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through the dewatering orifice cannot be utilized when calculating the 100-year <br />storm elevation because of its potential to become clogged; therefore, available <br />spillway storage must begin at the principal spillway riser crest. <br />The principal spillway designed by the procedures contained in this standard will <br />result in some reduction in the peak rate of runoff. However, the riser outlet design <br />will not adequately control the basin discharge to the predevelopment discharge <br />limitations as stated in 1-2.5.7 Minimum Requirement #7: Flow Control (p.64). <br />However, if the basin for a permanent stormwater detention pond is used for a tem- <br />porary sedimentation basin, the control structure for the permanent pond can be <br />used to maintain predevelopment discharge limitations. The size of the basin, the <br />expected life of the construction project, the anticipated downstream effects and <br />the anticipated weather conditions during construction, should be considered to <br />determine the need of additional discharge control. See Figure II-4.2.21 Riser <br />, <br />Inflow Curves (p.394) for riser inflow curves. <br />1 <br />[1 <br />r� <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />2014 Stormwater Management Manual for Western Washington <br />Volume 11- Chapter 4 - Page 390 <br />