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~ • III IIIIIIIIIIIII III <br />\J <br />• <br />• <br />TRENCH DESIGN INTO SEDIMENT POND 15-P2 <br />As previously stated, the runoff from the Pit 2 area in Sect. 22 <br />must cross the main Delagua drainage so that the runoff can be <br />handled in Sediment Pond 15-P2. Yhis is a better choice than <br />installing a new pond upstream of the Delagua drainage because <br />the area for a new pond contains an old stock pond that would be <br />very difficult to rework. By designing a wide, shallow trench in <br />the existing access road from the shop area across the main <br />drainage and into Sect. 22, a safe transfer of the runoff can be <br />achieved and the road can still be used for access to all areas <br />in Sect. 22. <br />The trench is designed to safely pass the 25 year-24 hour runoff <br />from the required area. The computer printout on the following <br />page contains the calculations of the 25 year-24 hour peak flow. <br />The computer printout on the second following page shows the <br />design of the trapezoidal earth channel across the Delagua <br />drainage. A freeboard of 0.4 foot is used which, in a shallow <br />trench, increases the safety factor of the design. Also, the <br />height of the berms between the trench and the Delagua drainage <br />will be increased O.5 foot so as not to interfere with the design <br />headwater for the main culverts in the Delagua drainage. Cross <br />section D-D' on Exhibit 4 shows the details of the trench <br />crossing. <br />143 <br />