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precipitation event without a head of water at the entrance <br />• unless suitable protection against erosion or fill saturation is <br />in place at the entrance and exit to the culvert. <br />In addition to this regulatory requirement, there are <br />several other criteria desireable from a design, operation and <br />maintenance standpoint: <br />a) The culvert should be accessable for <br />inspection and maintenance; <br />b) The culvert should be designed to minimize <br />damage and maintainence requirements due to <br />abrasion or sedimentation; <br />c) The culvert should be designed to <br />structurally support the weight of the~fill <br />and loading from mine trucks; <br />d) Debris such as trees, shrubs and large size <br />bed material should be trapped and prevented <br />from entering or blocking the culvert <br />entrance; <br />e) Provisions for a vacuum relief mechanism <br />• should be made if the culvert has a steep <br />grade or abrupt changes in grade; <br />f) The culvert should be designed to pass flows <br />resulting from a 100-year precipitation event <br />with minimal damage and the consequences of <br />flows resulting from a 500-year precipitation <br />event should be reviewed; <br />g) The inlet should be designed to create a <br />transition from the creek channel geometry to <br />the culvert to minimize losses and erosion; <br />h) The outlet should be designed to provide an <br />energy dissipator to reduce high velocity <br />culvert flows to natural stream channel <br />velocities and minimize bed and bank erosion; <br />i) Use of on-site construction materials should <br />be made to minimize construction costs. <br />j) The possible effects of seepage along the <br />culvert either from a water head at the <br />culvert entrance or seepage through the fill <br />should be investigated and mitigating <br />measures designed, if required. <br />• 2.7.3 Proposed Design Alternatives <br />Two conceptual designs that meet the criteria described <br />7 <br />