Stream Flow versus Quality

TABLE 8.11 Volume ratios R f) asssuming mixing of injectate with uncontaminated 1968 waters from sandstones A and B to produce the contaminated 1989 waters and predicted concentrations of the contaminated 1989 waters in mg/L, assuming average values 

an impossible value for sandstone A mixing. If average injectate acetone is instead 887 mg/L (well within the uncertainty), then Ry= 9.2. 

If overland flow and interflow from storms only dilute the concentrations of solutes in streams, then such concentrations can be simply determined as a function of discharge (cf. Hem 1985). First, rewrite Eq. (8.30) in terms of discharge, Q (measured in ftVs (cfs) or m /s 1 cfs = 2.83 x 10 m /s 1 mVs = 10 LVs). 

Now assume the lowest flow in a stream is baseflow of composition Cj and discharge Qi. If Q2 represents the flow due to overland flow and interflow, and C2 = 0, and since Q , = Q + Sz- we obtain 

Assuming constant baseflow discharge and composition, this is the equation of a straight line with a slope of 1 and an intercept of log C Q.  

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When strongly correlated and reproducible, concentration versus discharge plots can be used to predict stream flow from stream chemistry and conversely. The plots also suggest that the heavy metal load of a given stream may be predictable from its specific conductance or discharge. When identified, such relationships can be useful for the monitoring and management of surface-water quality. 

Stream-discharge quality trends are usually displayed in log-log plots (cf. Gang and Langmuir 1974 Lerman 1979 Levinson 1980 Hem 1985). Such plots are often linear or nearly so. Figure 8.1 6(b) shows dissolved silica versus discharge for a river in British Columbia (Kleiber and Erle-bach 1977). Theoretical dilution curves based on Eq. (8.33) have been added to the figure. The difference between a dilution curve and data regression line is a measure of the amount of additional dissolved silica contributed to the stream by increased flow. 

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