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i <br /> • Snowmelt runoff was quantified by determining the maximum daily reduction in <br /> water content at the Berthoud Pass SNOTEL site. This SNOTEL site has data <br /> from 1979. However, until about 1986, there were large and unexplained <br /> fluctuations in the reported water content in the records. From 1986 to present, <br /> such fluctuations became infrequent, thus making the information more useable. <br /> Therefore, only records from 1986 to the present have been used in design <br /> storm calculations. Recorded precipitation was added to the snowmelt amount <br /> to arrived at a liberal value contributing to run-off <br /> Rainstorm runoff was quantified using data from the NOAA Atlas for rainfall <br /> depths at varying return periods. The partial-duration NOAA values (May <br /> through October) were used for final design, since the snowmelt events were <br /> calculated separately. <br /> The tributary area contributing runoff to the pond is very small. Thus, the <br /> • Rational Method was used to determine peak flow and total storm volume. <br /> 2.3.1.2 Interceptor Ditch Design Parameters <br /> The interceptor ditch invert will be lower than the top of the existing pond liner at <br /> the crest of the pond dike to prevent runoff leakage into the impoundment <br /> (Figure 4). A minimum distance of 12 inches is used as shown on the cross- <br /> sections. The cross-sections and profiles are designed to provide a target flow <br /> depth of 9 inches or less for the 10-year rainstorm or snowmelt event and no <br /> more than 12 inches for the 100-year rainstorm event. <br /> The maximum slope of the ditches and swales is shown on Figure 4. By limiting <br /> the slope to these values, the expected flow velocity will be less than 2.5 fps for <br /> a 10-year event and less than 2.75 fps for a 100-year event. These velocities <br /> Am <br /> 7 <br /> Juro RJ.1999 <br /> TR.tluc <br />