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The minimum width will be the width of the natural downstream channel. The- riprap will be sized in • the field by:SCC's project engineer based on the "as-built" slope of the culvert and final configuration ofthe exit channel slope area. The sizing shall be based on the Federal Highway Administration's HEC No. 11 "Use of Riprap for Bank Protection" or other standard methods. All culverts will have a minimum cover of 12 inches. Culverts and drainage ditches will be maintained periodically to prevent accumulation of debris on the culverts inlets and outlets. The general design procedures used in the design of culverts is contained in Attachment 13-1 Tables 13-5 and 13-6 contain an inventory of existing and proposed culverts at the Seneca II=W Mine. All existing culverts .are adequate. Figure 13-3 and figure 13-4 show typical installation of culverts. Other applicable methods include the use of charts developed by the Federal Highway Administration, published in Hydrologic Engineering Circular HEC-5 IFHA, 19801, ahd Hydrologic Design Series HDS-3 IFHA, 19801 Charts published in HEC-10 IFHA, 1978) are also used; however, exit velocities must then be determined by other methods. Headwater conditions are typically examined by using HEC-5 inlet control Homographs. To be conservative and to allow for adequate freeboard, SCC usually uses "projecting" conditions. • As virtually all culverts have free outfalls, inlet control assumptions can be verified by the "Pipe Flow Charts" in HDS-3. If flow in the culvert has a tree surface, entrance control exists, and exit velocity can be approximated by using the greater of normal or critical velocity determined by the "Pipe Flow Charts" in HDS-3. Monitoring. A section of the Haul Road G alignment traverses the sideslope of a hill. Although the stability analyses indicate that the road cut will be stable, as an added safety measure, SCC will monitor the slope above and below the road alignment. Reber will be driven into the ground at locations indicated on Drawing No.-9111-5, Attachment 13-36 Ilvey Report). These monuments will initially be surveyed after installation prior io road construction. End-of-construction conditions are the most critical periods for cuts in clays. Therefore, the monuments will be surveyed for movement immediately after the cuts have been completed. They will be surveyed monthly fon the first quarter and quarterly on the same schedule as Pond 005. If no movement is detected after one year, monitoring will be suspended, upon approval by the Division. r, ~J 27 Revised 01!06!94