IV-332 



well as quality, of fresh water inflows to the estuaries 1s larqely 

 determined by upstream water use. Water diversion for irrigation, 

 impoundment for flood control , and a host of other uses tend to 

 cut the natural stream flow necessary to the successful assimila- 

 tion and diffusion of both natural and man-made wastes. An example 

 of upstream diversion of water is provided by the Texas Water Plan, 

 which is projected to alter streamflows radically into such pro- 

 ductive estuaries as Galveston Bay and those situated 1n the southern 

 Texas coast. Even 1f a tremendous planned diversion from the 

 Mississippi River for fresh water Inflows to the estuaries is com- 

 pleted on a timely basis, these estuarine systems are projected to 

 face overall reduction of fresh water supply and the accompanying 

 stresses both on the natural assimilative capacities of these estua- 

 ries and the biotlc communities presently existing there. 



Pressures for increased upstream diversion and use of fresh water 

 are certain to Increase 1n all biophysical regions, but the relatively 

 arid and high growth Western Gulf and the Southwest Pacific coasts 

 are projected to experience the greatest pressures on present estua- 

 rine systems for at least three main reasons: 



(1) Much of the upstream water 1s used to support irrigation 

 with accompanying actual loss of water to the inflow systems 

 by evaporation, transpiration, and absorption, as well as 

 mineralization through leaching. 



(2) The amount of rainfall and snow pack is highly variable 



