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Table 3—Undeveloped and Developed Flows (100-Year Storm Frequency) <br /> Area (basin) Calculation Undeveloped Developed Flow <br /> Method historical flows cfs Flows cfs Change cfs <br /> Operations B Rational 25.97 0* -25.97 <br /> Laydown, Rational 30.05 61.10 31.05 <br /> Stock iles C <br /> Access Road (F) Rational 26.62 35.03 8.41 <br /> Totals for the 100-year storm event(cfs): 82.65 96.13 13.49 <br /> The 100-year storm causes the largest increase in water flows when compared to the 10-year <br /> storm event. With flow from Basin B directed into the Contact Water Pond there will be a <br /> decrease in surface water runoff from the operations area (Basin B). This is shown in tables 2 <br /> and 3 as a flow of 0 for developed flows. The detention pond will allow release rates to be <br /> within '/z cfs of historical levels. <br /> To reduce the increase in flows, a detention-sedimentation pond is proposed at the end of the <br /> Onsite Stormwater Diversion Channel, north of the stockpile area. The pond will release water <br /> through a 24-inch corrugated metal pipe (CMP). <br /> The pond discharge is located a significant distance from adjoining properties. Water <br /> discharging from both areas and the road will flow through several hundred feet of undisturbed <br /> vegetated land before leaving the property. The vegetation will filter out sediments and <br /> improve water quality. There will not be any adverse impacts to surrounding properties from <br /> increased surface water runoff because of the proposed improvements. <br /> 1.1. Floodplain Designations <br /> Proposed development areas are shown as areas of minimal flood hazard on the FEMA FIRM <br /> map. FEMA Firmettes are presented in Appendix A. <br /> Drainage Basins <br /> The project is found in the Arkansas River Basin. The project is located on tributaries to Grape <br /> Creek. Grape Creek flows into the Arkansas River basin just before the river enters Canon <br /> City, Colorado. <br /> Major Drainage Basin <br /> Water leaving the project flows through tributaries and Grape Creek, located in undeveloped <br /> areas of the county. Vegetation is consistent within the project and downstream. The area has <br /> shrubs, pinon and juniper trees and native grasses. The Arkansas River is approximately 3 '/2 <br /> miles northeast of the project areas. <br /> Minor Drainage Basins o <br /> The project site has been divided into 6 basins with 6 subbasins. Each basin is described below. <br /> CO <br /> The tailings facility was designed by a different firm and is not included in this report. <br />