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dams, mulches, vegetation sediment filters, and other measures that reduce overland flow <br />velocity, reduce runoff volume, or trap sediment, and such other measures to minimize <br />erosion, resultant siltation, and disturbance to the prevailing hydrological balance as <br />required 6y the Division. <br />Ditches. Drainage ditches will be placed at the toe of all cut slopes formed by the <br />construction of haul roads with ditch relief cross drains constructed if necessary to meet <br />the requirements of 4.03.1(1)(a)•(6). eater will be intercepted before reaching a <br />svitchback or Large fill and drained safely away in accordance with the requirements of <br />4.03.1. Water from a fill or svitchback will be released, through conduits or in <br />riprapped channels, or other facilities to adequately protect the fill. The road surface <br />viii be designed and constructed to prevent ponding of water, to provide erosion control <br />and to provide road surface stability. <br />Culverts and 8ridoes. Culverts vith an end area of 35 square feet or less viii be <br />designed to safely pass the 10-year, 24-hour precipitation event without a head of water <br />at the entrance unless suitable protection against erosion ar fill saturation is in place <br />et the entrance and exit of the culvert. Culvert designs are shovn in Appendix 12-4. <br />Culverts vith an end area of greater then 35 square feet, and bridges with spans of 30 <br />feet or less, will be designed to safely pass the 20-year, 24-hour precipitation event. <br />Bridges with spans of more than 30 fee[ will be designed to safely pass the 100-year, <br />24-hour precipitation event or larger event as specified by the Division. <br />Culverts viii be designed, constructed, and maintained to sustain the vertical soil <br />pressure, the passive resistance of the foundation, and the weight of vehicles to be used. <br />Drainage pipes and culverts viii be constructed to avoid plugging or collapse and erosion <br />at inlets end outlets. AlL culverts viLl be covered by compacted fill to a minimum depth <br />of one foot. <br />Culverts will be installed to accommodate flow from intersecting drainages, end from road <br />surface drainage as necessary [o control erosion. Design for culverts rill be in <br />accordance with 4.03.1(4)(e) except where alternative specifications are approved. <br />Alternative specifications may be utilized upon approval by the Division of ter a finding <br />that such specifications viii not result in an increase in erosion. Such findings rill <br />be based on a demonstration by HCTI, based at a minimum, on consideration of precipitation <br />rates, percent of grade end soil properties appropriate to the site. <br />6 <br />