WATER LOSSES FRO:\[ WET AREAS 49 



iu the top inch of soil. About two months after the last heavy rain 

 in the spring of 1932, samples of horizontal sections of soil in various 

 tanks Avere collected for chemical analysis. The results of these analyses 

 are shown in Table 9. The salts shoAm are predominately sodium 

 salts, and extracts from the high carbonate soils were all black, indicat- 

 ing black alkali. There was no calcium present in the solution, due to 

 the high content of the carbonate ion. Also, the amount of sulphates 

 present is of no importance. The pH values at the Santa Aiia station 

 are very high, ranging from 8.4 to 10.6. These values indicate a highly 

 alkaline reaction. 



In the tanks of undisturbed soil where depth to water table was 

 2, 3, or 5 feet, the surface concentration of salts in the top inch of 

 soil was not excessive. With a water table 1 foot from the surface, 

 there was an extremely heavy deposit of salts in the top inch, measur- 

 ing as high as 3200 parts per million of carbonate. In general, greater 

 deposits occurred at or near the surface in those tanks having the 

 highest water tables. The same was true at the San Bernardino station, 

 although the bicarbonates exceeded the carbonates in amount, which 

 was the opposite of the Santa Ana condition. The pH values do not 

 indicate an excessively alkaline reaction. 



CONSUMPTIVE USE OF WATER 

 Evaporation from Soil Surfaces in Tanks 



In making studies of evaporation from bare soils at the Santa Ana 

 station, distribution of soil moisture under natural conditions as found 

 at the station site determined the initial maximum depth to the water 

 table in the first set of tanks. In excavating around the tanks as they 

 were filled, the upper 15 inches of soil was observed to be moist from 

 previous rains, while the soil from 15 to 30 inches iu depth was found 

 to be extremely dry. Below this dry belt was capillary moisture arising 

 from the perched water table found at a depth of 6 to 7 feet. It was 

 evident, therefore, that the limit of capillary rise in undisturbed soil 

 with which the tanks were filled was the difference between the depth 

 to the water table and the lower limit of the dry area, or slightly less 

 than 4 feet. This measure was, therefore, adopted as the depth to 

 the lowest water tables in the soil evaporation tanks. From this 

 4-foot water table, no soil evaporation occurred at any time during 

 the warm summer months between May and October. Data regarding 

 Aveekly amounts of evaporation from- soil surfaces obtained at the 

 Santa Ana station, where water tables were at different depths, are 

 found in Table 11. Monthly data relating to the same tanks are given 

 in Tables 13 and 14. 



No losses by evaporation occurred when the water table w'as at a 

 depth of 4 feet, but there were small losses when it was raised to 3 

 feet and still greater losses at 2-foot depths, confirming the initial 

 conclusion that the limit of capillary rise was about 4 feet. For a six- 

 month period during the winter of 1929-30, when evaporation was at 

 its lowest, the total evaporation from the tanks having 3-foot water 

 tables averaged but 0.913 acre-inch per acre. For the same period, 

 evaporation from tanks having water tables at a 2-foot depth was 

 1.775 acre-inches per acre. 



4—4503 



