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• <br /> 1-A. PROJECT OVERVIEW-CORE REQUIREMENT DISCUSSION <br />• Core Requirement#1 —Maintaining Natural Drainage Path <br /> All drainage entering and leaving the site has been maintained to retain its natural <br /> drainage path through the site. This includes runoff from the site traveling east into the <br /> adjacent wetland area to the east of the site. <br />• <br /> Core Requirement#2—Downstream Analysis <br /> See description below. <br />• Core Requirement#3 —Flow Control <br /> Flow control is provided by the installation of a new storm chamber detention <br /> system. In order to meet minimum orifice sizing(1/2" diameter),the designed <br /> lower orifice has been increased from 0.301-inches to 0.50-inches. Note that this <br />• increase has resulted in the 2-year runoff to increase to approximately 75% of the <br /> undeveloped 2-year runoff amount. Additionally, the runoff rates greater than the <br /> 2-year undeveloped storm have decreased from the initial rates. <br />• Core Requirement#4—Conveyance System <br /> In order to direct new drive aisle runoff into the storm chamber detention system, a catch <br /> basin"storm filter"has been designed which will drain into the new detention system <br /> with approximately 15-linear feet of 8" diameter pipe and 10-linear feet of 18" diameter <br /> pip prior to entering into the new storm chamber detention system. <br />• <br /> Runoff leaving the detention system has been designed to release through a 6"diameter <br /> pipe and flow into a dispersion trench. With approximately 60-linear feet of pipe at <br /> 2.5%, this outlet pipe has enough flow capacity to convey runoff from the detention <br />• facility to the dispersion trench in the case that the detention system fails. Refer to the <br /> drainage calculations section for 6" diameter pipe flow analysis and results. <br /> Core Requirement#5 —Erosion and Sedimentation Control <br /> The project is currently mostly developed resulting in minimal amounts of clearing <br />• needed for this development. Clearing and grading limits for the new development has <br /> been shown on the engineering plans. Clearing for the development mainly includes the <br /> removal of the existing garage located near in the southeastern area of the site. The <br /> remaining development area of the site has been previously cleared. A Grading permit <br />• must be issued prior to any grading on the site. <br /> E: /2011 / ill 103A/Drainage Report.doc <br />• <br />