an approximate measure of total dissolved 

 solids. Using the flow data in the tables, 

 these approximate dissolved solids values 

 were converted into tons-per-day of dis- 

 solved solids for the river station to give 

 a comparative measure of the dissolved con- 

 stituent increase between stations. These 

 values are shown in table 34 which indicates 

 that 63 percent of the yearly solids in- 

 crease in the Columbia River between Beebe 

 and McNary Dam is contributed by the Snake 

 River and that less than 1 percent is con- 

 tributed by the Wenatchee and Yakima Rivers. 

 A small portion of the remaining 36 percent 

 is contributed from the Entiat, Chelan, and 

 Walla Walla Rivers and Crab Creek, leaving 

 the major portion of this remaining 36 per- 

 cent solids increase to come from the solu- 

 tion of mineral matter in the stream bed, 

 from surface runoff and from ground water 

 inflow to the stream bed. On the basis of 

 solids discharged to watershed area, the 

 Wenatchee River discharges about twice the 

 tonnage of dissolved solids per unit of 

 watershed area than does the Yakima River. 

 The reason for this apparent anomaly is that 

 most of the Wenatchee watershed contributes 

 flow to the river whereas much of the Yakima 

 watershed contributes very little flow. In 

 the Wenatchee River watershed the annual 

 runoff is 2.9 c.f.s. per square mile while 

 in the Yakima River watershed it is only 

 0.57 c.f.s. per square mile. 



EFFECT OF PROPOSED IMPOUNDMENTS 

 ON FUTURE WATER QUALITY 



The reservoirs proposed for this study 

 area on the Columbia and Wenatchee Rivers 

 (see table 1, page 3) are not large in pro- 

 portion to river flow. Power installations 

 will be of the so-called run-of-river type 

 where the retention period for river water 

 in each reservoir will be from less than one 

 day during flood stage to perhaps a maximum 

 of 6 to 10 days during periods of low stream 

 flow. Average reservoir water depths will 

 be under 50 feet. During periods of low 

 stream flow (August to April) the entire 

 river discharge will pass through the tur- 

 bines whose intakes are located near the 

 reservoir bottom. Because of the shallow- 

 ness and large length-to-width ratio in 

 these impoundments, there should be good 

 vertical and horizontal mixing with little 

 stratification. Surface water temperatures 

 near the dam, when all river discharge is 

 going through the turbines, may exceed aver- 



age reservoir temperatures by 1 to 3° F. 

 In McNary Reservoir, which is similar to 

 the proposed reservoirs, very little strati- 

 fication was observed (29). Since these 

 hydroelectric facilities will be used for 

 "peaking" —' , large diurnal fluctuations in 

 downstream flow and fluctuations in reser- 

 voir elevation can be expected during the 

 period of low stream flow. The extent of 

 these "peaking" flow and reservoir fluctua- 

 tions will depend upon the operational 

 characteristics of each installation and 

 upon how much water is released to the in- 

 stallation from upstream impoundments. With 

 the ultimate development of this stretch in 

 the Columbia River (perhaps within the next 

 ten years) there will be a continuous up- 

 stream succession of impoundments and diur- 

 nal "peaking" effects will be apparent only 

 along the reservoir shorelines. The only 

 effect on water quality from these "peaking" 

 operations will be a tendency to increase 

 water temperatures slightly as water will 

 be impounded during periods of daylight and 

 released during hours of darkness or reduced 

 solar radiation. A considerable portion of 

 this diurnal impoundment increase will be 

 in the shallower reservoir areas. 



Maximum reservoir drawdown in these 

 run-of-river power facilities will normally 

 be from 5 to 10 feet. Therefore, unusually 

 high September water temperatures downstream 

 from these dams will not be experienced as 

 they are when the deep Grand Coulee and 

 Merwin reservoirs (_5) are drawn down in 

 September. This does not imply that high 

 water temperatures will not be experienced 

 in September at these reservoirs under dis- 

 cussion. The average August water tempera- 

 ture increase through four reservoirs in 

 the Columbia River Basin (5^) was 0.9° F. 

 for each 10,000 acres of impoundment area. 

 If this same temperature increase is experi- 

 enced in the Columbia River after the Wells, 

 Rocky Reach, Wanapum, Priest Rapids, We- 

 natchee and Ben Franklin Dams are completed, 

 the August 1956 mean water temperatures 

 (highest for the study period) will be 



1/ "Peaking" is the daily storage of water 

 in a reservoir during periods of lower 

 power demand (daylight and early morn- 

 ing hours) that is released through the 

 turbines during daily periods of higher 

 power demand (say from 5:00 to 11:00 

 P.M.) 



118 



