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Technical Review Guidelines for Gravel Mining &Water Storage Activities <br /> face of lateral berms are to be stabilized and protected using the methods proposed in Section <br /> 2.4—Pitside Bank Protection. <br /> Riprap, soil riprap, soil cement and grouted boulders are all viable options for reinforcing both <br /> Type A and Type B lateral berms. These methodologies are to comply with the requirements of <br /> Section 2.4.1—Riprap, 2.4.2—Soil Riprap, 2.4.3—Soil Cement and 2.4.4—Grouted Boulders, <br /> respectively. The general geometric characteristics of lateral berm protection will conform to the <br /> individual details for the selected method of protection except that the protection needs to extend <br /> to bedrock or 3 feet below the pit floor. <br /> 2.5.4 Spillway for Type A Lateral Berms <br /> A spillway will only be allowed for Type A lateral berm protection. The existing or future arterial <br /> road crossing associated with Type B lateral berms renders the spillway approach infeasible. The <br /> required length of the spillway for Type A lateral berms along the South Platte River will be <br /> determined using the following equation: <br /> Lsl = 2,5001,W-5 <br /> In which, <br /> LS1 = length of lateral berm spillway <br /> H = height between top of berm and spillway crest <br /> 2.6 Berm-Top Width—Riverbank Berms <br /> This section specifies the minimum top width for berms located adjacent to the South Platte River <br /> and subject to these Guidelines. The top-width requirements are specified to protect the berms <br /> from rapid failure during 100-year floods with overtopping lengths of time of two days duration. <br /> Such failure may result in the South Platte River flowing through the adjacent gravel pits causing <br /> the thalweg to drop, creating riverbed headcutting, resulting in loss of the river corridor and <br /> subsequently damaging property along the river. The berm-top width requirements consider long- <br /> term stability and safety along the South Platte River along with emergency equipment access and <br /> staging of emergency repair work, regional trails and the need to maintain a suitable Denver <br /> Metropolitan river corridor for multiple uses. Localized damages to the berms may result during <br /> large floods and may require periodic repair and maintenance. <br /> The top widths are broken into two classifications, one for an unprotected river bank and one for <br /> protected river banks. Unless otherwise indicated, the requirements of Sections 2.3—Riverbank <br /> Protection and 2.4—Pitside Bank Protection constitute adequate bank protection. <br /> January 2013 Urban Drainage and Flood Control District Page 23 <br />