Figure 7.9 



Highest Percentage Water Depletion (1975-2000) in a Dry Water Supply Year, by Water Resource Region 



to^ 



91 % and over 



At present, water quantity problems are of little 

 consequence in Alaska, nor are they expected in the 

 future. Consumption of water in Hawaii is increasing, 

 but is not expected to pose serious supply problems. 

 Water consumption in the Virgin Islands will greatly 

 exceed water supplies in the future, but this is not the 

 case in Puerto Rico. 



Adequacy of Instream Flow 



The "depletion" analysis can also provide infor- 

 mation about the adequacy of waterflows to support 

 aquatic life. To do this, it is necessary to estabHsh 

 criteria for describing the severity of various levels 

 of depletion. Tennant^ has described the instream flow 

 conditions for 60 (40 percent depletion), 30 (70 per- 



'Tennant. Donald L. Instream flow regimens for fish, wildlife, 

 recreation and related environmental resources. U.S. Department 

 of the Interior, Fish and Wildlife Service, Billings, Montana, 123 p. 

 1975. 



cent depletion), and 10 percent (90 percent depletion) 

 mean annual flow. 



"Sixty percent of average flow (40 percent deple- 

 tion) is the base flow recommended to provide excel- 

 lent to outstanding habitat for most aquatic life forms 

 during their primary periods of growth and for the 

 majority of recreational uses. Channel widths, depths, 

 and velocities will provide excellent aquatic habitat. 

 Most of the normal channel substrate will be covered 

 with water, including many shallow riffle and shoal 

 areas. Side channels that normally carry water will 

 have adequate flows. Few gravel bars will be exposed, 

 and the majority of islands will serve as wildlife nest- 

 ing, denning, nursery, and refuge habitat. The major- 

 ity of streambanks will provide cover for fish and safe 

 denning areas for wildlife. Pools, runs, and riffles 

 will be adequately covered with water and provide 

 excellent feeding and nursery habitat for fishes. Ripar- 

 ian vegetation will have plenty of water. Fish migra- 



294 



