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RULE 2 PERMITS <br /> (ET)in inches and runoff in inches and acre-feet(AF).Goodspring Creek,with the largest drainage <br /> area of 39.45 mit has the highest annual runoff followed closely by Wilson Creek. Goodspring <br /> Creek's drainage area is 1.49 times that of Wilson Creek,but the runoff is only 1.08 times as great. <br /> This may be a reflection of localized differences in precipitation near the watershed and the <br /> difference in the stream bed itself.Higher ET in the Goodspring Creek valley floor acts to consume <br /> water moving through the channel area. Taylor Creek, with a watershed 0.18 times the size of <br /> Goodspring Creek has a runoff volume 0.07 times the flow in Goodspring Creek. Again, this is a <br /> result of smaller basin area and localized precipitation differences. <br /> Table's 2.04.7-10 and 2.04.7-11 present the monthly water balances for Taylor, Wilson and <br /> Goodspring Creeks for the average year (October 1974 through September 1975). These data <br /> show runoff occurring primarily in the late winter and early spring months of February,March and <br /> April. These are the months of highest snowfall and saturated ground conditions which allow for <br /> runoff to take Place. It must be stressed that these data are for runoff, i.e., flow over and above the <br /> baseflow values. <br /> Runoff values for these watersheds are extremely low and range between 1.3% and 4.2% of the <br /> precipitation falling on the watersheds. ET ranges from 95.6% to 98.6% of total precipitation <br /> indicating that nearly all of the precipitation is evaporated in place. This is particularly true of <br /> winter snowfall,when dry winds occurring in the late winter and spring may evaporate significant <br /> depths of snow before it begins to melt,resulting in no stream flow.Obviously the amount of water <br /> left for infiltration and deep percolation is a minute fraction of the total. <br /> The computed runoff figures presented above appear to be reasonable estimates when compared <br /> to recorded flows in Table 2.04.7-8. As with all estimates of runoff for semi-arid regions, the <br /> probable error in many variables entering into the computations may range from negligible to as <br /> large or larger than the predicted runoff values. This is mentioned not to discredit the results, but <br /> to remind the reader that these figures are estimates, and would be subject to revision as additional <br /> data becomes available. <br /> Flow Estimates <br /> • <br /> Another part of the requirements for permit approval with respect to the hydrology of the basins <br /> in and adjacent to the mine permit area is an estimation of flow values for the high and low flows <br /> in each watershed. These calculations assist the mine operations personnel in designing runoff <br /> detention ponds, diversion conveyances and channel stabilization structures. <br /> The method used to estimate these flow values for each watershed was the United States <br /> Department of Agriculture, Soil Conservation Services' Triangular Unit Hydrograph Procedure. <br /> Flow records for Milk Creek, near the general area, from 1952 were analyzed for exceedance <br /> values. This information and the design storm,a 100-year, 1-hour precipitation event of 1.5 inches <br /> was applied to each basin to- yield peak flow estimates for each drainage. Table 2.04.7-13 is a <br /> summary of the flow estimates for each-basin. Average 7-day low flow for the 10-year return <br /> period (Q7-1o) ranges from 0. cfs for Taylor Creek to 0.29 cfs for Goodspring Creek. These <br /> estimates are substantiated by the data presented earlier in Tables 2.04.7-10,2.04.7-11 and 2.04.7- <br /> 12. High flow values for each basin, the 1-day high flow 100-year return period, ranged from 8.0 <br /> Rule 2 Permits 2.04-24 Revision Date: 2/13/20 <br /> Revision No.: TR-135 <br />