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g. East Run On Diversion Swale, Riprap Sizing: The table references Urban Drainage's formula. The <br />Urban Drainage riprap method is intended for subcritical flow regimes. Please provide verification <br />that the reaches for which this riprap is intended are subcritical, or use an appropriate riprap sizing <br />method (e.g., USAGE'S EM 1110 -2 -1601, Steep slope riprap design, or other appropriate method). <br />Response - Riprap sizing was recalculated using the Shear Formula method <br />h. East Run On Diversion Swale, Riprap Sizing; Assuming the same source of riprap as referenced on <br />Exhibit U -2, riprap specification, the riprap size will need to be adjusted accordingly to account <br />for the low specific gravity (i.e., 2.24). <br />Response - To increase the safety factor the riprap size specification was increased 50 percent. <br />i. Please clarify whether the discharge from the Central Detention Overflow is directed to the North <br />Detention Pond or to a discharge point parallel to the East Run On Diversion Swale discharge <br />point. <br />Response - Discharge from the Central pond flows to the North Pond prior to being discharged <br />from the site. <br />10. Exhibit U-4 - Designs, calculations and methodology. <br />a. North Detention Plan View: The spillway is proposed to be located very close to the West Diversion <br />Swale inlet and well away from what appears to be a natural drainage (near where the north end of <br />Section I -I intersect natural ground, /the former can lead to short circuiting in the sediment pond <br />(lowering the sediment trapping efficiency) and the latter may contribute to unnecessary erosion at <br />where the spillway discharges to native material. DRMS recommends the spillway be moved to a <br />location coincident with Section I -I to address both potential problems unless there is a compelling <br />reason to keep in the location shown on the drawing. <br />Response - Spillway was located at the location shown to maximize the distance from the existing <br />monitoring well Will relocate it to existing drainage per the DRMS's direction. <br />b. Spillway Riprap Design: The design flow' is 5.86 cfs. The table on Exhibit U -1 indicates the design <br />flow should be 3.01 cfs. Please provide some clarification on the difference in design flows. <br />Response - Spillway design flow was calculated as the sum of the flows for Basin PAN and PA -C as <br />the North pond is downstream of the discharge of the Central Pond To simplify calculations <br />the travel time for the flow from the Central Pond were not determine& <br />c. Related to Comment 7.b, if the riprap size is recalculated, note there is an error in the Cu value after <br />the adjustment for the low density rock (i.e., Cu = 1.95, instead of2.0). <br />Response - Riprap calculations have been updated. <br />d. West Diversion Swale Section H -H: There is a thick black line running diagonal through this section. <br />Please identify this line or remove it as appropriate. <br />Response - Line has been remove& <br />