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• <br /> 4. Flow Control and Water Quality Facility Analysis and Design <br />• <br /> Flow Control and water quality to be provided by a 1-cartridge storm filter and storm <br /> chamber detention system. Storm filter has been designed to intercept all new drive aisle <br /> runoff prior to it entering into the storm chamber detention system. Note that due to <br /> initial detention sizing not meeting minimum orifice sizing requirements,the storm <br />• chamber detention system was initially design to meet volume requirements and then re- <br /> calculated with a minimum 1/2"lower orifice size to show actual constructed runoff <br /> amounts. Re-calculated runoff rates resulted in a slightly higher 2-year runoff than <br /> initially calculated(approximately 75% of the 2-year undeveloped runoff rate)but <br /> decreased all storm events larger than the 2-year. <br />• <br /> Using the calculated orifice size from the initial vault analysis, a Stage Storage Discharge <br /> Table was manually inserted into WWHM based off of proposed storm chamber sizing <br /> and calculated discharge rates (Using orifice size formulas on pages 3-57 and 3-59 in <br /> Volume III of the 2005 DOE Stormwater Manual). Upon analysis of the storm chamber <br />• detention system, it was found that the calculated release rates were slightly lower than <br /> the calculated release rates of the initially design vault with the 1/2" lower orifice. <br /> Conclusion: Storm Chamber system has been designed to release the 2-year developed <br /> storm at approximately 0.77% of the undeveloped 2-year storm. All other storm events <br />• will be released at a much lower rate than the undeveloped storm. Storm Chamber design <br /> is acceptable to meet City release rate requirements. <br /> Refer to the WWHM calculations attached in section 5 for additional information. <br />• 5. Conveyance System Analysis and Design <br /> All new conveyance systems on site consist of 6" diameter pipes. Refer to pipe reach <br /> summary calculations for pipe flow capacity analysis. <br />• DRAINAGE CALCULATIONS <br /> Total Area of Site =24,800 sf. <br /> Total Developable Area of Site =20,059 sf. <br />• <br /> UNDEVELOPED (Current): <br /> Impervious Area(on-site): <br /> Unit 1/2 = 1,600 sf. (to remain) <br /> Unit 3/4 = 1,600 sf. (to remain) <br />• Ex. Garage = 638 sf. (to be removed) <br /> Total = 3,838 sf. (0.088 Ac.) <br /> E: /2011 / 111103A/Drainage Report.doc <br />• 7 <br />