CONSUMPTIVE USE OF WATER BY NATIVE PLANTS 

 GROWING IN MOIST AREAS IN SOUTHERN CALIFORNIA 



By Harry F. Blanet * 



CHAPTER I 

 INTRODUCTION AND SUMMARY 



INTRODUCTION 



In southern California the natural water supply is exceedingly 

 limited, while the demands for water are great and its value is high. 

 In some sections the value of continuous-flow gravity water ranges 

 from $100,000 to as much as $200,000 per second-foot,** depending 

 upon its use. Both present and future agricultural, domestic, and 

 industrial development depends upon the adequacy of the water supply. 

 Under these circumstances it is economically important to utilize the 

 available water supply to the fullest extent. For this reason federal, 

 state, county, city, and other agencies are working along lines to deter- 

 mine ways and means by which water, now wasted, may be conserved 

 for beneficial use. 



The Bureau of Agricultural Engineering in cooperation with vari- 

 ous agencies is making studies to determine the contributions of rainfall 

 to the ground water of valley floors, consumptive use of water by plant 

 life on both irrigated and nonirrigated lands, irrigation water require- 

 ments of different crops, replenishment of underground storage of 

 water by spreading, evaporation losses, and noneconomic use of water 

 by native plants growing in moist areas. This report deals with the 

 consumptive use of water by various types of indigenous vegetation 

 commonly found in meadows and swamps and along stream beds, evapo- 

 ration losses from soils without vegetative growth in areas of high 

 water table, and evaporation from free water surfaces. 



In considering the adequacy of public water supplies in the past, 

 too little attention has been given to use of water by noncrop plants. In 

 most instances such plants are so located that they get their supplies 

 of water before settled communities get theirs, and therefore such use 

 must be considered in estimating water available for other purposes. 



For areas where large amounts of money are spent to develop and 

 deliver water for irrigation at heavy annual cost to the irrigators, the 

 water that could be saved by preventing the growth of uneconomic 

 plants may be reckoned as approximating in value that of an equal 

 amount of water in storage. For citrus fruits the cost of water is 

 frequently as high as $15 to $20 per acre-foot and in some instances it 

 is much higher. Tules, willows, and alders growing in irrigation canals, 

 drainage ditches or stream channels or on their banks are usually 

 exposed in narrow strips to sun and wind so that their consumption of 



* Irrigation Engineer, Division of Irrigation, Bureau of Agricultural Engineering, 

 U. S. Department of Agriculture. 



** State of California Department of Public Works Bulletin No. 36, Cost of 

 Irrigation Water in California, by Harry F. Blaney and Martin R. Huberty. (1930.) 



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