2019-08-29_PERMIT FILE - M2019028 (3)

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Technical Review Guidelines for Gravel Mining & Water Storage Activities 2.4.4 Grouted Boulders Grouted boulders may be used to stabilize the pitside slope of riverside berms against erosion from overtopping. The geometric configuration of the grouted boulders should conform to the requirements indicated on Figure 2.7 and the USDCM. For berms with a 4H:1 V slope, the minimum boulder size shall be 36 inches. For berms with a 2.5H:1 V pitside slope, the minimum boulder size shall be 48 inches. Boulders shall meet the specifications listed in the USDCM. 2.4.5 Side Channel Spillway Side channel spillways may be provided between the river and the pit to minimize the potential for failure of the riverside berms. The stabilized spillway allows water to pass between the river and the pit and vice versa. A spillway on the upstream end of the pit and one at the downstream end of the pit will be required unless the pit is small and the differential head between the two ends is 2 feet or less, in which case one spillway will be sufficient. Side channel spillways should prevent the buildup of differential heads greater than 2 feet between the river and water in the pit. Because of the nature of the hydraulic response of the spillways, the differential head cannot be completely eliminated. The objective is to minimize, to the extent possible, the differential head between water in the river and water in the pit when the riverside berms overtop. The elevation of the side-channel spillway crest shall be approximately 1 foot above the 2-year flood elevation. When the riverside berm length of the gravel pit is less than 1,300 feet (i.e., assuming average slope of the river is 0.001 ft/ft), only one side channel spillway will be required, and it shall be located approximately in the midpoint of the berm. If the length of the berm is greater than 1,300 feet or the differential head between the two ends of the berm is no more than 2 feet,two spillways will be required and will be located along the berm approximately one-fifth of the berm length from the upstream and downstream ends of the berm. When the length of the berm is less than 1,300 feet and the crest of the berm is no higher than one foot above the 2-year flow elevation, the spillway bottom length shall conform to the following geometric relationship: Ls = AP/12,000 or Ls = 100 feet, whichever is greater. In which Ls = length of the side channel spillway Ap = area of pit measured in square feet at the high water line January 2013 Urban Drainage and Flood Control District Page 17