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FLOOD01787
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Last modified
11/23/2009 12:58:08 PM
Creation date
10/4/2006 10:21:40 PM
Metadata
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Template:
Floodplain Documents
County
Boulder
Stream Name
South Boulder Creek
Title
South Boulder Creek/ Flatirons
Date
12/5/1997
Prepared For
Boulder
Prepared By
Consultants
Floodplain - Doc Type
Community File
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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 />I <br />I I <br />I <br />I <br />I <br />I <br /> <br />SECTION III <br /> <br />PAST HYDROLOGY MODELING REVIEW <br /> <br />INTRODUCTION <br /> <br />The principal objective of this Phase II effort was to prepare new modeling for the <br />South Boulder Creek spill at Highway 36 and the West Valley Overflow <br />downstream to the Wellman Ditch. <br /> <br />The best way would have begun with the identification of a watershed subbasin <br />delineation map with a corresponding model schematic. Also, Phase 1 questioned <br />many of the parameters used in the Corps' SWMM model, noted that there were <br />gauge data upstream of Eldorado Springs which presumably had been used for <br />calibration purposes, and concluded that model verification studies probably had <br />been conducted and should be reviewed. <br /> <br />A formal letter requesting such information was sent to the Omaha Corps of <br />Engineers Office. A reply letter provided further study data such as rainfall; basin <br />of infiltration, percent impervious; and model sensitivity testing for the Boulder <br />Creek watershed. Unfortunately, no watershed map for the South Boulder Creek <br />watershed area below Gross Reservoir was received. Therefore, major and some <br />minor subbasins were delineated sufficient to correspond to the model data <br />provided by the Corps. <br /> <br />BASIN AND SUBBASIN DELINEATION AND COMPARISON <br /> <br />Detailed subbasins were delineated on the 1993 City topography and on the latest <br />versions of the USGS quadrangle maps. Major nodes were identified by reviewing <br />general area magnitudes of basins and subbasins, identifying subbasins that had <br />unique and larger magnitude areas such as Martin Gulch below Gross Reservoir, <br />South Draw below Scar Top Mountain which joins South Boulder Creek above the <br />gaging station; and Shadow Canyon, Bull Gulch, and Dowdy Draw below Eldorado <br />Springs. Figure 111-1 delineates many of these features. For basins above Highway <br />93 directly tributary to South Boulder Creek the model schematic and model <br />subbasin areas corresponded, with a slight overage in area by the Corps for a few <br />subbasins in and just above Eldorado Springs (380 acres). <br /> <br />Unfortunately, the subbasin basin areas and total area downstream of Highway 93 <br />did not check. As best as we can decipher, changes to some basins were made to <br />the model, as indicted such basins being out of order in the input data under a <br />"change card" that modified other hydrologic characteristics. The model appears to <br /> <br />111- 1 <br />
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