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From the Transactions of the Nova Scotian Institute of Science, Vol. IX, Session 1^96-97. I The EDITH and LORNE PIERCE COLLECTION of CANADI ANA ^eeris University at Kingston « » VI.— The Rainfall in 180G. Bv F. W. W. Doane, M. Can. Soc. C. E., City Engineer, Halifax, N. S. (Read 10th May, 1897.) The systematic and accurate reuistration of the rainfall is a matter of the greatest importance to the Engineer. It is abso- lutely necessary in order to enable him to design intelligently works for water supply, sewerage, water power, drainage of roads, bridges, culverts, &;c. ^ He requires certain data to enable him to design dams spillways, storage reservoirs, sewers, bridges, &c., so thlt every possible requirement may be provided for. The quantity of rain that falls annually in any one place varies greatly from year to year ; the extreme being sometimes greater than 2 to 1. As a general rule, more rain falls in warm than in cold countries, and more in elevated regions than in low ones. Local peculiarities and conditions however, sometimes reverse this, and also cause great difference in the amodnt in places quite near each other. It is .sometimes difficult to account for these variations. The earliest known records of rainfall were made in Paris in 16(58. Sir Christopher Wren designed the first rain gauge in 16G8. This great architect also designed the tirst recording gauge, but it was not constructed until 1070. The rainfall records of some })ortions of the United States cover perio.ls extending into the last century. In Canada, the average amount of rain falling in Ontario has I.een taken by the officials of the Magnetic Observatory at Toronto for the past 50 years. The meteorological station at Halifax was established in 1809, and observations began at Truro in 1873 ; a systematic registration of rainfall has been ma.le at Yarmouth since 1879, and the record at Sydney dates back to 1893. (279) I 280 THE RAINFALL IN 1896 — DOANE. An examination of the records of the United States reveals some interesting and important facts, which it may be well to quote at this stage for the purpose of comparison. The greatest annual rainfall on this continent is recorded at Grey town, the Atlantic entrance to the proposed Nicaragua (Janal. It there assumes the enoimous total of 240 inches (20 ft.), a figure which in only surpassed in the Western Hemisphere on the Mexican Gulf Coast in the West Indies, by Guiana and by the coast of Brazil. It is reported that from 7 to 10 per cent, of the total annual rainfall may descend in one day. The results of such a precipitation can be better imagined than described ; dry river beds become torrents in a few minutes, the water coming down in a wad several feet high ; marshes change to lakes, and the power so quickly developed is necessarily very dangerous to any work of man. The most remarkable rainfall is recorded at Cuyamaca Dara in San Diego Co., California, about 40 miles east of San Diego. Duiing a storm ending February 27. 1891, the record shows that 23.40 inches fell in 54 hours, of which 13 inches fell in 23 hours, and 7 inches in 10 hours. The elevation of the reservoir is about 4500 feet above sea level. The highest surrounding mountains are 6500 feet above sea level, and lie to the west of the reservoir between its watershed and the direction whence the storms come. The eastern boundary of the basin is on the riuj of the desert at an elevation of not over 5000 ft. The topography of the country is such that a rain gauge at the dam would not be likely to indicate the maximum precipitation on the three peaks that bound the water shed on the west. The most notable thing about the above remarkable rainfall, however, is that the place where it occurred is within a few miles of one of the very diiest regions in the world. The average annual rainfall at Indio, San Diego Co., a station on the Southern Pacific Railway, about 50 miles east of the Cuyamaca Dam, is given by General Greely as but 1.92 inches, and he says of this and Camp Mohave, Arizona, where the average rainfall is but 1.85 inches: " These stations, doubtless, have the smallest known THE RAINFALL IN 1896 — DOANE. 281 rainfall on the face of the globe. Statements have been nmde frequently that rain never falls in these localities, but there is no ytar at any station where A measurable rainfall has not be(n recovdef], the least observed being that at Indio, 0.10 in., during the seasonal year 1884 85." General Greely's "American Weather" gives the following instances of heavy rainfalls, which exceed the above record: Mayport, Fla., Sept. 20, 1882, 13.7 ins. in 24 hours; I^ewtown, Del. Co., Pa., Aug. 5, 1843, 13 in. in 3 hours ; and at Brandy wine, Hundred, Pa., 10 ins. in 2 hours. Nevada Co., California, reports the lainfall for the month from Dec, 23, 1861, to Jan. 23, 1862, 45 ins. Providence, R. I., lecords a rainfall Aug. 6, 1878, 4.49 ins. in 1 hour, 3.5 ins. of which fell in 3(5 minutes. At New York, the heaviest fall is Aug. 19, 1893, 1^ ins. in 20 minutes ; for 12 hours Aug. 23, 1893, 3.81 ins. ; 24 hours Sept. 23-4, 1882. 6.17 ins. ; month Sept., 1882, 14 51 ins. The aveiage annual rainfall at Halifax from 1869 to 1895 was 00.862 inches. It varies from 45 808 ins. in 1894 to 66.294 inches in 1888. A rainfall of 39.51 inches is leported for i860, but as the Meteorological Oliservatory had not been established at that time, it is doubtful if the record is leliable. There is no doubt, however, that the rainfall for that year was far below the average. The scarcity of water meagre supply from the lakes, and consequent inconvenience to householders lead to the pur- chase of the water works from the company in the following year, 1861. Reference to the records shows that the years of smallest rainfall are immediately followed or preceded by years of greatest rainfall. Thus in 1888 the rainfall reached the maximum 66.294 inches. In the following year it dropped to 48.659, within 2.851 inches of the minimum. In 1894, as already noted, the season was very- dry. The rainfall was the smallest recorded since the establishment of the Observatory at Halifax. The sources of our waier supply dried up so that there was danger of a water famine. Similar conditions were noted throughout the New I B 282 THE RAINFALL IN 1806— DOAXE. ■ Enorland Srates. In the following year the records show a total of C2.]o2 inches, while in 1896 Mr. Allison, Doni. Government Meterological a<-ent at Halifax, reports 09.802 inches, 3.oG8 ins. greater than that of any previous year. Rain or snow fell on 183 days. The greatest monthly rainfall on r. cord previous to 18% was 10.84 in February, 187C. In 1888 the heaviest monthly fall was 7.704, which is recorded in December. In 1890, 8,729 ins. fell in July, and 8.780 inches in March, while in September and October, the record shows 12.092 inches and 15.0:J9 inches, respectively. Rain fell on 16 days in September, and on 20 days in October. The fall on the 7th, 10th, 13th and 18th of September, was 1.232 ins., 3.912 in^s., 3.146 ins., and 1.0 10 inches, a total for the four days of 9.8 ins., or more than f of the whole precipitation for the month. In October, 4 394 ins. fell on the 19th, 29 per cent, of the rainfall for the month, and per cent, of the total for the year. The first month, January, gave the modest total of 1.72 inches, while for January, 1895, 10.131 inches is recorded. There were four heavy storms during the year. Early in the morning of July 31st, rain began to fall, and during 3.8 hours the gauge .showed 3.506 inches, or at the rate of .92 inche.s per hour. The rate of fall was the heaviest on record, although the quantity was exceeded in subsequent storms of greater duration. On Sept. 10th, rain fell during 7.5 hours, the quantity regis- tered being 3.912 ins., or at the rate of .52 ins. per hour, O.J 86 inches fell on the 11th during 4.1 hours, 0.13 ins. on the 12th during 2 hours, and on the 13th, 3.140 ins. fell during 9.5 hours, or at the rate of .33 ins. per hour. The total fall fo° the four days was 7.374 inches. On October 19th the maximum quantity was recorded, the precipitation being 4.394 inches during 14.3 hours, or at the rate of .30 inches per hour. The September rains referred to above raised Long Lake about 32 inche.s, the highest level reached being 10.5 inches above the waste weir. In October, the ground was saturated with THE RAINFALL IN 1896— DOANE. 283 water, and the rain fallinjor on the 19th flowed off rapidly. Long Lake was raised 20 inches by the heavy storm ot the 19th in about 24 hours. The water level was 25 inches above the .spill- way of the dam, while at Lower Chain Lake it overflowed the screen chambers and ran over the floor of the old jjate hor-,e. Drains and culverts were destroyed, roads washed out and bridges carried away. Jubilee Road was excavated by the rush of water for a length of lOG yards, the road metal being carried away for a width of half the roadway and a depth of G ft. Heavy stones were deposited at the foot of the hill, while the lighter material went to sea. The main trunk sewer on the common was not only full to overflowing, but a torrent of water followed its course on the surface, sweeping through the gardens and down South Park Street, until it found an outlet at South Street. The Meteorological Agent at Truro reports about 30 hours rain on the 18th and 19th October, the greatest on record with regard to duration. At Yarmouth and Sydney the rain fall was light. September 10th-13th, Sydney reports no rain ; Yarmouth and Truro comparatively light rains. July 31st, moderate rain- fall at Sydney, Truro and Yarmouth. Comparing the Halifax records by months we And : — July, 1896, 8.729 ins.— next— July, 1884, 8.294 ins. Sept., 1896, 12.092 " " Sept. 1876, 6.094 « Oct., 1896, 15.039 " " Oct., 1875, 9.98 " Mr. E. H. Keating, City Engineer, says in making his report on a design for the Halifax sewer system : — " The heaviest rainfall in a short time, of which I have any information, occurred on the 19th June, 1872. when 0.183 of an inch fell in half an hour." He also reports a rainfall of 4.406 inches in 18 hours on the 10th October, 1875. Our s.ewer system was designed to discharge a rainfall of 0.38 in.s. per hour, together with the house sewage when running 284 THE RAINFALL IX 1890— DOANE. two-thirds full. The desif(ner made a liberal estimate in detej- xnuuwjr the capacity required, and yet during the past year it was plainly demonstrated that the capacity of the sewers was not sufficient to carry off the rainfall, and great trouble, damage and inconvenience has been caused in consequence. Theie is not the slightest doubt that the greater part, if not the whole, of this trouble would have been obviated if records of self-recording rain gauges had been available. While the greatest rainfall on record in 187l) was .183 inches in half an hour, we had in 1896 a storm lasting 7.5 hours, with an average rate of fall of .52 inches per hour, and another lasting 3.8 hours, with an average fall of .92 inches per hour. The maximum rate must have been greatly in excess of even the latter figure, but as the storm came on the dark hours of the morning, and the rain was not measured by self-registering instruments, we can only guess at the maximum rate per hour. The design of sewers depends principally on two classes of storms. These are short storms of great rates of precipitation, and long storms of ordinary rates of precipitation. It is not sufficient to know the rainfall per hour. The severity of a storm often reaches a maximum during from 10 to 20 minutes only, and this maximum should be determined, if possible. It is also most important that the local conditions of the surface should be known. If the ground is saturated before the storm the rainfall will run oft' more rapidly. A chief purpose to be subserved by a rainfall record is not merely how often does the maximum rainfall occur at each point, for that is an event which jnly recurs once or twice in a century. The great desideratum is : How often do the heaviest rainfalls of various rates occur, and for how long a maximum and average time does such p rainfall continue ? The records from which such laws are deduced must neces.sarily be somewhat voluminous, and yet by proper study, aided by records of a number of years, a very close approximation to the real probabilities could be obtained and drawn graphically on charts, which would be of the greatest aid to hydraulic and city engineers ; and even without THE RAINFALL LN 1896— DOANE. 285 thi.s, t,he bare records would give to a man who mijTht be design- ing works at special points, material for digging ont for hims^elf some approach to a law where now all is guess work, and often very bad guess work. It is to be regretted that the Meteorological Stations in this Province are not supplied with the most modern self-recording instruments. With an ordinary rain gauge it is not possible to determine the rate per hour of the fall of rain during a storm, without noting the time with a watch ; and as it is very incon- venient, if not impracticable in the majority of cases to do this, it is very rarely done, and when it is, an average rate is all that is generally ascertained, although it may have been raining faster or slower at intervals during the time noted. By the use of a reliable self-recording rain gauge the different rat- s at which rain has fallen during a storm can be readily determined. I 286 THE RAINFALL IN 1896 — DOANE. Depth ok Rainfall and Melted Snow, and Duration of „ach Storm, FOR THE Year 1896. Jantary. February. March. April. May. June. o < w S 4J 3 4J s < 03 3 t 3 X 4J a < t 3 a < 3 1 0.18(» 0.020 1.5 2 4 .5 '6'065 o'eeo 0.030 6! 646 0.140 T 0.020 1.75 16.5' 2.5 i.'s' 4.66 0.440 *T. 1.310 o.oio 0.342 0.480 0.100 0.020 0.522 20. .... 0.089 0.094 0.510 0.186 7.2 3.5 6.7 4. 0.889 0.015 0.323 0.012 '5! 6 1. 6.5 0.5 OJOO 0.050 2^6 2.0 6 0.020 0.5 7 8 14. \. 6.5 3. 1. 1.7 7.75 030 0.596 re 7. T T. 6.130 0^5 0.770 0.970 0.090 0.444 10.1 11.3 2.3 8.5 10 11 12 6 0.30 1.619 15. 18 14 0.009 0.034 T. 0.040 0.015 020 0.010 1.0 2.0 '2^5 2.0 0.8 1.0 T. 0.841 0.086 6.010 0!050 15 14.5 3. 6!5 'i!5 16 17 18 19 20 21 10. O.260 'o!6i6 0.220 0.410 6.5 1 . 5.2 8.3 0.040 1.655 "o;020 1.498 2. 13.5 6'8 9.4 6.250 0.068 210 'i!o 3.0 3.5 22 0.050 7. a • O.-SO.'i 0.186 5.8 0.5 0.060 1.7 23 24 o'soo 0.270 0.045 0.010 16!" 12 5 1.75 0.075 2. . . . ' ' 25 2'- 0.192 1.450 1.7 8.5 0.230 0.200 o!700 4.0 3.7 27 0.247 0.014 0.540 0.426 3.0 f^ n 28 0.046 • • 29 8.3 30 0.274 0.503 8.2 7 3 31 • • • • • • • • 1.720 4.199 . . . . 8.786 1.413 ...1 2.532 4.071 .... * Trace. THE RAINFALL IN 1896— DOANE. 287 Depth of Rainfall and Mklted Snow, ani. Dubation of each Storm, FOB THE Year 1896. Day of Month. July. August. September October. November December, S < aj 3 O 4i E < X +3 u S '38 +3 si 3 X < 03 3 w +3 s m u 3 X 1 Of^O 0.020 2 3 4 0.938 — 0.354 5.0 0.378 5.0 o!ii2 0.764 9.5 552, 8.7 0.005 U.4 0.170 6.6 0.032 1.0 0.5 ' T. 362 i.524 0.020 T. .... 5 11.0 o 01 E v CJ CO CO c CO CD 't* O CO in in 1^ in CO CO CO 00 o OS S5 o OS m o C^l in p-H CO CO in ■* Tf ■«* in 0-1 o CO in o in in CO c in s GO OS ■n S «5 CO 0^ OS in ^^ in CO o CO -1< 00 in OS QO CO in IM CO m m in m OS en CS CO OI o CI CO CO m 00 00 CI g OS CO CO ^H CO CI CO CO CO CD in CO in o H THE RAINFALL IN 18f)6 — DOANE. 289 s s a < ■< . 65 O ■«! 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