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FLOOD02984
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Last modified
1/25/2010 6:26:00 PM
Creation date
10/4/2006 11:23:26 PM
Metadata
Fields
Template:
Floodplain Documents
County
Delta
Community
Hotchkiss
Basin
Gunnison
Title
FIS - Hotchkiss
Date
7/3/1985
Prepared For
Delta County
Prepared By
FEMA
Floodplain - Doc Type
Current FEMA Regulatory Floodplain Information
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<br />2.4 Flood Protection Measures <br /> <br />On North Fork Gunnison River, the Paonia Reservoir, located approxi-, <br />mately 15 miles upstream of Paonia, has been regulating flood flows <br />since 1961. The reservior, constructed by the U.S. Power and <br />Water Resources Service (formerly the U.S. Bureau of Reclamation), <br />contains 21,000 acre-feet of storage capacity and reduces the 10-, <br />50-, and 100-year floodflows at the Somerset U.S. Geological Survey <br />stream gage No. 09132500 by approximately 17, 13, and 6 percent, <br />respectively. No protection is afforded for the SOO-year flood <br />(Reference 8). <br /> <br />3.0 ENGINEERING METHODS <br /> <br />For the flooding sources studied in detail in the community, standard <br />hydrologic and hydraulic study methods were used to -determine the flood <br />hazard data required for this study. Flood events of a magnitude which <br />are expected to be equaled or exceeded once on the average during any <br />10-, 50-, 100-, or SOO-year period (recurrence interval) have been selected <br />as having special significance for flood plain management and for flood <br />insurance rates. These events, commonly termed the 10-, 50-, 100-, and <br />sOO-year floods, have a 10, 2, 1, and 0.2 percent chance, respectively, <br />of being equaled or exceeded during any year. Although the recurrence <br />interval represents the long term average period between floods of a <br />specific magnitude, rare floods could occur at short intervals or even <br />within the same year. The risk of experiencing a rare flood increases <br />when periods greater than 1 year are considered. For example, the risk <br />of having a flood which equals or exceeds the 100-year flood (1 percent <br />chance of annual exceedence) in any 50-year period is approximately 40 <br />perccnt (4 in 10), ~nd, for any 90-year period, the risk increases to <br />~pproxim~tely 60 fercent (6 in 10). The analyses reported herein reflect <br />flooding potentials based on conditions existing in the community at the <br />time of completion of this study. Maps and flood elevations will be <br />amended periodically to reflect future changes. <br /> <br />3..1 Hydrologic l\nalyses <br /> <br />lIyJrolog ic analyses \....ere carr ied out to establish the peak discharge- <br />frequency relationships for each flooding source studied in detail <br />o[fccting the community. <br /> <br />For North Fork Gunnison River, iJeak discharges for floods of the <br />10-, 50-, 100-, and 500-year recurrence intervals were computed by <br />the U.S. Army Corps of Engineers (Reference 8). For the u.s. Army <br />Cor~s of Engineers determination, u regional floodflow-frequency <br />analysis of 9;J.9iu9 station records was made to obtain generalized <br />rr=lali.on5hip3 of the mean, standard deviation and skew coefficients <br />to cJevelol' floc'dflow-frequency rel~tionships. This analysis <br />included a separate determination of rainflood and snowmelt peaks.. <br /> <br />6 <br />
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