300 400 500 600 



RIVER MILES FROM MOUTH OF COLUMBIA 



JULY, *UG, SEPT AVG 

 DEC 



FIG. 16 COMPARISON OF COLUMBIA RIVER WATER QUALITY - CANADA TO MOUTH 



Figures l^f, 15 and l6 are plots of 

 Columbia River water quality from Revel - 

 stoke, B. C. to Cathlamet, Washington, 

 using Canadian, U.S.G.S. and University of 

 Washington data. These figures show a 

 general reduction in, or uniform value in, 

 the constituents from Revelstoke, B. C to 

 the confluence of the Snake and Yakima 

 Rivers near Pasco. Most of the tributaries 

 in this stretch of the river are high qual- 

 ity waters. Maximum constituent values 

 occur in the vicinity of Maryhill. From 

 Maryhill to the mouth, most constituent 

 values decline because of the influx of the 

 western slop rivers that are lower in dis- 

 solved substances. Constituent values are 

 usually higher in December than during the 

 summer because of lower flows and lower 

 water temperatures. 



Yakima River: Figure 17 illustrates the 

 constituents found in the lower Yakima 

 River during a typical year. The constitu- 

 ents are fairly uniform in value from 

 December to July. After July through Novem- 

 ber, the river flow sharply decreases and 

 the constituents about double in value. As 

 discussed in a subsequent chapter on the 



YAKIMA RIVER AT KIONA 



IVERACE MONTHLY VALUES VEARS r953 - r954 



U.S.G S DATA. 



FIG. 17 



37 



