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4. Major Storm Water Channels <br />Two drainage channels will need to be constructed on the site due to two valleys being filled. Val- <br />ley Fill Area # 1 watershed (29.5 acres) area is much larger and drains a watershed twice as large <br />as Area #2(13.5 acres}. For easy of design and construction both channel designs will be based on <br />the Valley Fill Area #1. <br />Valley Fill Area # 1 <br />The topology of the site requires that storm water from above the site will need to be diverted <br />through the permit azea. This area is 29.5 acres based on USGS maps for the drainage azea. Due <br />to a gully being filled at the landowners request, the original natural drainage will be buried. The <br />valley fifil will be discussed later. This will cause storm water to flow across the main pit area <br />during mining and after reclamation in the middle of the irrigated field. If left uncontrolled storm <br />water would readily erode the valley fill material. The storm water channel will be divided into <br />two regions: Grass Lined and Grouted Rip-Rap. The channel begins at a small pond near the gas <br />well formed by a road installed before the current operation. "Phis pond will serve as a sediment <br />trap. The grass lined channel will direct water along the mild slope (2°io). The steeper sloped <br />(50%) portion of the channel will be grouted 12" rip-rap. Due to different channel widths a <br />grouted 12" rip-rap funnel will be built between the two sections. Below are the calculations per- <br />formed in SurvCAD to determine the channel characteristics. Initially, a Time of Concentration <br />calculations was performed to provide input for the Peak Flow calculation. From the Peak Flow <br />calculation, an erodible channel calculation was performed for the grass lined channel. The <br />grouted section did not need an erodible channel calculation due to the nature of its structure. <br />However, flow calculations were performed. Due to the high velocity discharge at the bottom of <br />the slope, three to four D50 = 5' boulders and rip-rap will be used as an energy dissipater before <br />allowing the water to dischazge into the natural drainage. <br />Cugnini 12/03 12 <br />