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Eahibil C CMLRB 112 Permit Application <br />Agile Slone Systems. Ine. <br />• 3.0 Watershed Studies <br />The Tallahassee Basin Area was defined over 287 square miles, 75 sub-basins and >5 <br />creeks. Digitized maps were purchased and used as input into the Eagle Point Software <br />which was specially designed to conduct such work. The creeks evaluated included the <br />Tallahassee, Currant, Cottonwood, 31 Mile Mountain and Various Minor Creeks. <br />BASIN ACRES SUB-BASINS <br />Smith Gulch 5,169 2 <br />Sheep Gulch 9.726 3 <br />Upper Currant Creek Basin 10,141 3 <br />Dick's Creek 4,957 2 <br />31 Mile Mountain 13,164 5 <br />Middle Currant Creek 34,875 13 <br />Mill Gulch 8,026 2 <br />Cottonwood Creek 63,457 25 <br />Tallahassee Creek North 8,469 4 <br />Tallahassee Creek Middle 9,496 5 <br />Tallahassee Creek South 6,404 3 <br />Tallahassee Creek Lower 5,568 2 <br />Lower Currant Creek 10,783 4 <br />Pazkdale Mine Area 2,795 2 <br />• TOTALS 193,030 75 <br />Each sub-basin was evaluated to determine their respective shape factors, soil types from <br />the Soil Conservation Survey for Fremont County, infiltration rates for each soil type, <br />vegetative cover percentages, curve numbers and channel routing. Curve numbers were <br />used to determine the quantity of water run-off based on the soil type and vegetative <br />cover. Weighted averages were determined for each basin. Channel routing identified <br />how fast and in which direction the water moved based the topography demonstrated in <br />the digitized surface maps. Infiltration rates noted how fast the water is absorbed into <br />and percolates through the soil and gravel types. <br />Infiltration percolation tests conducted by Azurite, Inc. 7/97 noted that the gravels on the <br />gravel bar surface and granite plant area aze extremely porous. 3 tests were conducted <br />demonstrating that water will percolate at rates of 1.56", 1.50" and 1.50" per minute. <br />Since the 100 yeaz storm event is 3.0"/24 hours, no surface drainage is likely to occur <br />obviating the need for ditches, swales, buffers, berms, etc. Nevertheless, this conclusion <br />was not followed and all of the latter items were dutifully engineered and will be built to <br />satisfy permit requirements. <br />The final storm event work focused on the 2, 10, 25 and 100 yeaz storms. The NOA <br />Atlas identified the various iohyets in Colorado. For example, the 100 year storm over <br />24 hours has historically resulted in 3.0" of rain. The 10 and 100 yeaz rainfall levels had <br />• an additional 0.5" added to them, respectifully, as a safety margin. The safety margin <br />5 <br />