2020-03-24_PERMIT FILE - C1981019A (5)

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RULE 2 PERMITS In the West Pit area the tributary to Taylor Creek will be reconstructed along the length of the disturbance. Also in the West Pit area, three additional ditches will be constructed including the West Pit Fill Ditch,the Gulch B Ditch, and the Final West Pit Ditch. other diversion ditches,built on existing natural ground, to collect and route runoff from disturbed areas include the North Prospects Ditch, the South Collection Ditch, Section 16 West Ditch and Section 16 North Ditch. It should be noted that once the West Pit is developed the Section 16 West Ditch, the Section 16 North Ditch, and the Temporary Section 16 Pond will no longer be needed. See Map 19 for the locations of all drainages. The stream channels of Wilson,Taylor and Goodspring Creek will be undisturbed.Although there will be some changes in the areas tributary to the intermittent and ephemeral drainages in the vicinity of the mine, there will be no, change in the major drainage areas tributary to Goodspring Creek, Taylor Creek or Wilson Creek. Premining and postmining tributary areas for the various drainage basins are summarized as follows: Estimated Tributary Areas Acres Basin Premining Postmining Differences Goodspring Creek 25,600 25,600 0 Tributaries to Goodspring Creek: Streeter Gulch 1,424 1,186 -238 Gulch"A" 419 648 +229 Prospect Gulch and 905 881 - 24 Other Drainages Taylor Creek 3,977 3,977 0 Tributaries to Taylor Creek: Taylor tributary 1,379 1,403 +24 All of the mining area drainages have been designed in accordance with the Colorado Mined Land Reclamation Board's regulations.Particular attention has been given to the design of the permanent channels draining Streeter Fill,the Gulch A mine area and the unnamed tributary to Taylor Creek. When designing channels constructed in erodible material, several criteria must be met. The channel must have adequate capacity to carry the maximum flow(in this case the runoff from the 100-year, 24-hour precipitation event) and it must have adequate stability to resist the erosive action of flowing water under all flow conditions. There are two main design procedures for insuring the stability of erodible channels. One procedure is based on a limiting velocity concept and the other on a limiting tractive force concept. Table 2.04.7-24 shows allowable velocities and tractive force values for several kinds of channels. This table is taken from Lane (1955) and is based on the work of Forier and Scobey (1926). When using the limiting velocity concept, one sizes the channel so that it has adequate capacity and so that the average velocity does not exceed the permissible velocity for any given material. It is estimated this maximum allowable non-erosive velocity in the Colowyo mine area is approximately 6 feet pet second. Rule 2 Permits 2.04-38 Revision Date: 12/20/19 Revision No.: TR-135