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The emergency spillway flowing 10-feet wide and 6-inches deep has a capacity of 16.76 cfs as <br />shown on page 5. The emergency spillway is therefore sized to pass the 8.62 cfs run-off <br />generated by the 25-year, 24-hour precipitation event. <br />The sediment pond will collect and contain the run-off from drainage areas 1 through 7. <br />Dueout Pond <br />The dugout pond, as is implied by it's name, was constructed by excavating in the natural ground <br />surface, therefore the dugout pond does not have designed embankments. <br />The dugout pond must be capable of containing the run-off generated by the 10-year, 24-hour <br />precipitation event from area 8. The run-off calculations presented on page 9 show that the <br />dugout pond must contain 0.01 acre-feet. The sketch on page 11 shows that the dugout pond does <br />have adequate capacity to contain the runoff from area 8. <br />The dugout pond has a combination, open channel, primary and emergency spillway. The <br />spillway is sized to handle the 0.16 CFS flow generated by the 25-year, 24-hour precipitation <br />event as presented on page 10a. The spillway is sized on page 6a to handle the design flow and a <br />section view of the spillway is presented on the sketch on page 11. <br />Ditches <br />Two collection ditches are sized on page Sa and 6. Ditch C collects flow on the east side of the <br />haul road and the north side of the gravel road that leads to the bathhouse shop area. Ditch C is a <br />triangular channel, a minimum 1 foot deep with 1.Sh:ly side slopes. A twelve inch (12") diameter <br />culvert is installed as CMP #1 and an eighteen inch (18") diameter culvert as CMP #2 where the <br />ditch crosses the roads. Ditch B is the collection drainage from the north edge of the coal pad. <br />This ditch collects drainage from nearly the entire site. Ditch B is a trapezoidal channel, a <br />minimum of 1 foot deep, 1.6 feet wide at the bottom with 1.Sh:ly side slopes. Fifteen inch (15") <br />diameter culverts (CMP #3 and #4) are installed where ditch B crosses the roads. Diversion ditch <br />A will be left in place. The culvert that previously conveyed the flow from diversion ditch A <br />under the haul road to the west undisturbed area will be plugged. <br />According to the Handbook of Steel Drainage & Highway Construction Products the maximum <br />flow that 12", 15" and 18" diameter culverts can handle without headwater is 2.3 cfs, 4.0 cfs and <br />6.2 cfs respectively. With only 3.75 inches of headwater, the 15" culverts can carry the design <br />5.63 cfs flow. CMP #3 and #4 are also located where failure to cant' the flow or incidence of a <br />larger flow does not effect the ultimate routing of the water to the sediment pond. <br />-4- <br />Rev. Julv 200 <br />TR~9 <br />PPRa~E~ <br />g(ia~os <br />