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to the final discharge point. At this final discharge point an erosion control "skirt" will be built. It <br />will consist of a plastic liner on the ground with 12 inch plus rock placed on it. The liner will <br />protect the underlying ground from erosion, while the rocks will disrupt and distribute the flow <br />coming out of the pipe. This will allow the discharge to enter Meehan Draw at a lower energy, <br />protecting against erosion. <br />In accordance with Rule 4.05.18, the discharge structures for Pond NHN -002 will not be within <br />the 100 foot buffer zone for Meehan Draw as shown on Map 2.05.3(4) -9. <br />The route of the discharge pipes can be seen on Map 2.05.3(4) -9. Portions of the pipe and skirt <br />that are laid on the surface will likely require securing to the ground with stakes or other <br />techniques that will be determined by the contractor in the field. During construction, temporary <br />sediment control will be in place around all construction areas. <br />Sediment Pond Capacity Demonstration <br />Pond NHN -002 needs to be able to store the 10 -YR, 24 -HR event and pit pumping on top of the <br />three year sediment volume storage. SEDCAD was used to analyze the hydrology and <br />sedimentology of the 10 -YR event scenario, and as can be seen in the SEDCAD Model 1 for <br />this scenario, the top of the water plus sediment storage is 2.14 feet below the emergency <br />spillway, and 0.14 feet below the top of the principal spillway riser entrance. The stage storage <br />curve on Map 2.05.3(4) -9 also shows that the design of Pond NHN -002 is more than sufficient <br />for the 10 -YR event. <br />The SEDCAD Model 2, which shows the 25 -YR, 24 -HR event with the pond design, shows that <br />the emergency spillway will safely convey the peak stage with over a foot of freeboard <br />remaining. The entire 25 -YR event discharge will pass out of the pond via the principal and <br />emergency spillway pipes. These two pipes will each between 18 inches in diameter. As can be <br />seen in the SEDCAD run in Model 2, the total pipe diameter needed is 21 inches, therefore a <br />pair of 18 inch diameter pipes will be sufficient. <br />APPENDIX 2.05.3(4) -8 PAGE - 5 - September 2014 (TR 06) <br />