22 DIVISION OF WATER RESOURCES 



if the size of tanks was extended to swamp areas the consumptive use 

 would decrease to a relatively small fraction of that used by exposed 

 tanks. Very little is known as to the proi^er factor to be applied, but 

 a limited investigation indicates that consumptive use of water by tules 

 or cat-tails in densely grown natural swamp areas may be as low as 

 30 per cent of the consumptive use by similar growth in isolated tanks 

 having extreme exposure to the elements. 



5. Willow uses more water than either of the two wild grasses 

 with which tests were made. A single clump of willow used 52.71 

 acre-inches per acre with a water table at a depth of 2 feet during 

 an eleven-month period. This was 83.5 per cent of the evaporation 

 from a standard Weather Bureau pan. The willow was fully exposed 

 and the consumptive use may have been higher than would be the 

 case from an area of equal size in a willow thicket. As a moist area 

 noneconomic growth, the willow is responsible for Avaste of water which 

 might other-wise be put to a more beneficial use. On the other hand, 

 willows will grow in gravelly river bottoms Avhere they furnish protec- 

 tion against erosion. Any benefit obtained by removal of such 

 protection to increase the water supply may be offset by damage by 

 floods carrying sand and gravel into valuable farm communities. No 

 data are available indicating a factor for reduction of consumptive 

 use by wdllow^s grown in exposed and isolated tanks to that used by 

 natural growth in large areas. 



6. Wire rush grows in a limited area in the Santa Ana Valley 

 where high ground water exists. Its consumptive use measured from a 

 2-foot water table is high, exceeding that from grasses or willow. In 

 July, 1931, it amounted to 13.75 acre-inches per acre, which was 2.8 

 times the amount used by salt grass during the same period and grow- 

 ing at the same location. As far as is known, wire rush has no value 

 for live stock and the water it consumes is an economic loss. No data 

 exists for determination of a factor to reduce consumptive use from 

 tank growth to that by natural field groAvth, but some factor should 

 be applied. 



7. Soil tests were made to determine mechanical analysis, moisture 

 equivalent, porosity, and apparent specific gravity of soils in tanks. 

 About 20 per cent of the soil at the Santa Ana station was fine 

 enough to pass a No. 200 screen. Soil in the San Bernardino tanks was 

 considerably finer. Moisture-equivalent values as determined at Santa 

 Ana were not constant, varying from 5.8 to 13.0 per cent in different 

 tanks. The moisture equivalent of the top foot of soil at San Ber- 

 nardino was about 30 per cent, or nearly twice that of the subsoil at 

 a depth of 3 feet. Porosity tests of soil in tanks show an average of 

 40.2 per cent at Santa Ana and 47.4 per cent at San Bernardino. 



8. Specific yield and specific retention in relation to high water 

 tables, the sum of the two equaling the total porosity, also were deter- 

 mined. Each of these varies with the depth to the water table, the 

 greater yield occurring with the least depth, and the greater retention 

 with the greater depth. Porosity of the disturbed soil is about the same 

 as in the undisturbed soil, but the specific yield is much less and 

 specific retention is correspondingly greater. In the Chino silt loam 

 at San Bernardino, the specific yield is small in comparison with the 

 specific retention. The percentages measured as specific yield and 



