibly eroding it, has also other important effects. The man- ner in which it is delivered to the farm may govern the choice of crops to be grown and their best irrigation method. It may require the use of a particular type of fur- How the Rule-of-Thumb Determination of Nonerosive Furrow Streams Works on Five Different Slopes. FURROW SLOPE LARGEST NONEROSIVE STREAM POSSIBLE EFFECT OF SLOPE ON EROSION OBSERVED PERFORMANCE Per cent 0.1 0.3 0.5 2.0 12.0 gmp 10 0.1 10 "03 10 0.5 = 100 = 33+ = 20 10 ~Z0 10 12 = 5 :0.8+ A 0.1 per cent slope falls within the range of minimal slopes where erosion effect of furrow capacity streams is negligible. A 0.3 per cent slope is near the upper limit where the erosion effect of furrow- capacity streams is negligible. Cultivated furrows with 0.5 per cent slope and stream capacities of 30 to 50 gpm will suffer harmful erosion unless furrow streams are adjusted to a lesser size than that of furrow capacity. Note: Corrugation-type furrows with 0.5 per cent slope have a small streamflow capacity which further restricts the size of furrow streams. A 2.0 per cent slope is considered the maximum nonerosive slope for any fur- row except the corrugation type. A 12.0 per cent slope is near the maxi- mum slope that can be considered prac- tical and safe for corrugation-type fur- rows. It is excessive for all other furrow types. 100 gpm is twice the carrying capacity of most furrows in use. However, the va- lidity of rule-of-thumb is supported to the extent that negligible erosion is caused by the maximum furrow stream that is physically possible to use. 33+ gpm is approximate the maximum stream size that furrows with 0.3 per cent slope normally carry without causing erosion. The 20 gpm stream approximates the re- duced size necessary to prevent serious erosion in furrows with a 0.5 per cent slope. The 20 gpm stream is at least twice the size of stream a corrugation with a 0.5 per cent slope will carry. No erosion from such lesser stream may be expected. 5 gpm approximate the maximum size stream that can be used in a furrow with a 2.0 per cent slope without caus- ing serious erosion. 0.8 gpm approximate the maximum stream that can be used in a corrugation- type furrow with a slope of 12 per cent without causing serious erosion. 11 FURROW IRRIGATION FIELD CONDUIT Z TREES VINES BUSHES ^ *4* *$* *f* Js & & <&> 4" RQ w 4^4- #> & CR0PS *fy> & «*> <&> Conventional layout for contour furrow systems. row, or it may be a deciding factor on whether furrows are suitable. The size of stream and its scheduling may be optional, or they may be fixed to suit cropping require- ments or to comply with some limiting physical feature of the water supply, topography, or local soil conditions. Delivery of water "on demand" of the user, both as to time and size of stream, is most ideal for furrow irrigation of any type. This plan is used in community projects and by water users who have their own ample water source. Water delivery on a fixed schedule often requires a parti- cular type of furrow irrigation, or a nonfurrow application method. The fixed project plan of delivering continuously an ex- ceedingly small stream of water to each farm generally calls for the adoption of the corrugation type of furrow ii i igation. This plan is often used on land with topography pi incipally made up of slopes too short, steep, and irregular for using large delivery streams. Deliver) of large amounts of water — such as 15 to 30 cfs (cubic feet per second) — makes furrow irrigation on normal-sized farms difficult Sporadic, undefined schedules, such as from a spring freshet, may require the management of a flood-size stream of wat' i and the planting of a crop that will mature without in' additional water. Fui ow irrigation and intensive row cropping is difficult under these conditions. CROPPING Furrows can successfully irrigate any commonly grown crop if the proper requirements as to soil, topography and water are present. Surface irrigation is the accepted method for all row crops. Trees, shrubs and vines may be ade- quately irrigated by special furrow layouts that reach all areas surrounding the plantings. Hay, grain and pasture crops may be irrigated satisfactorily by corrugations. Favorable crop planting conditions can be obtained when suitable furrow irrigation practices are followed. The beds between furrows provide the necessary dry-surface soil environment for those crops that become damaged when allowed to come in contact with water or wet ground. A firm, moist soil condition for germination and early growth of seeded crops is provided when preirrigation is followed by planting in the bottoms of the furrows, or on the ridges after they have been leveled off. A continuously moist, crustfree soil condition can be maintained at the ground surface by irrigating as long as necessary until the crop is up. Also, the arrangement of furrows, ridges and bods for variations of row spacing provide a flexible system for changing plant populations. Harvesting is accomplished over furrowed fields with special machines and procedures. In hay and grain fields corrugation-type furrows allow full use of the ground sur- 12 IRRIGATION FACTORS face for planting and also provide a sufficiently smooth ground surface for machine harvesting. Potatoes, sugar beets, corn, cotton, spinach and tomatoes are among the many furrow-irrigated row crops that are successfully har- vested mechanically. Furrow irrigated orchards commonly are disked, leveled and rolled so fruits and nuts which are allowed to drop, may be picked up by machine. FERTILIZER APPLICATION Irrigation water can carry fertilizer to the root system of a crop but the fertilizer program must be synchronized to a particular irrigation pattern and to the depth of rooting of the planted crop. Otherwise the fertilizer may be lost below the root zone, brought to the surface to remain unused, or made to reach harmful concentrations within the root zone (21) . The exact rule to follow varies with soil and crop and can be obtained locally from your Farm Advisor. PEST CONTROL Furrow irrigation may play a role in pest control in three respects. It may act as a vehicle for applying pesticides as well as fertilizers. A partial wetting of the soil area by furrow irrigation may help control certain types of root rot. And avoiding waste water ponding through careful regulation of furrow streams, or removal of the excess water by drainage outlet ditches or tailwater re-use systems will keep down mosquito breeding. Complete eradication, required for perfect pest control, is rarely accomplished by furrow irrigation because the water carrying the pesticide seldom penetrates to all parts of the planted row (see chart pages 4^6) . However, the temporary suppression of the pests accomplished by this means is sometimes sufficient to allow satisfactory crop production. Although better results may be expected where the pesticide can be applied by a basin preirrigation or by sprinkling, you will have to rely on furrow irrigation alone for pesticide application where the land slope is excessive or where sprinkling equipment is unavailable. ECONOMICS Costs of furrow irrigation systems vary (27, 40) . An ex- pensive land reforming operation may be undertaken to adjust the slope (23) or improvement may be limited to a less costly but also less desirable type of furrow irrigation. The irrigation stream may be carried without material water loss in pipelines (30, 32) flumes and lined channels (19, 35) . Often the use of an unlined earth ditch can serve the purpose and sometimes is most suitable. You may profitably install the most modern accessories for diverting and regulating the water flow into the furrows or, if neces- sary, the bare necessities can be made to serve, although with some sacrifice of convenience and efficiency. The job of irrigating may be meticulously performed by a capable person, or it may be done indifferently by an unskilled farmhand and a tailwater-reuse system can be installed that will perfect the operation. The various items in these alternatives are listed and evaluated here : Cost and utility comparison of various furrow-irrigation facilities and practices* FACILITY OR PRACTICE COST COMPARISONS Alteration of land surface Furrow systems designed to conform to Little or no earth moving expense required, steep and/or uneven topography. Suitable where expense of land grading is excessive, or exposure of subsoil is unde- sirable. Furrow systems designed to conform to Earth excavation required for land reforming Highly desirable for best use of land and long, moderate and essentially uniform may amount to 200 to 800 cu yds per acre. Esti- water, land slopes. mated average cost per acre $80. Head Conduit (Farm ditch, pipeline, or flume from which irrigation water is released onto field) Unlined earth Initial cost is minor. Usable where topography is suitably head ditch. smooth and loss of water due to seepage is small. Advisable for tentative layouts. Concrete-lined ditch. Initial cost per linear foot $1.50 to $2. Cost for a 40-acre field served by % mile of lined head ditch would range from $50 to $65 per acre. Usable where topography is smooth. Pre- vents ditch seepage and erosion. Unsuit- able where layout may prove temporary. Buried concrete head-pipeline including Overall initial cost per linear foot for furrow- Usable regardless of topography. Con- built-in water-control devices. irrigated fields $2 to $3. Cost for a 40-acre field serves soil, water, and cropland space. Un- served by % mile of head pipe line would range suitable where layout may prove tem- from $65 to $100 per acre. porary. Head flume. Initial cost usually small because of small size and wood construction in areas where lumber is cheap. Usable chiefly for steep contour furrow- irrigated fields. 13 FURROW IRRIGATION FACILITY OR PR\< riCE COST COMPARISONS Check (Dam, gate, or valve to raise the level or pressure of the head-conduit stream) Portable fabric or plastic sheet tappoon. Initial and replacement costs per acre nominal Best type for unlined earth head ditches. when usual number of two to four per % mile of ditch is required. Portable metal tappoon. Initial and replacement costs per acre are rela- Best type for concrete-lined head ditch, tively minor. Permanent gated wood or concrete struc- Initial cost per acre nominal when usual number Convenient to use, but hinders machine ture. of two to four per x /± mile of ditch is required, cleaning of unlined earth ditches. Gated stand, or line valve. Cost included in the stated overall cost of buried A necessary part of many buried concrete concrete head-pipeline systems. head pipelines. Turnout (Head conduit facility for releasing a multi-furrow stream) Open cut. (Temporary opening through Outlay is minor and entirely for labor. Usable in earth head ditches. Simple to lower bank of earth head ditch) perform if properly managed. No hin- drance to ditch cleaning. Portable siphon. (Tube placed to function Initial cost per acre minor because only a small Best type for most head ditches, as siphon over lower bank of head ditch) number required. Permanent structure. (Gate-controlled Initial cost ranges from 64 to 12(? per linear foot Convenient to use, but hinders machine tube or channel through lower bank of of head ditch. Cost for an 40-acre field served by cleaning of unlined earth ditches, head ditch) % mile of head ditch would range from $2 to $4 per acre. Alfalfa or orchard valves. Cost is part of the stated overall initial cost of A necessary part of all buried concrete buried concrete head pipe lines. head pipe lines. Outlet (The facility for releasing unit furrow streams) Open cut. (Temporary opening through Outlay is minor and entirely for labor, lower banks of earth head-ditch systems opposite each furrow) Advantageous for low-cost operation of earth head-ditch systems. Poor arrange- ments for close regulation of furrow streams. Spile. (Tube placed through lower banks Acceptable when the total initial cost is less than Good arrangement for close regulation of of earth head-ditch systems opposite each for portable siphon-tube outlets. furrow streams. The practice of using one furrow i per furrow is the limiting economic factor. Portable siphon. (Tube placed to function Present costs of siphon outlets per second/ft ca- Highly suitable and most generally used as a siphon ovei the lower bank of a head- pacity when used singly or two or more per fur- type of outlet for lined and unlined head ditch system) row to discharge maximum and minimum unit ditches. Streams of 35 and 8 gpm ranges from $60 to $100. On this basis, the cost per acre for a 40-acre field served by a Vi mile head ditch and a 3 second/ft irrigation stream would range from $4 to $8. Portable gated pipe, (Short lengths of Present cost of aluminum-gated pipe used in con- Generally the best outlet where pipe line pipe, gated to match the furrow spacing, junction with buried head pipeline to discharge turnouts are spaced 20 to 100 ft and the temporarilj connected to head-pipeline maximum and minimum unit streams of 35 and 8 soil W1R is high. Gated pipe can serve turn-outlets one after another during gpm is approximately $1,85 per foot. On this basis also as the head conduit, but such use irrigation) 1 1 ■<- eo-t pei ,i. m l.n a Id acie field seived by Vi usually is temporary and is not considered mile of head pipeline and a 3 second/It irrigation here, Btreara would be (lost to $17. 11 IRRIGATION FACTORS FACILITY OR PRACTICE COST COMPARISONS Tailwater systems for disposing of runoff from furrow irrigation Surface drain. (Ditch across the lower Outlay for initial construction and necessary Effective when well maintained, end of furrows that has a natural or com- maintenance usually is small. wasteful of water to user, munity-provided outlet) . but Re-use System. (Drain, sump, pumping The initial and annual expenses for a typical Highly advantageous for conserving high- plant and conduit as may be required). tailwater re-use system are estimated to be $43 priced water that otherwise would run to and |3 per acre, respectively. waste. * Different soils, topographies, irrigation water-delivery services, and shapes and sizes of fields make cost and suitability of the various furrow irrigation facilities and practices vary widely. This table shows how the various furrow irrigation items compare in cost and utility. Prices and practices at some future time and for other places and site conditions than those stipulated will change the overall costs. SYSTEMS To use irrigation furrows to best advantage, one has to be familiar with the five systems available. The systems are rated and illustrated on the following pages : FLAT-LAND FURROW SYSTEMS PRINCIPAL FEATURES Slope: Slight and even — 0.1 per cent best; 0.05 to 0.2 per cent advisable limits; 0.05 to 0.4 per cent usable. Alignment : Essentially straight. Shape: Shovel-excavated deep V. Generally the best type for production of row crops on land that has little slope except when furrows of different shapes and arrangements are required for special purposes. Length: As long as can be efficiently irrigated and within practical limits of Hg to % mile. Capacity: As large as cropping practices permit, or up- wards of 50 gpm. Flat-land furrow layout with open-cut out- lets through the bank of an earth head- ditch system. 15 FURROW IRRIGATION CORRUGATION-TYPE FURROWS PRINCIPAL FEATURES Slope: Moderate to steep — 1.0 per cent best; 0.5 to 12 per cent advisable limits; 12 per cent to 20 per cent usable. Alignment: A course essentially perpendicular to the surface contour. Shape: Small V or U shaped groove approximately 0.25' deep. Length: Largely governed by length of natural slope. Common minimum 150'. Usual maximum % mile. Capacity: Relatively small (10 gpm to trickle size < 1 gpm). Most widely used and generally recognized as suitable to furrow irrigate close-growing crops in areas where the topography is steep and uneven, to better distribute the water. Also suitable to surface irrigate row crops where the land slopes are moderately steep and uneven. Corrugation-type furrow irrigation. The 2' scale shows the width of the furrow stream to be only about 1/10 of the row-crop spac- ing. This leaves most of the ground surface unflooded, often a desired feature. CONTOUR FURROWS ContOUT-furroW irrigation — headland view. Photo: Soil Conservation Service, I Sl)\. IRRIGATION FACTORS PRINCIPAL FEATURES Slope: Moderately steep and even — 1.0 to 2.0 per cent One of the two ways to furrow-irrigate steep and usually advisable. uneven slopes. Usable and sometimes desirable, but often hazardous in high-rainfall areas. Alignment : Follows contour curvature of hillside locations. Shape: Notch type with fill-made bank on downhill side. Length: Generally made to match topography of land — usually ranges from 200 to 400 ft. Capacity: May be constructed extra large to accommodate runoff from rainfall. FURROWS OF MISCELLANEOUS SHAPES PRINCIPAL FEATURES Slope: Same or slightly steeper than for flat-land fur- rows. Alignment: Essentially straight. Shape: Special cross-sections made necessary because of unusual condition. Length: As long as can be efficiently irrigated between practical limits of He to % mile. Capacity: As large as cropping practices permit, or up to 50 gpm. Helpful for solving special soil-, slope-, and crop- production problems. Among furrows of miscellaneous shapes is this long-sloping side furrow, used here for salinity control. FURROWS OF MISCELLANEOUS ARRANGEMENTS PRINCIPAL FEATURES UTILITY Slope: Same or slightly steeper than for flat-land fur- Mostly useful in orchards and other similar per- rows. manent plantings for wetting the soil in the rows between trees and vines. Alignment: Circuitous or straight. Generally desirable also for reducing slightly excessive furrow slope. Shape: Generally V or broad base. Length: As long as permissible or desirable to obtain effi- cient irrigation, or as may be determined by size of field. 17 FURROW IRRIGATION Two examples of furrows of miscella- neous arrangement are these zigzag furrow patterns used especially for irrigating citrus orchards. 18 II FLAT-LAND FURROW SYSTEMS Flat-land furrows (photo, page 15) usually are char- acterized by their V shape, slight slope, straight alignment, large capacity, long reach and extensive use for field row crops. Under proper conditions they offer the following ad- vantages : • They allow a wide range in the size of furrow stream. This is useful in the furrow-stream cutback procedure to obtain high water application efficiency. • The large capacity of the furrows permits rapid irriga- tion when required by soil or crop. • The long and straight furrows and crop rows reduces tractor hours (less time lost in turning) and saves crop space that otherwise would be required for additional headlands. • Soil erosion hazards are practically nonexistent be- cause the slight furrow slope is essentially nonerosive and the flat landscape and large furrow size afford little opportunity for gullying. FACTORS AFFECTING USE Topography As the name indicates, only relatively flat land that can be graded economically to the required slope is suitable for this type of furrow irrigation (23, 27). The earth-moving necessary to make the long and uniform slopes, calls for a knowledge of engineering, experience in earthwork and ownership of earthmoving equipment that is beyond most farmers. The surveying and computing in preparation for the plans and specifications are usually done by specialists, and the work itself by a contractor who makes a business of it. Soil The depth of top soil that may be removed to provide the required slope often depends on the quality of the subsoil. Stockpiling and returning the layer of fertile topsoil, to avoid possible damage because of subsoil exposure by strip- ping, usually is too costly. In case of doubt, it is important to evaluate the quality of subsoil. In some instances this information is already at hand. Where it is not, a green- house procedure may be used. It consists of fertilizing sam- ples taken from different depths, potting them in pairs with the same unfertilized subsoil and observing the response of plant growth in each. Chemical and mechanical analyses of the soil can be helpful in determining the possible deficien- cies, but generally they alone are insufficient for the pur- pose. Water The irrigating is essentially a full-time job while it is in progress. If both the water and the irrigator's time are to be utilized efficiently, the stream of available water must be relatively large. The size that one man can manage and which should be available varies from about 2 cfs for low WIR soils to 7 or 8 cfs for high WIR soils. Crops Planting and cultural practices determine which crops may be grown. Most crops that are planted in rows and culti- vated may be irrigated in flat-land furrows. Crops that are broadcast seeded call for either another kind of furrow, or a different method of irrigation. CONSTRUCTION AND MAINTENANCE Construction and maintenance of flat-land furrows dif- fer with the various planting and cultivating requirements and practices, but the irrigation objectives are the same. Ideally, the furrows are made extra large so they can carry initially a stream of water large enough to travel at nearly constant rate along a course of the specified slight slope and maximum length. The length may be as much as one- half mile, the slope as little as 0.05 per cent and the stream as large as 50 gpm. The normal shape is a deep V, with side slopes at an angle at which the soil will stay in place. If the first irrigation is applied prior to planting, or follow- ing ridge planting, the V-shaped furrows are constructed full-size initially in one operation with a furrow shovel of the largest permissible size (photo, page 20, top). Follow- ing flat planting and cultivations the furrow making may be different. It may be necessary to open them gradually to the maximum size that can be made without damage to the emerging crop. In general, the cultivation consists of work- ing the soil away from the planted row and throwing it back again into the ridge. The tool that finally shapes the furrow for irrigation is a furrowing shovel of the largest usable size. Where the turning space for cultivators and other ma- chinery at the upper ends of the crop rows causes furrow maintenance problems, the furrow making can be done in a manner that will lessen the trouble. This is accomplished, as shown in the sketch on page 20, center, by making a limited number of furrows singly or several at one time in a manner so that only half are left out of shape at the head- land ends. The photo on page 20. bottom, shows a tractor-mounted tool that might be developed to remake the flat-land furrows in headland strips. So far it has been used mainly for mak- ing corrugations. It consists of a suitably housed rotary 19 Flat land furrow openers. Wtittm/ttwnmHnntfmtrmmwnii «»£? •«* "5!?Z,9, E *~ ; ° ' T c M ^7^//^^/^^/////////MW//////^WW^^/////^y^ l 'i'//^'Mi WIDTH OF STRIP CULTIVATED AT ONE TIME — WITH A TRACTOR-DRAWN THREE-ROW IMPLEMENT Furrow plan (above) to minimize manual furrow reconstruction in headland strip. After making the (urn in the headland strip the furrower is hacked up against the head ditch he- fore starling down between the next crop rows. Thus li.ill the Eurrowi across this area are machine made, and half arc left to he opened by hand. i ii .kII.ukI fnrrower (right). A.*- Furrows made with headland furrower. cutting blade of a length equal to the width of the headland strip. During its operation the tractor travels from one end of the headland strip to the other, alternately stopping and moving forward as the blade is lowered, revolved to scoop out each furrow lineally, and raised free of the ground sur- face for the move forward. The job it does is shown above. HEADLAND FACILITIES The headland layout consists of all of the facilities required for handling the irrigation water from the place where it enters the field to the furrows. More specifically it includes: a ditch, flume, or pipeline for carrying the main stream; "checkdams" for open channels and "gated standpipes" or line valves for pipelines to raise the level or pressure of the water so it may be diverted; "turnouts" for systems that make use of "forebays"; and "outlets" to release the unit streams into the furrows individually. How the water is ponded and released depends a great deal on the means used to carry the main stream, i.e.. whether it is an unlined head ditch, concrete-lined head ditch, or head pipeline. Hence, the various practices that may be followed are dis- cussed under these main headings. Unlined head ditch systems Design and construction. An earth head ditch for flat- land layouts is either trapezoidal or V-shaped. It follows a slope of 0.1' or less per 100' of length. Its flow capacity usually ranges from 2 to 8 cfs. Its construction is simple and inexpensive, and usually can be done by one or two passes with a farmer-owned ditch plow (photo, above, right) . Preferably it is made on a ditch pad placed for the purpose when the field is leveled for irrigation. Otherwise the necessary bank material is obtained by deepening the channel. Since the extra expense is small, the ditch usually Construction of earth head ditch with tractor-drawn ditch plow. is made large and the banks high and heavy enough to pro- vide amply for settlement and freeboard. Head ditches may be operated for temporary use during each irrigation or for a part of the growing season, but generally they are permanent. Control devices and procedures. How head ditches may be equipped and operated to best advantage depends largely upon the type of outlet used to release the unit fur- row streams. The three suitable types of outlets are open cuts, spiles, and siphons. Open-cut outlets and related structures. As the name implies, an open-cut outlet is a temporary opening dug through the bank or ridge of the earth head ditch sys- tem opposite each furrow. It is opened and backfilled by hand with least effort with a special light-weight irrigator's shovel. The manufactured article may be improved by drilling several %" diameter holes through the steel blade to break the suction of the wet earth. The erodability of the open-cut outlet and the force of the relatively large stream of water that passes through it requires a special set of rules for managing the head ditch system and the irrigation stream. The earth head ditch system needs to be prepared in three ways to receive the water. The first preparation helps to subdivide the relatively large head ditch stream into the many smaller unit furrow streams. To this end the head 21 FURROW IRRIGATION Head ditch-forebay arrangement. ditch should he paralleled on the furrow side hy a series of rectangular basins, or a secondary ditch blocked at suit- able intervals (photo above). This arrangement allows suitable partitioning of the main stream by turnouts into a number of forebays and each of the forebay streams to be released by the open-cut outlets into a number of furrows. The turnouts for releasing the main stream may be either siphon tubes (photo above) that are moved to serve one forebay after another, permanent gated structures, spaced to discharge into each forebay individually, or open cuts similar but larger than the outlets. It will be assumed that when the outlets are open cuts the turnouts will be open cuts also. Rectangular forebays also provide a nonfurrowed space for turning field machinery. The second preparation avoids the necessity of backfil- ling open cuts to stop stream flow. All turnouts except the lowest are earth filled. Irrigation begins in the lowest por- tion of the head ditch and then proceeds upstream by open- ing successively the field turnouts. The third preparation spots the places along the head ditch where checkdams will be required and provides a wood support for them at each site. Checkdams are re- quired in any head ditch that has sufficient length and fall to make stoppage and pondage of the irrigation stream necessarj to properly release the water onto a field. Either permanent gale structures or portable sheet tappoons (photos, righl column) with wood support can be used but, as explained later, lappoon- are more appropriate for an earth head ditch with open-cul turnouts and outlets. The wood support consists of a pole that span- the channel and slats '>'>" to 1"" apart resting at an angle against its upper face and driven slightbj into the ditch bottom. To form the dam a died of plastic material or treated canva9 is laid and made tight across its upper face. \\ iili these preparations made, the job of managing the u.itei eon-i-t- at In -i of stabilizing the turnouts and outlets and regulating the stream How for the first Bel of furrows to be irrigated. Ii is no easj ta-k to stabilize these openings while upwards of .">() gpm furrow streams are passing Top. Permanent wood checkdam for earth head ditches. Bottom: Portable sheet-tappoon checkdam with wood support. through them. Any lining material such as strips of sod, pieces of burlap, or empty fertilizer paper sacks can be used. When the time arrives to start the water in the second set of furrows upstream, the irrigator first unplugs the re- quired number of turnouts and outlets, secondly completes the necessary number of checkdams, and thirdly, returns to the job of stabilizing the turnouts and outlets and regulat- ing the furrow streams. Only the checkdam operation need be discussed further. The job of installing the tappon sheets in a large ditch while it is carrying upwards of I to 8 second-feet of water is difficult unless performed as follows: The tappoon sheet, which is usually a piece of canvas 8' to 12' long and 4' to 6' wide, is made ready for transport and use by rolling it onto a light-weight pole. The irrigator must get into the ditch to install it. While facing the up- stream side of the wooden support, he unrolls 3' or I' of sheet and places il against the support at the desired height and with liberal strips resting on the bottom and nearest hank of ihe ditch. The end and bottom edges are fastened 22 FLAT-LAND FURROW SYSTEMS down by tucking them into the wet soil with the blade of the irrigator's shovel. At this juncture the irrigator begins standing on the bottom strip as it is laid and tucked into the soil. The tappoon sheet is then unrolled further, a little at a time, and its edges anchored in the same manner until the ditch stream is stopped and the new set of furrow streams start flowing. This procedure is unnecessary for small-capacity head ditches. Tappoon sheets as well as other types of checkdams can serve as terminal barriers to stop the ditch flow, or as inter- mediate weirs to restrict the flow. In the latter case, part of the water is allowed to escape over the top of the dam, or through an adjustable opening. Where a terminal dam only is needed, two tappoon sheets are required. During water changes the one in use must remain intact until the second is made ready to function at the next upstream location. In this case the time required for setting up the second dam. dismantling the one previously used, rolling the tappoon sheet on a pole, and carrying it forward where it will be used next should require only a small fraction of the in- terval between changes. In this way the irrigator can devote most of his time to stabilizing the outlets and regulating the furrow streams. As fall increases along the head ditch, more dams are required which reduce the amount of time that the irrigator has for furrow regulation. This water distribution system has advantages in low initial cost, low maintenance cost, and ease of replacement. The disadvantages are high operational cost and low ir- rigation efficiency. Spile outlets and related structures. Spiles are short, straight tubes that extend from below the ponded water surface in the head ditch or forebay, through the interven- ing bank and into each furrow. They are installed level and at a depth that will make them flow properly. Their flow capacity varies with the diameter of the tube and with the difference in elevation of the water surface on the two ends (Appendix B) . When properly placed they divide the flow into equal furrow streams. Later each spile can be regulated to match the basic WIR of the furrow. Spiles may be installed in two ways. They may be deeply and permanently embedded in the bank of the head ditch next to the furrows, or they may be placed on the relatively low banks of forebays opposite each furrow and temporar- ily installed for each irrigation by pressing them into the soil to a depth that will make them flow properly. In either case one spile per furrow usually is provided and left at the head of each furrow during the irrigation season. Because many are needed, their cost should be low. Commonly used are junk tubing from oil-well operations or discarded rail- way car hose connections. The flow in a set of spiles may be regulated by raising or lowering the check dam. Individually, the spile flow may be regulated by changing the elevation of the outlet end of the temporary installations or by placing wood slats over the inlet end in the permanent installations as shown in the photos on this page. aSfefl!* Use of spite outlets in earth head ditch. Top: one spile outlet is required for each furrow. Bottom: A wood slat is used to regulate the flow. The management of the irrigation stream for spile out- lets may be different from that of open-cut outlets. Spiles can easily be closed against a head of water, thus irrigation need not be started along the extreme lower end of the head ditch and progress upstream. This is a big advantage where tappoon sheet checkdams are used, because these dams can be set up more conveniently in the dry channel. Where the spile arrangement is temporary, water man- agement includes the following: The uppermost reach of head ditch that receives the water first is made ready by arranging the required number of spiles and by setting up the tappoon to pond the water. The tappon sheets are placed across the dry ditch and made watertight by draping them properly over the pole and slat supports, embedding their edges a few inches deep into the bottom and sides of the ditch and weighting the bottom strip down with a few shovelfuls of earth. The adjoining reach downstream that receives the water next is prepared in the same manner while the irrigation water is being applied in the first sec- tion. When it is time to start irrigating along the second 23 FURROW IRRIGATION ,,.^ ' ^ Semipermanent, low-cost checkdam Tor earth head ditches, made Portable siphon outlet tubes operating from an earth head ditch, of wood and preservative-treated burlap. reach, the tappoon sheets and corresponding turnouts in the first section are removed and the corresponding outlets are closed. This same procedure is continued until irriga- tion along the lowest reach of head ditch is completed. One of the main goals of this plan is to facilitate ditch cleaning by keeping the head ditch free of structures. This requires rcmovahle turnouts. As shown in the photo on page 22, column 1, siphon tubes serve the purpose and preclude the necessity of spile removal until time of cultivation. Where the spile arrangement is permanent, the aim is different. Permanently installed spile outlets make it neces- sary to forego low-cost ditch cleaning by cultivation. The main reason for installing spiles permanently is to make the irrigating more convenient. Their use eliminates the need for forebays and allows permanent instead of the tap- poon checkdams. Usually gate structures built of redwood lumber are used, as shown in the top photo on page 22, column 2. Another type of checkdam is made partly of fabric as shown above, left. The fabric portion is a pre- servative-treated burlap apron attachment, which is em- bedded in the bottom and sides of the head ditch to seal the structure in place. This type is cheaper but can be used only one season. Both types of permanent checkdams are convenient to use: they are read\ where and when needed and are made |o function merely by raising or lowering a gate, or by placing or removing flash-boards (wood slats) in the openings. The spiles, tOO, are ready for use and are quickly and easily regulated as shown on page 23. The head ditch of permanently installed spiles is maintained by grazing, burning, application of chemicals, or hand labor. The decision to use Bpiles as the outlets usually depends on whether the\ can be obtained 81 low COSt. Siphon outlets and related structures. The most modern and best-liked outlet device for earth head ditches is a bent aluminum or plastic tube that operates as a siphon when primed (filled with water) and properly laid over the bank of the head ditch or forebay. (Photo, above, right.) The siphon action that makes these tubes flow may be started in several ways. Usually small sizes (%" to 2^" diameter) are used as outlets for furrow irrigation. They are filled with water by placing one end deep in a stream of water, capping the upper end with the palm and raising the tube, rapidly lowering the tube with the palm removed to allow air exhaust and repeating rapidly until the tube is full. Less dexterous siphon operators may find it easier to fill the tube initially by submerging it and then proceeding as described above. The larger siphons (greater than 21/2 " diameter) commonly used as turnouts from head ditch to forebay, require starting facilities. Usually these are 2' or so of light canvas hose, telescoped and clamped onto the discharge end of the siphon, and a short piece of chain or handle attached conveniently close to the same end. To start these larger siphons, the whole tube with canvas hose end open is submerged to fill; while under water the hose is twisted tightly closed to keep the siphon primed; with the inlet kept under water, the sealed discharge end is lifted by the handle, carried over the ditch bank and lowered into the forebay; the canvas hose then is allowed to open up and the siphon action starts. Siphon flows vary with the diameter of tube and the dif- ference in elevation of water on the two sides. An initial rale of How is gaged to reach the lower end of the furrow quickly. The initial flow is then reduced to match the basic WIR in one of three ways: the discharge end of the tube is raised, a gate fitting into the discharge end of the tube is partially closed, or one or more of the tubes initially used per furrow are removed. 21 FLAT-LAND FURROW SYSTEMS To allow siphon outlets to function in the manner de- scribed, water surface in the head ditch must be several inches higher than it is in the furrows. The material for the extra bank height may be obtained by excavating the ditch 6" to 8" deeper than necessary, or by making a ditch pad for it at the time the land is graded. Management of siphons is distinctive in several respects. Notably, the forebay arrangement is much less essential than it is for other types of outlets. Use of the temporary- type checkdams is preferable. In contrast to the procedure for open cuts or spiles, siphons are moved to serve one set of furrows after another until finally they are removed from the ditch site and stored for future use. This use of siphon tubes over and over during an irriga- tion make them relatively inexpensive. According to best practice where one siphon per furrow is being used, the number required may be several times the number required for the first setting. Where two siphons of the proper size are used in each furrow the number required is greater, but the saving in tube capacity reduces their cost to less than half that of the single large siphons. (See Appen- dix D ) . When 1" and 2" diameter siphons are used, a total of 155 are required, but only 115 when 2%" diameter siphons are used exclusively. However, the two smaller siphons can be used more efficiently because of their capacity, and their cost runs only about 60 per cent of that for the 2Vo" size. As calculated here, the total cost of the 2 1 /o" siphons would be approximately $276 while for the two smaller sizes it would be about $160. Temporary tappoon-sheet checkdams have the same maintenance advantages in siphon operation as discussed on 22 and 23. A forebay arrangement is not necessary with siphons be- cause the division of the main stream into many furrow streams poses no problem. Also, unlike with spiles, there is no need to install the outlets in forebays to keep the head ditch free of permanent structures, or to provide space for the turning and manipulating of farm machinery because the ditch space can serve this purpose. The irrigation stream is managed in much the same manner as with spiles. The irrigation is started at the inlet end of the head ditch which provides a dry ditch for instal- lation of checkdams. Siphon tubes are the best outlet for earth head ditches, with two major exceptions: If only the bare minimum capital cost can be borne, open cuts must serve the purpose even though they are most difficult to regulate. And spile tubes are satisfactory where they can be obtained econom- ically. Lined-head ditch systems A variety of materials and types of construction are em- ployed to build head ditches (19, 35) , but only unlined and concrete-lined earth types are used to any extent in Cali- fornia. Assurance that a lining will prove worthwhile calls for a good reason that it is needed; for equipment and ex- perience to perform the construction properly; and for a practical method of construction. Concrete linings prevent loss of water by seepage and eliminate the problems caused by vegetal growth in head ditches. On the other hand, linings make head ditches per- manent and this may prove a detriment where system changes may be desirable. Also, a single permanent head ditch across the high side of a furrow-irrigated field inter- fers with farm implement operations. However, these dis- advantages may be of secondary importance to the water saving and seepage prevention. Design. Concrete-lined ditches must be designed care- fully to avoid unnecessary cost. The best shape — which pro- vides a near-maximum capacity and is practical to con- struct — has a one-half hexagon cross-section, a flat bottom, 1:1 or 1— IV2 ; 1 side slopes and a usable depth of one-half of the average width. Extra depth to obtain bank material, such as is permissible for unlined earth head ditches, is uneconomical. The ditch is made in a well compacted earth pad of sufficient depth and width to raise the banks to the desired height. Only minimal freeboard is required, be- cause the lining prevents clogging by vegetal growth. Usually, 2" or 3" extra height of sidewall lining will suffice to prevent its being overtopped because of curved align- ment and the fluctuations that normally result from manag- ing the ditch stream. Channel slope and roughness of lining must be correctly evaluated to determine the required ditch size. The engineering hydraulics calls for technical assist- ance can be arranged through your local Farm Advisor. Construction methods. The first three photos on pages 26 and 27 show the three types of concrete head-ditch lin- ings commonly used: hand laid, shotcrete, and slipform (19, 35). The hand-laid type is the least mechanized and usually is installed in places inaccessible to slipform or shotcrete machinery. It is usually laid in alternate 6' to 8' sections. The forming consists of 1" x 4", or 2" x 4" wood strips set on edge and embedded to allow for about 3^}" thickness of lining. Steel reinforcement ordinarily is not used. At first every other section is laid and allowed to cure. The forms are then removed and the alternate sections are laid. This procedure allows free access to each section for the spreading, tamping, striking (leveling off), and trowel- ing that must be done manually. The whole job. including carting and mixing the cement, gravel and sand, may be done by hand. The items that must be purchased can be limited to lumber for forming and cement for concrete. Shotcreting or guniting is contracted because it requires patented machines and an experienced work crew. The process consists of mixing, at high velocity r in a nozzel, properly proportioned streams of cement, sand and water, and releasing under comparable high pressure the admix- ture as a spray until from 2" to 2 1 .0" thickness of concrete slab is formed. Specified volumes of cement, clean coarse sand, and water are loaded or piped into a special machine 25 FURROW IRRIGATION Hand-laid concrete lining for earth head ditches. Shotcrete ditch lining. which provides the force and is equipped with regulating facilities to produce the jet of fluid concrete. Before lining, the bottom and sides of the ditch are made solid and fairly smooth, and both are covered with a 6" x 6" mesh 10 gage wire netting to serve as reinforcement for the lining. The work is done by a two-man team. One raises the reinforcing net slightly with a metal hook while the other manipulates the nozzle to spray on the concrete to as nearly the same level as can be judged by eye. No forms are provided other than a header board along the upper edge on each side. The finishing work is usually limited to the removal of sand particles that failed to embed. They are swept or scraped in piles and shoveled onto the ditch banks. These operations leave the surface of the finished lining abrasive and some- what uneven. Slipform lining must also be contracted. It requires spe- cial machines for excavating, compacting, and accurately shaping the earth ditch, delivering the concrete, spreading concrete and making a smooth surface finish. The lining is laid without reinforcement in a continuous sheet about .''>' 2" thick and scored transversely to confine cracks that may be caused by temperature variations. One machine docs the work necessary to prepare the ditch and another pcrfonns the spreading and finishing. Needed are a com- mercial concrete mixing plant nearby and facilities to de- liver the ready-mixed concrete al the ditcb side. Currently in California more farm ditchc> are being concrete lined in this manner than in any other way. Control devices and procedures. The facilities For re- leasing fni iow streams differ in three respects from those di cribed for unlined earth ditch systems: Checkdams of special types are required; the only outlet needed is a siphon; and tin forebaj arrangi ment is unnecessary. Checkdams. Two kinds of checkdams are suitable- one for gunite-lined head ditches; the other for those lined manually or by the slipform method. The latter is a tappon- type dam consisting of a sheet of metal, shaped and edged with rubber or rubberized fiber material to fit the ditch cross-section snugly when placed at an obtuse angle with the direction of stream flow as shown on page 27, column 2. If need be they are gated. Like the canvas, or plastic tap- poon dams used in earth ditches, two or more are set, re- moved, and reset during an irrigation in the positions re- quired by the ditch slope and the size of the main stream. This type of a metal tappoon checkdam is unsuitable for gunite-lined ditches, because it is difficult to obtain a satis- factory seal between it and the rough surface of this kind of lining. Instead, removable slide-gates, or flashboards that fit into grooves in the lining, best serve the purpose. Suitable grooves can be prepared for each required check- dam location by excavating and forming for a 4" thick by 6" wide slotted bottom and side section across the ditch. The sections are then constructed of concrete by the gunite process monolithically with the rest of the lining. The only possible shortcoming of this arrangement is the fixed loca- tion of the checkdams which may not always remain suit- able. Its special advantage over any other type of perma- nent construction that would serve the purpose is that the slotted sections are flush with the bottom and sides of the ditch so that the maximum flow capacity of the channel is left unimpaired. Outlets. The siphon tube is usually the only type of out- let that is considered practical for concrete lined head ditches that serve flat-land furrows, because concrete linings har cutting the ditehhank for the purpose and a manu- factured gate or valve for each furrow generally is too COStly. None of these shortcomings apply to siphon-tube outlets. 26 FLAT-LAND FURROW SYSTEMS Slip-form concrete ditch lining. Metal tappoon checkdam for hand-laid or slipform lined head ditches. Forebays. A forebay arrangement for a concrete-lined head ditch system conflicts with the essential purpose of linings and is generally unsuited. Forebays are not needed as distributing basins because, unlike in open-cut outlets, main-stream subdividing and furrow-stream regulating present no problem. Furthermore, the same reasons that justify the lining condemn the use of forebays because they, even more than the head ditch before it is lined, may be expected to cause excessive loss of valuable water and cause drainage troubles. Hence, even though headland space for turning and manipulating farm machinery is especially necessary where head ditches are lined, it is advantageous to put up with the extra time and expense necessary to re- construct the furrow inlet ends by hand. Head pipeline systems Head pipelines usually consist of low-pressure, prefabri- cated three-foot lengths of 12" to 14" diameter tongue-and- groove concrete pipe. These are laid and mortared together in a trench deep enough to allow an earth cover of 18" to 24". Sometimes they are made in place underground mono- lithically. In either case, standpipes and ventpipes set vertically in the line and left open at the top serve as escape- ways for entrapped air, water pressure regulators, shock chambers, and gate structures. The turnouts consist of valves mortared to the tops of riser pipes that connect with the pipeline and extend vertically to the height required for releasing the water. In California little use is made of rubber or plastic head pipelines except where they are needed temporarily. Ex- perience has shown that any advantage they may have as a portable surface system is outweighed by the superior con- venience and durability of buried concrete head pipelines. Buried concrete head pipelines have four important fea- tures that determine where they may be used to good ad- vantage. They are essentially leakproof which makes them useful where seepage is a danger; their placement below ground prevents damage and eliminates obstruction of ma- chine operations; they operate perfectly along a course that would be too steep or uneven for a ditch ; and they are clog- proof from vegetal growth and wind-blown materials. Design and construction. (30) The pipe diameter and hydraulic pressure must be sufficient to provide the needed carrying capacity, and the latter small enough to prevent breakages. Provision must be made for withstand- ing the shock and thrust that occurs at points where the stream is turned or stopped. Vents or stands are necessary to release the trapped air at high points, top of descents, terminal ends, and at intervals along lengthy lines. Construction that assures good service calls for expert workmanship and strict compliance to specifications. Most important are the following: Acceptance of the pipe by a competent inspector; expert pipe laying that will result in a pipeline with solid foundation, strong tight points, and a smooth unobstructed interior; taking care of the freshly laid pipeline until the mortar work is properly cured ; and testing, inspecting and otherwise readying the system for use. The surest way to obtain a good installation is to leave the planning to an experienced engineer and to make cer- tain that the construction is done by a reliable pipelaying concern. Control devices and procedures. Most names of the devices for controlling the irrigation stream apply exclu- sively to pipelines even though they serve the same purposes as do the control devices for head ditches. Check gates. Pipelines in individual fields that are suit- 27 FURROW IRRIGATION ably leveled for flat-land furrow irrigation rarely require check gates or line valves to raise the level or pressure of the water so it may be delivered to the land. Usually the water enters the line with sufficient pressure to make it rise a foot or so above the ground surface at any point where i( is necessary to release it. However, it may be necessary hi stop the flow in long lines to reduce priming time. It also may be necessary to have a check to divert the irrigation stream from one head pipeline to another. Check gates are installed in stand pipes that breach the pipeline and are operated by long gate stems from the top of the stands. The head ditch counterpart is the checkdam. Turnouts. A turnout facility is essential for tapping the pipeline, conveying the water to the ground surface, and releasing a stream of sufficient size to serve a number of furrows. A turnout (photos, below) consists of an orchard or alfalfa valve mortared to the top of a concrete riser pipe which is set vertically and mortared into the supply line at intervals of 15' to 100' or more. The precise spacing, size of riser, and size and type of turnout valve depend upon the number of furrows to be served and the kind of crop to be irrigated. Orchards and similar permanent plantings usually need a turnout valve for each planted row. Vine- yards and bush plantings call for minimal spacing and the small orchard-type turnout valve with a protruding valve- stem handle which must be located so not to interfere with farm implement operations. In vineyards and the like this is possible because the valves may be placed at the head- land end of each row and used to serve a single furrow or two on either side. Alfalfa valves are larger than the orchard type and have a recessed valve-stem handle that makes them more or less immune to damage from farm ma- chinery. They are further shielded if they are installed 3" or 1" below the ground surface, and covered with a dis- carded plow disk and earth; also, their locations may be staked. They may be placed at any interval and be of any required size. For fields to be planted year after year to an- nual row crops, the wide spacings and large diameters of riser pipe and outlet valve are most practical and econom- ical. However, frequently the planning must be done for another method of irrigation, as when row crops are rotated with alfalfa and the latter is flood irrigated. Forebays. Unlike with concrete-lined head ditches, the use of forebays in conjunction with buried pipelines often is permissible. Exceptions are cases where the primary reason for having the pipeline is to prevent loss of high- priced water and to avoid drainage troubles. Two types of forebays are used: A small, levee-contained, circular sump, termed "Duck Nest," that surrounds each turnout valve and narrow rectangular basins that abut each other endwise. The latter usually is used for cultivated row crops. The basins may be formed in two ways: Either a broad bottomed channel on the furrow side with upper bank deflected to encompass the turnouts and earth dams midway between turnouts, or a string of narrow basins di- rectly over the buried pipeline, made by constructing a levee on either side of the line and midway between ad- jacent turnouts. The "Duck Nest" arrangement is suitable only where the turnouts are fairly closely spaced as may be the case in orchards. They usually range from 6' to 8' in diameter. Both types of forebays require reconstruction following cultivating. Outlets. With forebays, the outlets can be any type de- scribed previously — open cuts, spiles, or siphons. Otherwise, gated pipe, gated hydrants and turnout valves can serve as outlets. Each operates directly from pipeline to furrow and thus eliminates loss of water from the time the irrigation Turnout valves for buried concrete pipeline. Lejt: Orchard valve. Right: Alfalfa valve. 2.': FLAT-LAND FURROW SYSTEMS Surface gated pipe outlets for buried concrete head pipelines. The force of the issuing stream is being dampened by burlap sacks. Closed-chamber pipeline hydrant, often called a "bonnet." stream enters a field until it reaches the furrows. Pipelines have a special advantage in saving water and preventing drainage problems. Gated pipe (photo, above) is excellent for buried con- crete pipe systems that have valves spaced far enough apart to make the use of gated pipe worthwhile. Aluminum pipe generally serves the purpose best, but galvanized iron, plas- tic and rubber makes are also available. Aluminum gated pipe is made in sections of 30' or less and in diameters ranging from 4" to 12". Data for determining the required pipe size may be found in Appendix B. Each pipe section is equipped with quick-coupling connections which allow them to be rapidly assembled into multiple-section lengths. The outlets arrangement consists of finger-tip operable rub- ber slidegates that are spaced to match the furrow interval. As illustrated on this page, above, left, the assembled lengths are connected to the supply line by hydrants that are temporarily installed for this purpose on the turnout valves. The two types that may be used are shown in the adjoining column, above and below. The closed-chamber hydrant is held in place and regulated externally by a rod that hooks into the turnout valve stem and both cinches down to make the connection secure and turns to open or close the pipeline turnout valve. The open-ended sheet-steel cylinder hydrant, approximately 24" in diameter by 4' high, is installed for temporary use by placing it verti- cally around a turnout riser pipe and forcing it into the soil sufficiently to make it fairly leakproof. A long handled hook is used to operate the turnout valve. This open-ended cyl- inder hydrant is usually satisfactory and is much less costly than the closed-chamber type. The operation of surface gated pipe is comparable to that of a set of siphon-tube outlets of one size. Initially the slide gates are opened wide to release the maximum permissible furrow streams and finally they are closed to allow the mini- mum required flows. The same gated pipe equipment re- peatedly is set up and used for one set of furrows after another until the irrigation of a field is completed. The foot- age of pipe and number of portable connecting hydrants needed may be determined experimentally or by formula in the same manner as explained for siphon-tube outlets. (See Appendix D). After an irrigation all of the outlet equip- ment may be removed from the site and the turnout valves covered so that the headland space can be freely used for turning and manipulating farm machinery. No repair work is necessary for the next irrigation. Open-ended cylinder hydrant for connecting surface gated pipe to buried concrete head pipeline. To provide an outlet for each furrow, sufficient gated pipe is attached to eichcr side to reach halfway to the next pipeline turnouts. -^"M. J ■* 29 FURROW IRRIGATION Gated hydrants, like gated pipe, release water individ- ually to several furrows at one time from each pipeline turnout, though on a much smaller scale. Each hydrant usually serves only from two to four furrows. They are designed for use in vineyards and similar plantings where the rows are closely spaced and the pipeline turnouts are correspondingly located at the head of and in line with each row. They usually consist of a single joint of 12" to 14" ID concrete pipe set vertically around and permanently mor- tared at the hottom to the turnout riser pipe. The outlets consist of slide-gate controlled small tube openings through the hvdrant wall. They are located slightly above the ground and spaced circumferentially around the hydrant for best access to the furrows. The hydrant is left open at the top to allow access to the turnout valve and outlet slide gates. A typical installation is shown below. Turnout-outlets deliver buried pipeline water directly into the individual furrows without the aid of a hydrant, gated pipe, or a forebay arrangement. This dual use of pipeline turnouts is practical only for vineyard and similar arborieultural layouts that have one or two furrows between rows and a turnout valve at the head of each row. The ar- rangement is similar to that for gated hydrants, but there are no gates to operate and the water must be deflected sideways to the furrow on either side. SURFACE DRAINAGE Surface drainage will be poor on land that has little or no slope for excess water to run off, and too tight a soil for the water to escape downward. Excess water can be caused by rainfall as well as irrigation. In California, storm-water runoff from flat lands usually is of little concern, but is a major problem in other parts of the country and in other countries that are regularly sub- jected to cloud bursts or monsoon rains. The solution lies in surface drainage in great detail, including extensive fur- rowing of the land surface. The runoff problem caused by irrigation stems from the difficulty of controlling the large unit streams in the long flat furrows which may result in harmful ponding of water in the lower end of fields. The three remedies, already dis- cussed, are: elimination of the surplus water by careful irrigation; disposal of the water by surface drains; and collection and return of the water for re-use by means of a Tail-Water re-use system. Gated hydrant outlets for buried head pipelines, spaced 15' for use in \ineyard. 10 III. CORRUGATION SYSTEMS In irrigation practice, all small furrows are called corruga- tions or corrugation-type furrows. They are unique in that they are designed to run on a relatively steep grade and are supplied with water at a suitably slow rate from a small ditch, flume, or pipeline. Occasionally they serve for sur- face drainage only. Corrugation systems have the following applications: • Upland terrain too steep or uneven for flat-land fur- rows. • Soils that require slow irrigation because of low WIR. • A water supply which makes available only a relatively small stream of water on a continuous basis. • Close-growing, furrow-irrigated hay crops that require a smooth ground surface for machine harvesting. • Newly planted, imperfectly leveled or steep stripchecks that require keeping the irrigation water spread be- tween levees. • Crops seeded in dry soil that require an uncrusted ground surface for satisfactory plant emergence follow- ing furrow irrigation. • Flat land and slowly permeable soil that require a cor- rugated ground surface to facilitate the removal of standing water following flood irrigation. FACTORS AFFECTING USE Topography The sketches on this page illustrate how corrugation-type furrows can be adapted to extremely steep and irregular topography (24, 38, 41) . These layouts emphasize the rules that govern the design of most furrow systems of this type. Note that the general direction of irrigation is directly downhill ; the location of the head ditch facility is for the most part along the top of the slope ; the furrow slope neces- sarily may vary to some extent; some transverse slope may be unavoidable; and furrow lengths may be limited to those of the natural land slopes. Most layouts are less extreme in these respects because the topography of lands classified as irrigable by corrugations are less steep and more uniform than those shown. Also, it is often possible to do a complete job of land reforming so that fields can be rectangular and furrows long and of uniform slope as shown in the photo on page 16, top. The land slopes on which corrugations are to be used, may limit the lengths of furrows to unequal short reaches, or they may permit lengths up to one-fourth mile, if the small unit streams that must be used will travel that far. Short, uneven furrow lengths, combined with irregularly HEAD DITCH SYSTEM RAVINE LAYOUT RIDGE LAYOUT Typical layouts for extra steep and irregular land slopes. SLOPE GUIDELINES FOR CORRUGATION-TYPE FURROWS Furrow slope Transverse slope Crop Per 100 feet Uniformity Optimum Maximum Optimum Range Optimum Tolerance Machine harvested, close-growing crops feet 2-4* 2-4* 1.0 feet 1-12 lt-12 0.5-8 Uniform Uniform Uniform per cent change 50 50 25 Level Level Level per cent of minimum furrow slope 1234 Pasture \2y 2 Cultivated row crops 25 * Increase within this range if furrows are to be poorly maintained. t May approach where surface drainage alone is the purpose. 31 FURROW IRRIGATION shaped fields and many field ditches, can make irrigation and other farm operations unduly burdensome and encour- age the development of tolerances to avoid these handicaps. According to experience, the ranges and variations of per- missible funow and transverse slopes are listed in the table on page 31. These slope improvements may be confined to the limita- tions of spot-leveling, or perfect land reforming may be Feasible. In either case, insufficient depth of top soil and the presence of an adverse subsoil may restrict these operations to a greater extent than usual. Spot-leveling usually accounts for most of the earthwork. It consists of minor to moderate earthmoving at scattered locations, which often can be successfully carried out piece- meal without the aid of engineer or contractor as the need for it shows up. Suitable site conditions for the perfect land reforming improvement are much less prevalent than in the valley areas. \\ here it is feasible the same rules apply as for sim- ilar land reforming for flat-land furrow irrigation. \\ here corrugations are used, uplands are either original formations that are undergoing erosion, or ancient table- land-. The latter have a variety of cemented subsoils which in -nine cases can be broken and removed, in others perma- nently shattered, but topsoil removal often permanently prevents crop rooting. Before deciding to do any reforming of such land, it is advisable to investigate the subsoil and the effectiveness of any treatment. The subsoils of undisturbed parent materials likewise may he determining land-reforming factor. Generally they lack the decomposition and leaching to make good topsoil. The cost of developing these soils should be considered. Subsoils may be tested by the greenhouse method previ- ously described. \\ here corrugation-type furrow irrigation is inadvisable, suitable alternatives are contour furrowing, sprinkling, flooding from closely spaced contour ditches, or flooding from steep, narrow strip checks. Soil Corrugation-type furrow irrigation is especially suitable for soils thai either drain -lowly or wet horizontally at a fast rale. Ii i- also one of the best ways to irrigate tijjht soils in order to obtain satisfactory vertical water penetration. Soil- with a final Will up to I" per hour are not difficult to irrigate efficient l\ . The way corugations are formed with a sled-type runner leaves the bottoms compacted and Bmooth. This feature reduces the WIR and tends to equalize the movement ol watei verticall) and horizontally. Coupled w illi the narrow w idlh of the fin rov -I nam. il reduce- the volume of water lost by deep percolation. The capacity of some soils to transmit water horizontally lend- in make irrigation efficient, because ii reduces the time required to wel the -oil between the corrugations and the watei I"-- h\ deep percolation. Some volcanic ash, aeolian. and silt soils are especially suitable for corrugation- type furrow irrigation. Corrugation systems are well suited for tight soils be- cause continuous possession of the irrigation stream allows water application at the necessary slow rate; the furrows are small enough and steep enough to avoid crop damage by flooding; and irrigator time can be held to a minimum. The extremely tight soils that may be irrigated with some success include those with a WIR as low as 0.1" per hour. (See table on page 2.) Small irrigation stream Situations that require water users to irrigate on a continu- ous basis with small streams of water occur either where such streams are developed for individual landholdings, or where community irrigation systems are designed and op- erated to deliver water in this manner. Machine harvesting of close-growing crops Corrugations are sufficiently small and shallow to be passed over without difficulty by mowers, balers, threshing ma- chines and the like. This clears the way for furrow irrigat- ing hay and grain crops in areas where the soil, land slope, and size of irrigation stream make the practice desirable. The harvesting is done most efficiently by confining the operation to one narrow strip of crop after another. The strips parallel the direction of irrigation to keep to a mini- mum furrow crossing and damage to the corrugations at the ends of the strips. The use of a special furrowing tool will repair the un- avoidable damage done by machinery in hay fields and by animals in pastures. Two alternatives to corrugation-type furrows are sprink- lers and flooding. Sprinkler irrigation uses water more efficiently but is more expensive. It can be practiced so it does not interfere with cropping and it is well adapted to steep and uneven terrain and the use of a small water stream. Flooding from closely spaced contour field ditches is less costly but not as efficient in water application. Water control within border strips Border strips that are flood irrigated (22) and planted to hay or pasture crops often must be grooved in the direction of irrigation to make the water spread evenly between levees. Grooving is especially important with new crops and steep slopes because the water may tend to channelize and leave some areas cither dry or eroded. Such situations call for corrugation-type furrow irrigation to get the crop well established, or until the crop growth is dense enough to spread the water. The grooving that may be desirable varies. Where the need is slight, the marks made with a di>k cultivator may Buffice, hut in extreme cases, even for tin- temporary use. il m;i\ he advisable to Corrugate in the best maimer pos- sible. The headland requirements also vary. Where the checks .''.2 CORRUGATION SYSTEMS are flattened for the first 50' and the type of groove suits the particular need, no different head ditch or head pipeline outlet facility is required from the one that will be used when the grooving becomes superfluous. Otherwise it may be necessary initially to release the water into each coruga- tion individually. Pre-eniergence irrigation Crusting of the soil surface at the time of plant emergence can cause a poor crop stand. This happens when the soil surface following crop seeding is flooded with water and then allowed to dry without being disturbed. This happens in many soils, except the highly organic, extremely coarse, and exceptionally friable types. One of the chief advantages of corrugation-type furrow irrigation is that it prevents crusting. Several of its char- acteristics help to make this possible. The exceedingly shallow depth of furrow activates the movement of water laterally by capillarity across and upward to the surface of the intervening planted ridges or beds. This manner of wetting the soil surface is noncrusting. Also, the accom- panying slow rate of irrigation that is neccessary because of the smallness of the furrow streams and the steepness of the slope allows time for the capillary action to be completed. Also, the special way corrugations are smoothed and com- pacted lessens the downward movement of water while it spreads sideways. Corrugations are not the only way to deal with a soil crusting problem. Sprinkling soil at a rate lower than the WIR will leave the soil friable and noncrusted. However, this may prove too expensive a solution of crust prevention. Preirrigation by any type of furrow also may prevent crusting. As soon as permissible after the preirrigation, the seeding may be done either in the bottom of the furrows, or on the ridges after they have been floated down to firm moist soil. Both practices have proved successful. Timely planting is still another way to prevent soil crusting but requires favorable climatic conditions. Where rainfall has wet the soil profile adequately and mild weather ensues, the crust may be broken and a crop established without further wetting. These alternative ways to deal with the soil crusting prob- lem show that crust prevention need not be the deciding factor for its adoption. Removal of ponded water A corrugationed-basin arrangement can also be used to re- move excess water following a surface irrigation or heavy rainfall (25) . This is particularly useful in fields with poor drainage, where the WIR of the soil is such (0.1" per hour or less) that the vertical drainage is inadequate and the slope of the land is insufficient (0.05 per cent or less) to carry the surface water away (2) . Correction of this condi- tion is especially required where flat-land pastures are sur- face irrigated by a flooding method. In such a situation prolonged flooding is harmful to a newly seeded crop, may kill an established crop which then often is replaced by near-worthless watergrass and sedges, or cause mosquito infestations. A corrugation-contour check system, as shown on page 34, may at least partly overcome these difficulties. In this case the corrugating is part of a contour-check system intended primarily for drainage. Hence, the layout is different. The water is ponded in the checks to accomp- lish irrigation, but then the corugations help carry the sur- plus off. The facilities normally used to distribute water by corrugations are not present. The system is designed and constructed according to the following special plan. To prepare the field, the land must be graded uniformly to its negligible natural slope. The corrugating must be done next, as permanently as possible in the direction of the maximum slope. To accomplish lasting corrugations, a heavily weighted sled-type corrugator should be used. The field is then divided into rectangular checks by a sys- tem of contour and cross levees. A road grader or similar implement capable of making ridges at least 3' high and of leaving a well defined ditch on either side of the formed ridges should be used. The spacing of the contour levees range from 150' to 300', and the cross ridges are about 660' apart. The layout is completed by excavating a series of head ditches — one for each string of checks down slope. These ditches cross the checks midway between cross levees and are equipped with a permanent bulkhead gated check- dam (photo, page 35, top left) at each contour-levee cross- ing. The earth excavated from the ditches is carted off and placed on the nearest contour levee, thus leaving the ditch banks level with the ajacent land surface. The sketch on page 34 shows the completed layout. The system is operated by first opening and then closing the checkgates, one at a time, beginning with the highest in each series so that each check is first flooded and then surface drained as may be required. The closing of a check- gate causes the irrigation stream to overflow the sides of the head ditch and flood the levee-enclosed land on either side. The subsequent opening of the same headgate causes the surplus and potentially injurious ponded water to drain backwards through the corrugations and the depressions along the levees into the head ditch and hence into the next check downstream. This type of construction has the disadvantage of limiting the useful life of the system. Once the corrugations become clogged, or any other major parts become worn to the point where replacement is needed, they cannot be fully restored short of levelling and reconstructing the whole system. The period of service that may be expected depends largely upon the character of the soil and how the construction is done. Where the soil has been extra tough and heavily weighted implements were used to press the corrugations into shape, systems of this type have been in service after twelve years of use in a sheep pasture. These systems are useful primarily in pasture irrigation 33 FURROW IRRIGATION CROSS LEVEE ^^r ^r / — •M ± JL JL Jc ±. > UJ Corrugation layout for removal of ponded water. Arranged to flood quickly and then drain thoroughly each levee-surrounded plot, b eginning with the highest, next to the supply ditch. The corrugations are designed to drain off completely all surface water from < ,i< li plot after it is flooded. bi i ause they permit no cultivation or other operation that would be destructive to the corrugations and levees. Oilur ways to irrigate such lands may be found and prove worth) of consideration. The land surface could he reformed to provide the necessary slope for flat-land fur- rowsorfoi border irrigation. (22), \ sprinkler system (31, 35 i could be designed to operate v\ ithoul causing the pond- ing. Oi a mole- -\ ~tf in of -uIhi i i'.iiion may !><• a suitable solution. CONSTRUCTION AND MAINTENANCE Special implements and tool an n [uired to make the con- ventional smooth, shallow and narrow corrugation-type furrow. Originally, a homemade implement like the one shown on page 35, center, served the purpose and, if need he, still can be made to do the job fairly well (24) . Today, however, tractor-mounted manufactured tools are com- monly used (18) . The relatively inexpensive and simply designed tool shown on page 35, bottom, left, is most common in areas where corrugation-type furrow irrigation is extensively practiced. It can be bought bul also homemade on a farm equipped to do welding and blacksmith work. It consists of two pieces of steel approximately 18" to 24" long by 5" to 6" wide by l/j" thick welded together lengthwise along one ed'.'e at an angle of about 90° to form a trough which is > lo ed vertically at both ends in the same manner with metal :;i CORRUGATION SYSTEMS ?&S ' V«? Gated bulkhead checkdam. *' u Home-made corrugator. Tractor-mounted tool for making U-shaped corrugations. pieces. A small shovel and tool-bar hitch is attached to the forward end. This angle-iron shaped, groove-making tool may be weighted by filling it with concrete or tension mounted by a spring for use in tough or cloddy soil to make a smoother channel than otherwise would be possible. Also it may be equipped for use in a loose or cloddy soil with a cross bar to level off the top edges of the corrugations as they are being made. The tool shown above makes a narrow U-shaped cor- rugation instead of the V-shaped one made by the angle- iron-type tool. Some growers perfer this type of corrugation for crops especially susceptible to water damage. It is Tractor-mounted tool for renovating corrugations in hay and pasture fields. Tractor-mounted tool for making V-shaped corrugations 35 FURROW IRRIGATION claimed that the U shape narrows and screens the surface of the corrugation streams so that overhanging vegetation i- k< pt out of the water during the irrigations. This type of tool is strictly a commercially manufactured item. However, its performance can be closely duplicated with the primi- tive, home-made, sled-type implement if its runners are of the proper shape. The tool shown on page 35. bottom, right, makes a rela- tively jagged groove. It is used for renovating the corruga- tions in hay and pasture fields that were orginally made by the V-shaped tool. It serves the purpose best because it most effectively cuts through such vegetation and is also suitable where the nature and density of a crop makes it unnecessary to maintain the orginal shape of the cor- rugation. The fourth tool has been described and illustrated on page 20. bottom. It is especially designed for reconstructing the ends of corrugations in the headland strip following cultivations. According to owners and operators, it is a valu- able tool where row crops are grown and the irrigation water is distributed from a concrete-lined ditch or other headland facility that warrants protecting. On the other hand, there is no need for it in pastured fields and where hay or wheat, barley, oats, and similar crops are grown. Also the usual earth headland system for most corrugation- irrigated fields is easily and inexpensively reconstructed which further limits the necessity of the special tool. HEADLAND FACILITIES Except when corrugations are used for surface drainage only, the facilities are mostly the same as for flat-land sys- tems. The main differences are the smaller required flow capacities and the need for erosion safeguards. Though a concrete lined ditch, pipeline, or flume may serve as the headland channel facility, and their use is warranted in some cases, an unlined earth ditch is usually used. Unlined head ditch systems The earth head ditch is characterized b) long total reach, small capacity and hillside contour location. These features, and the procedures the} make necessary, are markedly different from those discussed under flat-land furrow sys- tems. The location along a contour of a steep hillside can he extra hazardous. Serious gully erosion might result from failure of the earth bank on the downhill side. The cause of failure could be either Improper construction, impair- ment of channel capacity, or storm-water runoff. Construction and maintenance. A particular kind of head ditch construction ma) he necessar) to overcome the tendency of steep cross slope to decrease the depth of channel when made in tin- ordinar) manner will: a ditch plow. 'I he sketch do this page ill u- 1 1 .it i - how much ditch capacit) i- lost a- tin- cross dope increases, where it he- comes excessive, and how it can be restored by excavating uphill and filling downhill to form a contour ditch. This can be done by ditching and casting the excavated material downhill with a single two-way mole-board plow and V crowder, or with a road grader. Poor maintenance may be responsible for lowered chan- nel capacity because a small ditch can easily become clogged and the operator often tends to put off thorough cleaning. Frequently all the ditch maintenance that is ever done is performed by the irrigator while attending the water and consists of partial removal of the vegetal growth and other accumulated materials, with a shovel, hoe, or scythe. Watch especially for sudden clogging by windblown tumble-weeds, paper fertilizer sacks, and other materials while the irrigator is busy elsewhere. Siormwater runoff may be extremely important. If rain- fall is intense enough and the catchment area above a head ditch is sufficient to generate a damaging floodwater stream, extra channel capacity may be required to prevent ditchbank failure. Obviously no extra capacity is required ^^WM ■ -A ' W ' .v.f :■■ ■ III DITCH tlOE SLOPE Cross-slope effect on ditch capacity! Within limits of percentage of slope, loss of ditch capacity is minimized by placing as much excavated soil as necessary in the downhill hank of contour ditches. CORRUGATION SYSTEMS for head ditches at or near the top of a slope, but reserve capacity and perhaps other safeguards may be necessary when a large expanse of either virgin hillside, or steep ir- rigated slope lies above a contour head ditch. As precaution it is usually advisable to make full use of the special hillside method of earth ditch construction. As an extra safeguard it may be advisable, in some cases, to equip a head ditch with bypasses to take care of excess stream flow. Where there is doubt that an earth ditch can be made secure by these means, either a pipeline, flume, or concrete lined ditch may be required. Control devices and procedures. Water can be released from an unlined earth head ditch or forebay into corruga- tions by open cuts, spiles and siphons. What has been said about these outlets in the previous section, also applies here, with two noteworthy differences: A much smaller facility is required, and little or no variation of unit stream size is possible during an irrigation (see pages 9, 10, and 11). The latter restriction makes it almost impossible to use two streams — a relatively large one to make the water reach the lower end of the furrow as quickly as practicable, and a small one to continue the irrigation slowly until the re- quired depth of water has been applied. The small size of the initial stream leaves little opportunity to reduce it to a smaller final flow. Open cuts. When open cuts are used for outlets a small groove serves the purpose. Actually, instead of making an open cut the bank of the head ditch or forebay opposite each corrugation is reinforced with clods of sod or small pieces of fabric and the outlet is pressed into shape on top of the prepared site with a hoe. or the edge of the irrigator's shoe. This was the first type of outlet used, but falls short of pres- ent-dav standards except for use in pasture and hay fields. Spiles for corrugation are small. Wood spile outlets may be made by nailing together lengthwise four building lath to form a square tube; or by using especially grooved wood slats to form semicircular or circular tubes of 1" diameter or less. Pieces of bamboo cane make satisfactory spiles and are frequently used where obtainable at little or no cost. Siphons, too, are smaller than those previously de- scribed. The sizes range downward from what is minimal (1" diameter) for any other type of furrow to the smallest size manufactured — y>" diameter. The %" size, operated singly or in sets of two or three, has proved most useful. Checkdams, turnouts, and forebay. The special checkdam-turnout-forebay layout shown on this page points up the distinguishing features from those already de- scribed. They are needed to overcome extraordinary ero- sion hazards that attend some corrugation layouts. The design of system allows the ditch flow to bypass channel obstructions and provides dual escapeways for stormwater. The checkdams are designed to operate as spillways with Contour head ditch-forebay system for extra hazardous conditions. Extra wide, weir-type, crest-controlled checkdams, turnout and forebay overflow structures provide large capacity for safe con- duct of flood-water runoff. as liberal overflow capacity as possible so the head ditch can serve effectively as one of the emergency stormwater runoff channels. The turnouts and forebays are designed to serve as the second stormwater escape channel by inter- connecting the latter with spillway structures and using flume-type turnouts set properly to function both as turn- outs for the multiple furrow streams and as escapeways for excess head ditch flows. Under normal condition this elab- orate head ditch arrangement is unnecessary. The tappoon sheet that ordinarily serves as the checkdam also is different. Because the main irrigation stream, head ditch, and tappoon sheets are very small, it is unnecessary to follow the tappoon installation and management procedure described in Section II. Frequently the tappoon sheet is cleated across one of its sides to a narrow board which serves as the support. Otherwise the support is like the tem- porary one previously described only much smaller. No special technique is required to install these small dams regardless of whether the head ditch is full of water. Nor is any special order required for releasing the water along the ditch because the furrow streams are never so large that they are difficult to stop. Lined-head ditch systems The land slopes must be relatively long and fairly uniform in one direction to make economical the use of concrete- lined head ditches for corrugation-type furrows. Accordingly, their use usually is confined to fields that are approximately rectangular with lengths ranging from 300' to 1.000' or more (assuming the WIR of the soil makes them useable) and degree of slopes ranging from 0.5' to 8' fall per 100' of length. Construction. The methods of placing the concrete are the same as those previously described except for the hand- laying procedure. Because the ditches are small enough to allow all of the handwork to be done from the banks, little or no forming is required and the laying need not be done in alternate panels. Outlets. Outlet facilities that require many openings 37 FURROW IRRIGATION through the lower bank of a concrete-lined head ditch make the lining expensive. Forebays in which such openings might be used are not needed and even undesirable. This leaves siphons the only acceptable outlet. Turnouts anil forebays. As just stated, these facilities are not needed. If an earth ditch must be lined to prevent water loss, forebays should be barred. The arrangement shown on page 37 provides no advan- tages either. The concrete lining prevents vegetal growth and channel clogging; its smooth surface allows it to be swept clean of wind-blown trash which tends to make it immune from stoppage on that account; and its strength forestalls bank failure. Furrow reconstruction across the headland space where farm equipment must turn is easier with corugations than with flat-land furrows. On cultivated slopes even a deep mark made with a hoe often serves the purpose. Where a mechanical job is called for, it can be done by a headland furrower such as shown on page 20, bottom. Checkdams. The discussion of checkdams for lined head ditches serving flat-land furrows applies here also. Head pipeline systems The principal features regarding head pipelines are the same as for flat-land furrows, except for some less favorable circumstances that govern their adoption. Frequently the topography is such that the length of pipeline and number of required checkgates, turnout valves, hydrants, etc. makes this type of system less suitable. In areas where this is the case, there tends to be too little concrete pipe making and laying experience to promote the use of buried concrete pipelines. Head flume systems To a limited extent a contour head flume for small-tract use serves as the headland system. In such cases the irrigated tract is seldom other than a garden, home orchard, or small berry plot. The flume usually is constructed for permanent use of redwood plank 1" thick by 8" to 12" wide and is sup- ported slightly above ground on slabs of rock, cement build- ing block, or the like. The only means used to manage the irrigation stream consists of round gated holes in the flume opposite each corrugation to serve as outlets and removable groove-contained wood slats to serve as checkdams. SURFACE DRAINAGE Surface drainage is required because of the extra amount of runoff that is inherent in much of the practice of corruga- tion-type furrow irrigation. This runoff is unavoidable be- cause it is not practicable to attend continuously the small irrigation stream that is used, and virtually impossible to start the unit streams in a relatively large number of cor- rugations of different slopes and length so all of them will reach the far ends of the furrows and no further, without being frequently regulated. At least 20 per cent runoff may be expected. This water needs to be drained mostly because of its value or its nuisance. It rarely damages the crops in the field where it originates. Either an outlet drain or a tailwater re-use system will serve the purpose. Both have been discussed in Section II. IV. CONTOUR FURROW SYSTEMS Contour furrow systems (3, 17, 26) like those for cor- rugations, are designed to fit comparatively steep or uneven terrain. However, in type and arrangement they usually are completely opposite. The head ditch facility runs downhill instead of closely paralleling the contour at the top of the slope. The furrows follow in the general direction of the contours instead of crossing them as nearly perpendicular as possible. The differences extend also to size, shape, man- ner of construction, and soil erosion potential. They are built to carry large instead of miniature streams of water. If site conditions are favorable and surface irrigation is wanted, contour furrow systems are of advantage in the following situations: • For row crops where the land surface is a little too steep and uneven for flat-land furrows. • For orchards, vineyards, and bush crops where the land is steep and the irrigation streams are relatively large and are rotated among users. FACTORS AFFECTING USE Topography Where the terrain is uneven, the slopes less than about 5 per cent, and contour furrow irrigation is practiced, most of the details concerning the design, construction and operation of system are. in effect, the same as those for flat- land furrows. The shape and manner of constructing the furrows and, in fact, all features except alignment and length are essentially the same. The field layout, though, can be less desirable for irrigation. Usually fields must be broken up into a number of irregular plots to obtain satis- factory furrow slopes. This tends to require more head ditch and an assortment of furrow and row lengths all of which are handicaps. In most cases these drawbacks are sufficient to warrant the moderate amount of earth moving necessary to prepare such land for flat-land furrows. As explained earlier, steeper terrain requires a contour furrow system which is an entity unto itself. It calls for entirely different design and operation than does any other furrow system. This poses many problems which are re- solved in ways described in this section. Soil In addition to the soil and subsoil characteristics that affect other furrow systems, stability against being melted down or breached by the furrow water is a major concern. This is because of the gully erosion that would occur on steep slopes by a furrow breakthrough from one furrow to another. Water The extra effect of water in the contour furrow system comes from the rainfall intensity. Streams caused by storm waters are not subject to control by the irrigator. Hence, it is expedient to know what the stormwater runoff will be and, if necessary, to design for additional surface drainage capacity. FURROW DESIGN AND CONSTRUCTION Shape The best way to shape hillside furrows becomes very similar to the best way to shape a hillside contour ditch when the slope becomes steeper. Both undergo a loss of carrying capacity when made in the ordinary manner with a ditch plow or furrow shovel. For both, this loss can be overcome by excavating and turning the soil downhill. The need for this type of head ditch construction is amplified by the height the water must be held in the ditch to get it out onto the land. This does not apply to contour furrows; their capacity is sufficient to irrigate properly where the cross slope ranges up to possibly 15 per cent but because of stormwater runoff, reinforced lower furrow ridges may be needed where the cross slope is much less than 15 per cent. Such construction provides a necessary extra protection from the effects of intense storms or rainfall while an irriga- tion is in progress. The special furrow with extra bank on the downhill side can be made by an angle blade attached to the rear of a small tractor, a road grader, or a V-crowder. Before a V- crowder is used to do the final shaping, the ground surface has to be broken, and the furrow opened and partly formed with a moldboard plow. Guidelines If the area to be contour furrowed is steep and uneven it is important to have a contour map to study the topography and determine the furrow and crop-row pattern. Otherwise this trial-and-error procedure must be carried out much less conveniently in the field. In either case, such a slope must be subdivided, with a system of guidelines, into segments, and for each a suitable set of furrow and crop-row pattern is decided upon. The guidelines are laid out to follow the irrigation grade or furrow slope and generally should be about 50' apart. Where the unevenness of land slope causes them to spread in places to 100' or more, a closer average spacing is war- ranted. In general, the furrow slope can be, and sometimes must 39 FURROW IRRIGATION 4% 4% 10% 15% Lond Slope 20% 25% Suggested slopes for steep hill-side contour furrows. Diagram to estimate the furrow grade best suited to steep hillside land. It is based on the assumption that the grade must be sufficient to pro- vide carrying capacity for large runoff streams that possibly may be generated by intense rainfall, and that suitably small irriga- tion streams will be used (see table on page 11). Example A: You have a piece of land with a 7 per cent average slope and a usable furrow length of 600'. To plant and irrigate on the con- tour, your furrow grade should be about 2.1 per cent. Example B: Your slope is 20 per cent and usable furrow length 100' — the furrow grade should be about 1.9 per cent. Initially the lines are staked about every 50' with wood lath. For permanent marking a post may be placed at each end of the lines. Layout and construction The furrow making becomes more and more complicated as the slope and unevenness of the land surface increases. Characteristically contour furrows converge and diverge, as do the guidelines, in the places where the land slope al- ternately steepens and flattens. Hence, it may be necessary to terminate them because of insufficient space, or to start them anew to occupy widening spaces that otherwise would not be irrigated properly. The sketch on page 41, top, iden- tifies these component parts and shows where they might be needed and how they are started and terminated. Through furrows start from the head pipeline or head flume and con- tinue through to the natural runoff channel that serves the area. Spur furrows start from the headland conduit and join an adjacent through furrow. Fill furrows branch off and rejoin a through furrow. Spike furrows take off from a through furrow and continue on to the natural runoff channel. The need for many fill and spike furrows and corresponding crop rows can make the labor cost of cul- tivating and irrigating excessive and might well be an im- portant factor in determining the feasibility of contour- furrow irrigation. be, steep. This is warranted by potential damage from stormwater. Such a slope is permissible chiefly because con- tour furrows must be short, and increasingly so as the land slope becomes greater because this will limit the size of stormwater streams that can generate in them. Also, such slopes are permissible for irrigation because the size of stream that can be used efficiently in the short furrows can be small enough to be nonerosive. The graph above suggests the range of furrow slope that will afford maximum op- portunity for water disposal without damage of extraordi- nary stormwater runoff. The gradeline locating and marking is a surveying job. It can be done by a surveyor or one who knows how to use an engineer's level or. as shown below, with a grade board. Use ol a grade board for locating contour-furrow guidelines. HEADLAND FACILITIES Because the main irrigation stream must be carried di- rectly down a relatively steep slope and distributed laterally to the furrows, the type of usable headland facilities is limited. The head conduit must be a pipeline or flume, and the turnouts and outlets are limited to those that can be operated from these types of headland channels. The check- dam facility often must serve to dispell excess pressure head or velocity of the main stream as it descends, and also to provide the necessary energy gradient to divert and dis- tribute the water to the furrows. Head-pipeline systems A buried low-pressure concrete pipeline is the best head- land facility where it can be permanent and its initial cost can be borne. Its design, construction, and operation are the same as those described for flat-land furrow irrigation excepting for the following features: Checkgates, valves, and overflow stands. The re- quired checkdam facility is either a float-operated valve or an overflow partition which is built or installed in stand- pipes and operates automatical!) to keep the water le\el or pressure constant (30). The standpipes are spaced as needed along the pipeline and the valves or partitions are set to keep the water pressure within prescribed limits — sufficient for delivering the water to the furrows, but within the safety limits for low pressure concrete pipe This feature CORRUGATION SYSTEMS Sample layout for a contour fur- row-irrigated orchard planted on a steep hillside. It requires piecemeal planning and con- struction. The hillside is divided into narrow strips by guidelines that follow the furrow grade. These strips widen and narrow with changes of land slope mak- ing necessary an arrangement of through-fill-spur-spike furrows to utilize land space efficiently. increases the need for expert design and construction of head pipelines. Outlets and turnouts. The types of outlets that can be used and how they operate depend upon the slope of the pipeline. When the slope is great, only gated pipe and closely spaced outlet-turnout valves can be used. Also, the number of furrows that can be served by them is limited. The number that can be reached directly from each turn- out-outlet valve may be four or less, and the sections of gated pipe may be limited to two short lengths connected separately to the turnout hydrants on their downhill and uphill sides. The pipeline turnouts must be placed cor- respondingly close together. Head-flume systems Flumes rather than ditches typify the open-channel head- land systems. Their range of application is more limited than of buried concrete pipe, particularly as to the maxi- mum slope on which they can operate successfully and the largest stream of water that can be managed properly. Their advantages lie in lower initial cost and the option of installing them permanently, or making them in sections so they may be assembled and used and taken apart and re- moved as need be. The least costly of such structures is a V-shaped wood trough formed by nailing two 1" by 12" planks together Flume built in sections from planks and assembled by overlapping. lengthwise along one of their edges and by fastening the other two together with a 1" by 2" cross-tie nailed in place across the top of the V. It usually is built in sections for portable use and is assembled as shown below by lapping 6" or so of the lower end of each upstream section onto the upper end of the adjoining downstream section. When a flume is permanent, its cross-section is usually rectangular, about 12" wide and 8" deep. It is usually constructed of redwood or concrete. Checktlams and outlets. Either a cleat about 2" hieh 41 FURROW IRRIGATION placed across the bottom of the rectangular flume in a slant- ing position, immediately downstream from each furrow outlet, or a small obstruction (such as a rock of proper size and shape ) similarly placed in the portable V-shaped flume, serves as the checkdam. This arrangement provides the energy gradient necessary for diverting the furrow streams, cither l>y changing slightly the direction of flow of the flume stream toward each outlet as it is reached, or by still- ing the flow opposite each outlet. To some extent the cleats, or obstructions, help by retarding the stream velocity. The obstruction that constitutes the checkdam is, in reality, a part of a checkdam-outlet arrangement for each furrow. The outlet opening itself consists of a 1"- to 2"-di- ameter hole through the side next to the furrows and level with the flume bottom. It usually is equipped with a metal slide gate either at the inlet or outlet end to regulate the size of opening. CROPPING The crops that may be grown and contour-furrow irri- gated on hillside slopes of more than 8 per cent are limited almost entirely to trees, shrubs, and vine-type perennials. Possible exceptions are manually cared for garden-size plots such as small strawberry farms. Trees and tree-like plant- ings are suitable because of their terrain-stabilizing advan- tages and the conformity of their spacing to that of contour furrows. The terrain-stabilizing advantage comes from the permanent and elaborate reinforcement of the soil by the root systems of the plantings and from the fact that cultiva- tion is not necessary. Tree spacing in orchards is not being interfered with by the way the furrows must be built, with a wide embankment on the downhill side and little or none uphill; yet, such furrows may make the spacing entirely wrong for row crops and render the ground surface too uneven for hay and grain. SURFACE DRAINAGE Natural draws, gullies, or coulees usually are suitably spaced and sufficiently well developed and stabilized to take care of all needs for surface drainage, provided the topo- graphy and vegetal cover are kept essentially as they were originally and the irrigation is managed with reasonable care. However, changes often are made to obtain better arrangement of fields and to grow crops of greatest value. Generally, such changes seriously and unpredictably dis- rupt the natural surface drainage, particularly by storm- water runoff from steep terrain. Control structures of stone and concrete will be needed in the altered runoff channels, but where and of what type they should be, usually must be determined by trial and error. The whole problem of surface drainage makes the prac- tice of hillside contour-furrow irrigation risky. Largely because of this, but also because of the lowering cost of sprinkling systems, the latter is gradually replacing the use of contour furrows for irrigation of steep land. V. FURROWS OF MISCELLANEOUS SHAPES Some soils, waters, crops, and irrigation slopes make desirable the use of furrow and seed-bed shapes other than those already described. The shaping of the furrows and seed-beds may provide planting strips essentially free of harmful salts, where salt in the soil or irrigation water is a problem. An unusual shape may be called for by the cul- tural practice that is followed. A shape that affords the greatest opportunity for water intake may be needed. Or a shape may be used to correct a small but troublesome ex- cess irrigation slope. The use of special furrow shapes for such purposes is limited by the topography and the crop row spacing. The latter must be sufficient to accommodate the unusual kind of furrow, and the fields usually must be fairly flat. The headland arrangement, facilities for controlling the irriga- tion stream, and management of the water generally are the same as those for flat-land furrow systems. LONG, SLOPING SIDE USES Salinity control Salinity problems that can be solved by a suitably shaped furrow and seedbed (4) have been described in Section I: relatively low salt concentrations in the soil or water that will harm only the germination and early growth of seeded crops. Such salinity problems can be taken care of because the dissolved salts tend, during irrigation, to advance with, and concentrate at, the wetted front as it moves upward from the water line in the furrows to the top of the beds. The way the salts can be made to move and concentrate without becoming harmful, is illustrated below. In general, for salinity control there must be a peaked bed arrange- ment, as shown in the photo on page 17. This isolates the greater part of the harmful salts along the top of the beds when the water is left in the furrows long enough to com- plete the movement. The long, flattened slope from the top of the bed down to the edge of the water in the furrow, affords a relatively salt-free strip of the proper width for planting. The graph on page 44 shows more precisely how salinity control can be achieved when this alone is the aim and when crops are planted in rows 30" and 40" apart. The furrow must be designed in a way that no excess soil remains on one side of the bed when the peaked bed is flattened by cultivation. This conversion is permissible after the seedlings are established because by that time the roots have penetrated into the salt-free soil beneath the fur- rows and are relatively unaffected by the salts that subse- Sloping-bed furrow construc- tion for salinity control. Harmful salts move to the top of the planted ridge dur- ing the irrigation. Under these conditions, poor seed germination and plant emer- gence can be improved by peaking the ridges so they contain most of the salts, and by planting along the sides where salt content is lowest. SINGLE ROW BED HIGH SALT ACCUMULATION LOW SALT ACCUMULATION SEED FAILS TO GERMINATE SEED GERMINATES WETTING FRONT s*\. iL^p. Z*<\ 4 : N njflifflBr J 1 " ACCUMULATION DOUBLE ROW BED HIGH SALT ACCUMULATION SEED FAILS TO GERMINATE WETTING- FRONT LOW SALT ACCUMULATION SEED GERMINATES x HIGH SALT ACCUMULATION SLOPING- BED FURROW CONSTRUCTION FOR SALINITY CONTROL 43 FURROW IRRIGATION f *** ■J :.:. ~>\r -^rT ikj: - 'f*~ &k> T ' • ... - I 1 :::: " " * i -vr— i ' 1 1 1 : : : : ' ' ' ' fy- ' ".:. K. ; ::-. ;:i: ::u :_:• -— — ] ■ — — - — .__,. ,„ ~~ 30 INCH SPACING :::: ril::~ :?:: !:: — ~1 fPf : : : : ip \ :±i r t :: | — Solid line indicates profile of sloping bed shape. Dotted line indicates standard flat- topped beds which may be formed by cultivation, without moving soil across the plant rows. \ J y^- \ -""V T~ ^ \~~~- k-^7* s^- \ \ --^\ ^ — -^ -=;_ N_ ._• V -.T^ 40-INCH SMONG This diagram shows how alkali-control furrows can be designed for conversion into standard furrows. Solid line represents profile of peaked-bed shape, dotted line that of the standard flat-topped bed which is formed by cultivation without moving soil across the planted row. qucntly accumulate in the flat-topped beds. The conversion is important because it permits the use of conventional equipment for cultural operations. The initial shaping operation requires the use of an implement similar to the one shown below. It usually is made to order locally for the purpose. The irrigation practice differs from two mentioned ear- lier ("irrigation before planting, either in the bottom of the furrows, or on top of the ridges after they have been leveled) in that it causes neither loss of moisture or soil crusting. The water is applied as shown on page 43 so that it wets the planting strip by capillary action only. It is ap- plied in this manner at first in the alternate furrows ad- jacent to the gently sloping surfaces. Later, after the seed- lings have become established and following conversion to the flat-topped beds, it is applied in every furrow. Early crop maturity A special furrow and bed design, similar to that for salinit) control and which can serve that purpose, too, is used for hastening the development of early-market crops. The similarity and dual Utility lies in the sloping seedbed Shapei lor making alkali-control furrows. that is required for both types of furrow. In this case, the main purpose of the sloping bed is to expose the plant rows to the sun. This requires an east-west row alignment and a south exposure. If a saline-salt problem also is present, as sometimes is the case, the salt-free planting strip and peaked bed top are essential. Otherwise it is necessary only to plant and irrgate so that the crop- row will be above the water in the furrow at all times. The planting must be done along the south side of each bed and the irrigating in every fur- row. The implement for shaping the furrows and beds is like the one shown below except that the framing may be different. BROAD-BASE FURROW USES Three situations may warrant the use of extra wide, com- paratively shallow flat-bottom furrows: soils that require as much water intake opportunity as possible; the need to avoid cultivation to prevent soil compaction; and irriga- tion slopes between 0.1 and 0.5 per cent. The furrows used for these purposes usually are less than half the depth of flat-land furrows and range in width from 30" to 36". As shown on page 45. the equipment for ex- cavating the furrows and the scarifying attachment that may be necessary for some soils consist of a V opener fol- lowed by a rotating circular harrow mounted as a single unit or in gangs for making one or more furrows at one time. Increase of water-intake opportunity Soib thai arc naturally tighl because of a physical condi- tion and some that have suffered compaction that adversely low eis their \\ II!. may be irrigated with n furrow shape 11 FURROWS OF MISCELLANEOUS SHAPES Tractor-mounted implement used for making broad-base furrows. that affords a maximum water-intake opportunity. The broad-base shape fits this need (39) and it is used, except when barred by steep slope, narrow spacing of crop rows, or cultural practice. The following features make broad-base furrows especially suitable: The broad base is effective for increased water intake because the broader a furrow is the greater is its wetted soil area and its opportunity for water intake. In this respect, it has a similar effect as flood irrigation by the border method. The manner in which the furrow is made and can be maintained increases the water-intake effectiveness of its large wetted surface. This consists of forming the furrow in broken ground and scarifying the broad bottom as may be needed to maintain the fractured surface. The ground breaking usually is done with a disk plow and the furrow- ing and scarifying with the V opener and revolving circular harrow attachment shown above. The broad base and roughened surface retards the veloc- ity of the furrow streams and slows down irrigation to provide extra time for water intake. Minimizing of soil compaction Noncultivation often is used to prevent a soil from be- coming excessively compacted, because tilled soil usually will compact more. Soil compaction needs to be prevented particularly in orchards, vineyards, and other permanent plantings in which farm machinery must traverse between the rows many times a year for fertilizing, mowing, dusting, spraying, harvesting, and pruning. Experience has shown that soils withstand compaction by such operations best when the ground surafce is firm and sodded. The following characteristics of broad-base furrows make them especially suitable in these respects: The wide, flat bottom and broad, low intervening ridges are such that the wheels or runners of equipment will follow or cross them without materially damaging the furrow channel. Thus, the ground surface is little disturbed. The shallow depth and large area of the furrow channel permit effective grass and weed control by mowing. This takes the place of cultivation for grass and weed eradication and thus saves disturbing the soil surface. Also, since the sod that forms as a result of the noncul- tivation affords a superior bearing surface for the wheels and runners of farm equipment, it further lessens the tendency of the soil to become compacted. Cultivation can also be avoided by resorting to chemical weed control. However, in such case the superior bearing quality of a sodded surface is sacrificed. Irrigation slopes of 0.1 to 0.5 per cent Broad-base furrows are esssentially a flat-land type, but they ordinarily require more slope, This makes them useful for dealing with the slightly excessive 0.1 to <0.5 per cent slope range. Fields that are furrow irrigated often are graded to a slope that is too flat for either contour or corrugation fur- rows and a little too steep for flat-land furrows — a range of slightly more than 0.1 per cent up to approximately 0.5 per cent. Slopes in this range must be dealt with because fields of 40 acres or more usually are graded to conform with the average natural land slope when it falls within this range. Furthermore when furrow-irrigated crops are grown in rotation with those that are border-irrigated, which is com- mon practice, the ideal slope of at least 0.2 per cent for the latter is provided, if possible, rather than that of 0.1 per cent or less which is best for flat-land furrow irrigation. In such cases the job of irrigating by the furrow method calls for use of the flat-land furrow layout in ways that counter- act these excess slopes. One such way is to adopt the broad- base furrow shape. 45 VI, FURROWS OF MISCELLANEOUS ARRANGEMENTS Furrows arranged differently from those already dis- cussed may be used to advantage to deal with one or more of the following irrigation difficulties: Crops that require special furrow patterns because of their planting arrange- ment or growth characteristics; streams of water too small for irrigating strip checks; irrigation slopes that are exces- sive for flat-land furrows; and poor furrow WIR. These furrows, like those of miscellaneous shapes, re- quire only an alteration of one of the three principal fur- row systems. Except as noted, the lay of the land, head-ditch facilities, and management of the water are the same as those for flat-land systems. CROPS Orchards Trees make special furrow arranging necessary. When young they occupy little of the space that must be provided for their future growth. When fully grown they require con- siderable space and some a great deal more than others. Trees that characteristically are low branching, and for production reasons must remain so (such as citrus), monopolize the space beneath them, while those with branches high enough to be out of the way (such as decidu- ous fruit and nut trees) allow close-up access for furrowing. Citrus trees, when furrow irrigated, are planted in rows about 20' apart and spaced the same distance in the rows. The furrow layout, while the trees are young, is designed in a manner similar to that shown below, limiting irriga- tion to the area where it is needed close around the trees. The water is conveyed along each row by a single furrow and made to change course every 20' to encircle each tree. After the trees become old enough for their root systems to extend materially into the open space that surrounds them, the furrow layout is changed to a permanent one similar to that shown on page 18, to irrigate from tree to tree both in and between the rows. The water is conveyed along each side of each row by a single broad-base furrow which changes course to turn into and back out of each interval between the trees in the rows. As stated, the use of broad- base furrows is a particularly important feature of the final layout, because it permits a noncultivating cultural practice which helps to prevent soil compaction between the rows. To make the single-furrow pattern for the young trees, a furrow is opened in the ordinary way with power equip- ment close up and parallel to each row, and then blocked at each tree with a mound of earth by excavating and adjoin- ing the encircling sections by hand with a shovel. The zig-zag two-furrow pattern for the older trees is con- structed by first furrowing in the ordinary way with power equipment both between and across the rows and then fin- ishing the job manually by terminating and breaching the furrows as required where they cross. The amount of hand work required to construct the fur- rows for the young trees and then for the older trees is not a serious disadvantage, because the final layout usually is permanent. Deciduous orchards need different furrow patterns than citrus groves. In general they consist of two, four, six, or eight parallel furrows per tree row depending upon the age of the trees and their spacings. The sets are arranged so that half of them are parallel to the tree rows on one side and half on the other. Deciduous fruit trees usually are planted in rows 20' to 24' apart; for nut trees the distance between rows varies from 24' to 60 / . The furrow interval ranges from 4' to 6'. Single-furrow arrangement for irrigating newly planted trees. 47 FURROW IRRIGATION A TO v. U . . • ' J£_*i «/ > r rf -^ ? l ... . w .< ' J J , - Cl~ " * ' J J t to . V7 ' ' — *■>/» 50* .-:^ ■■A."- *- - C< - Z a- i, ir ', r ,. - - a -, Jo t- -'-' '*, %'*- -I J ^ =r 7 a , ^ ^ : :^ - a r /. L O / J ^- V ' y w I inn i.isouis to show how ii.ii I. hkI, dedduotu orchard furrowa may he arranged to best advantage. / "/■ i* ^ the lust three or loin m.iis .iiiii planting :i two-furrow tyitem will suffice for each row. Second: Later, a four-furrow arrangement is required and will l»< mffident tot 2H' x '_'0 plantings. Third and bottom: \ six <>i eight-furrow system is needed for trees (such as nut trees) of greatei rool ipread which «.iii foi ipadngi up to r )0' and (»0'. i:; FURROWS OF MISCELLANEOUS SHAPES y///////////////M ^ v, V////////////// //// //////////7////A \ t 1^^^^^^^^^^^^^ t i\ ^^^/T^^Z^ZZZ^l /////////////7\ ± // vine row; t V///////////////// / ////////////A 4 /, \ Y////A V///////////7&W/////////////////A » -7777 Z 'M X///////7777//?//////, '///////////', 777T7777777} " S/Z'/ // /'/ , s////S'/ 77 ////////// Three-furrow single-course furrow arrangement for irrigating vines and bushes. The 12' row spacing commonly followed is com- pletely traversed both laterally and lineally by this arrangement. The course followed by the furrow stream, as shown by arrows, allows extra time for water penetration often needed in vineyards because of compacted soil. The top sketch on page 48 shows how fruit and nut trees may be irrigated to best advantage while they are young. The single furrow on each side of the rows can be made close enough to the trees to insure adequate irrigation across the rows for the young trees and far enough apart to make their use suitable later for the older trees. This is true also of the arrangement shown on page 47, it saves water, reduces the need for weed control while the trees are young, and construction is fast and inexpensive. As the trees grow older, the number of furrows is in- creased until they occupy half the space on either side of the rows are shown in the second sketch on page 48, when four furrows suffice. This is the final furrow pattern for irrigating trees that are planted in rows from 20' to 24' apart, which includes most fruit orchards and some nut groves. It also serves as an interim furrow arrangement for trees that are planted in rows further apart, but not mature enough to fully occupy the space between the rows with their root systems. The six-furrow pattern, third sketch on page 48, is an interim furrow arrangement, the eight-furrow pattern, the bottom sketch on page 48, is the final one for irrigating full-grown nut trees, such as English Walnut, that require 50' to 60' row spacings. Vineyards and bush plantings Normally, commercially grown vines and bushes are closely planted in hedgerows spaced 12' apart. This row spacing is unusually exacting for arranging furrows and confining for the operation of equipment that must be used between the hedgerows. The following three furrow pat- terns have been found useful in these situations: The three-furrow single-course arrangement, shown above, is especially devised to furrow the 12' strip be- tween the hedgerows as completely and efficiently as pos- sible. It consists of three furrows blocked and connected in a manner to provide only one course for the furrow water to follow. The three furrows are opened and the blocking and interconnecting is done in one operation by the ma- chine shown below. Furrowing and blocking machine for making the three furrow single-course pattern. 49 FURROW IRRIGATION How to furrow in vineyards to reduce soil compaction. Dry runways are provided for the wheels of the numer- ous pieces of equipment used in vineyards. Furrows are made as far apart as possible on either side of the inter- space between the headrows, with a third furrow midway in between. The two-furrow pattern takes the place of the three-fur- row single-course pattern when needed and suitable. The two-furrow arrangement, for instance, may be advantage- ous where the two furrows are shaped so they are tracked without affecting their shape or alignment by the wheels of the cultural equipment. The plan is satisfactory when the soil will not compact readily when wet. The three-furrow plan shown above avoids tracking furrows with implement wheels where soil compaction is a serious problem (5). This is accomplished by providing two relatively dry ridges that are located and shaped so the) can be easily tracked by the wheels of implements. To this end, during cultivation at the start of each season, the soil is pulled away from each side of the rows sufficiently to form under-plant furrows. A V-shaped furrow is then made midway between the rows, completing the pattern. All three of these furrow layouts are left intact as far as possible throughout the irrigation season. Ordinarily, no disking or working up of the soil is done except at the end of the growing season and in the spring when the furrows arc made again. During the season a grass or weed mulch i- established or allowed to develop which is chopped as the need arises. SMALL IRRIG V HON STREAMS \ pecial furrow pattern may be used with a stream of watei too small for contour-check or strip-check irrigation. If possible, irrigation checks should be Hooded quickly with a I. ii". tream but, if necessary, a relatively -mall Btream Combination basin-furrow system for orchards for which an extremely small irrigation stream is available. >0 FURROWS OF MISCELLANEOUS ARRANGEMENTS ■ ' ' ' ' ■' ' ' - i ' ' ' 'I I'M!), ,fO t 1."{\ f ■ HEAD DITCH "■nun <)>i,\,' 'I .| i, >).i i>i' / "> Two-furrow single-course pattern for reducing slope in the direction of irri- gation. 4^. 4* e^7 £7 -ty 4" + ?Z2> iIi' i m i m i .i.h n i yin # can be made to spread properly across them by furrows. (See photo on page 50, bottom.) The combined furrow and strip-check system must be constructed step by step. First the furrowing must be done either in the direction that affords the shortest average length of furrows within the checks or across the rows of widely spaced permanent plantings. They are made in the ordinary manner with tractor-mounted furrow opening shovels of the proper size (photo page 20, top) . The levees that form the checks are then made with a border disk. An important feature of their construction is the small trenches left on either side of them. They serve as the head ditches for the furrows in each strip-check. The system is completed while irrigating by blocking these secondary head ditches at the proper places to make the water fill all of the furrows. The crop determines whether and how the combined fur- row and strip-check arrangement can be used. Deciduous orchards and some row crops can and occasionally must be irrigated by this means. Deciduous orchards are suitable because the trees are out of the way of both furrow and levee construction at all times. Row crops can be planted before the levees are in place and grown without cultivation or other operations requiring the use of implements on the ground between the rows. These are prerequisites because of the extreme shortness of the crop rows. The sorghums are particularly suited for this type of irrigation. REDUCTION OF FURROW SLOPE The special furrow arrangements that are useful for dis- posing of excess slope in the direction of irrigation include the three patterns shown on pages 18, 47, and 49, top, and a fourth arrangement shown above. The circuitous course of the furrows in each of these patterns increases the distance water must travel to reach the lower end of fields and there- by decreases the slope in the direction of irrigation. Gen- erally from 0.1 to 0.2 per cent excess slope may be disposed of in this manner. The pattern shown above — the checkback system — consists of two furrows which are alternately blocked and interconnected so that a single stream of water serves both. As shown by the arrows, the single stream of water is turned into one of the furrows which it follows until stopped by an earthen fill and diverted through an open cut into the second furrow. In the second furrow it moves both ways — down-stream until it is blocked again and diverted back into the first furrow, and upstream as far as it will back up. Upon return to the first furrow the flow pattern is repeated as often as may be required before reaching the end of the irrigation run. Obviously there is a practical limit to how much the water level can be raised at the earthen fills and how far the stream can be made to back up into the upper halves of the furrow sections. In general, the length of pat- 51 FURROW IRRIGATION tern in relation to the slope in the direction of irrigation should be such that both furrows may be filled with water throughout their lengths. The plan can be applied to each of the multiple-furrow orchard patterns shown on page 48, but it is perhaps of greatest value for reducing the slope of row-crop furrows. The best furrow slope for rows crops is 0.1 per cent or as much less as can be kept uniform. When this slope is be- tween 0.1 and 0.5 per cent it usually is necessary to slow down the stream flow and raise the water level in the fur- rows to provide moisture high enough in the rows for the germination and early growth of seeded row crops. This is most easily done by the checkback furrow procedure. It requires simply that the rows be cut through and the furrows blocked at the proper places. If the irrigator is adept at the job, the water will run properly without further attention. The two other means — changing the direction of irrigation to one of less slope, and checking the flow in each furrow by placing barriers along each furrow — are more troublesome for reasons already cited. INCREASE OF FURROW WATER INTAKE Any alignment of furrows that makes water stand high in them during irrigation, or that keeps them out of the way of the wheels of machinery during cultivation, may be help- ful in dealing with critically low furrow WIR problems. These are additional reasons for using the circuitous furrow patterns shown on pages 18, 47, 49, and 51. APPENDIX A: CONVERSION TABLES Table A-l LENGTH: UNITS FOR STATING FURROW LENGTHS, DEPTHS, WIDTHS, SPACINGS AND SLOPES; PLANT ROOTING DEPTHS, AND OTHERS Useful approximations: 4" = 10 cm; l' = 30cm; 33' 10 mi = 16 km. 10 m; Inches (") (in) Feet (') (ft) Statute Mile (mi) Centimeters (cm) Meters (m) Kilometers (km) 1 0.083 2.54 0.254 12 1 30.48 0.305 5,280 1 1,609 1.609 0.394 0.0328 1 0.01 39.37 3.281 100 1 001 3,281 0.6214 1,000 1 Table A-2 AREAS: UNITS FOR STATING AREA OF LAND IRRIGATED Square feet (ft 2 ) Acres (A) Square meters (m«) Ares (a) Hectares (Ha) 1 0.0929 0.00093 43,560 1 4,047 40.468 0.405 10.764 1 0.01 0.0001 1,076.40 0247 100 1 0.01 107,640 2.47 10,000 100 1 Useful approximations: 1 m 2 = 11 ft 2 ; 1 A = 0.4 Ha; 1 Ha = 2.5 A Table A-3 VOLUME: UNITS FOR STATING VOLUMES OF WATER AND DEPTHS OF WATER APPLICATION USED FOR IRRIGATION depth of wiitar od or hectare of land. Oallom • i [can) ( Jallons (Imperial) imp. (gal) 1 nine feci (ft») Acre-inches (A-in)' Acre-feet (A-ft)* Liters (H) Cubic-meters (m3) Arc- Centimeters fa-cm)* Hectiire- Centimeters (Iln-cni)' 1 1 201 27.154 0.827 1 220 0.134 (i 161 1 8,630 U 560 n 0363 13 l 12 0007 973 083 1 (i 0008 ii 081 3.785 4.546 28 32 1 1.000 100,000 0.0038 0.0046 0.028 102.8 1,239.0 0.001 1 100 o oo:is 0.0045 0.028 102.8 1,280.0 0.001 1 100 00028 1.028 12.39 ooooi 01 1 APPENDIX Table A-4 PRESSURE: UNITS FOR STATING WATER PRESSURES SUITABLE FOR HEAD PIPELINES AND NECESSARY FOR OPERATING SPILE, SIPHON, AND SURFACE GATED PIPE OUTLETS Pounds per square inch (psi) Feet of water column (ft head) KilogTams per square centimeter (kg/cm') Meters of water column (m head) 1 0.433 14.22 1.422 2.307 1 32.81 3.281 0.070 0.030 1 0.1 0.703 0.305 10.000 1 Important components: 1 cu ft of water = 62.4 lbs. lm'ofwater = 1,000kg. 1 liter of water = 1 kg. Table A-5 TIME: UNITS FOR STATING WATER INTAKE RATE OF SOILS (WIR) AND ADVANCE RATE OF FURROW STREAMS (WAR), RATE OF WATER APPLICATION Hours per 1-inch of water intake Hours per 1-centimeter of water intake Minutes per 100 feet of furrow- stream advance* Minutes per 100 meters of furrow- stream advance* Hours per 1-inch per acre water application* Hours per 1-centi- meter per are water application* Hours per 1-centi- meter per hectare water application* 1 2.54 0.394 1 10 3.048 32.81 10 1 0.01 1 0.01 1 0.01 1 0.01 1 Bases of conversions: Identical soil and same size furrow and irrigation stream. * Conversions differ from those shown to extent that 1" = 2.54 cm and 1 hectare = 2.47 acres. Table A-6 FLOW RATES: UNITS OF FLOW FOR STATING FARM- SIZE IRRIGATION STREAMS AND FURROW STREAMS Gallons per minute (American) (gpm) Gallons per minute (Imperial) (gpm) Cubic feet per second (ftVsec) Liter per second (lt/sec) Cubic meters per second (m'/sec) 1 1.201 448.8 15.852 15,852 0.827 1 373.7 13.196 13,196 0.00223 0.00268 1 0.353 35.3 0.063 0.076 28.3 1 1,000 0.000063 0.000076 0.0283 0.001 1 Usef u 1 approximation : 1 cu ft/sec of water flowing on 1 acre for 24 hours sq ft in 1 acre 2 feet depth of water application 1 X 60 X 60 X 24 = 1.98 acre feet per acre. Also 43,560 1 cu ft/sec of water flowing on 1 acre for 1 hr sq ft in 1 acre or 1 X 60 X 60 X 1 1 inch depth of water application 43,560 0.08264+ feet depth of water application = 0.992 inches depth of water application. 53 FURROW IRRIGATION APPENDIX B: CAPACITY TABLES AND CHARTS FOR HEADLAND FACILITIES UNLINED HEAD DITCHES Bases: Coefficient of roughness (n) = 0.03 (channel fairly w ell maintained) . Velocity of stream (V) = feet per second. Rate of flow (Q) = cubic feet per second. How to determine the required ditch size. Given a 1.200 gpm (2.67 cfs) head ditch stream. The common earth head ditch gradient of 0.1 per cent and 1 il 1 /^ side slope are to he used. Generally, under these conditions the velocity (V) of the prescribed stream of water (in this case 1,200 gpm) is ideal for head ditch operation and can be counted on to be nonerosive. Any of the underlined capacities in the table below meet these requirements and show the bottom width of ditch and depth of stream flow that would be called for. Added to the latter should be at least 6" for free-board. Limited land space and the equipment available for the ditch making may further restrict the design that can be used. Table B-l CAPACITY OF UNLINED HEAD DITCHES Fall in ft per 100 Depth of flow in feet Characteristics 0.4 0.6 0.8 1.0 1.2 1.4 1.6 V Q V Q V Q V Q V Q V Q V Q Bottom width — 1.5' 0.1 .51 .43 .67 .96 .79 1.71 .91 2.73 1.04 4.11 1.15 5.80 1.26 7.86 Side slopes — ty&'-l 0.2 .72 .60 .96 1.38 1.13 2.44 1.32 3.96 1.48 5.86 1.64 8.27 1.79 11.17 0.3 .89 .75 1.18 1.70 1.39 3.00 1.63 4.89 1.82 7.21 2,02 10.18 2.20 13.71 0.4 1.03 .87 1.37 1.97 1.61 3.48 1.88 5.64 2.11 8.36 2.33 11.74 2.54 15.85 0.5 1.16 .97 1.53 2.20 1.80 3.89 2.10 6.30 2.35 9.31 2.61 13.15 2.84 17.72 Bottom width — 1.5' 0.1 .51 .39 .67 .84 .79 1.45 .90 2.25 1.03 3.34 1.13 4.59 1.22 6.05 Side slopes— 1:1 2 .72 .55 .96 1.21 1.13 2.08 1.30 3.25 1.46 4.73 1.60 6.50 1.74 8.63 3 .89 .68 1.18 1.49 1.39 2.56 1.56 3.90 1.80 5.83 1.97 8.00 2.14 10.61 4 1.03 .78 1.37 1.73 1.61 2.96 1.86 4.65 2.08 6.74 2.28 9.26 2.47 12.25 0.5 1.10 .88 1.53 1.93 1.S0 3.31 2.01 5.03 2.29 7.55 2.55 10.35 2.77 13.74 B ttom width— 2' 1 .52 .54 .70 1.22 .83 2.12 .97 3 40 1.09 4.97 1.20 6.89 1.32 9.29 Side slopes— lVfcl 2 .75 .78 1.00 1.74 1.20 3.07 1.38 4.83 1.55 7.07 1.71 9.82 1.87 13.16 0.3 .92 .96 1.23 2.14 1.46 3.74 1.69 5.92 1.91 8.71 2.10 12.05 2.30 16.19 4 1.07 1.11 1.42 2.47 1.69 4.33 1.96 6.86 2.20 10.03 2.42 13.89 2.65 18.66 0.5 1.19 1.24 1.59 2.77 1.89 4.84 2.19 7.67 2.47 11.26 2.72 15.61 2.97 20.91 Bottom width 2' 0.1 .52 .50 .70 1.09 .85 1.90 .97 2.91 1.08 4.15 1 19 5.66 1.28 7.37 Side slopes — 1:1 0.2 .75 .72 1.00 1.56 1.20 2.69 1.38 4.14 1.53 5.88 1.69 8.04 1.82 10.48 3 .92 .88 1.23 1.92 1.46 3.27 1.69 5.07 1.89 7.26 2.08 9.90 2.24 12.90 4 1.07 1.03 1.42 2.22 1.69 3.79 1.96 5.88 2.18 8.37 2.40 11.42 2.58 14.86 0.5 1.19 1.14 1.59 2.48 1.89 4.23 2.19 6.57 2.44 9.37 2.69 12.80 2.89 16.65 Bottom width— 3' 0.1 .54 .78 .74 1.73 .87 2.92 1.04 4.68 1.17 6.74 1.29 9.21 1.41 12.18 Side slopes— 1H:1 0.2 .81 1.17 1.07 2.50 1.30 4.37 1.48 6.66 1.67 9.62 1.84 13.14 2.00 17.28 3 .99 1.43 1.32 3.09 1.60 5.38 1.82 8.19 2.06 11.87 2.26 16.14 2.46 21.25 4 1 14 1.64 1.53 3.58 1.86 6.25 2.13 9.59 2.38 13.71 2.61 18.64 2.84 24.54 0.5 1.29 1.86 1.71 4.00 2.07 6.96 2.38 10.71 2.66 15.32 2.92 20.85 3.17 27.39 Bottom width V 1 .55 .75 .75 1.62 .90 2.74 1.05 4.20 1.17 5.90 1.29 7.95 1.40 10.30 loped 1:1 0.2 .81 1 10 1.07 2.31 1.30 3.95 1.48 5.92 1.67 8.42 1.84 11.33 1.99 14.65 3 .99 1 . 35 1.32 2.85 1.00 4.86 1.82 7.28 2.06 10.38 2.26 13.92 2 44 17.96 4 1.14 1 55 1.53 3.30 1 , 86 5.65 2.13 8.52 2.38 12.00 2.61 16.08 2.81 20.68 0.5 1.29 1.75 1.71 3.69 2.07 6.29 2.38 9.52 2.66 13.41 2.92 17.99 3.15 23.18 II 1 Depth of flow in eet .5 •i 5 1.0 1.25 1.5 \, 1 / .45 211 .59 .51 .72 1 01 .85 1.76 .97 277 \. y II 2 til .29 .83 .71 1 HI 1 . 40 1 21 2.50 1.88 3.95 -^.y ii :i 7s .35 1 02 ss 1 27 1 7S 1.49 :i 08 1 . 69 1 88 i 'H .41 1 III 1.02 1 is 2.07 1.72 3.56 1.95 5.58 0.5 1 02 40 1.33 1 14 1.65 2 31 1.92 8 '.'7 2.19 6.26 -.1 APPENDIX .3 - 1 Capacity of concrete-lined head ditch. 55 FURROW IRRIGATION SMALL CONCRETE-LINED HEAD DITCHES Bases: Coefficient of roughness (n) = 0.015 and 0.016 (applicable to slip-form and hand-laid types) ; side slope 1:1; bottom width (b) = 8" and 10"; depth (d) as shown on the chart. How to determine the required size of ditch. (See chart, page 55.) Given a ditch grade of 0.08' per 100' and a required ditch flow of 2500 gpm. Assume n = 0.016 (most common applicable value) and start with slope = 0.08 on the right side of scale ®. Continue through 2500 on gpm scale ®, to depth of water 1.4' when d = 8" or 1.33' and b = 10". Then add at least 3" for free-board. HEAD PIPELINES Bases: Prefabricated, dry mix (tamped or packerhead) concrete pipe not more than 21" in diameter and in pipe units not more than 3' long, in which mortar joints are not finished by hand on the inside of the pipe. Flow of water in concrete pipe via Scobey's formula Cs = 0.310. How to find the diameter. (See chart below.) To determine diameter of pipeline that must flow at least 3 cfs while operating with a head of 10' follow broken lines from 10' on horizontal scale and 3 cfs on vertical scale until they meet. Because this intersection falls between the di- agonal lines representing the rates of flow of 10" and 12" diameter pipe and a pipe of intermediate size is not manu- factured, it is necessary to use the 12" size. SMALL RECTANGULAR WOOD HEAD FLUMES Bases: Smooth interior, checkdams removed and outlet gates on outside of flume. Coefficient of roughness (N) = 0.012. (See table B-2.) Table B-2 CAPACITIES OF SMALL RECTANGULAR WOOD HEAD FLUMES Inside width Grade Carrying capacity for depths of: 3 inches 6 inches 9 inches 12 inches inches feet per 100 1 0.2 5 10 2.0 cubic feet per second 10 0.214 0.304 479 0.679 0.961 0.575 0.816 1.29 1.82 2.58 12 1 2 5 10 2 0.27 0.39 0.60 0.87 1.25 0.75 1 06 1.88 2.37 3.35 1 30 1.84 2.91 4 12 5.19 18 1 2 5 1 27 1.82 2.88 2 25 3.18 5.07 3.30 4.69 7.50 SPILE TURNOUTS AND OUTLETS Bases: Construction material usually is concrete for turn- outs and metal for outlets. The diameter ranges from 4" to 10" for turnouts and from 1" to 3" for outlets. The tubes are straight and from 2'-8' long. Flow rated according to (inside diameter) of tube and pressure head as shown below. How to determine the size-tube outlet needed. (See top chart, left, page 57.) Assume the unit furrow stream re- quired is 25 gpm and the effective head (H) is 4". Follow the broken line vertically from 25 on the horizontal scale and horizontally from 4 on the vertical scale until they meet. The intersection shows that a l 1 /^" diameter spile is too small for the purpose and that it is necessary to adopt the next larger size which is 2" in diameter. 5.0 10 FEET Pen 1,000 FEET HEAD + "T- water surface SUBMERGED HEAD CENTER OF DISCHARGE FREE FLOWING Capacity of prefabricated concrete head pipeline. Head measurement! tor, spile-tube outlets and pipe turnouts. The vertical distance! labeled "head" must be known to determine the discharge, (See graphs <>n pages 89 and 21.) APPENDIX - ' 1/ 1 / / i ' -2 - / 1 ,.. (o !^ - / -^ 1 "^ 1 1 ! " - 20 30 40 FLOW-GALLONS PER MINUTE J Q / o ^ *>/~ y */ 1 ." / / / *) to/ / / , \5< / $S / ,oii^ / _jj^-i / / 0.9 1.0 I.S CUBIC FEET PER SECONO Top: Flow through siphon-tube outlets. Bottom: Flow through siphon-tube turnouts. furrow stream required is 20 gpm and the effective head (H) is 4". Follow the broken lines vertically from 20 on the horizontal scale and horizontally from 4 on the vertical scale until they meet. The intersection shows that a 1%" di- ameter siphon is too small for the purpose and that it is necessary to adopt the next larger size which is 2" in diameter. HEAD PIPELINE TURNOUT VALVES Table B-3 gives the required pressure head through vari- ous sizes of buried concrete pipeline turnout valves (Alfalfa and Orchard types, photos on page 28, sketch on page 59, top) for a wide range of discharges. Flows are given for valve disks completely open or removed. Bases: The table is based on the orifice formula: Q = CAV2gh where, Q = the discharge cfs and/or gpm. A = cross-sectional area of valve opening in sqft. C= orifice coefficient, g = acceleration of gravity, 32.2 ft sec. h = pressure head in feet depth of water. The studies made of the C values indicate that, for 8", 10", and 12" riser pipes with webs inserted in the valve seat, valve seat submerged to various depths, and for veloc- ities (V) ranging from 0.9' to 6' per second, C = 0.9V- 0123 This relationship has been extended in table B-3 to cover a wide ranee of valve sizes and rates of flow. 57 FURROW IRRIGATION Table B-3 HEAD LOSS THROUGH ALFALFA VALVES Discharge CFS .2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.5 5.0 5.5 6.0 7.0 8.0 9.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0 35 40 GPM 90 180 270 360 450 540 630 720 810 900 (WO 080 170 260 350 440 530 620 710 800 025 250 475 700 150 600 050 500 400 300 200 100 000 900 Mill 700 ,600 500 750 000 Diameter of opening .02 .09 .23 .45 .73 1.12 1.58 2.11 2.72 3.50 4.34 5.29 6.20 7.52 8.87 .03 .06 .12 .20 .31 .43 .58 .75 .96 1.18 1.47 1.76 2.03 2.34 2.72 3.20 3.58 4.10 4.53 5.87 7.58 9.40 10" 14" 18" 20" feet of water .07 .11 .16 .21 .28 .36 .44 .54 .64 .74 .89 1.01 1.16 1.30 1.50 1.67 2.16 2.72 3.43 4.17 5.82 7.95 10.35 13.0 .09 .12 .16 .19 .24 .28 .33 .39 .44 .52 .58 .66 .73 .96 1 21 1.52 1.85 2.57 3.51 4.53 5.72 8.83 12.35 .08 .10 .12 .14 .17 .20 .23 .26 .29 .33 .37 .48 .61 .75 .92 1.28 1.74 2.24 2.95 4 35 6 04 8.28 10.7 .08 .09 .11 .12 .14 .16 .18 .20 .26 .34 .42 .51 .71 .96 1.24 1.60 2.41 3.40 4.53 5.87 7.59 9.38 .06 .07 .08 .09 .11 .12 .16 .19 .25 .29 .42 .57 .73 .94 1.43 1.98 2.67 3.50 4.42 5.47 6.50 8.0 .06 .07 .08 .10 .12 .15 .18 .26 .35 .46 .58 .89 1.23 1.67 2.15 2.74 3 43 4.18 4.90 5.80 6.68 9.74 13.05 24" .05 .07 .08 .11 .15 .20 .26 .38 .55 .73 .96 1.21 1.52 1.85 2.23 2.59 3.08 4.28 5.73 30" .07 .09 .14 .20 .27 .35 .44 .56 .68 .82 .95 1.11 1.58 2.10 How to determine the required size of turnout valve. Assume the water is distributed from each turnout valve to 10 furrows hy forebays and that 450 gpm must he released per valve. As tahle B-3 shows, a 6" diameter valve will discharge the stream when the pressure head is less than lliit which is equivalent to a column of 1' of water. Since such a pressure is well within that provided hy most pipelines, the 0" size more than likely would he sufficient. However, this might not I"- the case if the water is in he distributed to the furrows l'\ gated-pipe, or if the Bame valve must at limes discharge a much larger stream of water fur flood-irrigated crops. SURFACE GATED PIPE OUTLETS llii-en: Rates ( >f flow a- determined for W. \\. Ames Co., aluminum pipe equipped with "Flo-( lontrol" pressure gat< - a< i ording to: (1) The available pressure head at each gate. (2) The velocity in the pipe past the gate. (3) The fractional amount of the gate opening. The available head at any point along the pipe is the height in feet that water would rise in an open column if attached to the pipe at that point. The velocity in the pipe depends upon the pipe size, the initial flow in the pipe, and the number of gates open upstream from a given point. The flow through a gate when there is no velocity in the pipe past the gate (as would he the case for the last gate of a line) is shown in table B-4 for various openings of the gate. Whin there is flow in the pipe past a gate, the dis- charge is reduced as the velocity in the pipe increases. The graph on the right shows the curves for velocity as a func- tion of flow rale in gallons per minute in the pipe. APPENDIX TURNOUT VALVE RISER PIPE Cross section of a typical pipeline riser and turnout valve. Table B-4 DISCHARGE IN GALLONS PER MINUTE FROM GATED PIPE AT HEADS FROM 1 TO 5 FEET, WITH ZERO VELOCITY IN THE PIPE Head Gate opening Full 3/4 1/2 1/4 1/8 1/16 feet gallons per minute 1.. 48.8 67.2 80.1 S7.7 94.2 35.7 50.0 60.8 69.5 77.1 22.8 32.3 39.1 45.3 50.6 10.6 15.3 18.3 21.4 23.7 5.0 7.0 8.5 9.7 10.7 2.3 2 3.2 3 3.8 4 4.3 5 4.8 1000 800 600 * 3 400 200 - /J" / - / - - /-? - / ^^ - "~~^X> SliE 1.0 2.0 3.0 VELOCITY IN FT/SEC Velocity in pipe as a function of flow rate 4.0 5.0 The quantity of water flowing past a given gate depends upon the quantity introduced into the pipe, the discharge from each gate upstream, and the number of gates open upstream. If Q represents the initial quantity in gpm, q the discharge from each gate, and n the number of gates open above a given gate, the quantity of flow past the gate is then Q-nq. Table B-5 DISCHARGE IN GALLONS PER MINUTE AT HEADS OF 1 TO 5 FEET WITH A VELOCITY OF 1 FOOT PER SECOND IN THE PIPE Head Gate opening Full 3/4 1/2 1/4 1/8 1/16 feet gallons per minute 1.. 45.3 63.7 76.6 84.2 90.7 32.8 47.1 57.9 66.6 74.2 21.3 30.8 37.6 43.8 49.1 10.2 14.9 17.9 21.0 23.3 4.9 6.9 8.4 9.7 10.7 2.2 2 3.1 3 3.7 4 4.2 5 4.7 Table B-6 DISCHARGE IN GALLONS PER MINUTE AT HEADS OF 1 TO 5 FEET WITH A VELOCITY OF 2 FEET PER SECOND IN THE PIPE Head Gate opening Full 3/4 1/2 1/4 1/8 1/16 feet gallons per minute 1. . 41.6 60.0 72.9 80.5 87.0 29.6 44.0 54.8 63.5 71.1 19.8 29.3 36.1 42.3 47.6 9.1 13.8 16.8 19.9 22.2 4.5 6.5 8.0 9.3 10.3 2.1 2 3.0 3 3.6 4 4.1 5 4.6 Table B-7 DISCHARGE IN GALLONS PER MINUTE AT HEADS OF 1 TO 5 FEET WITH A VELOCITY OF 3 FEET PER SECOND IN THE PIPE Head Gate opening Full 3/4 1/2 1/4 1/8 1/16 feet gallons per minute 1.. 40.0 56.4 69.3 76.9 83.4 26.7 41.0 51.8 60.5 68.1 18.2 27.7 34.5 40.7 46.0 8.8 13.5 16.5 19.6 21.9 4.3 6.3 7.8 9.0 10.0 2.1 2 3.0 3 3.6 5 4.1 5 4.6 59 FURROW IRRIGATION Table B-8 DISCHARGE IN GALLONS PER MINUTE AT HEADS OF 1 TO 5 FEET WITH A VELOCITY OF 4 FEET PER SECOND IN THE PIPE Head Gate opening Full 3 4 1/2 1/4 1/8 1/16 feet gallons per minute 1.. 34.3 52.7 05. 6 73.2 79.7 23.6 37.9 48.7 57.4 65 16.6 26.1 32.7 39.1 54 4 8.2 12.9 15.9 19 21.3 4.1 6.1 7.6 8.8 9.8 2.1 2 3 3 3 6 4 4.1 5 4.6 Tallies B-5 to B-8 show the outflow through the gates with pipe velocities 1, 2, 3, and 4 ft/sec past the gate. When pipe is used to convey water over some distance or a long line of gated pipe is used with only the lower gates open, head loss due to friction will occur in this section of pipe. The head loss in pipes with no flow through the gates is shown in the chart below, measured in feet per 100 feet of pipe. IOOO 800 600 1- < * O 400 200 fu / J N / 1 1 1 JO) 1 la / /Wo /o /.O ll /■ / / '// "\0 '/ / tTVMOS »x* ' ! 1 .. 1 1 EXAMPLE 1 Assume you have a flow rate of 500 gpm with a head of 5' at the intake end. The flow passes through 700' of 8" pipe before it reaches the 8" gated pipe. You have 50 gates on a 3' spacing and wish to deliver 10 gpm from each gate. Head loss ( from the chart below) Available head at first gate Velocity in pipe at first gate ( from chart, page 59, bottom) = 0.4 ft/100 ft = 0.4 x 7 = 2.8 ft. = 5.0 ft-2.8 ft = 2.2 ft. 3.2 ft/sec To obtain 10 gpm (from table B-6) set gate halfway be- tween % an d Yi opening. It should be remembered that there will be some head loss in the section of gated pipe. That loss, however, is much smaller than for closed pipe of the same size and length, because some of the water is being discharged from the gates. EXAMPLE 2 Assume you have 500 gpm with a 4' head at the first gate in 10" gated pipe. You have 25 gates on a 40" spacing. The discharge per gate will be — - = 20 gpm. The velocity in the pipe (from chart, page 59) = 2.0 ft/sec. The gate setting (from table B-6) = ^4 opening. Friction loss in closed pipe as a function of flow rate. 30 100 ISO HEAD LOSS FT/IOO 2O0 APPENDIX APPENDIX C: DESIGN OF SYSTEMS FOR RE-USE OF IRRIGATION TAILWATER These two sketches are general layouts for two common types of t ailwater-re-use systems. In Plan I (left) the water is re-used on the field it originates; in Plan II (right) it is transported for use on an adjoining plot. The essential features of the two plans are: A — High-value irrigation water is implied. Some gravity waters and most pumped supplies justify re-use of the tailwater. B — High loss of valuable water during its transmission onto the field is implied. A buried concrete head pipeline or other essentially seepage-proof head channel is assumed to be necessary. C — A shallow earthen ditch properly designed and maintained so that it efficiently collects and conveys the tailwater to the lowest point of the irrigated field. D — A collection reservoir or tank for the drainage ditch to discharge into. E — A pumping plant that operates automatically to empty D. F — A pipeline or elevated ditch will carry the tailwater to the intended point of reuse. — • » — Directions of stream flow. 61 FURROW IRRIGATION These two sketches give the details of Plan I and Plan II. Their essential features are: 1 — Inlet pipe of large diameter (14" and 16") to sump and pump well. 2 — Silt-trap and trash-screen arrangement. 3 — Electric contact switch to start pump when water level in pump well requires lowering. 4 — Flexible coupling. 5 — Poured discharge connection to insure rigidity. 6 — Cone and air vent for return concrete pipeline. 7 — Valve for draining return pipeline. 8 and 9 — Capstand and vent at discharge end of discharge pipe- line. 10 — Flap valve to prevent water from draining backward through return pipeline and column pipe of pump during inter- vals of nonpumping. 1 1 — Access to return pipeline flap valve. APPENDIX D: METHODS OF DETERMINING THE NUMBER AND COST OF SIPHON OUTLETS NEEDED \ can be seen from Appendix I> graphs, a 2^" diameter otherwise than staled. The costs given are based on the fol- siphon is the smallest size that will discharge the 38 gpm lowing unit retail prices: hi. while the 1" and 2" diameter tubes are the mini- mum i/'- thai will togethei discharge the initial stream, and tin I" diameter tube is the smallest size that will dis- chargi the final '<'• gpm Btream. I Be <>f larger than these 1 1 1 1 >• i/' would raise tin- costs and make them compare Siphon diameter 1" 2" 2%" Unit price $0.82 1.65 2.80 62 APPENDIX Table D-l MANAGEMENT OF TWO SIPHONS PER FURROW SHOWING NUMBER AND OPERATION OF EACH SIZE Stream available for siphon starts 2" diameter siphon 1" diameter siphon Siphon startings Newly started Total operating Idled by lack of water Newly started Total operating Idled by lack of water Remarks gpm 1,500 1,180 932 732 900 956 956 Number needed Number needed 1st 40 40* 40 40 Initial starting No additional 2" diameter siphons needed after this time 2nd 3rd 31 25 19 31 25 19 9 15 21 31 25 19 71 96 115* 31-2" carried forward and started anew. 31-1" extra required. 25-2" carried forward and 4th started anew. 25-1" extra required. 19-2" carried forward and started anew. 19-1" extra required. No additional 1" diameter siphons needed after this time 5th . . . 24 25 25 24 25 25 16 15 15 24 25 25 99 93 93 16 22 22 40-1" made available from 6th 1st starting. 31-1 " more made available 7th from 2nd starting. 25-1" more made available from^Jrd starting. ' Total number required for operation except that a few extra may be needed to replace those lost or damaged. The results in table D-l may be arrived at experimentally as shown or they may be calculated as follows: Let: Q = Size of main stream Qx = Large siphon stream Q 2 = Small siphon stream X = Total number of siphons needed for operation M = Total number of large siphons needed N = Total number of small siphons needed n = Number of small siphons needed for 1st starting nj = Number of small siphons needed for 2nd starting n 2 = Number of small siphons needed for 3rd starting n 3 = Number of small siphons needed for 4th starting Then: X = M + N Q M = Qi + Q. N = n + n x + n 2 + n 3 n= o7To: _Q-(nxQ 2 ) "1 = Qt + Q Q_[( n + Nl ) + Q 2 ] n 3 = Q. + & Q- [(n + iu + na) Q2I Q, + Q 2 [1] L2J [3 J 63 FURROW IRRIGATION Table D-2 MANAGEMENT OF ONE SIPHON PER FURROW SHOWING NUMBER AND OPERATION Stream available for siphon starts 2i ' diameter siphon Siphon startings Newly started Total operating Idled by lack of water Remarks gpm 1,500 1,180 932 732 900 93G 956 Number needed 1st 40 31 25 19 40 71 96 115* 2nd 3rd 1st starting. 4th 2nd starting. 19 extra required by release of 732 gpm of water from 3rd starting. No additional siphons needed after this time 5th 24 25 25 99 93 93 16 22 22 40 siphon tubes carried forward from 1st starting. 31 siphon tubes carried forward from 2nd starting. 25 siphon tubes carried forward from 3rd starting. 6th 7th * Total number required for operation except that a few extra may be needed to replace those lost or damaged. The results in table D-2 also may be determined experi- mentally as shown or calculated as follows: Let: Q = Size of main irrigation stream Q t = Size of inital furrow stream Q 2 = Size of final furrow stream X = Total number of siphon tubes needed for operation n = Number of siphon tubes needed for 1 si starting 11] = Number of siphon lubes needed for 2nd starting n 2 = Number of siphon lubes needed for 3rd starting n 3 = Number of siphon tubes needed for 1th starting Then: X = n -f n x + n.. = n ( _Q-(nxQ 2 ) rii = Q. Q- -[(n + ni ) xQ,] Qi Q- - [(n + n, + n 2 ) x Q 2 ] Q» [4] SELECTED BIBLIOGRAPHY 1. \\te||. J. 1).. anil Doneen. I,. 1).. The use of gypsum iii irrigation water. Better Crops with Plant food Magazine 33:16-18, Nov. L948. 2. Brown, J. B., The contour-check method of orchard irrigation. Univ. of California. Coll. of A.gri., Calif. Agr. Expt. Sta.Cir.73, revised by J. C. Marr, I'M'). '.. Brown, L. Y. Planting and irrigating on the contour. I niv. of California, Calif. Agr. Expt. Sta. and Ext. Serv. Cir. 523, 1963. 1. liiiui. I,.. Fireman, M. and Harvey, 0. V. Soil salinity hazard to seed. I niv. of California, California Agriculture. 12 (9 ept.1958. 5. Christensen, I .. P., I niv. of California, Vi Ext. Serv., Irrigation and I drainage Letter 1 9, Oct. L962. 6. Minion. I'. M.. Invisible irrigation on Erin Bench. Reclamation Era, 34,1 KM : L82, I'M;:. -.1 APPENDIX 7. Conrad. J. P.. and Veihmeyer, F. J., Root development and soil moisture. Hilgardia 4(4) : 113-34, May 1929. 8. Criddle. W. D., Davis, S., Pair, C. H., and Shockley, D. C, Methods for evaluating irrigation systems. U.S.D.A., Soil Conserv. Serv., Agric. Handbook 82, 1956. 9. Doneen, L. D., and Henderson, D. W., Soil conditions affecting infiltration of water and root development of crop plants. Proc. Amer. Soc. of Sugar Beet Technologists, 1 10. Fox. R. L.. Phelan, J. T., and Criddle, W. D., Design of subirrigation systems. Agric. Eng. 37(2) :103-07, Feb. 1956. 11. Gardner. W. R.. Dynamic aspects of water availability to plants. Soil Science, 89:63-73, Feb. 1960. 12. Haise. H. R., How to measure the moisture in the soil. Water — The Yearbook of Agriculture, U.S.D.A., pp. 362-71, 1955. 13. Haise. H. R.. Donnan, W. W., Phelan, J. T.. Lawhon, L. F.. and Shockley. D. G., The use of cylinder infiltrometers to determine the initial characteristics of irrigated soils. U.S.D.A., Agr. Res. Serv. and Soil Conserv. Serv., ARS 41-7, May 1956. 14. Henderson. D. W.. Lindt. J. H., and Pearl, R. C, Use of moles for subirrigation. Univ. of California, California Agri- culture. 8 (8): 5, Aug. 1954. 15. Houston, C. E.. and Schade, R. 0., Irrigation return-water systems. Univ. of California, Calif. Agr. Expt. Sta. and Ext. Service Cir. 542, Nov. 1966. 16. Houston. C. E., Drainage of irrigated land. Univ. of California, Calif. Agr. Expt. Sta. and Ext. Service Cir. 504, 1961. 17. Kohler, K. 0.. Jr.. Contour-furrow irrigation. U.S.D.A., Soil Conserv. Serv., Leaflet 342, Sept. 1953. 18. Larsen, D. C. Moden, W. L., Jr., Furrow slickers — a boon to surface irrigation. Univ. of Idaho, Idaho Agr. Ext. Sen., Bull. 460, May 1966. 19. Lauritzen, C. W., Lining irrigation laterals and farm ditches. U.S.D.A. Agr. Research Serv. in cooperation with Utah Agr. Expt. Station, Agr. Info. Bulletin No. 242, 1961. 20. Lawrence. G. A., Furrow irrigation. U.S.D.A., Soil Conserv. Serv. Leaf. 344, 1953. 21. Lorens, 0. A.. Placement makes the difference. Fertilizer Review, pp 5-6, March-April, 1949. 22. Marr. J. C, The border method of irrigation. Univ. of California, Calif. Agr. Expt. Sta., and Ext. Service, Cir. 408, 1952. fourth printing 1954. 23. Marr, J. C, Grading land for surface irrigation. Univ. of California. Calif. Agr. Expt. Sta. and Ext. Serv. Cir. 438, revised in 1952, and 1965. 21. Marr. J. C. The corrugation method of irigation. U.S.D.A. Farmers' Bull. 1348, May 1922. 25. Marr. J. C, Surface irrigation — changing conditions and requirements affecting water application practices. Univ. of California. California Agriculture. 11,(4) :27, April 1957. 26. McCullock. A. W.. Contour irrigation of potatoes. U.S.D.A., Soil Conserv. Serv. (Pacific Coast Section), unnumbered mimeo manual. April 1948. 27. Moore. C. V.. Guides to selecting an economical surface irrigation system. L T niv. of California Agr. Ext. Serv. AXT- 161, 1964. 28. Phelan, J. T., Design Procedures and Research Needs for the furrow method of irrigation. Paper presented at Agr. Research Serv. — Soil Conserv. Serv. U.S.D.A. Workshop, Denver. Colo., Feb. 9-10, 1960 29. Phelan. J. T.. and Criddle. W. D.. Surface irrigation methods. Water — The Yearbook of Agriculture, U.S.D.A., pp. 258-66. 1955. 30. Pillsbury, A. F., Concrete pipe for irrigation. Univ. of California, Calif. Agr. Expt. Sta. and Ext. Serv., Cir. 418, 1952. 31. Quackenbush. Tyler H., and Shockley, Del G., The use of sprinklers for irrigation. Water — The Yearbook of Agricul- ture, U.S.D.A., pp. 267-73, 1955. 32. Reeves, A. B.. Use and economy of concrete-pipe irrigation systems. Amer. Soc. of Civil Engineers., 81, Separate 622, Feb. 1955. 33. Richards. S. J., and Hagan R. M., Soil Moisture Tensiometer, Univ. of California, Agr. Ext. Serv. Leaf. 100, Feb. 1958. 34. Renfro, G. N., Jr., Applying water under the surface of the ground. Water — The Yearbook of Agriculture, U.S.D.A. pp. 273-78, 1955. 35. Rohwer, C, Canal lining manual. U.S.D.A., Soil Conserv. Serv. Div. of Irrigation and Water Conservation (Colo. Agr. Expt. Sta. cooperating) Unnumbered mimeo, Nov. 1946. 36. Scott, Verne H.. Sprinkler irrigation. Univ. of California, Calif. Agr. Expt. Sta. and Ext. Serv. Cir. 456, Oct. 1956, reprinted Sept. 1962. 65 FURROW IRRIGATION 37. Scott, V. H.. and Houston. C. E.. Measuring irrigation water. Univ. of California, Calif. Agr. Expt. Sta. and Ext. Serv. Cir. 473, 1959. 38. Stanley, W. R.. Corrugation irrigation. U.S.D.A., Soil Conserv. Serv. Leaf 343, 1954, reprinted 1962. 39. Taylor, C. A.. Irrigation problems in citrus orchards. U.S.D.A., Soil Conserv. Service, Div. of Irrigation, Farmers' Bull. 1876, April 1941. 40. Tovey, R.. and Myers, V. I.. Evaluation of some irrigation water control devices. Univ. of Idaho, Idaho, Agr. Expt. Sta., Bull. 319, Dec. 1959. 41. Tovey, R., Myers, V. I. and Martin. J. W., Furrow erosion on steep irrigated land. Univ. of Idaho, Agr. Expt. Sta. Res. Bull. 53, May 1962. 42. Veihmeyer, F. J., and Henderson. A. H., Methods of measuring field capacity and permanent wilting percentage of soils. Soil Science, 68, ( 1 ) : 75-94, July 1949. To simplify the information, it is sometimes necessary to use trade names of products or equip- ment. No endorsement of named products is intended nor is criticism implied of similar products not mentioned. Co-operative Emersion work in Agriculture ond Home Economics, College of Agriculture, University of Colifornio, ond United States Deportment of Agriculture cooperating. Distributed in furtherance of the Acts of Congress of May 8, and June 30, 1914 George B. Alcorn, Director, California Agricultural Extension Service. H 66 To obtain additional copies of this manual or a catalog listing other manuals and free publications available, see your University of California Farm Advisor (offices located in most California counties) , or write to: Agricultural Publications 207 University Hall 2200 University Avenue Berkeley, California 94720 Orders of 10 or more copies of any one manual take a 20 per cent discount off the list price. All manuals are shipped prepaid. When ordering manuals, send orders and payment to the above address. Make checks or money orders payable to The Regents of the University of California. THI« SOOK I* ' ON THF " ' * I'