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<br />of the gaging station analyses be used for discharge estimates, The results of the gage analyses
<br />may be extended to other locations using Equation 2, Based on the stated limits of Equation 2,
<br />the results for station 09073700 may be extrapolated to drainage areas between approximately 3
<br />and 12.5 square miles. The results for station 09074000 may be extrapolated to areas between
<br />20,5 sq miles and the confluence point with the Roaring Fork River at Aspen (approximate
<br />drainage area of 43 sq miles), For drainage areas between 12,5 and 20,5 square miles, discharge
<br />values may be determined by interpolation of results at the two gaging stations based upon
<br />drainage area, For drainage areas less than 3 square miles, a detailed hydrologic analysis is
<br />recommended as the CWCB regional regression equation appears to underpredict discharges for
<br />smaller drainage basins on this stream system,
<br />
<br />Ivanhoe Creek, Gaging station records exist for two locations on Ivanhoe Creek, The USGS
<br />gage, Ivanhoe Creek Near NasI, Co, (station no, 09077610), has only 7 years of record (1976-82)
<br />which was deemed insufficient for meaningful analysis, A second gage, Ivanhoe Creek Near
<br />Norrie (station no, 090776(0) was maintained from 1964 to 1976 and has 13 years of record.
<br />Though still a minimal period of record, frequency analysis has been carried out for this gage and
<br />the computed loo-year discharge is 260 cfs, Regional regression analysis using Equation 1
<br />indicates a discharge rate of 394 cfs for the same location and event. Because gaging station
<br />records are very limited, it is recommended that the more conservative results of the regional
<br />regression analysis be used for analysis of loo-year discharges on Ivanhoe Creek.
<br />
<br />North Fork of Frvingpan River, The USGS intermittently maintained the gaging station, North
<br />Fork Fryingpan River, Near Norrie, Co. (station no, 090785(0) for a period of 40 years between
<br />1911 and 1982, Frequency analysis has been carried out for this station and the computed 100-
<br />year discharge is 1,100 cfs, Regional regression analysis for the gage location using Equation 1
<br />indicates a very similar loo-year discharge rate of 1,190 cfs. Because the results of the frequency
<br />analysis are site specific and based upon a relatively long period of record, it is recommended
<br />that these results be used in lieu of the regional regression equation approach. Equation 2 may
<br />be used to extrapolate the results of the frequency analysis to other locations within the stated
<br />limits of 0,5 to 2 times the drainage area at the gage, For areas outside these limits, a detailed
<br />hydrologic analysis would provide the best results, In lieu of such an analysis, the regional
<br />regression approach of Equation 1 could be applied. Comparison of this equation to historical
<br />data from the USGS gaging station indicates fairly good agreement between the two approaches,
<br />
<br />Owl Creek, The USGS maintained the gaging station Owl Creek Near Aspen. Co, (station no.
<br />09076520) for a period of 14 years between 1975 and 1989, Though a minimal period of record,
<br />frequency analysis has been carned out for this gage data and results in a lOO-year discharge of
<br />117 cfs, Regional regression analysis for the gage location using Equation 1 indicates a
<br />substantially higher loo-year discharge rate of 312 cfs, Because gaging station records are so
<br />limited, it is recommended that the more conservative results of the regional regression analysis
<br />be used for determination of loo-year discharge rates on Owl Creek,
<br />
<br />Approximate Streams With No Gage Data. For all other streams studied by approximate
<br />methods. in the 1988 AS, it is recommended that either detailed hydrologic analysis or the
<br />regional regression approach of Equation 1 be utilized for the determination of l00-year
<br />
<br />6
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