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for these spiawaya have been cakvlated to be 8.2 cis and 5.7 cis respectively. The capacity <br />of the 18-Inch diameter culvert is estimated to bs 12.7 cfa, and is thers}oro eapabk of <br />• transporting anticipated flows. <br />If the sediment pond was storing water and sediment generated by tM 10-year, 24hour <br />event, the outlet pipe has the capacity to transport calculated flows at approximately 8.2 <br />cubic feet per second (efs, or 3,680 gpm at average dspthl, dewatering tM pond in about 25 <br />minutes. Maximum flows are not recommended, however, dw to high outlet velocities and <br />potential erosion of the hillside below the railroad embankment. M high flow rates ors <br />intended, it is suggested that grouted-krplaa riprap be placed bebw the discharge point down <br />to the Highway 133 drainage ditch. <br />The concrete retaining wall will include an emergency spillway. This spillway is located <br />immediately west of the 8-inch steel pipe outlet, as shown in Drawing 95255-03. This <br />spillway will be constructed within the concrete watl to transport flows generated by a 25• <br />year, 24hour storm event (Rule 4.05.81511b11. Side sbpss for the spillway will be 1:1, wRh <br />a 1.5-foot bottom width and 1.5-foot depth. Flows generated by the storm wiY produce & <br />inches of depth on the 1 percent bottom grade (leaving 12-inches of dry freeboardl, at a <br />calculated flow rate of 5.78 cts. Riprap placed below the spilway on the downstream side <br />of the sediment pond wall should be 24inch maximum rock size, grouted into place. Heavy <br />rip•rap must be in place to ensure the integrity of the track embankment under falling water <br />discharging from the emergency spillway. The protection should extend several feet beyond <br />the spillway on both sides, and within the existing raikoad track drainage ditch. Olsdtergs <br />from the spiNway wi be routed down the ralroad trade drainage ditch to bs tronaported to the <br />opposite side of the trades via existing downstream cuNarts. <br />4.2.8 Maiittensrroa <br />Maintenance of the sediment port will be coneerttrated on the removal of accumulated <br />sediment. The iroquengr of the sediment removal wip haw to be determined in the field, <br />depending on raYrfa6 twndkions. A caGbroted pok or other device should be set within the <br />sediment pond to trade aedlment depth ao proper maintenance can be employed when the <br />sediment is too deep to adequately hold the despn storm. Vehkle access to the sedanent <br />pond will be via the sediment pond access road as described in Section 4.1.4. <br />86266/1424.RPT Cwl Mln~ WM~ 9~nk l]a~ fa tlr 9~nban t}~elc MM <br />oeraMr t eae wlstt:e, inc. ~ s <br />