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Mamm Creek Pit 4 November 16. 2000 <br />described in the Division's "In-Stream Aggregate Extraction and Reclamation Guidance <br />Document." <br />8. If there is a utility located in the easement at the west edge of the permit area, it must be included in <br />the list of structures within 200 feet of the affected land. Depending on the location and type of <br />utility involved, the Division may require further evaluation of proposed setbacks from the <br />easement. <br />9. The maps and discussion included in the application indicate that the Applicant has taken care to <br />site the topsoil and overburden stockpiles outside the floodplain or as far from the river channel as <br />possible. If stockpiles must be sited in the floodplain, they must be in the shape of a windrow and <br />aligned with the potential floodwater Flow direction. Also, long stockpiles of more than 40 or so <br />feet should be sepazated by gaps in the windrow to allow efficient movement of potential <br />floodwaters past the piles without creating a damming effect. There is generally not a concern that <br />stockpiling in the floodplain at a gravel pit will cause an increase in floodwater elevations since <br />substantial removal of mined product from the floodplain will more than compensate. <br />10. The application indicates that there will be a 19 foot drop in water surface elevation in the series of <br />reclaimed pits from east to west. The application briefly discusses the installation of water <br />impounding berms between pits, but provides little detail. Depending on the size and configuration <br />of the proposed berms, there could be dam safety issues and floodway or floodplain impediment <br />issues involved. The applicant must provide details on the location, configuration, and construction <br />of any proposed berms. The applicant must further provide an evaluation of [he berms or native <br />ground `dikes' that will be left between reclaimed pits and how they will respond during a flood. <br />Urban Drainage and Flood Control refers to these structures as lateral berms, and states: <br />Lateral berms are constructed, or left in place, between pits and are perpendicular to the general <br />direction of flow of the (river). These lateral berms separate gravel mining pits from one <br />another. Lateral betms may be overtopped during major foods. When overtopped, the betms <br />are subject to erosion due to the relatively high velocity flow and, in tune, may fail resulting in a <br />rapid release of water. This phenomenon can propagate in the downstream direction potentially <br />increasing with each successive failure. By protecting lateral berms from catastrophic failure the <br />likelihood of such downstream propagation can be significantly decreased. <br />This quote is from the Urban Drainage and Flood Control document referenced previously. <br />The Applicant should be advised [hat both of the guidance documents referenced in [his memo are <br />available for purchase from the Division of Minerals and Geology. <br />cc: Tom Schreiner, DMG <br />m:\min\acs\mamm creek.doc <br />