of these elements in the tributary 

 waters. 



Beneficial effects; 



Decrease in the suspended solids 



content 



Due to the reduction in stream 

 velocity, the reservoir acts as a 

 settling basin and permits the 

 removal of settleable matter by 

 sedimentation. Since turbidity 

 was generally very low in the 

 Wenatchee eind Chiwawa Rivers, 

 additional reduction would be in- 

 cidental except during the spring 

 freshets. 



2. Reduction of color due to the 

 bleaching action of sunlight. 



Color was usually very low in both 

 rivers, and any further reduction 

 would be insignif iceint , except 

 possibly during the heavy spring 

 runoff. 



3. Improvement in the sanitary quality 

 of the impounded water , due to the unfavor- 

 able environment for intestinal bacteria. 



While no bacteriological data were 

 obtained during this investigation, 

 the general lack of sewage dis- 

 charge into these streams would 

 indicate that they have no more 

 than the normal surface water bac- 

 teriological contamination. Since 

 neither stream is used for public 

 water supply, this improvement is 

 not of much significance. From 

 the standpoint of recreational use 

 of the reservoirs it might be of 

 some importance. 



4. Cooler river water below the lake 

 in the summer and warmer water during the 

 fall '(Smith 1/). 



Reservoirs that eire long and deep 

 generally discharge relatively 



warm water in the winter and 

 relatively cool water in the summer 

 (Sylvester, 1957). This may be a 

 major improvement, from the stand- 

 point of fish life since it has 

 been previously shown that maximum 

 water temperature in the Wenatchee 

 River basin occurred in August. 



Effect on the Biological 

 Water Quality 



In addition the effect impoundment has 

 on the biological water quality is subject 

 to a number of variables. Those noted in 

 Roosevelt Lake on the Columbia River (Robeck 

 et al , 1954) are listed below: 



1. The annual deposition of settleable 

 matter from the entering water creates 

 unfavorable bottom conditions. 



2. The sharp drop-off at the shore 

 line and lack of shallow areas limits aqua- 

 tic vegetation and bottom fauna. 



3. The large winter and spring draw- 

 down inhibits the natural development of 

 shore vegetation. 



The biological changes that might take 

 place due to the impoundment, such as those 

 noted in Roosevelt Lake (Robeck et al , 1954) 

 are listed below: 



1. A seasonal build-up of plankton 

 populations which could have an effect on 

 downstream water uses, 



2. A change in bottom animals to less 

 desirable types as far as fish food is con- 

 c erned. 



3. A change in fish population with 

 more rough and forage species present and 

 less food and game species. 



4. A general decrease in biological 

 productivity due, for the most part, to the 

 large winter drawdowns. 



SUMMARY 



_!/ "Report on the Lewis River salmon conser- 

 vation progrcim" by Richard T. Smith. 

 Washington State Department of Fisheries. 

 Unpublished manuscript. 35 pp. 1943. 



A study of the physical and chemical 

 characteristics of water in relation to the 

 environment was made in the Wenatchee River 

 Basin during 1954, 1955 and 1956. Data 



32 



