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• <br />Roadside North Portal Reclamation Drainage <br />Calculation Rational and Results Summary <br />SEDIMENT POND AND SEDIMENT FENCE <br />Rationale: <br />Calculated using SEDCADT"" 4 for Windows <br />Areas, slopes and flow paths obtained from electronic media, Exhibit 8C. The <br />drainage area is limited by the upper diversion ditch to the north. This ditch will <br />be left in place and will be maintained functional until the DMG approves the <br />removal of the sediment pond and sediment fence. <br />The soil map, Exhibit 23 shows the soil type as 66 - "Torriorthents, Warm-Rock <br />Outcrop" and 15 "Cameo". Generally the soil samples for this and other <br />disturbance areas indicates the soil is sandy to silty loam (Tab Section 9) which <br />equates to a "B" soil group. The following CN was used in the calculations: <br />86 - B soil group, fallow, bare soil. Used for topsoil piles, ponds and <br />reclaimed areas. <br />• <br />Soil K factor of 0.24 represents a sandy loam and fine sandy loam soil. <br />A "C" factor of 0.52 for the disturbed (reclaimed) run-off areas indicates 1/4 tons <br />of straw mulch per acre, Figure 8 "C" Values for Quantities of Mulch, SCS <br />Technical Notes #50, January 1977. <br />25 year 24 hour storm event of 1.8" used for emergency spillway design <br />10 year 24 hour storm event of 1.4" used for all other run-off calculations <br />Results: <br />The sediment pond is shown on Exhibit 8C. The two year sediment storage <br />requirement is 0.31 ac-ft. The actual sediment storage capacity in the pond is <br />from elevation 4782 to 4784 = 0.35 ac-ft. (0.31+ 0.038). The "live" water storage <br />capacity is from elevation 4784 to 4788 = 0.89 ac-ft (0.931 - 0.038). <br />Peak discharge 10 year event = 10.03 cfs <br />25 year event = 16.46 cfs <br />Primary spillway is a valved 6" PVC pipe with invert elevation of 4784. <br /> <br />14-6-53 <br />(New 11/00) <br />