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• location in Phase I (West Plant) The proposed reclamation plan should be modified to <br />increase these distances to at least the minimum recommended 225 feet (see Fig~Ue 3 <br />showing the locations). If the distance is increased but is still less than 300 feet, rip-rap <br />slope protection as shown on Figure 4(surface rip-rap) or Figure 5(buried rip-rap with <br />vegetation) will be required over the portion of the pitside bank that has a setbacl: <br />distance of less than the 300 feet. Per Section 2.4 of the UDFCD guidelines, it will not be <br />necessary to construct the pitside bank protection measures until such time as gravel <br />extraction is completed. <br />Interior Berms <br />Interior (lateral) berms aze berms constructed, or formed by native material left ii.1 place, <br />between pits and are perpendiculaz to the general direction of flood flows. These interior <br />berms separate gravel mining pits from one another. Interior berms may be overt~~pped <br />during major floods. When overtopped, the berms are subject to erosion due to the <br />relatively high velocity flow and, in time, may fail resulting in a rapid release of water. <br />This phenomenon can propagate in the downstream direction, potentially increasing with <br />each successive failure. By protecting interior lateral berms from failure the likelihood of <br />such downstream propagation can be significantly decreased. <br />The UDFCD guidelines recommend a minimum interior lateral berm top width of 100 <br />feet for stabilized berms. Lateral berms with a top width of over 250 feet do not require <br />• stabilization. Application of the recommended 25% reduction would allow a mirrimum <br />top width of 75 feet for a stabilized berm, and 188 feet for anon-stabilized berm. <br />Interior lateral berms aze to be protected and stabilized in a manner similar to thy; <br />requirements for the protection of the pitside slopes of riverbank berms. In general, the <br />crest of the interior lateral berms are to be revegetated and the downstream face of the <br />lateral berms are to be stabilized and protected with rip-rap as shown on Figures 4 or 5. <br />Acceptable stabilization may also be provided in the form of a spillway through the <br />interior berm. The stabilized spillway allows floodwater to pass from the upstre<un to the <br />downstream pit in a controlled manner. Spillways can prevent the build-up of large <br />differential heads between adjacent pits. The UDFCD guidelines recommend a spillway <br />meeting the requirements as shown on Figure 6. <br />The Reclamation Contour Map shows that final reclamation as currently proposed would <br />result in two interior lateral berms that would be at least 150 feet in width and a~~e located <br />between a proposed water storage reservoir and a proposed "open valley" pit, with the <br />water storage reservoir being on the downhill side of the berm. During a flood event, <br />rising water levels in the upstream open valley azea will actually create an equalization of <br />water surface elevations on either side of the lateral berm. When the berm is overtopped <br />only a slight differential head will exist between the adjacent pits, and therefore, should it <br />occur, erosion of the berm will have negligible effects on flow rates. In addition, if the <br />reservoirs aze filled, then the downstream faces of the lateral berms will be submerged <br />• and the recommended rip-rap protection on the downstream face is superfluous. <br />7 <br />