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<br />I <br />I <br />I <br />I <br />I, <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />, <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />regulations. If a formal agreement was made with Denver Water to sustain <br />their historic operating practices, or other arrangements made for providing <br />flood storage, then the hydrology downstream would be lower, mainly from a <br />total flood volume and duration perspective. Peak flows in the urban areas <br />are dominated by storms occurring in Eldorado Canyon and the downstream <br />watershed. <br /> <br />2. The rail line to the Moffatt Tunnel provides, we believe, significant flood <br />storage on the south tributaries from the foothills to above Gross Reservoir. <br />We are familiar in detail with one site on South Draw where about 80 to 100 <br />acre feet of storage occurs and reduces the 1 OO-year flood peak by more <br />than half. <br /> <br />There may be as many as 20 to 30 storages that exist, that vary from the <br />very small to a size such as that found in South Draw. Since agreements are <br />not in place to sustain these storages, they have not been included. These <br />storages exist, benefitting the downstream conditions for most events, but <br />also may present a hazard, as the storages are not engineered for flood <br />control and may be susceptible to breeching during large floods. <br /> <br />3. When flood control facilities, floodplain mapping, or refined surveys are <br />available, the hydrology model can be further refined to better depict flow <br />splits and hydraulic controls. Thus, we can envision further revisions to the <br />hydrology model in the future. <br /> <br />4. The UDSWMM program has very limited stream flow routing algorithms. We <br />feel it is inadequate to simulate the dynamic floodplain storage routing of the <br />South Boulder Creek below Eldorado Springs and the West Valley Overflow. <br />Thus the peak flows in these areas, determined in this study, are probably <br />high. Effectively, the peaks of the hydrographs are "trimmed" and sent to <br />the West Valley Overflow without the natural attenuation that exists. <br /> <br />5. Our limited sensitivity tests indicate that the model is highly responsive to <br />the geometry given for the South Boulder Creek main stream. While our <br />work for the Colorado State Parks has afforded the opportunity to <br />incorporate field survey of representative sections at Eldorado State Park, it <br />may be worthwhile to conduct field surveys of representative sections at <br />other locations in order to better represent the mountain streams. <br /> <br />RECOMMENDA TIONS <br /> <br />1 . The hydrology modeling herein appears reasonable and should be adopted on <br />an interim basis. <br /> <br />1- 19 <br />