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<br />002242 <br /> <br />( <br /> <br />The next step was to route the flood event along the <br />river channel between confluence locations. A professionally <br />accepted computer model (the DWOPER model) was used to route <br />the unsteady state (dynamically changing) flow levels. The <br />results were verified using the ~ureau of Reclamation's <br />steady state model (PSUEDO) which has a long history of use <br />for lower Colorado River stage modeling. <br /> <br />'During 19B3, several areas along the river experienced <br />flows in the 35,000 to 40,000 cfs range. The water surface <br />levels predicted by the flood routing model compared <br />favorably with real time data collected during the recent <br />high flow periods. <br /> <br />RECOMMENDATION <br /> <br />The Task Force recommends the adoption of the processes <br />defined in the previously referenced Methodology report to <br />determine the duration of the one-in-one hundred year river <br />flow and the river water surface levels. <br /> <br />V. ISSUE <br /> <br />( Define the Floodway boundaries. <br />DISCUSSION <br /> <br />The Floodway boundary is that area necessary to safely <br />convey the determined flood event in that specific section of <br />the river. The flood routing process discussed in Issue IV <br />identified a maximum water surface elevation for a given <br />location along the river. Real life experience and the <br />identification of these water surface levels on maps of the <br />river channel confirmed that these flow rates were, in most <br />areas, confined to the existing well defined river channel. <br />In some locations, areas outside of the river channel would <br />be flooded at relatively shallow depths but would contribute <br />very little to the capability of the river channel to carry <br />the flow. <br /> <br />It is human nature to use these areas lying near a <br />flowing river. To provide better opportunity to manage these <br />areas in the future, the Technical Subcommittee decided to <br />determine the effect on the water surface level if it was <br />assumed that these "overflow" areas (Colorado River Floodway <br />Fringe) were filled or otherwise prevented from flooding. <br />Further model studies assuming no overbank flow resulted in <br />water surface levels less than 1 foot greater than the <br />initial studies. At the October 25, 19BB meeting of the full <br /> <br />l <br /> <br />V-5 <br />