PERMFILE122596 - Laserfiche WebLink

Home Browse Search

wide opening in the gravel berm. During a very lazge peak flow, portions of the gravel berm may still wash out. If this occurs, it will have to be re-built using gravel from above the low flow area. In this way, siltation in the river will be minimized. The flow handled by the 75 feet wide opening is calculated below: - Assuming a flow depth of 5.0 feet (still providing 6.0 feet height from water to bridge), - a Manning's n of 0.25 - channel grade of 1.4% The flow would be 2300 cfs @ approx. 6.0 ft/sec. Using the same pazameters for the 40' opening in the berm, this azea would handle 1226 cfs. There- fore, the combined flow for both azeas is 3526 cfs. This is considerably more than the average peak flow of approximately 2500 cfs. Appendix B has flow data from neazby USGS gages in the North Fork of the Gunnison River. Since 1997, the highest flow from a gage immediately upstream of the site was approximately 3250 cfs. At the end of the mining term (3 to 4 yeazs), the bridge will be removed during the low flow period. In order to remove the bridge in 3 years, the third yeaz mining may include two yeazs (140,000 tons) of extraction, which would be moved to the River Bottom Pit site and sold over the 3rd and 4"' years. 4. Water Information. Ri¢hts and Auementation Since the mine will encounter water in the mining operation below 3-4 feet of excavation, and a permanent lake will be left as part of the reclamation plan, it is demonstrated in this section that there are sufficient water rights/augmentation for this operation. A well permit is being applied for with the Division of Water Resources. The North Fork of the Gunnison River at this location is over appropriated. Therefore, a substitute water supply plan and augmentation plan will be formulated for that submittal. There will be no real consumptive uses for the operation other than the 4% loss North Fork Pit March 04 21