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4.6.1.3 Protection of the Hydrologic Balance <br />4.6.1.3.1 Diversions and Conveyance of Overland Flow <br />Temporary Diversion Structures <br />Overland flow from undisturbed areas will be directed away from disturbed areas <br />by temporary diversions designed to safely pass the peak runoff from at least a <br />~ 10-year, 24-hour precipitation event. Oesign criteria, including drainage area <br />divisions, curve numbers, and rainfall data, are included in the final design <br />section of Appendix 4-B. <br />Temporary diversion systems, including ditches, detention basins, and energy <br />dissipators are shown on Drawings D-4-5, D-4-6, D-4-7, D-4-8 and D-4-9. Flow <br />from disturbed areas will be conveyed by temporary diversion ditches to sediment <br />control structures. Sediment control structures are discussed in <br />Section 4.6.1.3.2 of this document. <br />Permanent Diversion Structures <br />Permanent diversion structures will be required as part of the post-mining <br />reclamation plan. Permanent diversions are designed to safely pass the peak <br />runoff resulting from at least a 100-year, 24-hour preceipitation event. These <br />ditches include a 6-inch freeboard with 1v:2.5h side-slopes and are stabilized <br />with riprap. -Drawing D-4-16 shows permanent diversions in the reclaimed mine <br />area. These ditches are designed to carry undisturbed runoff away from <br />disturbed areas and to North Thompson Creek. Permanent diversions to carry <br />runoff away from the reclaimed refuse disposal area are also shown on Drawing <br />D-4-16. These ditches will serve to protect the refuse pile from erosion and <br />will help to maintain the long-term stability of the structure. The design cri- <br />teria are included in the final design section of Appendix 4-B. <br /> <br />4-103 <br />