PERMFILE128459 - Laserfiche WebLink

Home Browse Search

VII. SUlPIARY AND CONCLUSIONS ~B The G.E.C. Minerals, Inc. (G .E.C.) Coal mine located near Florence, Colorado, vas evaluated for two conditions, present-mining condition and post-mining condition. The water and sediment runoff was evaluated for the two-year, 10- , year, and 25-year, 24-hour storm events for present-mining conditions and the 100-year, 24-hour storm event for post-mining conditions. The information in this report is based on the report entitled "Preliminary Data Base far Application of MULTSED program, G.E.C. Minerals, Ine., Florence, Colorado". Adjustments to the preliminary data base were made during calibration of the model and are dis- cussed in Chapter II. The purpose of the study was for determination of the hydrologic consequences. l~ This vas done by evaluation of the present-mining conditions for adequacy of ex- l fisting and proposed drainage structures, and design criteria for these structures ~^ to meet Colorado regulations and maintain the hydrologic balance. The post- . mining condition was considered for reclamation of drainage channels. The con- ceptual design of the drainage system and restoration vas presented in this report. This report recommends design criteria for hydraulic structures and channel restoration. However, the final design should be based on an economic analysis as determined by G.E.C. Minerals, inc. As a result of this study, the following recommendations and conclusions are drawn: 1. The present condition of major diversion channels of Magpie Creek are ' quite unstable and add significant quantities of sediment to the runoff. This is verified by the model analysis and results of runoff monitoring. The proposed designs greatly reduce the erosion potential of the di- version charnels and the modeling results show no significant increase in sediment concentration with the recommended channel designs. 2. Runoff volume and peak discharge were estimated for a precipitation event and snowmelt. The snowmelt runoff volume is a main concern for secinent pond design. However, it was determined that design of sedi- cent ponds for the peak discharge and runoff volume from a precipitation event would be adequate to control the snowmelt runoff from an ec•~ivalent return period. This was discussed in Section 6.3.1. 3. The eater runoff results of the model were compared to results from regression equations developed for the specific area. The model results were comparable and realistic.