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estimates of r*, were then correlated to reach-average slope, giving the values shown in Figure8. <br />A least squares fit of the data in this figure gives the equation <br />ti*r=2.18S+0.021 <br />(2) <br />where S is the average channel gradient. This relation is statistically significant (rz = 0.70 and p <br />0.001), and suggests that r*r increases linearly with increasing channel gradient. This result is <br />counterintuitive, but explained by hydrodynamic effects associated with poorer sorting of the bed <br />material in high gradient channels. The monitoring site near RM 176 has an average gradient of <br />S = 0.002, thus the estimated r*C for that location is 0.025. <br />0.1 <br />0. <br />fib. <br />a <br />0.0001 0.001 0.01 0.1 <br />Slope <br />Figure 8. Variation in r*r as function of slope with error bars indicating potential range of r*r <br />values for individual data sets. A logarithmic scale is used for the x-axis to highlight the <br />range in values for moderate-high slopes. One outlier (solid symbol) was excluded (from <br />Mueller et al., 2005). <br />The shear stress available to move sediment on the channel bed varies temporally as the <br />discharge rises and falls, and spatially as the flow accelerates or decelerates over the topography <br />20