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The pond will be designed to contain the 100 yeaz runoff of 0,63 acre-feet and 0.1 ac-ft for sediment <br />buildup using a sand and gravel dam that will detain the water for 24 hours but will allow it to seep <br />through into the ground so that the water is returned to the natural drainage. The dam will be less <br />than 10 feet high and will have 2.SH:1 V sideslopes. The pond area as shown on Map C-2 is 0.25 <br />acres, therefore the average depth is 2.5 feet. Much of the volume will be attained by excavation <br />within the pond area. <br />Collection Ditches #4 and #5 will be v-ditches of 1.5 feet depth and 2:1 sideslopes cut out of the <br />natural gravel and shale below the gravel deposit. The slopes of the collection ditches will be less <br />than 4%. No lining is needed. <br />D) Culvert #1 in West Drainage must be designed to handle the peak runoff from 17.1 acres of <br />undisturbed area upstream. It is designed for the 100 year event since it will remain after <br />reclamation. <br />Time of Concentration (SCS Methodl <br />• Curve Number: 86 <br />Length of Flow (ft): 1100.95 <br />Average Land Slope (percent): 33 <br />Time of Concentration (hrs): 0.08 <br />Graphical Peak Dischaz¢e Date: 12/21/05 <br />Location: West Drainage Culvert Checked: GL Date: 12/21/05 <br />Present Conditions <br />1. Data: <br />Drainage azea :....................A = 744433.6740 Sq Ft <br />Runoff Curve Number :.............CN = 86 <br />Time of Concentration:...........Tc = 0.08 <br />Storm Type :....................... = II <br />• Pond and swamp azeas spread <br />BellgazdtPit 1/06 <br />14 <br />