11 



Five-year FWC's for TDS at 989 mg/L (Figure 3.5) for 1995 continued to approach, but 

 remained below the long-term objective of 1000 mg/L. The maximiim monthly value calculated 

 in 1995 was 981 mg/L. This gradual increase in five-year FWC for TDS is due to low surface 

 runoff in the late eighties/early nineties, particularly reflected in the spring flows, which has not 

 allowed for sufflcient flushing of Cookson Reservoir. 



A linear regression analysis was applied to the daily TDS values, as generated from the daily 

 specific conductance readings from 1982 to 1995 (Figure 3.6). The regression line shows a 

 gradual increase in TDS over this period. The positive trend is probably due to drought conditions 

 in southern Saskatchewan during the latter part of the 1980' s, and the early 1990' s. Hence, a 

 larger overall contribution of ground- water to the flow in the East Poplar River. The upward trend 

 could also be attributed in part to higher rates of evaporation from Cookson Reservoir during the 

 hot, dry period of the late 1980's, and to the fact that the Reservoir has received very little 

 flushing over the period of record, due to the need to conserve cooling water. It should be 

 understood though, that this regression line has a low R-squared value, which means that it is only 

 a very general indicator of long-term trends, and should not be thought of as a predictive tool. 



The relationship between TDS and conductivity generated from data collected from 1975 to 1995 

 is as follows: 



TDS = (0.639 X specific conductance) + 11.286 

 (R} = 0.87, n = 517) 



