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• 38 <br />6.2.1 Culvert Design <br />The des lgn discharges for the eu lverts are based on the peak 10-year discharges for the units <br />within which they are contained. The culvert on Newlin Creek is located at the outlet of channel <br />unit CH-8 and the culvert on the Magpie Creek diversion is at the outlet of channel unit CH-17. The <br />culvert capacities were estimated using "Hydraulic Charts for Selection of Highway Culverts" <br />(Federal Highway Adm inistratfon, 1965). The culverts were checked considering both fn let and outlet <br />control, however, both existing culverts have to let control. Based on field invest igattons, <br />entrance types were chosen to be projecting for bath culverts. The size and length of each culvert <br />were measured and the slopes were estimated in the field. If pading is required to pass the design <br />discharge, protection against erosion and piping must be provided. Table 9 gives the dimensions and <br />spec if lcat tons for both culverts. <br />6.2.2 Existing Culvert Adequacy <br />The culvert at the Magpie Creek diversion outlet requires a headwater depth of 17 feet in <br />order to pass the 10-year peak discharge. However, there is adequate area avatlab le fora headwater <br />depth of 17 feet. Vith proper protection against erosion and piping of the haul road fill, the <br />existing culvert can provide adequate drainage. <br />The existing culvert on Newlin Creek, under the haul road, is Inadequate. The capacity of <br />this three-foot diameter culvert is greatly exceeded and to pass the 10-year, 24-hour peak discharge <br />would require a headwater depth of greater than 20 feet. Before this depth is reached, the roadway <br />would he over-topped. To provide adequate drainage of the 10-year, 24-hour peak discharge, several <br />difference culvert combinations are possible. Table 10 gives six poss ih le combinations. The first <br />three combinations are designed fora headwater/diameter ratio of one, thus, there will be no <br />submergence of the inlet. The second three eanbinations are designed for a headwater/diameter ratio <br />of 1.5. All six culvert combinations were designed assuming inlet control fora projecting type <br />entrance. <br />• <br />