USE OF WATER BY NATIVE VEGETATION 



By 



Arthur A. Young — ' 



and -, / 



Harry F. Blaney — ^ 



CHAPTER 1 

 INTRODUCTION 



The purpose of this bulletin is to bring together con- 

 veniently in a single report the results of studies of consumptive 

 use of water by a number of species of native vegetation, as 

 determined by the Division of Irrigation for various western 

 climatic conditions, and some of the results of similar investi- 

 gations by other agencies. Such studies have been carried on for 

 many years. 



It is not the intention of the authors to minimize the 

 value of vegetation as its growth on mountain watersheds, as 

 elsewhere, constitutes a very necessary protection to the soil. 

 Water consumed by most native vegetation is used beneficially and 

 is not considered as wasted. The moisture requirements of the 

 natural ground cover are satisfied before water becomes available 

 for other purposes. In considering the water supply of a region, 

 therefore, the difference between precipitation and run-off plus 

 deep percolation constitutes the consumptive use by the native 

 growth. It is for those concerned with the natural resources of 

 soil and water that these data on use of water by native vegeta- 

 tion are presented. 



The usefulness of such data are recognized by administra- 

 tors and investigators in regions where water rights are in dis- 

 pute locally, or where interstate water supply and water use are 

 not in balance. Valley or basin investigations to determine a 



17 Associate Irrigation Engineer and Irrigation Engineer, 

 respectively, Division of Irrigation, Soil Conservation Service, 

 U. S. Department of Agriculture. 



