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A lateral weir structure and storage area were defined in the unsteady model to <br /> reflect the geometry of the inlet spillway for Pond 4 and the storage stage- <br /> capacity of Pond 4. The unsteady model output for the spillway/pond structures <br /> is given above in Table 6.4.7-3 HEC-RAS Unsteady Flow Output for Lateral <br /> Structure (Pond 4 Inlet Spillway) and Storage Area (Pond 4). The table <br /> shows that the spillway is adequately sized to fill the empty pond before the <br /> floodwaters breach the river bank elevation of 4807.63 and therefore preventing <br /> flows from entering the pond outside of the spillway before the pond is full. When <br /> floodwaters do then breach the river bank, full ponds will prevent large head <br /> differentials and therefore prevent head-cutting and stream capture. The <br /> unsteady model was only run for the largest pond to test the sizing criteria used <br /> to design all of the inlet and outlet spillways. The idea is that if the criteria works <br /> for the largest pond, then it should also work for the smaller ones. <br /> Spillway Slope Revetment <br /> Floodwater velocities at the bank stations during the 100 year event were taken <br /> from the NRCR and used in the following formula to determine rock sizing for <br /> slope revetment on the spillway inlets. <br /> D50 = {VS° 17/4.5(Gs-1)0.66] <br /> Where: <br /> V = mean channel Velocity (ft/sec) = 9.46 ft/sec <br /> S= longitudinal channel slope (ft/ft) _ .0013 <br /> D50 = mean rock size (ft) = 3" <br /> Since 3" angular rip-rap may not be commercially available, type VL (D50 = 6") is <br /> specified for the spillway inlets. The horizontal and vertical extents of rip-rap for <br /> spillway inlets are shown in Exhibit F Sheets 4-11. it should be noted that for the <br /> interconnect spillway between ponds 2 & 3, soil cement is specified for the inlet. <br /> This is deemed appropriate since interconnect inlet is not adjacent to the river <br /> and therefore will not be subjected to the erosive power of river channel <br /> floodwater velocities and depths. <br /> For the spillway outlets and pit slope rundowns, soil cement was selected for the <br /> type of slope revetment. The horizontal and vertical extents of soil cement for <br /> spillway pit slope rundowns are shown in Exhibit F, Sheets 4-11. <br /> Amen Aggregate Resource <br /> Specific Exhibits <br /> Page 41 of 84 <br />