in the summer is high quality water dis- 

 charged into the reservoirs during the 

 spring runoff. Some calcium and magnesium 

 is apparently taken into solution in the 

 reservoirs. A slight rise in temperature 

 is shovm through the reservoirs. Dissolved 

 oxygen below Merwin Dam ranged from 78 to 

 over 100 percent saturation. There was a 

 slight increase in carbon dioxide content 

 through the reservoirs with a corresponding 

 decrease in pH. The decrease in ammonia is 

 probably caused by an oxidation of the 

 ammonia to nitrites or nitrates as the 

 water passes through the reservoirs. Water 

 quality observations below Merwin Dam in 

 November, December and March give generally 

 higher constituent values (see Table C, 

 appendix) for the reservoir discharge than 

 for the inflow. This increase is small. 



Columbia Basin Irrigation Canal: Irriga- 

 tion canals were sampled in the Columbia 

 River Basin Project to give information on 

 the water quality as it traversed the land 

 and to give some indication of the quality 

 of future return flow waters from the pro- 

 ject, once a stablized water table is 

 reached. The project was-but partially 



developed in the summers of 195^ and 1955 

 when sampling was conducted. A total of 

 110,000 acres of a future total of some 

 1,000,000 acres was under irrigation in 

 1954. The U. S. Bureau of Reclamation fore- 

 casts that 600,000 acres will be under 

 irrigation by I96I. They expect to apply 

 about four acre-feet of water per acre of 

 land during the irrigation season of which 

 perhaps fifty percent will ultimately find 

 its way back to the Columbia River as return 

 flow. Figure 8 shows the location of the 

 sampling stations in the Basin development. 



Figures 2k and 25 are a plot of aver- 

 age Bummer water qualities at selected 

 stations along the main canals. The water 

 for irrigation is pumped from behind Coulee 

 Dam to the main canal which traverses two 

 artificial lakes to its diversion into the 

 west and east canals. Some 80 miles from 

 Coulee Dam, the spent and excess irrigation 

 waters are collected in the Potholes Reser- 

 voir which in turn supplies the Potholes 

 East Canal. The last sampling station 

 plotted (station I5) is on this canal. At 

 station 15, the irrigation water had tra- 

 versed some 150 miles of canals and 



CANAL WILES FROM COULEE DAU 



AVERAGE WATER QUALITY IN IRRIGATION CANALS 



SUMMER 1954 ■ t955 



COLUMBIA BASIN PROJECT 

 FIG 24 



CANAL HLES FROM COULEE DAM 



AVERAGE WATER QUALITY IN IRRIGATION CANALS 



SUHER 1954 - 1955 



COLUMBIA BASIN PROJECT 



FIG. 25 



UO 



