Laserfiche WebLink
Idyllvale Shores – SWMP October 2024 <br />Civil Methods, Inc.Page | 3 <br />4.STORMWATER MANAGEMENT REQUIREMENTS <br />4.1 RUNOFF VOLUME CONTROL <br />Runoff volume control must be provided in an amount equal to one inch times the area of <br />regulated site impervious area. The amount of on-site impervious area under proposed <br />conditions is 85,746 SF, resulting in a volume reduction requirement of 7,146 CF. Drawdown of <br />water levels in infiltration basins must occur within 48 hours. Using an infiltration rate of <br />0.25 IN/HR, determined from the best available information about site soils, this would allow <br />for an overall ponding depth of 1.0 FT. The infiltration basins as designed will retain a volume <br />of 8,097 CF at a depth of 1.0’. This design meets the infiltration volume and depth <br />requirements. <br />4.2 RUNOFF RATE CONTROL <br />Stormwater management measures must limit peak runoff flow rates to that from existing <br />conditions for the 2-, 10-, and 100-year storms. The rate control requirement is determined in <br />aggregate from the site. This requirement is also met with the three proposed stormwater <br />infiltration basins. The following table summarizes the aggregate peak flow rates for both <br />existing and proposed conditions. <br />Table 1: Summary of Peak Discharge Rates <br />Location <br />Conditions Existing Proposed <br />Node 1R 1R <br />2-YR STORM 12.6 10.5 <br />10-YR STORM 30.4 27.2 <br />100-YR STORM 77.0 75.9 <br />Final Discharge (Aggregate) <br />145