2. The stream flow characteristics of 

 the incoming streams. 



3. The general characteristics of the 

 impoundment area, such as geology, 

 soil mantle, vegetation, configura- 

 tion, depth, etc. The amount of 

 logging, clearing of timber and 

 underbrush prior to the inundation 

 is also of importance. 



4. The climatic conditions of the 

 region, such as rainfall, air tem- 

 perature and amount of sunlight. 



5. The depth of drawoff from the 

 reservoir . 



6. The amount of drawdovm. 



The more important changes that may 

 take place in the physical and chemical 

 characteristics of water due to impoundment 

 are listed under two categories: adverse 

 and beneficial, along with specific comments 

 concerning the Wenatchee and Chiwawa Rivers. 



Adverse effects : 



1. Increase in surface water tempera- 

 tures from the upstream to downstream por- 

 tions of the reservoir and possible thermal 

 stratification in deep reservoirs. 



In addition to the natural climatic 

 and physical features of the 

 impounding basin which jointly con- 

 trol the water temperature in 

 natural lakes, the position of the 

 dcim and the depth of drawoff have 

 a major effect on temperature in 

 impounded waters (Ellis, 1940). 

 Studies on existing Columbia River 

 impoundments have indicated little 

 or no thermal stratification 

 (Robeck, Henderson, and Palange, 

 1954). It is probable that very 

 little area of shallow water depth 

 will result from impoundments on 

 the Wenatchee and Chiwawa Rivers. 

 Therefore, if it were not due to 

 the drawoff from the bottom of the 

 dam, the seasonal cycle of air 

 temperatures would produce a sea- 

 sonal cycle of water temperature 

 changes similar to that found in 

 Lake Wenatchee. 



2. Decrease in dissolved oxygen 

 saturation with depth. 



The deposition of silt and organic 

 debris of natural origin in the 

 impoundment creates an oxygen 

 demand which tends to reduce the 

 oxygen saturation. Upon inundation 

 the organic constituents of the 

 reservoir bottom and the non-woody 

 vegetation thereon also contribute 

 to the oxygen demand. In view of 

 the high oxygen saturation and lack 

 of significant amount of organic 

 matter in the Wenatchee and Chiwawa 

 Rivers, it is believed this deple- 

 tion will not be of auiy importance. 

 If careful cind adequate cle airing 

 of timber and underbrush is not 

 carried out prior to the damming 

 of the streams, a temporary in- 

 creased oxygen demand may result. 



3. Increase in carbon dioxide concen- 

 tration with depth. 



The deposition of organic matter 

 and the subsequent decomposition 

 will contribute carbon dioxide. 

 In the proposed reservoir the in- 

 crease of carbon dioxide with 

 depth should be very similzir to 

 that noted in Lake Wenatchee. As 

 previously stated, if the impound- 

 ment area is not properly cleared 

 of trees and brush, the resultant 

 decomposition may create a tempo- 

 rary high concentration of carbon 

 dioxide . 



4. Decrease of pH with d epth as a 

 result of the increase of carbon dioxide. 



If the carbon dioxide concentra- 

 tion becomes excessive, it may 

 reduce the pH of the poorly buf- 

 fered incoming waters to a rela- 

 tively low value. It is doubtful 

 whether the pH would be reduced 

 below 6.0, the lower limit believed 

 necessary to support good fish 

 fauna. (Ellis, Westf all , and 

 Ellis, 1946.) 



5. Concentration of toxic elements 

 such as copper, lead and zinc. 



This is believed to be of minor 

 significance due to the absence 



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