PROBLEMS FROM LAND OCCUPANCY 189 



There are successful water-spreading projects in several 

 western states and in a few eastern states. Southern California 

 has taken the lead in this field and has some of the oldest, 

 largest, and most successful spreading projects. In the Upper 

 Santa Ana Valley near San Bernardino, for example, artificial 

 recharge was begun in 1912; the quantity of recharge has 

 averaged about 15,000 acre-feet a year, but has ranged from 

 none in several dry years to 68,000 acre-feet in 1922. Mitchel- 

 son and Muckel summarized numerous California studies in 

 1937, and pointed out that water spreading there has long 

 since passed the experimental stage, and is a well-proved prac- 

 tice. 27 



In several areas a vegetative cover has proved effective in 

 maintaining a high rate of infiltration. Experiments in an 

 offstream spreading basin along the San Gabriel River in 

 California showed that infiltration in a grass-covered basin 

 was 50 per cent greater than in an adjacent basin bare of 

 vegetation. This increased infiltration was six to eight times 

 the estimated water cost in transpiration from the vege- 

 tated basin. 28 From their studies of 15 water-spreading areas 

 in southern California, Mitchelson and Muckel conclude that 

 the consumptive use by vegetation is negligible in comparison 

 with its beneficial effect on the percolation rate. Since the most 

 effective use of underground storage may require putting 

 water into the reservoirs, as well as taking it out, artificial re- 

 charge can be expected to become of progressively greater 

 importance to water development, with vegetation in spread- 

 ing areas playing a significant role. 



Precipitation occurs on an "if, as, and when" basis that 

 makes control more difficult than with stream water. It is a 

 major factor in the recharge of some ground-water reservoirs, 

 particularly in wet years, as shown, for example, in studies of 



27 Mitchelson, A. T., and D. C. Muckel, Spreading Water for Storage Under- 

 ground, U.S. Dept. Agr. Tech. Bull. 578, 1937, 80 pp. 



28 Muckel, D. C, Some Factors Affecting the Rate of Percolation on Water- 

 spreading Areas, Trans. Am. Geophys. Union, vol. 17, p. 472, 1936. 



