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The cross sections for the revised reach of Brush Creek were based on as-built construction surveys and associated topographic information for the new bridges and channel. The input and output HEC-2 data and the engineering report were used in recoding the original HEC-2 model into one HEC-RAS model. Two additional cross sections were analyzed using normal depth in order to determine the flooding extent of a divided flow condition. The model for Brush Creek incorporates the addition of the new bridges in addition to the minor grading that has occurred in the floodplain as a result of the development of Eagle County Ranch Development, namely the Capital Street Bridge, Sylvan Road Bridge, and Eagle Ranch Bridge No.1. In the vicinity of new bridge structures, as-built surveys were completed to verifY the channel grades and bridge geometries (Reference 23). Field surveys were completed at various times between December 2001 and January 2003. Geometry data for small existing bridges that have remained in place since the effective information were developed from field measurements in February 1997. Cross sections for the backwater analyses of Gypsum Creek were obtained from topographic maps at a scale of I: 1,200, with a contour interval of 2 feet (References 24 and 25). All bridges were field checked to obtain elevation data and structural geometry. Starting WSELs for the Colorado River were calculated using normal depth at the beginning of the study with a gradient of 0.00954. The upstream ending water surface was also computed as normal depth downstream of the 1-70 bridges at a gradient of 0.00244. Mapping indicates the channel gradient is greater upstream of the confluence with the Eagle River. The starting WSEL for the Eagle River model was computed based on the known WSELs from the Colorado River model at Cross Section 44. This appears to be a reasonable and conservative assumption because a coincidental flood peak in the Colorado River would create backwater upstream on the Eagle River through Cross Section 5. By viewing the Eagle River profile, it is apparent that either a large deposit of volcanic ash and debris, or channel degradation from the Colorado River propagating up the Eagle River, has caused a relatively steep slope in the Eagle River channel near the confluence. Because of the steep channel slope in this area, a normal depth calculation would produce a lower water surface on the Eagle River than the backwater elevation caused by a 100-year flood on the Colorado River. The upstream ending water surface on the Eagle River was computed as critical depth near the town limits of Minturn at a county bridge structure, a hydraulic control structure. This is a reasonable assumption as a result of the steep gradient, narrow channel geometry, and limited conveyance capacity of the bridge. Starting WSELs for the Eagle River near Minturn were obtained using the slope-area method at a starting cross section 800 feet downstream of the Town of Minturn corporate limits. Starting WSELs for the Eagle River near Red Cliff were calculated using critical depth downstream of the corporate limits of the Town of Red Cliff. 25