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RULE 2 PERMITS <br />Monthly flow data for each of these drainages are presented in Figures 2.04.7-3, 2.04.7-4, and 2.04.7-5. <br />These figures are a graphical representation of the data presented in Table 2.04.7-8 and further show the <br />seasonality of flow and runoff responses of each of the watersheds. Seasonal sustained flow values are <br />nonexistent for Taylor Creek. Sustained seasonal flows in Wilson Creek and Goodspring Creek show the <br />predominant influence of snowmelt runoff in the spring and early summer months with flows decreasing <br />in late summer and early fall to baseflow conditions. This trend is confirmed with the additional flow data <br />obtained by Colowyo and presented in the Annual Reports. <br />Hvdrologic Balance <br />An integral part of any watershed study is the hydrologic balance or fate of precipitation in the <br />watersheds. Since recharge and infiltration rates are low (see Groundwater Section presented earlier), <br />precipitation is highly variable by season and by month, and evapotranspiration rates are high, the water <br />balance is most applicable to long-term estimation of average streamflow volumes. A typical water year <br />(October 1974 through 1975) was used as the basis for the calculations presented in Tables 2.04.7-9, <br />2.04.7-10, 2.04.7-11, and 2.04.7-12. <br />Table 2.04.7-9 is a summary of the water balance estimates for Goodspring, Taylor and Wilson Creeks <br />based on drainage area in square miles (mi), precipitation in inches (in), evapotranspiration (ET) in <br />inches and runoff in inches and acre-feet (AF). Goodspring Creek, with the largest drainage area of 39.45 <br />miz has the highest annual runoff followed closely by Wilson Creek. Goodspring Creek's drainage area is <br />1.49 times that of Wilson Creek, but the runoff is only 1.08 times as great. This may be a reflection of <br />localized differences in precipitation near the watershed and the difference in the stream bed itself. Higher <br />ET in the Goodspring Creek valley floor acts to consume water moving through the channel area. Taylor <br />Creek, with a watershed 0.18 times the size of Goodspring Creek has a runoff volume 0.07 times the flow <br />in Goodspring Creek. Again, this is a result of smaller basin area and localized precipitation differences. <br />Tables 2.04.7-10, 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 show <br />runoff occurring primarily in the late winter and early spring months of February, March and April. <br />These are the months of highest snowfall and saturated ground conditions which allow for runoff to take <br />Place. It must be stressed that these data are for runoff, i.e., flow over and above the 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 indicating <br />that nearly all of the precipitation is evaporated in place. This is particularly true of winter snowfall, when <br />dry winds occurring in the late winter and spring may evaporate significant depths of snow before it <br />begins to melt, resulting in no stream flow. Obviously the amount of water left for infiltration and deep <br />percolation is a minute fraction of the total. <br />The computed runoff figures presented above appear to be reasonable estimates when compared to <br />recorded flows in Table 2.04.7-8. As with all estimates of runoff for semi-arid regions, the probable error <br />in many variables entering into the computations may range from negligible to as large or larger than the <br />predicted runoff values. This is mentioned not to discredit the results, but to remind the reader that these <br />figures are estimates, and would be subject to revision as additional data becomes available. <br />Flow Estimates <br />Another part of the requirements for permit approval with respect to the hydrology of the basins in and <br />adjacent to the mine permit area is an estimation of flow values for the high and low flows in each <br />Rule 2 Permits 2.04.7-18 Revision Date: 6/23/08 <br />Revision No.: MR-91