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Stantec <br /> CENTERVILLE SURFACE WATER MANAGEMENT PLAN <br /> HYDROLOGIC CALCULATIONS /MODELING PARAMETERS <br /> September 2012 <br /> 4.0 HYDROLOGIC CALCULATIONS /MODELING PARAMETERS <br /> 4.1 WATER QUANTITY <br /> As stated in Chapter 6, rate control must be provided within each development that maintains <br /> existing runoff conditions for the 2 -year, 10 -year, and 100 -year storm events. For each <br /> proposed development, supporting calculations or modeling must be submitted. The <br /> calculations or modeling shall be based on NRCS methods. The parameters for the calculations <br /> or modeling shall be as follows: <br /> • NRCS 24 -HOUR Type II design storms based on Technical Paper 40 from the U.S. <br /> Weather Bureau: <br /> 1 -year storm = 2.4" <br /> 10 -year storm = 4.2" <br /> 100 -year storm = 5.9" <br /> • Assume Antecedent Moisture Condition II (AMC II) <br /> • For the purpose of determining existing runoff conditions for land currently used for <br /> agriculture, curve numbers (CN values) shall be based on pre - agricultural condition with <br /> a mixture of pasture, brush, and woods. The CN value for this land shall be 58. <br /> • Other CN values shall be based on NRCS standards (Table 2 -2a, Technical Release <br /> 55, "Urban Hydrology for Small Watersheds ", NRCS, June, 1986) <br /> 4.2 NURP STANDARDS <br /> The design storm for determining compliance with Nationwide Urban Runoff Program (NURP) <br /> standards for storm water ponds shall be 2.5 inches. See Chapter 6 for additional details. <br /> One Team. Infinite Solutions. <br /> 4.9 <br /> 28 <br />