observed in August and September. The 

 depth of the thermocline would vary from 10 

 to 125 feet, depending upon wind velocities 

 and duration. Below 100 feet in depth, the 

 lake temperature will usually be under 50° 

 F. Figure 39 (page 101) is a plot of typi- 

 cal temperature gradients observed in the 

 spring, summer and autumn. Vertical mixing 

 of the entire lake can be expected in the 

 overturn periods in the spring and autumn. 



WATER QUALITY CHANGES FROM UPSTREAM 

 TO DOraSTREAM LOCATIONS 



Figures 40 and 41 depict the change 

 in water quality in the Columbia River 

 during the month of August 1956 as the 

 river flows from the upstream station at 

 Beebe Orchard Bridge to the downstream 

 station at McNary Dam, a river distance of 

 212 miles. In general, the Columbia River 

 water quality changes are small between 

 Beebe and Pasco. The increase in water 

 ten^erature is the only significant change. 

 Values shown below Vantage for temperature, 

 calcium, sodium and conductivity tend to 

 be high because of the sampling station 

 location. The decrease in alkalinity, 

 hardness and conductivity below Beebe is 

 due to the dilution afforded by the higher- 

 quality water in the Chelan, Entiat and 

 Wenatchee Rivers. An abrupt increase in 

 constituent values occurs between Pasco and 

 McNary Dam, caused by the warm, mineralized 

 Snake River which is tributary to the 

 Columbia River below Pasco. For the period 

 depicted on figures 40 and 41, the water 

 temperature increases from 66.4 to 67.5* F. 

 between Pasco and McNary Dam; total alka- 

 linity from 60.5 to 79 mg/1 ; total hardness 

 from 66.5 to 75 mg/1; sulfates from 11 to 

 19 rag/1; calcium from 19.4 to 21.4 mg/1; 

 sodium from 2 to 5 mg/1; total solids from 

 100 to 140 mg/1; and conductivity from 145 

 to 176 micromhos per cm. 



Figures 42 and 43 (pages 105 and 106) 

 show the change in water quality for the 

 ■i\natchee River in August 1956, as it flows 

 iiom Lake iVenatchee to its confluence with 

 the Columbia River, a distance of 55 river 

 miles. Nearly all quality values Show a 

 gradual increase from Lake Wenatchee to the 

 river mouth. Water temperature increases 

 from 57.5 to 64.9° F.; total alkalinity 

 from 9 to 18 mg/1; total hardness from 8 to 

 16.5 mg/1; calcium from 1.5 to 5.3 mg/1; 

 magnesium from 0.4 to 2 mg/1; sodium from 



0.9 to 2 mg/1; total solids from 21 to 58 

 mg/1; and conductivity from 20 to 49 micro- 

 mhos per cm. The decrease in sulfates 

 below Lake Wenatchee was caused by dilution 

 of Lake Wenatchee water with lower-sulf ate- 

 bearing water in the Chiwawa River and 

 Nason Creek. A reduction in conductivity 

 is shown between the station below Plain 

 and Tumwater Canyon. This reduction is not 

 correct as all other data show a slight 

 increase in conductance between these sta- 

 tions. The apparent reduction was caused 

 by one sample at Plain having an excessive 

 conductance reading which might have been 

 deleted for this monthly summary. 



WATER QUALITY CHANGE 

 1910-11 to 1954-57, Wenatchee River 



In 1910 and 1911 Walter Van Winkle 

 made a comprehensive study of the chemical 

 quality of Pacific Northwest streams for 

 the U. S. Geological Survey (27). The 

 Wenatchee River at Cashmere was included 

 in this study. Between 1911 and 1954 

 (beginning of the University of Washington 

 study) very little water quality data were 

 obtained on the Wenatchee River (28). 

 Table 30 (page 107) and figure 44~and 45 

 (pages 108 and 109) show the constituent 

 values in the Wenatchee River at Cashmere 

 for 1910-11 and at Sleepy Hollow (near the 

 river mouth) for 1954-57. Sleepy Hollow 

 data are comparable with Cashmere data as 

 there are no intervening tributaries and 

 the stations are only 5 miles apart. The 

 data presented can be compared only in a 

 general way since the flow was different 

 for each month and since the sampling fre- 

 quency was not uniform for both periods. 



Between 1910 and 1950 the population 

 in the Wenatchee River watershed increased 

 from 6,200 to 12,000 persons while the ir- 

 rigated acreage increased from 19,000 to 

 26,000 acres. Irrigation works were in 

 their maximum period of development around 

 1910 (7). Impoundments for power and irri- 

 gation diversion are minor. Domestic and 

 industrial waste discharge to the river 

 has had no significant effect on the water 

 chemistry. Principal watershed changes 

 during this 45-year period have been in 

 roadbuilding, agriculture and in logging 

 where many coniferous trees have been 

 replaced with deciduous trees. It is then 

 to be anticipated that the water chemistry 

 in 1954-57 would show some increase in 



102 



