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Eagle and Colorado Rivers Floodplain Information Report Eagle and Colorado Rivers Floodvlain Information Report le Count)1, Colorado Ea Colorado the cross BIBLIOGRAPHY AND REFERENCES to the but does "blocked obstruction' the conveyance area, The gravel ponds are modeled by filling the bottom of the pond with a elevation of the spillway. This technique removes the pond bottom from not presuppose the pond is "ineffective flow. Colorado Ie Minturn, Ea Insurance Stud Flood Federal Federal Emergency Management Agency, H Eallle Count Colorado, August 1978 3 1975 Colorado, May Gore Creek Floodolain Information. VaiL Ea Hydro-Triad, Ltd. 4. EaJ!le River The topographic mapping for the Eagle River was flown over a two-week period during the middle of October 1998 when the flow was approximately 270 to 300 cfs at a location downstream of Gypsum. This is a relatively low flow for the Eagle River, and represents only 3.5% of the 100-year flow of 8,030 cfs. The average depth of water in the channel during the mapping was negligible. The model input channel geometry assumes negligible channel geometry below the water surface at the time of the aerial mapping. le and Pitkin Ea Rivers le Fork and Ea 1997 Computer 1977 s. 2002. 13 May e River Flood Hvdrolo LLC, Ea 10. Water Resource Consultants Detailed field survey measurements were taken along the bridge decks, and at every cross section upstream and downstream of the bridges. In addition, supplemental survey cross sections were included for some of the channel cross sections. Surveyed cross sections are distinguished shown of the floodplain mapping with hexagons rather than circles, and all surveyed cross sections have been described in the model. This survey information was completed between May and October of 2002 and has been incorporated into the electronic GIS files and use of the ortho-rectified field investigations were determined from roughness Channel and overbank aerial imagery. An informal levee exists along the north bank of the Eagle River at the gravel ponds in Dotsero (cross sections 5 through 7). This levee was field investigated and determined to be "non-FEMA compliant," meaning it does not have a formal maintenance program, may not withstand 100-year flooding, and does not have the required freeboard. Further, the field investigation indicated that once the floodwater does breach the levee, it would be effective flow. August 22, 2003 Page 14 ~~u.~~", In general, it is fortuitous that most existing major developments along the banks of the Eagle River are located outside the 100-year floodplain. Exceptions to this are the subdivisions in Gypsum between cross sections 51 and 71 August 22, 2003 Page 13 iM1 MlIixU.~~", 'V"' ;".......'1____ _.~ into Eagle Coun manually incorporated Town of J.P. Sato & Associates, Hydro Counties. Colorado, December 30, 5 Digital pictures of all bridges A total of 42 bridges are located within this study reach of the Eagle River. have been linked to the hydraulic model. Scale U.S. Department of the Army, Corps of Engineers, Hydrologic Engineering Center, Program, HEC-RAS 3.1.0 Water-Surface Profiles, Davis, California, March 2001 Colorado, Colorado-Federal February 11. 1999. Summa U.S. Department of the Interior, Geological Survey, 7.5-Minute Series 1 :24,000, Contour Interval 2 feet: Colorado (1987) calculated channel geometry below the water surface depth was sectional geometry determined from the aerial mapping. Insurance Stud Insurance Stud Federal Emergency Management Agency, Flood Unincoroorated Areas), Revised January 25. 1983 Agency, Flood Emergency Management Colorado, March 1980. Federal Count 1 2. and wood the bridge deck to Only one bridge is located within this study reach of the Colorado River. The bridge is a cable bridge used for livestock to cross the river. Survey measurements were taken along complete the cross sectional data determined from the contour mapping. Data. Annual ical U.S. Department of Commerce, Climatolo A 6 7 8 9 There are four old concrete arch bridges on the Eagle River: an abandoned bridge at Gypsum (cross section 68.5), an abandoned bridge between Eagle and Wolcott (cross section 196.5), Highway 131 Bridge at Wolcott (cross section 226.5) and old bridge with a new deck on the County Road at Minturn (cross section 401.5). These bridges have limited hydraulic capacity and provide little or no freeboard during a loo-year flood. Of these four bridges, only the Highway 131 Bridge is not overtopped in a flood. The Gypsum Bridge and the bridge between Eagle and Wolcott have failed structurally and are no longer used for vehicular traffic.