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still wash out. If this occurs, it will have to be re-built using gravel from above the low flow area. In <br />this way, siltation in the river will be minimized. <br />The flow handled by the 75 feet wide opening is calculated below: <br />- Assuming a flow depth of 5.0 feet (still providing 6.0 feet height from water to bridge), <br />- a Manning's n of 0.25 <br />- channel grade of 1.4% <br />The flow would be 2300 cfs @ approx. 6.0 R/sec. <br />Using the same parameters for the 40' opening in the berm, this area would handle 1226 cfs. There- <br />fore, the combined flow for both areas is 3526 cfs. This is considerably more than the average peak <br />flow of approximately 2500 cfs. Appendix B has flow data from neazby USGS gages in the North <br />Fork of the Gunnison River. Since 1997, the highest flow from a gage immediately upstream of the <br />site was approximately 3250 cfs. <br />At the end of the mining term (3 to 4 years), the bridge will be removed during the low flow period. <br />In order to remove the bridge in 3 years, the third year mining may include two years (140,000 tons) <br />of extraction, which would be moved to the River Bottom Pit site and sold over the 3rd and 4°' yeazs. <br />4. Water Information, Rights and AuEmentation <br />Since the mine will encounter water in the mining operation below 3-4 feet of excavation, and a <br />permanent lake will be left as part of the reclamation plan, it is demonstrated in this section that <br />there are sufficient water rights/augmentation for this operation. A well permit is being applied for <br />with the Division of Water Resources. The North Fork of the Gunnison River at this location is over <br />appropriated. Therefore, a substitute water supply plan and augmentation plan will be formulated <br />for that submittal. There will be no real consumptive uses for the operation other than the 4% loss <br />from the raw material, since the gravel will be wet and no dust control is needed. Also, all process- <br />ing is done at the River Bottom Pit. All consumptive uses are shown below: <br />Scenario 1 -During Mining_ <br />2) Additional evaporation will occur as a result of mining the gravel and exposing it to air before it <br />is run through the crushing/screening operation and trucked off site. This evaporation use is esti- <br />mated at 4% of the annual excavated tonnage, which will be based on the maximum annual tonnage <br />North Fork Pit Mazch 04 1 g <br />