<br />-19-
<br />
<br />comparative purposes. The spring snowmelt phenomena produces the peak
<br />streamflow discharges for the main stem Gore Creek. The values derived
<br />
<br />from the fourteen log-Normal snowmelt discharge probability analysis
<br />
<br />were utilized in developing the Snowmelt Discharge curves, as pre~
<br />
<br />sented on Figures 111-7 to 1II-12. The curve fitting process included
<br />
<br />a least squares computation for the best fit or mean discharge curve
<br />
<br />and fitting an upper envelope curve based upon a 1.5 standard deviation.
<br />The upper envelope'curve provides a confidence level of 93+% that
<br />resultant peak discharges will fall below the curve. Due to the relative
<br />
<br />shortness of many of the streamflow records. the upper envelope curve
<br />
<br />was utilized in defining peak discharges for the floodplain compu-
<br />tations in this study.
<br />The 500 year snowmelt discharge curves were established by
<br />
<br />extrapolating the curves for other recurrence intervals based upon a
<br />
<br />criteria defined by the Colorado Water Conservation Board and in
<br />accordancewithF.I.A.practices. Amore detailed discussion of the
<br />procedures and the data are contained in the technical addendum to
<br />this report.
<br />Effects of Development on Discharges
<br />Increased imperviousness within the Gore Creek Valley is not
<br />expected to increase snowmelt flooding. This is because snow in the
<br />lower valley will be melted early in the thaw before the creek is
<br />near flood stage. Consequently. any additional runoff caused by
<br />development in the valley will have already been discharged days
<br />
<br />before the peak. Increasedimperviousnesswil1,however, increase
<br />discharges within the very small basins where the development occurs.
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