Laserfiche WebLink
<br />rate in the lower surcharge ranges which would be the most frequently <br />utilized. The minimum permissible slope of the line at the higher eleva- <br />tions is governed by the rate of increase in spillway discharge that may <br />be considered acceptable during infrequent and extraordinary floods. <br />~. Analyze recession characteristics of inflow hydrographs to ob- <br />tain a recession constant that will be used in predicting a minimum in- <br />flow volume that can be expected when only reservoir elevation and the <br /> <br />rate of rise of reservoir elevation are known. For conservative results <br /> <br />the assumed recession curve should be somewhat steeper than the average <br /> <br />observed recession and normally can be patterned after the spillway- <br />design flood recession. The recession constant can be obtained by plot- <br />ting the recession curve as a straight line on semi log paper, with the <br />flow on a logarithmic scale and time on an arithmetic scale. The reces- <br /> <br />sion constant. T. is defined as the time required for the discharge to <br />decrease from any value. say QA' to a value QB' where QB equals QA/2.7. <br />d. A relationship to compute the volume of water that must be <br />stored for a hydrograph receded from an initial flow to a constant out- <br />flow can be derived from continuity considerations. Consider fig. 6.02. <br /> <br />a <br /><I <br /> <br /> <br />Fig. 6.02. Schematic hydrograph <br /> <br />6-05 <br />