B-1166 November 1976 ~5--‘-‘.l?" i“ i}? n‘ i The Texas Agricultural Experiment Station, J. E. Miller, Director, College Station, Texas, The Texas A&M University System Contents Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Agricultural Flood Plain Management . . . . . . . . . . . . . . . 6 Flood Hazard Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Federal Flood Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Flood Insurance in Texas . . . . . . . . . . . . . . . . . . . . . . . . . 13 Economic Considerations . . . . . . . . . . . . . . . . . . . . . . . . . 15 Environmental Considerations . . . . . . . . . . . . . . . . . . . . .'19 Policies and Tools of Management . . . . . . . . . . . . . . . . . 21 References i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Photographs Cover - Milam Street became a canal in 1935 Houston flood. Title page — Helicopter view shows standing water around Houston in 1973. The middle photograph on page 7 and the lower photograph on page 8 courtesy of the Soil Conserva- tion Service, U.S. Department of Agriculture. All other photographs Copyright (c) The Houston Post Co. z °QQ%VQT9)PQQQ’§‘$ '+»zx»~#¢¢s% I <;'g<---z»9;*4~ve§ , '.\"<-(/ Q I z-vggx‘ kalrfif~tt>kkl<€§ *6 f» L % ¢ s 9° _" _ * raaaatveox "T um »nu4s¢¢ 1 John G. McNeely and Ronald D. Lacewell Professor Associate Professor The Texas Agricultural Experiment Station (Department of Agricultural Economics Houston Post Summary Floods will continue to cause damage as long as development continues upon flood-prone lands. Inevi- tably flooding occurs, damage ensues, and personal suf- fering and loss create a public burden of rescue and relief operations at the expense of all taxpayers. Flood control projects cannot protect against all damage, and not all flood hazard areas are amenable to flood control projects. An alternative to the continued construction of engineer- ing works for flood protection is the management of the flood plain, which, to be effective, must be brought about through political and legal means. The purposes are to minimize the consequences of flooding and to achieve in the long run the optimum use of flood plains. The Small Watershed Program of the Soil Conser- vation Service has emphasized flood protection to ag- ricultural land. Other agricultural program purposes, such as drainage and irrigation, have comprised a signifi- cant part of the program in regions where they are needed and adaptable. Flood records indicate that the frequency of natural overbank flows has not changed sig- nificantly since flood losses became so large as to justify Federal efforts to control them. Increases in agricultural flood damages are the result of a more intensive utiliza- tion of flood plain acreage. The practice of more inten- sive use of flood plain land can be expected to continue in agriculture because the flood plain is among the most productive land in an area. A method of analysis was developed so that agricul- tural flood damages can be estimated by a computer 2 Houston Post Houston Post model for any specific area or field within a flood With this knowledge regarding the incidence of p, damages, the relationship between a crop’s exp, flood damages and net returns can be estimated flood plain location. A program of agricultural fl v; surance is now feasible along with profit maximi flood loss minimizing land uses. This degree of de the flood threat is needed for urban areas. a The flood damage hazard in the United S highly concentrated. As few as 2 percent of all dw a»; incur more than half of the annual flood damages. j than 1O percent of all dwellings have any significant; hazard, hence 90 percent or more are free fro, serious or measurable flood hazard. Many people inf? ' _ flood-risk areas are uninformed about the extent of flood damage which they face. ’ Federal action against flooding has been esc since 1966. Executive Order No. 11296 of that y. quires Federal agencies to take the flood hazard? account in the uses of flood plain lands. In 1968, gress established a voluntary National Flood Ins i} Program to provide limited coverage to the victi flood disasters. The Flood Disaster Protection t‘ 1973 is an expanded flood insurance program, int . as a substitute and eventual replacement for ‘~- disaster relief for flood occurrences. It combines; sidized flood insurance for existing developmentfl required insurance based on actuarial rates for development in flood-prone areas. f An immediate problem for the Federal Ins Administration (F IA) has been the documentation I flood risk for purposes of ratemaking. The U.S. Engineers is making a limited number of flood information studies. Flood-prone areas are divid zones reflecting varying degrees of flood risk from” able floods of specified magnitude. Where deg studies are not made by a Federal agency, oflicial, maps are prepared for the F IA by a contractor. l’ Problems arise when the costs due to flood F, . i are greater than the benefits due to location. Eco, j analyses indicate that an annual flood premium of, $2 per $100 property value approaches the limit nomic rationality for dwellings, and perhaps for a property also. When flood costs get to this general y, the implication is that land should be in some oth over the long run. In the short run, with the inves-l p‘ on Post Houston Post the present buildings already made and with sub- '0 é ed flood insurance available, continued use of exist- dwellings makes economic sense as public policy. '~ subsidy, to the owner and to the lender as well, may necessary and desirable until the present buildings no longer habitable. l _i The National Environmental Policy Act of 1969 re- es persons doing planning for future development to fuate the total environmental consequences of their attaining decisions. The objective is to blend proposals individual landowners and local groups with protec- of the resource base to yield a desired complex of lic values. A balance is sought between development protection of the different ecological units of the cape, such as streams, rivers, marshes, shorelands, plains, ground water recharge areas, woodlots, sts, and upland fields. The extent and frequency of ;'ng should serve as the basis for adjusting human ‘ ities. Flood plain regulations reduce future damages by f iring that the flood plain be used for purposes that § not subject to flood damage or that suffer only mini- damage. Also, regulations provide for the necessary iway capacity so that flows are not obstructed or heights increased significantly. Several devices are _ able to the community that wishes to achieve flood in management. Zoning is a legal tool used to implement and enforce jled plans resulting from land use planning pro- ‘ s. Designated floodways may be reserved by estab- y. g encroachment lines that clearly define flooding ls. Used by local governments to specify the manner Q hich land may be divided, subdivision regulations 1 prescribe the width of streets, curbs and gutters, lot elevations of land to avoid area flooding, size of aways, and other requirements affecting the welfare safety of the community. Building codes can contain i, isions that assure the structural soundness of build- 7 during flood periods. Flood conscious governmental i, ies that limit the extension of public roads, utilities, other services into flood-prone areas can play an rtant indirect role in shaping overall development. t‘ ate development often follows the extension of pub- jrvices. Continuing study and review of flood plain igement considerations is important in maintaining -range appropriate land use. Houston Post Houston Post Introduction A large percentage of the Nation’s population and tangible property is concentrated in flood-prone areas. These areas are comprised of flood plain land and thin coastal strips, and they total at least 5 percent of the N ation’s territory (19). An indication of the magnitude of the flood threat by location is provided in Table 1 and Figure 1. A streambed and the flood plain lands immediately adjacent are integral parts of every natural watercourse. The flood plain is formed from sediment deposits or re- moval accompanying the natural, intermittent overflow of the stream above its ordinary bed. Overbank flows are not abnormal. The flood plain acts as a natural reservoir TABLE 1 TOTAL FLOOD PLAIN ACRES AND URBAN ACRES IN FLOOD PLAIN (1973 Estimates) and temporary channel for the excess water. T river uses some portion of its flood plain about to 3 years. At average intervals of perhaps 25, years, the river may inundate its entire flood considerable depth (13). Records of floods permit estimation of fre p flooding but not forecasting of the year a flood on any watercourse. Flood records suggest tha quency of natural overbank flows in the Unit it has not changed significantly in the years si losses became so large as to justify Federal control them. However, flood damages have creasing in the United States in recent years. mary cause is more intensive use of flood p 3 consequent increases in dollar values of l0sses.f The full social costs of flood plain occupan s; immediate expenses of development. Also inc damages to be borne by the occupant or the protective measures undertaken to reduce the i“ and extent of flood damage. Finally, costs incl ages shared by society in disaster relief and r 110D (19). l Since 1936, the national approach to flood p generally has been for the Federal governm sume the major obligation to protect develop from damaging floods. In addition, Federal have cooperated with National, State, and l ' in providing relief and rehabilitation assistance; ' of flood disasters. The U.S. Army Corps of t estimates that the Federal government has more than $9 billion in flood control projects sin); But flood damages have been increasing each 1936, and the Corps estimates that flood los, come to almost $2 billion annually (3). " i u. s . Total Flood Plain Urban areas in flood plain Percent 0f fl Water-Resource Region (1000 Acres) (1000 Acres) in urban =f New England 1,350 223 16.5 a Middle Atlantic 3,330 555 14.31 South Atlantic-Gulf 13,500 39s 2.9 Ohio 9,000 700 7.8 a Great Lakes 2,720 214 7.9 l, Upper Mississippi 10,300 64 .6 ; Souris-Red-Rainy 1,810 12 .7 Missouri 14,300 14s 1.0 Arkansas-White-Red 10,500 77 .7 Lower Mississippi 35,660 130 .4 Rio Grande ' 130 21 16.2 '7 Texas-Gulf 9,560 162 1.7 Colorado 570 113 " 19.8 _,. Great Basin 500 59 11.8 California 3,070 354 11.5 Columbia-North Pacific 3,900 65 1.7 3; Alaska 8,000 5 ’.1 Hawaii 140 21 15.0 Puerto Rico & Virgin Islands 250 50 f 129,140 3,372 2.6 (201 ,780 (5,269 (2.6%)?! Sq. Mi.) Sq. Mi.) f Source: Corps of Engineers Internal Summary, 1973. The regions are delineated in Figure 1. 4 Lovell (13) reports that Federal flood control pro- i s have been credited with preventing $14.8 billion ood losses. Under current conditions of project de- pment, benefits attributable to flood control works p, estimated in excess of $1 billion annually. Lovell lists ting flood control programs as including some 900 fjects consisting of more than 260 lakes, 6,000 miles of es and flood walls, and more than 8,000 miles of ‘ nel improvement work. Structural measures, al- p ugh proven as efficient corrective action, have not ‘in able to keep pace with the rapidly growing flood l iblems of our nation. Flood control projects were not intended to protect inst all damage,'since the typical project was de- i, ed to afford protection against a specified flood level. f‘. control construction agencies had little control f events which caused flood losses to continue to unt. The Task Force on Federal Flood Control Policy Tinted out several types of development situations in :0 plains (19). New construction occurred in areas ‘ch were not protected because of lack of local con- l, information, and (or) local cooperation. Many small _‘ s, suburban areas, and seashore resorts fit this de- Pption. Sometimes flood-prone lands adjoining pro- f ed areas were built up. Along rivers, where some f 'on of the flood plain had been provided protection reservoirs, adjacent but lower lying lands were de- veloped. Most damaging of all were losses to areas which were protected according to physical and economic criteria but were visited by catastrophic floods exceeding protection limits. The Task Force (19) found that the major purpose of engineering projects was changing from the protection of established property to the underwriting of new de- velopment. Increasingly, Federal funds were used to support projects justified on the basis of future develop- ment. A similar trend was found on approved Soil Con- servation Service flood prevention and watershed pro- tection projects. Individual beneficiaries from engineering protec- tion works were not, in many instances, bearing a share of the costs proportionate to their share of benefits. This latter factor, combined with the bias in favor of river control alternatives, relieved many individual flood plain occupants of fiscal responsibility for their actions. The general public bore all or a major part of flood protection works and subsidized the use of the flood plain. Boulding (2) suggests that we need an entirely new philosophy for flood control, which may involve treating the river not as an enemy to be conquered but as a rather dangerous friend with whom one has to learn to live. It is perfectly possible to design cities on the flood plain to accommodate floods instead of taking on the impossible task of trying to prevent them. - _ 13L‘). Grand;- TGXSS-Gulf .fijj-‘ Puerto Rico Lower Mississippi l. L _ _ _ _ _ _ -_ GSSGSSITIGHI. Misc. Pub. No. 1290, Washington, D.C., May 1974, p. 39. Figure 1. The 18 water resource regions delineated by the Water Resources Council for the second national Source: Our Land and Water Resources, Economic Research Service, U. S. Department of Agriculture, Agricultural Flood Plain Management The Flood Control Act of 1936, as amended in 1937, gave the U.S. Department of Agriculture authority to make preliminary examinations and surveys in the watersheds of all waterways in which U.S. Army Corps of Engineers’ surveys were authorized. That legislation, however, did not provide for any structural works. The 1944 Flood Control Act authorized the first installation of improvements in 11 watersheds, but these projects, I which then consisted mainly of accelerated land treat- ment, contained no structures. After 1948, U.S. De- partment of Agriculture watershed reports began to in- clude proposals for structural measures. Small Watershed Program In 1954, the 83rd Congress passed P.L. 566, the Small Watershed Program, providing flood protection to farmland in upstream areas (11). Originally, this law au- thorized the Secretary of Agriculture to help local or- ganizations plan and carry out works of improvement for flood prevention and such agricultural water manage- ment purposes as irrigation and drainage in upstream watersheds not exceeding 250,000 acres. The law was thus designed to fill the gap between water-related con- servation practices on individual farms and large downstream river basin projects of the Corps of En- gineers. The scope of the Small Watershed Program has since been greatly enlarged by a series of congressional amendments. The first, in 1956, provided that the Fed- eral government pay all construction and engineering costs for flood prevention and share in construction costs for agricultural water management. Currently, the Fed- eral share for both drainage and irrigation is 100 percent of engineering costs and is limited to a maximum of 50 percent of construction costs. The Food and Agriculture Act of 1962 stipulated that cost sharing be consistent with similar government programs (11). The 1956 amendment also expanded the program to include nonagricultural purposes, such as municipal and industrial water supply and streamflow regulation. But no Federal funds could be used for these purposes. 6 Three other amendments to P.L. 566 added ~31 gram authorizations. In 1958, fish and wildlife improvement was added as a project purpose und same Federal cost sharing provisions applicable ricultural water management at that time. Recr was added as a valid project purpose in 1962 whe i need was demonstrated, and harvest provisions a added to fish and wildlife deyelopment. This t ment provides Federal costs sharing for recreatio- fish and wildlife up to 50 percent of all costs inc Q land costs. Then, in 1965, maximum flood prev), storage capacity was increased from 5,000 to 12, l feet per structure. The Small Watershed Program has emph flood protection to agricultural land througho, lifetime even as other purposes were added or exp by congressional amendments to the original law. agricultural program purposes, such as drainage rigation, have comprised a significant part of th gram in regions where they are needed and adap The net result is that the total program has bee dominantly agricultural thus far (11). i’ The flood control programs of the Corps n?’ gineers and the Soil Conservation Service hav tected some agricultural and nonagricultural areas flooding. Despite these Federal flood control i I ments, flood losses have been increasing. Flood show that the frequency of natural overbank flo not changed significantly since flood losses i] I large as to justify Federal efforts to control them. l. fore, increases in flood damages are not due to ,9 crease in intensity and frequency of rainfall but - we result of a more intensive utilization of flood plain age. Studies indicate that flood plain encroachme curs because of 1) ignorance of the flood hazard, ticipation of further Federal protection, and 3) profi . g ity to the private owner (19). 9' Alarm over the extent of agricultural flood and interest in flood protection programs are incr as the flood plain becomes more intensively uti The increasing use of flood plain land can be exp ~ l continue in agriculture since the flood plain is amo most productive land in an area. Usually as flood lands are converted to more intensive uses, vulner, to flooding increases. This is explained through lanp characterized by low per acre returns and a high d of tolerance to floodwater, such as native pastu woodland being replaced by row crops or alfalfa A have higher per acre returns but a low degree of ance to floodwater. Therefore, with more intensive of flood plain, damages" from flooding will contink increase (5). fil- Flood Plain Evaluation Increases in agricultural flood losses call for two. tinct but related types of flood plain evaluation. Th flood protection to curb or reduce the increasing e5 attributable to flooding. This type of evaluation invo_ - nomic appraisal of the reduction in flood damage 1 lting from alternative flood protection measures ulated for a particular watershed. In addition to flood protection proposals, a thorough _}~ plain evaluation considers land use organization the effect of alternative adjustments. Flood damage mates for alternative land uses throughout a flood n facilitate such an evaluation and aid entrepreneurs ' eir effort to develop an optimum cropping pattern. wledge of the incidence of flood damages permits a _ lating returns net of average annual flood damages A production costs by land use and flood plain loca- By utilizing these data, flood plain land use and "a organization can be directed toward increasing pro- or reducing the risk associated with flooding or some T bination of both (5). i It is useful to identify both average annual flood ages and expected profit by land use throughout the plain since efforts to minimize or reduce flood ages will not necessarily yield a profit maximizing ,0; tion. For example, flood plain land use adjustments ttain large profit increases may be associated with easing flood damages because an allocation of flood .0 to higher value land uses may also result in greater g0 losses. Conversely, increased flood damages could T esent a reduced profit or an inefficient flood plain l oachment. imating Flood Damages Both types of flood plain evaluation discussed above ire procedures for estimating flood damages. Gov- W ental agencies working with flood losses and in- i ' ed in watershed evaluation have formulated proce- for estimating losses resulting from floodwater. se procedures estimate flood damages with either a orical or a frequency method. The historical method liputes damages based on the record of actual floods e watershed and considers up to 150 separate , n s. The frequency method calculates flood damages as many as six flood sizes with the flood sizes selected epresent the distribution of floods in the watershed; , annual flood, every 2 years, 5 years, etc. , up to a 50- 00-year flood (5). ; Flood damage estimates are computed for an evalu- a reach. Reaches are delineated such that hydraulic acteristics are similar throughout the reach. A flood age value applies to the flood plain reach, with a A§ection being the elevation profile of a flood plain at ‘ point on the channel; i.e., elevations at points or ions across a flood plain at one channel location. The ation of the flood plain within an evaluation reach is iesented by measured points on one or more cross 'ons. The distance between cross sections frequently 3,000 feet. Evaluation reach data from which estimates evolve include cross section eleva- i , composite acre of the reach, crop yield, crop , crop damage factors, and flood data. A composite a is a hypothetical acre of flood plain composed of the Soil Conservation Service Houston Post The flood plain is among the most productive land in an area. 7 same percentage of each land use as in an evaluation reach. Crop damage factors are the percentage reduction in gross value for a given depth of inundation increment and season. Damages are computed by applying appro- priate damage factors to the composite acre and expand- ing to the acres inundated. Lacewell and Eidman (l0) developed a method whereby flood damages can be estimated for a specific field with respect to the particular characteristics of that field; i.e., land use, productivity, depth of inundation, and location. More accurate estimates of the incidence of average annual flood losses help establish l) more equi- table assessments of the local costs of flood protection, 2) annual premiums for crop flood insurance, and 3) op- timum cropping patterns. Benefits received by indi- vidual landowners from flood protection can be tied di- rectly to reductions in depth of flooding on individual fields. Annual insurance premiums for specific fields can be related to the particular crop grown on the field. And the land use maximizing returns net of production costs and average annual flood damages can be identified for any flood plain location. A general model was developed to estimate values associated with flooding on any specific area within a Soil Conservation Service project size watershed which is defined as less than or equal to a 250,000 acre drainage area. The values associated with flooding that the gen- eral model was developed to estimate are: 1. Acreage inundated by specific flood sizes with al ative systems of structures. 2. damages for specific storms and average annual flood damages on any selected area within the flood plain of the watershed. 3. Average annual benefits from proposed systems of structures for specific fields and to land own- ers. 4. Flood damages with alternative land use pat- terns. In the Lacewell and Eidman analysis (10), the gen- eral model was converted to an optimizing routine. The purpose of the modification was to develop a decision model for selecting that land use at each flood plain loca- tion which maximizes returns net of average annual flood damages and production costs. Additional data forthcom- ing from the modification are estimates of the optimum flood plain cropping patterns, associated net returns, and flood damages for alternative systems of structures as well as with no structures. Using the Lacewell and Eidman method of analysis, flood damages can be estimated by a computer model for any specific area or field within a flood plain. With im- proved knowledge regarding the incidence of flood dam- ages, the relationship between a crop’s expected flood damages and net returns can be estimated for any flood plain location and in turn a profit maximizing as well as flood loss minimizing land use designated. Information of this type can be used for flood plain management and to effectively administer a flood insurance program for agriculture. 8 Houston Post ..... .. Soi/ Conservat/on Serv/ce Every watershed in Texas has flood problems to some deg Iood Hazard Studies ' The Soil Conservation Service conducts flood u». studies in Texas through a joint coordination eement entered into in November 1973 between the Conservation Service (SCS) and the Texas Water ' elopment Board. The SCS is authorized to provide nical assistance to Federal, State, and local govern- A bodies in carrying out flood hazard studies under jlic Law 556 as amended. . A typical SCS flood hazard study contains the fol- 'ng information: 1. A description of the watershed, including topo- 3 graphic and stream characteristics, present and anticipated future land use, cause and charac- teristics of flooding, past floods, and study pro- cedure used. ' . ' 2. A discussion of the principal aspects of a local S flood plain management program. - 5: 3. A general map of the area showing watershed i, boundaries and the limits of the study reaches. _ 4. Flood hazard area maps showing the area subject ‘ to inundation by the 100-year and 500-year fre- _ quency floods under present conditions. i5. Profile drawings showing the 10-year, 50-year, A 100-year, and 500-year frequency floods through the study reaches for existing conditions and the 100-year flood under anticipated future condi- tions. . Drawings 0f selected valley cross sections show- ing the elevations of the 10-year, 50-year, 100- . year, and 500-year frequency flood events for f3 existing conditions and the 100-year flood for an- ticipated future conditions. . Photographs of various locations showing the depth of flooding that would occur from the lOO-year and 5OQ-year frequency floods. . A map of the area showing soils, a narrative de- scribing the soils, and interpretations on certain selected uses. A ‘- An accompanying brochure showing a summary of the study results and the need for a local flood plain management program (4). Flood hazard studies are one of several alternatives that the Soil Conservation Service considers in trying to resolve flood problems in upstream watershed areas. Flood hazard studies do not reduce flood losses, but the land use and management requirements that can be de- veloped from the studies control unwise development in the flood plains, thereby reducing the rate at which flood losses increase. Individual homeowners and local, State, and Federal governing bodies find these studies to be valuable tools in flood plain planning processes (4). The SCS considers flood hazard studies to have three major uses. These are 1) to identify physical fea- tures and problems relating to flooding, 2) to make gen- eral suggestions to overcome the flooding problems through flood plain management, and 3) to identify soils and make interpretations for selected uses on these soils (4). Factors Affecting Flooding Every watershed in Texas has flood problems to some degree. Several factors affect flooding problems, and in most cases these are interrelated. If a watershed is located within or adjacent to a large metropolitan area, the land use patterns and physical features are in a state of dynamic change. As agricultural land is converted to urban land, highways, buildings, and parking lots proliferate. The direct result is an increased amount and rate of runoff, increased flow depths, and increased damages and monetary losses. Cities within or adjacent to a flood hazard analysis area are delineated on aerial photographs and described within the narrative of the study (4). The general climatic zone in which a watershed is located partially determines what type of flooding prob- lems will occur. The intensity, duration, distribution, and time of occurrence of rainfall are all significant fac- tors concerning flooding. For this reason, a general de- scription of the climate is included in flood hazard study reports. Geology is another important element affecting flooding in a watershed. Storm runoff is affected by both surface and subsurface geologic materials. For example, a watershed that has rock exposed on the ground surface will produce much more runoff than a watershed that has a deep sand underlain by rock. A detailed geologic analysis is included in flood hazard studies. Steepness of slope determines how fast the water will rise and fall and how large the peak discharges will be. For instance, in a watershed that has very steep slopes, the water will rise and fall very fast, and gener- ally the peak discharges will be very high. The converse is true in watersheds with very flat slopes. This informa- tion is displayed in the narrative and tables of flood hazard studies (4). The width of the flood plain generally determines how deep the water will get for a given flood. A watershed with narrow flood plains will tend to have deeper water from a given flood than one with wide flood plains. This is displayed in the study report document by use of water surface profiles and flood hazard area maps. 9 Stream densities and flow conditions tend to deter- mine the volume of runoff and to a lesser extent the rate of runoff. A watershed with a dense pattern of perennial streams will tend to produce more runoff and a higher rate of runoff than one with few intermittent or ephem- eral streams. This information is presented in narrative, table, and map form. Present land use and treatment has a large effect on runoff and resultant flooding. An agricultural watershed with good conservation treatment will produce less runoff and lower peak discharges than one with poor conservation treatment. Urban watersheds with parks, greenbelt areas, and properly designed flood water re- moval systems will produce less runoff and smaller peak discharges than one with little vegetation and poorly de- signed flood water removal systems. Present land use is displayed in narrative and table form in the report document (4). Anticipated land use can affect flooding adversely or favorably. If the projected conditions are for an agricul- tural watershed to evolve into an urban watershed, flooding and resultant damages can be expected to in- crease if development is uncontrolled and haphazard. If the anticipated conditions are for providing parks, greenbelt areas, and other less intense uses than are there at present, then flooding and damages can be ex- pected to decrease. This information is displayed in nar- rative, profile, and map form. Flood Plain Management Practices The second major use of a flood hazard study report is the portraying of suggested general solutions to flood problems through flood plain management practices. Flood damages can be minimized by careful planning and proper flood plain management. Flood plain man- agement programs should contain both preventive and corrective measures. Preventive measures do not prevent flooding, but they do reduce the threat of damage and loss of life from flooding by discouraging unwise development in the flood plains. Preventive measures include but are not limited to such practices as encroachment lines, zoning, subdivision regulations, building codes, development policies, greenbelts, tax adjustments, flood insurance, and flood warning systems. Corrective measures also do not eliminate flooding. These measures reduce the extent of flooding and flood damages. Corrective measures are usually physical in nature and include but are not necessarily limited to land treatment, floodwater retarding structures, channel rectification, permanent evacuation, and flood proofing (4). The above items are presented in each flood hazard analysis as items for local consideration. Final decision as to what measures to apply are left to the judgment of the local governing body. As a future tool to aid decision makers, a table of suggested flood plain uses is included in the study 10 document. This tabulation presents some selected ‘ and provides both the suggested degree of prot required and the permissible location and lowest a entry elevation. _ The third major use that can be made ofa i, hazard study is from the information presented on tification and interpretation of soils. The soils that considered in this section are the soils that lie withi 500-year flood plain. Technical descriptions, gener ricultural uses, and locations of these soils are disp j in narrative and map form. These data are pres much like a standard county soil survey but in less, vi <4). Houston Post f“- w z: t“ 11*‘ Floods of the same or larger magnitude as those that have? curred in the past can occur in the future. deral Flood surance In 1966, President johnson transmitted to Congress iiReport of the Task Force on Federal Flood Control y and issued Executive Order N0. 11296 (19). This fr required the agencies responsible for a wide range ederal programs affecting the use of flood plain lands _= e the flood hazard into account in their administra- fof those programs. This order has had comparatively w effect according to the National Water Commission because the necessary flood plain maps and man- a ent plans are not available for the flood plain areas ‘ ich the agencies operate. A considerable degree of ‘rtainty exists as to the hazard at a designated loca- j in a particular flood plain. r Before 1968, the sole relief available to the victims ' 00d destruction had been special Federal disaster s. Because of the high risks and the lack of under- l ‘ng standards, flood insurance had not been made F‘ able through the private insurance industry (24). ‘ In 1968, Congress passed the National Flood Insur- -- Act that offered a voluntary insurance program to ide limited indemnification to the victims of flood F: ters. The two principal objectives of the 1968 Act 1e 1) to make available to residents of flood-prone as flood insurance at reasonable premium rates (ugh the means of a Federal subsidy and 2) to require i" jurisdictions to enact land use and control measures ‘gned to guide the rational use of the flood plain as a g ition for the availability of federally subsidized flood irapce (24). ' Despite the efforts of the Federal Insurance Admin- tion to carry out the Congressional intent for land and control measures as provided by the act, it be- obvious that without mandating provisions to bring i t these measures, no, real accomplishment could be i ted in this respect (24). ,,The Flood Disaster Protection Act of 1973 is an _ ded flood insurance program. It is specifically in- {ed as a substitute and an eventual replacement for jral disaster relief for flood occurrences. This act will e property owners more aware of flood hazards and will permit them to contribute to their own protection. Property owners also will be more fully indemnified when a flood loss occurs. Requirements The act requires the purchase of flood insurance in connection with receiving any form of Federal financial assistance for acquisition or construction purposes in any area identified by the Secretary of Housing and Urban Development as having special flood hazards. This fi- nancial assistance includes loans, grants, guarantees, and similar forms of direct and indirect assistance from Fed- eral agencies such asF HA and VA mortgage insurance. It also includes similar forms of assistance ‘from federally insured or regulated lending institutions, such as banks, savings and loans institutions, and credit unions. Acqui- sition or construction purposes include all forms of con- struction, reconstruction, repair, or improvement to real estate for both private and public recipients (24). In return for making low-cost insurance available for existing property in flood plains, the Flood Disaster Pro- tection Act of 1973 places certain obligations upon com- munities entering the program. They are required to adopt and enforce land use and other control measures that will guide new development in flood-prone areas so that future flood damage is avoided or reduced. In most communities, the flood problems have not been pre- viously documented. Requests for flood plains studies are made by local governments through the Texas Water Development Board under the continuing authority granted by Section 206 of the 1960 Flood Control Act as amended. Studies are made and reports are prepared under the direction of the U.S. Army Corps of Engineers using a standard format. The study area is divided into reaches having hy- drologic characteristics fairly representative for the en- tire length of each reach. Flood frequency data for the various streams in the study are developed from dis- charge-frequency relationships based on regionalized hydrologic analyses. Using the peak discharges obtained in the hydrologic analyses, water surface profiles are de- termined. Floods of the same or larger magnitude as those that have occurred in the past can occur in the future. Dis- cussion of future floods in the studies is limited to those that have been designated as the 10-year, 50-year, 100- year, and 500-year frequency floods. Frequency curves of peak flows are constructed on the basis of available information, and flood flows up to the magnitude of the 500-year flood are computed from these curves. Fre- quency curves thus derived reflect the judgment of en- gineers who have studied the area. Floods larger than the 500-year flood are possible but are extremely rare. The 100-year frequency flood is defined as a flood having an average frequency of occurrence of once in 100 years at a designated location, although the flood may occur in any year and possibly in successive years. It has a one-percent chance of being equalled or exceeded in 11 any year. Perhaps more significantly, it has about a 25- percent chance of being equalled 0r exceeded during a 30-year mortgage period. Area maps, profiles, and selected cross sections are provided in each report to define the limits of flooding that would occur during the 100-year flood and a 500- year flood. In addition, profiles for 10-year and 50-year floods may be shown (3). The hazards to life and extent of damage caused by any flood depend on the topography of the area flooded, depth and duration of flooding, velocity of flow, rate of rise, and developments on the flood plain. Velocities greater than 3 feet per second combined with depths of 3 feet or more are generally considered hazardous to life as well as property. Water flowing in excess of 4 feet per second is capable of transmitting sediment and causing severe erosion of streambanks and fill around bridge abutments. Where velocities drop below 2 feet per sec- ond, debris and silt deposits can build up, extending the flood damages and creating adverse health conditions (3). By definition, a floodway is the channel of a watercourse and that portion of the adjoining flood plain required to provide for the passage of the 100-year fre- quency discharge (discharge having a one-percent chance of occurrence in any given year) with an insignifi- cant increase in the water surface above that of the pre- flooding condition. Unless state or local requirements indicate a specific allowable increase, an insignificant in- crease is considered not more than a foot at any location. As a further definition, the “flooding fringe” is the por- tion of the 100-year flood plain located between the floodway boundary and outline of the 100-year flood (3). City engineering staffs are given the opportunity to review and comment on the drawings showing the limits of the floodway. Although great care is taken in defining the floodway base line (centerline) and encroachment limits, the floodway delineations require additional ad- justments. City officials are informed that the actual legal definition of the floodway for purpose of incorpora- tion into zoning ordinances or other uses is their respon- sibility 12 Houston Post An estimated 1,200 communities in Texas have present or tential flooding problems. ~ Houston Post l’ Flood Insurance in Texas An estimated 1,200 communities in Texas have pre- sent 0r potential flooding problems (I2). Lists of com- munities with newly identified special flood hazard areas are regularly published in the Federal Register in ad- vance of the effective date of the identification. About 600 Texas communities have received desig- nation by the Federal Insurance Administration (FIA) as having flood-prone areas. This is done in the form of a Flood Hazard Boundary Map. This map delineates the areas of special flood hazard subject to inundation by the IOO-year flood. The community can challenge the accu- racy of the map and has 6 months to provide data show- ing that it is not flood-prone or has corrected the flood hazard. Together with the map, FIA sends a letter of transmittal explaining the map, application forms, and program information to community officials (24). The community must commit itself to flood plain management that protects new construction from future flooding. Flood plain management means the operation . of an overall program of corrective and preventive mea- sures for reducing flood damage including emergency i, preparedness plans and any regulations aimed at the fu- ture use of the flood plain. Such regulations refer to specific local codes and ordinances which provide I standards for the location and design of new develop- ment within flood-prone areas. These regulations typi- acally take the form of zoning, subdivision or building regulations, or special purpose flood plain ordinances. To participate in the National Flood Insurance Program, a community must adopt flood plain management regu- lations that meet minimum standards published by the Federal Insurance Administration (24). The Texas Water Development Board has been des- ignated as the state agency to coordinate activities of the flood insurance program. The Board assists communities in adopting required flood plain management regu- lations and in qualifying for the program. It is the re- sponsibility of the local community to adopt and ad- minister these flood plain management regulations. The regulations do not apply retroactively to existing struc- tures in the flood plain unless a structure is substantially impaired to the extent of half or more of its market value. And they do not apply to new construction outside of the special flood hazard areas (24). Communities entering the flood insurance program usually do so in twophases. They first become eligible for the sale of flood insurance in the Emergency Pro- gram. Under this program, only half of the programs total limits of coverage are available, and all such insur- ance is sold at subsidized premium rates. To qualify for this program, a community must require building per- mits for all new construction and substantial improve- ments and review the permit to assure that sites are reasonably free from flooding. For its flood-prone areas, the community must also require l)proper anchoring of structures, 2) the use of construction materials and methods that will minimize flood damage, 3) adequate drainage for new subdivisions, and 4) new or replace- ment utility systems located and designed to preclude flood loss (24). The Texas Water Development Board listed 438 cities and 4O counties in Texas in the Emergency Program as of August 31, 1976. Any property owner whose building is located in a community that has been approved for the sale of flood insurance may purchase a policy. Owners or tenants may also purchase insurance on building contents. Policies may be purchased from any licensed property and casu- alty insurance agency or broker as soon as the commu- nity qualifies for the sale of flood insurance. Direct flood and flood-related losses are covered by the insurance. This includes losses from river and stream floodway, coastal flooding, flooding along the shores of lakes, and flood-related erosion as a result of storm activity. Wharves, piers, bulkheads, growing crops, land, shrub- bery, livestock, roads, bridges, motor vehicles, and simi- lar items are not covered (24). When a community enters the Regular Program, it must require that all new construction in identified areas of special flood hazard be elevated or flood-proofed to the level of the base flood. Additional standards are re- quired within any designated floodway or coastal high hazard area. The available limits of insurance coverage are double those available under the Emergency Pro- gram. The second half of coverage at actuarial (non- subsidized)rates is available together with the subsidized first half of coverage for all existing structures. All cover- age under the Regular Program for new structures in the flood hazard areas is made at actuarial rates reflecting the degree of flood risk for each property (24). The Texas Water Development Board reports that 66 cities and 11 counties in Texas were approved for the Regular Pro- gram as of August 31, 1976. I3 The information presented in Table 2 was prepared and distributed by the U. S. Department of Housing and Urban Development to summarize flood insurance ratemaking under the Emergency and Regular Pro- grams. The table sets forth the available limits of cover- age as well as appropriate premium rates under the pro- gram. Under the Emergency Program only the first layer or subsidized flood insurance is available. With the Regular Program, full coverage (first and second layer) is available. Actuarial rates are paid for all coverage on new construction and on substantial improvements in the flood hazard areas. On existing structures and on new construction outside the flood hazard area, actuarial rates are paid for the second layer of coverage and either the subsidized or the actuarial rates for the first layer, whichever is lower (24). A Flood Insurance Rate Map is furnished to the community by the Federal Insurance Administration. This map is the result of an engineering study and is used to further refine the boundary lines of flood hazard areas. These reflect the flood elevations that would occur during a flood with a one-percent chance of occurrence in any given year. The actuarial or non-subsidized pre- mium rates reflecting degree of flood risk are deter- mined from this information. Local officials are con- sulted on available data to verify or correct potential flood levels, and a public meeting is held to obtain additional information. Flood elevations on the rate map may be appealed by citizens for 9O days after the maps are published, and any appropriate technical data can be submitted for substantiation (24). Communities that have been identified as having one or more areas of special flood hazard by publication of the Flood Hazard Boundary Map have until De- cember 31, 1976 or one year from notification, whichever is later, to qualify for the program. If the community has not qualified, no Federal or federally related financial assistance may legally be provided for the construction or acquisition of buildings in the com- munity’s identified special flood hazard areas. Such assis- tance will remain unavailable until the community has qualified. The financing of buildings outside these areas is not affected. Houston Post Many people in high flood-risk areas are uninformed a - extent of risks of flood damage which they face. Houston Post TABLE 2. AVAILABLE LIMITS OF COVERAGE AND PREMIUM RATES OF THE FLOOD INSURANCE PROGRAMl Emergency program2 Regular program3 First layer Second layer Subsidized ~; rates Actuarial Total lim' Limit (Per $100) Limit rates 0f cover ,_ Single family residential $ 35,000 25c $ 35,000 Varies $ 70,0005 Other residential 100,000 25¢ 100,000 " 200,000 Non-residential 100,000 40c 100,000 " 200,000 . Contents, residential (per unit) 10,000 35c 10,000 " 20,000 . Contents, non-residential (per unit) 100,000 75c 100,000 " 200,000 l5 lSourcez U. S. Department of Housing and Urban Development. 2Only the first layer of coverage is available under the emergency program. Full coverage is available under the regular program for all structures in the community. 14 Economic Considerations a In its concern for the general welfare, the Federal government has a proper interest in measures to hold flood damages to an economic minimum. It has a respon- ‘_ sibility to discourage flood plain development which .would impose a later burden on the Federal taxpayer and which would benefit some citizens only at the ex- ;pense of others. Under previous policies, flood plain property own- ‘ ers in, unprotected or partially protected areas bore only i a portion of the cost, their price being exacted when l damage occurred. Some shouldered full losses; others relied on public relief and assistance in rehabilitation. They paid a minor fraction, through payment of general a taxes, of the public cost of relief and rehabilitation. The a general public, by bearing all or a major part of the cost eof flood protection works and thus lessening the indi- viduafs damage costs, further subsidized flood plain oc- cupants in their use of the flood plain. Flood insurance is intended to provide financial as- sistance to flood disaster victims in restoring their prop- I erty. In addition, flood insurance is to be a mechanism to help prevent unwise use of land where flood damages mount steadily and rapidly. y Many factors affect average annual flood damages for any property in any location, but the two most impor- tantpharacteristics of the flood-risk zone in which the property is located are the frequency of flooding and the depth of flooding. The hydrologic approach is based upon flood magnitude-frequency and depth-damage re- lationships. i The flood damage} hazard in the United States is highly concentrated. As few as 2 percent of all dwellings can expect to have more than half of the total average 21*’. nual flood damage. Less than 1O percent of all dwel- I 'ngs have any significant flood hazard, and the other 90 ercent or more are free from any serious or measurable flood hazard. If everyone contributed equally to a flood insurance program, through a uniform premium rate, this would be quite inequitable in view of the wide range in degree of flood risk (19). Many people in high flood-risk areas are relatively unconcerned about the risks of flood damage which they face. They are grossly over-optimistic about the proba- bility that their property will not be flooded, or they expect public help to bail them out when the inevitable flood disaster strikes. There is a maximum limit to the amount any large group of flood plain occupants will pay for flood insurance, even with the subsidies extended under the present program (19). Managing the Flood Hazard The prime measure to reduce flood damage hazard is to avoid unwarranted occupancy of the flood-prone areas. If the new occupant of such areas bears the full cost of flood insurance premiums, then he has to weigh the advantages of occupancy against the costs of flood plain occupancy. In some circumstances, it may be eco- nomic to occupy an area with relatively high hazard of flood damage, such as summer homes along the coast. The sea frontage makes these locations valuable but at the same time makes the risks of damage high. In many situations, the full costs of occupying high-hazard areas are greater than the probable advantage. Under those circumstances, flood insurance premiums that place the full cost on those benefiting from the location can oper- ate to keep unwarranted occupancy to a minimum (19). Alternatives exist that allow use of flood-prone areas. By careful site planning, land development, and site preparation and by special flood-proofing measures, the monetary damage from floods can be reduced con- siderably. In the case of industrial and commercial prop- erty, special measures can be taken to protect machin- ery, equipment, supplies, and stock from damage. Some of these measures can be taken on older buildings, al- though both physical and economic possibilities are greater for new buildings. F lood-prone areas, both riverine and coastal, are often valuable regardless of the risk of flooding. Many industries needing a lot of water, or having the need for major discharge of wastes into water, want locations bor- dering streams or the Gulf. The amenity or recreation value of a flood plain location for a vacation or permanent home is also important. In some cities, the flood-prone area may be well located with respect to the rest of the city. In these and other situations, people may wish to locate their primary home, their vacation home, or their business in a location subject to flood hazard (19). Problems arise, however, when the costs due to flood hazard are greater than the benefits due to loca- tion. If everyone were perfectly informed and if circum- stances never changed, presumably no one would ever be located where costs exceeded benefits. Many persons have, in fact, located where flooding costs proved to be far higher than they expected when they located there. Sometimes a location that was valuable when a building was first erected is no longer so valuable when condi- tions have changed. 15 Flood Insurance on Developed Flood Plain Flood insurance premiums can be useful in identify- ing for the potential buyer 0r builder the true flood risk. For the examples that follow, it is assumed that a flood insurance premium is set at the average annual flood damages per $100 of building and contents. Actually, a flood insurance premium that is not subsidized will ex- ceed average annual flood damages since flood damages and all overhead costs of the program must be included in the premium, hence the effect of flood insurance on prqperty values is greater than that of the actual flooding r1s . The value of property in a flood plain considering flooding risk can be estimated using the following equa- tion: B+F A( 100 i V=L+B+F— (l) where V = value of land, buildings, and contents considering flooding L = land value with no flooding risk B = building value in absence of flooding F = furnishings or building contents value in absence of flooding A = average annual flood damages per $100 building and contents value i = interest or discount rate. Basically, the calculation takes property value in the absence of flooding and subtracts the expected present value of all future flooding damages. Assume a development in the flood plain which has a land value of $10,000 and flood damageable property in building and furnishings of $40,000. This would give a total value of $50,000 for land, building, and furnishings if the development was not subject to flooding. How- ever, the location in a flood plain means a flood risk is assumed, and this risk can be reflected in reduced prop- erty value. The magnitude of the reduction in property value is directly related to the flood risk; i.e., the greater the flood risk, the greater the loss in property value. In the example, if average annual flood damages were $1 per $100 flood damageable property value, the total prop- erty value would be reduced $4,000 calculated as ($1 X 400 » 10% leaving $46,000 property value rather than $50,000. This, of course, is calculated using a 10 percent discount rate. At $5 average annual flood dam- ages per $100 property value, the reduction in property value due to flooding risk would be $20,000, or the $50,000 value would be reduced to $30,000. Figure 2 shows the percent reduction in flood dam- ageable property value that is associated with alternative flooding risks (average annual flood damages). A 10 per- cent discount rate is used to develop the graph. With average annual flood damages of $10 per $100 of building and contents, the value of the building and contents is 16 Reduction in value of building and contents Percent 100.0 90.0 -- 80.0 -- 70.0 -r 40.0 -- 30.0 ~- 20.0 - 10.0 - 7.5 -- 5.0 ‘r 2.5 - 1 00 2.00 - 3 00 o 8 8 8 8 c. 8 3.