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<br />A sample hydrograph showing the 100--year, 50-year, 25-year, 10-year, 5-year and 2-year
<br />present development conditions is included below. The vertical axis shows discharge in cfs,
<br />while the horizontal axis shows the time in hours.
<br />
<br />Due to the small period of historical stream flow data and small precipitation events
<br />available for Walnut Creek and Woman Creek (USGS, 1976), it was not possible to
<br />accurately calibrate the model to published historical Rocky Flats stream flow data,
<br />
<br />FIGURE C-.4
<br />INFLOW TO POND A-4
<br />(SWMM ELEMENT 169)
<br />6-HOUA STORM, PRESENT DEVELOPMENT CONDITION
<br />
<br />During this study, the output flood flows and volumes were verified two ways. First, the
<br />data were checked internally to ensure consistency of flows between sub-basins taking into
<br />account their different basin characteristics, Second, the data were checked with those
<br />presented in previous reports by the U.S. Army Corps of Engineers (USACE), ASI, and
<br />UDFCD for the same hydrological design points, These data are presented in Tables IV-9
<br />and IV-lO,
<br />
<br /> ~.
<br /> 100 YEAR
<br /> ~.
<br /> '0 ,yEAR
<br />;;;
<br />c
<br />8
<br /> ~.
<br /> "
<br /> ".
<br />
<br />
<br />"
<br />
<br />Two checks were performed to ensure internal consistency of the calculated CUHP /SWMM
<br />peak flows, First, the peak flow per unit area in units of cfs per square mile for each of the
<br />Buffer Zone sub-basins were plotted on a semi-log scale, The sub-basins were separated
<br />into four categories with similar soil infiltration characteristics, The results are presented
<br />in Figures IV-3 to IV-6, As expected, there is progressively less runoff from basins with
<br />higher soil infiltration rates. Also, as expected, the smaller basins had higher runoff per unit
<br />area than the larger basins.
<br />
<br />
<br />.
<br />.
<br />
<br />TIME (HRS)
<br />
<br />SAMPLE HYDROGRAPH
<br />
<br />A second check of the internal consistency of the CUHP /SWMM calculated flow data was
<br />done to compare flow calculated by CUHP for the sub-basins and routed by SWMM against
<br />flow calculated using CUHP by combining sub-basins into one large aggregate basin, The
<br />results are presented in lines I, J, K, P, Q, and R of Table IV-9. The flows calculated using
<br />the two methods were similar in the Standley Lake Basin (P, Q, R) and the tributary to
<br />Great Western Reservoir (J), Because of the relatively homogeneous nature of these basins,
<br />this result can be expected, The calculated flows for the Great Western Basin (I, K) were
<br />higher using the SWMM analysis, Part of the basin consists of the highly developed Core
<br />Area with correspondingly low permeable area; the remainder is generally undeveloped,
<br />with high permeability, CUHP combines these areas into one area with aggregate
<br />characteristics and hence does not as closely model the physical situation as SWMM, The
<br />high Core Area runoff is routed quickly downstream, The corresponding peak flows have
<br />similar time to peak and, being additive, result in higher flows. The calculated SWMM flow
<br />can therefore be expected to be higher than the CUHP flow,
<br />
<br />The total100-year volume of runoff leaving the plant site through Woman Creek, Walnut
<br />Creek, and unnamed tributaries to Standley Lake and Great Western Reservoir (SWMM
<br />elements 129, 127, 126, 124, 123, 108, 180) is 692 acre-feet for present conditions and 795
<br />acre-feet for future basin development,
<br />
<br />Calibration and Verification of COOP ISWMM
<br />
<br />Calibration and verification of any CUHP /SWMM model is desirable to better ensure the
<br />reliability of the results obtained, CUHP was developed by the UDFCD using data from
<br />the Denver area, and is suitable for Rocky Flats application,
<br />
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