Laserfiche WebLink
embankments. The flood control plan should address mitigation measures including pit side <br />armoring, river site armoring and outflow channels, or other appropriate measures. <br />The potential for berms around gravel pits to be damaged during flooding is discussed in <br />detail in the 1987 Urban Drainage and Flood Control District (UDFCD) Publication <br />"Technical Review Guidelines for Gravel Mining Activities within or Adjacent to 100-year <br />Floodplains." Strips of native ground or constructed fill between the stream and the gravel <br />pit, and generally aligned with the flow direction of the stream are referred to in the UDFCD <br />document as riverside berms. Strips of native ground or constructed fill between the adjacent <br />pits and generally perpendicular to the stream are referred to as lateral berms. The Western <br />Sugar Reclamation Land Development Project is located outside of the political boundaries <br />of the UDFCD, but technical floodplain factors that led to the formulation of the UDFCD <br />guidance document still apply. <br />The Division has concerns about the lateral berms and riverside berms. There is the potential <br />the berms may erode and become unstable during a flood. If the pits are excavated and <br />dewatered, or if the pits are reclaimed but the water levels in the ponds are low, floodwaters <br />spilling into the pits could result in erosion, rapid downcutting, and potentially failure of the <br />berms with exposure and damage to the gas pipelines which are located within the lateral <br />berms on the site. For this reason, the Division will require further analysis of the proposed <br />riverside and lateral berms and a design mitigation that will ensure stability during a 100 year <br />flood event. <br />Alternatively, the Applicant may mine to the berm crest widths (100ft) proposed in their <br />permit application for the riverside berm with installation of any of the numerous mitigation <br />designs included in the UDFCD guidance document. To mine within 100 feet of the river, <br />UDFCD standard designs require both riverbank and pitside protection in the form of <br />reinforced berm cores, armored side channel spillways, or bank stabilization using riprap or <br />soil cement. These same types of hard stabilization methods are required by the standard <br />designs in order to leave a lateral berm of 100 feet crest width. Following the UDFCD <br />guidelines would save the Applicant the time and expense involved with site specific <br />hydrologic investigations and designs. Please provide the Division with a comprehensive <br />flood analysis and flood control plan to justify the proposed setback distance from the river <br />and the widths of the lateral and riverside berms, or revise the Reclamation Plan to <br />incorporate the guidelines in the UDFCD document. <br />6.4.12 Exhibit L - Reclamation Costs <br />12. The Applicant has stated approval will be obtained from the Division of Water Resources <br />that acknowledges compliance with the SEO's requirements pursuant to C.R.S. 37-90- <br />137(11). Please commit to providing the Division with the appropriate documentation from <br />the Division of Water Resources prior to exposing groundwater.