4326 CRESCENT AVE 2025-07-14 - Laserfiche WebLink

Acre Short Plat Stormwater Site Plan A standard flow control riser/structure assembly is proposed at the outlet of the detention tank to control the release rate of storm water to the off-site, downstream system.The size and number of control orifices on this riser have been designed such that developed stormwater discharges match the existing site durations for the range of existing discharge rates from the 10-year peak flow through the full 100-year peak flow. Peak runoff rates from the developed site shall not exceed existing site runoff rates in the 25-year and 100-year return intervals. Refer to the WWHM results in Appendix C for more thorough information regarding the pre-developed and developed peak flow rates. E. Stormwater Treatment Plan Since this project site discharges to the combined sewer system, water quality treatment is not required. The project also proposes less than 5,000sf of new pollution generating impervious surfaces within the project boundary. As such, a formal water quality facility is not required. The proposed detention tanks and catch basin structures will allow for some sediment storage. E. Conveyance Analysis Surface water collection and conveyance for the project is proposed by means of grading, grated inlets, and below grade pipes. The collection system is composed of roof drains,catch basins, and piping that discharges all water into a subsurface detention tank system. A control structure located outside this detention facility discharges site runoff to the public combined sewer system. All facilities have been sized and designed per COESWMM requirements. Rational and Backwater calculations will be provided upon request. G. Maintenance and Operation Plan The on-site storm drainage conveyance facilities for this project will be privately maintained. The facility has been designed in accordance with the COESWMM and a site—specific Maintenance and Operation Plan is provided in Appendix E. i October 15, 2021 Page 19