1808 MERRILL CREEK PKY 2016-01-01 MF Import

DETENTION PIPE �" Because of the small size of the tributa.ry drainage basin, the detention pipe was not sized according to the SWMM model. Instead, the SBUH method was used to determine the allowable release rates and the required volume. The detention pipe was sized to attenuate the 25-year developed flows to the 5-year pre-developed flo�vs. The control structure consists of a 12-inch standpipe with ttivo orifices sized for the two design storm events. The standpipe also acts as an overflow riser to release storms greater than the 25- year event. Release Rates (Existine Cm�ditio�il There is approximately 1.60 acres tributary to the proposed detention pipe. Although this area has been cleared, the existing condition lias been modeled in its once forested condition (CN = Sl). The esisting condition hydrographs are as follows: TOTAL AREA: I.GO Acres BASGFLOWS: 0.00 cfs ItAINFALL TYPE: Type IA TIME INTERVAL: 10.00 min TIME OF CONC: 30.13 min AI3STRACT. COLP'F: 020 PERVIOUS AREA [MPERVIOUS AREA AREA: 1.60 Acres AREA: 0.00 Acres CN: 81.00 CN: 95.00 T�Reacii - Slieet Fiow: L: 100 feet n,: 0.4000 p2yr: I.55 s: 0.0490 ft/ft T� Reach - Shal. Cona Flo�v: L: 575 feet k,: 5.00 s: 0.0500 ft/ft HYDROGRAPH SUMMARY Starm Precip. Peak Flow Volume Time of Peak in CPS Ao-fi min 2-Year 1.55 0.04 0.05 540 5-Year 1.93 OA9 0.07 490 10-Year 2.23 0.14 0.10 490 25-Year 2.63 0.22 0.14 490 100-Ye�r 3.21 0.34 0.20 490 STORM DRAINAGE RGI'ORT FOR IN7'ItAWLS'1'-SF.A\VAl' - PAGE IS