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J 79 4. Culverts under the major haul road were evaluated for existing capacity and required capacity for the 10-year, 24-hour discharge. The culvert on Newlin Creek is inadequate and replacement is required. The culvert at the end of the Magpie diversion can handle the design discharge with a build up of head. The existing depression area just upstream of the culvert provides storage and attenuates the peak discharge out the • culvert. Culvert design and adequacy were discussed in Section 6.2. 5. Sediment pond storage and configuration were discussed in Section 6.3. Sediment pond evaluation was based on design data and field inspection. The sediment pond calculations are not proposed to be exact. For de- tailed pond evaluation, field survey of pond geometry is required. ~ 6. The location of proposed Sediment Pond 'E" has been changed. The orig- - inal location vas directly on the channel which received the Magpie ~' Creek diversion flow. The new location is shown on Hydrology Mao 2, • Appendix A. 7. All sediment ponds are temporary structures and evaluated for the 10- year, 24-hour precipitation event. The design criteria for emergenry spillways is based on the 25-year, 24-hour precipitation event. 8. Minor diversions are temporary structures and designed for the two-year, 24-hour peak discharge. Minor diversion channel "E" vas designed for the 10-year, 24-hour peak discharge because of the large contributing drainage area. If the final designs for proposed diversions follow the criteria presented in this report, they will be adequate in terms of capability and stability. 9. Location of proposed minor diversions "E" and "F" have been changed from the proposed G.E.C. mine plan to eliminate the need for channel protection (Hydrology Map 2, Appendix A). 30. The present Dorchester Maggie Creek diversion is considered permanent and thus, required the design of major diversion channels PM-CH-15 and PM-CH-17 for permanent conditions. 11. The existing slope and location of the Dorchester Magpie Creek diversion required that the major diversions be designed with slopes greater than • the natural gradient requiring significant riprap protection. 12. The restoration channels were designed for stability and conveyance of flows during the 10-year, 24-hour discharge. Overbooks should be sloped at 10:1 for conveyance of discharges exceeding the 10-year, and up to the 100-year, storm event.