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<br />Estates Subdivision and damage to the piers of the Plateau Road <br />Bridge. The damage to the bridge was severe enough that the struc- <br />ture was removed by county crews in 1979 to avoid a complete failure. <br />Figure 2 taken on June 5, 1979 long after the peak flow on the <br />North Fork Gunnison River shows the bridge area and to the left <br />a home in the Riverside Estates Subdivision threatened by the <br />flood waters. <br /> <br />Recent documentation of flood damage on Minnesota Creek is unavail- <br />able. However, it was observed that the potential for flood damage <br />from the 100-year flood and greater is primarily to undeveloped <br />land and is caused by several undersized stream crossings. <br /> <br />2.4 Flood Protection Measures <br /> <br />With the exception of entensive rip-rapping on the North Fork <br />Gunnison River channel banks, especially in the vicinity of the <br />Riverside Estates Subdivision, no flood protection measures are <br />in existence in the Town of Paonia. Numerous water storage and <br />irrigation ponds are located in the Minnesota Creek watershed <br />upstream of paonia. These ponds significantly affect normal flow <br />on Minnesota Creek; however, during periods of major flooding <br />will not significantly reduce the peak flood flows. <br /> <br />On the North Fork Gunnison River, the Paonia Reservoir located <br />approximately 15 miles upstream of Paonia has been regulating <br />flood flows since 1961. The reservoir, constructed by the Power <br />and Water Resources Services (formerly Bureau of Reclamation) <br />contains 21,000 acre-feet of storage capacity and reduces the <br />10-, 50-, and laO-year flood flows at the Somerset stream gage <br />No. 1325 by approximately 17, 13 and 6 percent, respectively. <br />No protection is afforded for the 500-year flood (Reference 6). <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 equalled or exceeded once on the average during any <br />10-, 50-, 100-, or 500-year period (recurrence interval) have been selected <br />as having special significance for flood plain management and for flood <br />insurance premium rates. These events, commonly termed the 10-, 50-, <br />100-, and 500-year floods, have a 10, 2, 1, and 0.2 percent chance, <br />respectively, of being equalled or exceeded during any year. Although <br />the recurrence interval represents the long term average period between <br />floods of a specific magnitude, rare floods could occur at short intervals <br />or even within the same year. The risk of experiencing a rare flood <br />increases when periods greater than I year are considered. For example, <br />the risk of having a flood which equals or exceeds the 100-year flood <br />(1 percent chance of annual occurrence) in any 50-year period is approxi- <br /> <br />6 <br />