SECTION OF IRRIGATION AND METEOROLOGY. 
25 
nary to the construction of a reservoir which has but recently been 
built, is classic in irrigation literature. The observations were car- 
ried on for less than four days in 1849. T-anks 20 inches (50cm) in 
diameter and 2 feet high were made. In one the water was still ; in 
the other an iron disk nearly of the same diameter as the tank, with 
holes through it, was slowly raised and lowered in the tank. The 
water passing through the numerous small holes, kept the surface in 
agitation, something like the surface in small ditches with rapid fall. 
The loss under these conditions was more than a third more from 
agitated than from the quiet water, or a loss of 1.66 inches from the 
quiet water, and of 2.32 from the rough water.* 
ESTIMATE OF EVAPORATION FROM RESERVOIR. 
§ 31. From the preceding data we may estimate the amount 
of evaporation under reservoir conditions. Any such estimate is 
subject to the uncertainties already mentioned, and to the condition 
that the evaporation may vary much from year to year, and from 
one body of water to one immediately adjacent. Nevertheless we 
may make what may be considered a reasonable estimate from the 
observations. 
January 
February — 
March 
April 
May 
June 
Evaporation. 
1.5 inches. 
2.0 “ 
3.5 “ 
5.0 “ 
6.5 “ 
July 
August 
September 
October 
November 
December 
Evaporation. 
8.5 “ 
6.5 “ 
4.5 “ 
2.5 “ 
1.5 
Total ... 
§ 32. The following are other cases of evaporation which have 
been observed. On several lakes in California, observations were 
made in 1879 by J. D. Schuyler, now consulting engineer, of Los 
Angeles, Cal. They are reported in William Ham Hall’s report as 
State Engineer of California in 1880, and in Physical Data and Sta- 
tistics of California : 
Reeder lake is a narrow lake with wooded shores, water 12 to 
15 feet deep. Evaporation pans two by two feet square and one foot 
deep were used. They were protected from the wind but exposed to 
the sun. From June 25th to July 11th, a total of sixteen days, the 
loss was 1.21 inches, or an average of .24 inch per day. The tem- 
perature of the water from five observations taken late in the after- 
noon, varied from 82° to 92°, which would be higher than the aver- 
age temperature. 
In Panama Slough, California, July 9th to August 20th, 1879, a 
loss of 2.46 inches in a little over seventeen days, was noticed, or an 
average of .145 inch per day. The temperature of the water was 
from 64° to 72°. 
* Debaave, Manuel de ITugenieur, Des Eaux en Agriculture, p. 170. Parrochetti, Manuale 
pratico di Idrometria, pp. 256-8. 
