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<br />River Mec:henlcs end Geomorphology <br /> <br />e <br /> <br />be exerciled with this latter option since gages are typically located at bridge <br />constrictiuls and may not be indicative of general changes in less.<:onttolled reaches. <br /> <br />2.3.5 System I~esponse - <br /> <br />Prediction of general river response to man's local activities may be accomplished <br />quantitatively using the methods described elsewhere in this manual, provided accurate <br />data of die appropriate type are available. In cases where it is not, a qualitative <br />assessment may still be possible using a version of Lane's Relation (1955): <br /> <br />(QS - QPSO) <br /> <br />(EQ2'1) <br /> <br />Where Q is the water discharge, S is the channel gradient, Q, is the bed material <br />sediment (lischarge, and Dso is the median grain size. <br /> <br />Applicatic<I of this relation requires balancing changes to the variables on each side of <br />the equati,)n. For example, in the case of downstream impacts from a reservoir (which <br />reduces tile sediment discharge) if it is asswned that discharge and grain size remain <br />constant, :he slope must decrease (degnldation) as shown in Figure 2-4. Simons and <br />Senturk (1976) present a detailed discussion of this method. <br /> <br />FIGURE 2. 4 <br /> <br />Clear wat..r release below a dam (Reprinted from Chang, 1988) <br /> <br />Clear Water <br />Release at Dam <br /> <br />'-.... <br /> <br /> <br />CD <br />g. <br />Ui <br /> <br />..... Head Culling <br /> <br />................................................. <br />Braided Stream <br /> <br />~ <br />~ <br /> <br />/" <br />Scour & Channel <br />Degradation <br /> <br />Final Bed <br /> <br />Mean Discharge <br /> <br />e <br /> <br />10 <br /> <br />COlorac:\.) Erosion COntrol Manual <br />