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FLOOD10358
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Last modified
1/26/2010 10:13:14 AM
Creation date
10/25/2007 3:10:38 PM
Metadata
Fields
Template:
Floodplain Documents
County
Eagle
Stream Name
Eagle River, Colorado River
Basin
Colorado Mainstem
Title
Correspondence presenting Revised Copies of FIRMS for Incorporated Eagle County
Date
12/16/2005
Prepared For
Arn Menconi, Chairman, Eagle County Board of Commissioners
Prepared By
Kevin Long
Floodplain - Doc Type
Correspondence
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<br />650 station year events occurred outside those 3 months. While floods as a result of rainfall <br />alone could be important for small drainage areas, peak flow records show snowmelt is the <br />primary cause of peaks at the stations studied. Rainfall may have contributed some runoff to a <br />few of the annual peak flows, but it is very difficult to identifY the amount of contribution from <br />available hydrologic records. During spring months, much of the precipitation that occurs as <br />rainfall will be retained in the snowpack. The ground is often stIll frozen during the spring <br />snowmelt season, so runoff occurs with very little infiltration. Rainfall did not result in <br />significant independent peak discharge events because the annual peaks occurred during the <br />snowmelt season. <br /> <br />The Hydrometeorological Branch of the National Weather Service, in cooperation with other <br />Federal agencies, made a major effort to identifY historic thunderstorms in the Rocky Mountain <br />region during probable maximum precipitation (PMP) studies. The results were documented in <br />u.s. Commerce Hydrometeorological Reports No. 55A and No. 49, dated June 1988 and <br />September 1977, respectively. They found that a few severe thunderstorms have occurred in the <br />mountains of Colorado, New Mexico, and Utah. However, these storms are very rare, and <br />precipitation data for them are sparse, partially because only a limited number of rainfall gages <br />are located at high elevations. Thunderstorm, or local storm, rainfall is a significant factor for <br />small drainage areas at the extreme PMP level, but it has not been observed often enough to be a <br />significant factor at the more frequent flood levels considered in this floodplain study. <br /> <br />The best technical evaluation procedure would be to determine an independent series of <br />exclusive snowmelt and rainfall events that could be analyzed independently and combined on a <br />probability basis into an all-season flood frequency curve. However, this is not possible, so as a <br />practical matter, the peak annual events that were recorded at each of the gaging stations, <br />whether exclusive snowmelt or with some rainfall contribution, were analyzed and their <br />frequency determined for application to this study. The streamflow records reflect the flood <br />history at those stations. <br /> <br />Discharges for specific frequencies are needed for performing hydraulic analyses in the ungaged <br />reaches that are part of this study. Discharges and drainage areas were subjected to regression <br />analyses using a log-log relationship. Drainage area was adopted as the only predictor because <br />previous studies by GAl indicated that additional predictors did not improve the correlation <br />coefficient. <br /> <br />A review of a plot of the discharges for specific frequencies versus their drainage areas shows <br />that the three smallest basins, all of which have areas under 4 sq. mi., plot low compared to other <br />stations. These three stations were located close to Gore Creek, but were at high elevations that <br />exceeded 9,000 feet mean sea level (msl). They were eliminated from the fmal regression <br />analysis to avoid distorting the lower end of the regression range. The 17 stream gaging stations <br />listed below were used in the fmal regression analyses. <br /> <br />IDNo. <br /> <br />1 <br />2 <br />3 <br />4 <br />5 <br />6 <br />7 <br />8 <br />9 <br />10 <br />II <br />12 <br />13 <br />14 <br />15 <br />16 <br />17 <br /> <br />Gaging Station Name <br /> <br />Bighorn Creek Near Minturn <br />Pitkin Creek Near Minturn <br />Middle Creek Near Minturn <br />Booth Creek Near Minturn <br />Red Sandstone Creek Near Minturn <br />Black Gore Creek Near Minturn <br />Piney River Below Piney Lake Near Minturn <br />Gore Creek at Upper Station Near Minturn <br />Beaver Creek at Avon <br />Turkey Creek Near Red Cliff <br />Homestake Creek at Gold Park <br />Eagle River at Red Cliff <br />Brush Creek Near Eagle (Discontinued 1972) <br />Gore Creek Lower Station at Vail <br />Piney River Near State Bridge <br />Gore Creek at Mouth Near Minturn <br />Eagle River at Eagle (1911-24) <br /> <br />19 <br /> <br />Drainage <br />Area (sq. mi.) <br />4.5 <br />5.3 <br />5.9 <br />6.0 <br />7.3 <br />12.6 <br />13.0 <br />14.4 <br />14.8 <br />23.8 <br />36.0 <br />70.0 <br />71.4 <br />77.1 <br />86.2 <br />101.0 <br />629.0 <br />
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