REV97265 - Laserfiche WebLink

Home Browse Search

Rates During the ]0-year. 24-hour storm event the peak flow from the last pond in the series. Johnson pond ~~10, is passed by the principal spillway alone. PYEATT GULCR DRAINAGE AND SEDIMENT CONTROL PLAN The Pyeatt Gulch watershed was divided into three watersheds for purposes of designing a drainage and sediment control plan for areas disturbed by mining. The three watersheds are West Pyeatt, Middle Pyeatt, and East Pyeatt; the watershed boundaries are shown on the Pyeatt/Johnson Drainage and Sediment Control Plan Map, Map TR-486-1. The drainage and sediment control plan for the Pyeatt watershed consists of one ditch and six sedimentation ponds. The West Pyeatt watershed is small, 63 acres, with only five acres of dis- turbed area. Runoff Erom the West Pyeatt drainage will be diverted into the Middle Pyeatt drainage for passage through the system of sedimentation ponds. Diversion of the West Pyeatt runoff will be through West Pyeatt Diversion Ditch dkl. The location of West Pyeatt Diversion Ditch ~kl is shown on Map TR-486-1, Johnson/Pyeatt Drainage and Sediment Control Plan, and [he ditch design is presented on Figure 2, West Pyeatt Diversion Ditch ~~1 Design. The Middle Pyeatt watershed consists of 411 acres with 246 acres of disturbed area. Runoff from Middle Pyeatt and West Pyeatt watersheds will be passed through a series of three sedimentation ponds at [he bottom of the Middle Pyeatt drainage. The locations of the Middle Pyeatt sedimentation ponds are shown on the Johnson/Pyeatt Drainage and Sediment Control Plan Map, Map TR-486-1, and on the Middle Pyeatt Sedimentation System Map, Map TR-486-3. The capacities and El ow volumes for each pond are shown in Table 1, Johnson and Pyeatt Sedimentation Pond Summary Information. Design information for each dam is presented in Table 2, Embankment Designs, and Figure 2, Typical Sedimentation Pond Embankment Cross Section. As with Johnson Gulch, the effectiveness of the Middle Pyeatt series of sedi- mentation ponds was determined by the use of a hydrologic model. During a 10-year, 24-hour precipitation event, the peak settleable sediment concentra- tion is predicted to be 0.0022 ml/l. Input parameters, along with complete results from the hydrologic modeling are included in Appendix B, Middle Pyeatt Hydrologic Models, Appendix D, Curve Number Determinations, and Appendix E, Sedimentology Parameters. The design for each impoundment in Middle Pyeatt Gulch is shown on [he Middle Pyeatt Sedimentation System Map, Map TR-486-3, and on Figure 2, Typical Sedi- mentation Pond Embankment Cross Section, along with Table 2, Embankment Design. The East Pyeatt drainage contains 1,240 acres and will require a series of three sedimentation ponds for sediment control. The total disturbed area in [he East Pyeatt watershed will be 516 acres. The total capacity of the East Pyeatt sedimentation system during a 10-year, 24-hour storm event is 13.79 acre-feet as shown in Table 1, Johnson and Pyeatt Sedimentation Pond Summary c 2 Revised 8/86