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<br />As the project will not be operational within 12 months of completion <br />of this study, the dam was not considered in this study. <br /> <br />Improvements such as dikes and bank protection have been made <br />at various locations along the river upstream of Olathe. Significant <br />flood protection from the 100- and SOO-year floods is provided <br />by several irrigation canals that branch off from the river at <br />different locations upstream of the study area. These canals <br />are part of the Uncompahgre Project, which was completed in 1931. <br />This project included many diversion dams and canals, as well <br />as the Gunnison Tunnel and the Taylor Park Dam (Reference 6). <br /> <br />Concurrent with periods of snowmelt runoff, maximum allowable <br />flow (all gates open) is usually in effect for the irrigation <br />canals in order to meet the requirements of agricultural areas. <br />During periods of excessively high flows on Uncompahgre River, <br />transbasin diversions from Gunnison River to the Uncompahgre River <br />valley are reduced to alleviate flood conditions. <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 50 a-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 SOO-year floods, have ala, 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 1 year are considered. For example, <br />the risk of having a flood which equals or exceeds the lOa-year flood <br />(1 percent chance of annual occurrence) in any 50-year period is approxi- <br />mately 40 percent (4 in 10), and, for any gO-year period, the risk in- <br />creases to approximately 60 percent (6 in 10). The analyses reported <br />here reflect flooding potentials based on conditions existing in the <br />community at the time of completion of this study. Maps and flood eleva- <br />tions will be amended periodically to reflect future changes. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish the peak discharge- <br />frequency relationships for floods of the selected recurrence <br />intervals for each flooding source studied in detail affecting <br />the communi ty. <br /> <br />9 <br />