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<br />RMA2 begins with the assumption of a universally flat water surface elevation. Using <br /> <br />revision cards and hotstart files, a simulation can be stepped down to reflect real world <br /> <br />conditions. As the simulation is stepped down, the previous solution is used to provide initial <br /> <br />guesses to the next solution. If the simulation is stepped down too quickly, the solution is <br /> <br />likely to diverge and the model will crash. The time needed for a given step is dependent on a <br /> <br />number of factors including the size of the mesh, the speed of the computer, and the relative <br /> <br />change in flow characteristics in each step. With a PIIISOO processor and 256MB of Ram, <br /> <br />each iteration in a model with 20,000 elements can take up to 3 minutes to process assuming <br /> <br />nothing else is running on the computer. A total of 1,000 successful iterations may be <br /> <br />required to step the model down to a real world condition. During this process, it may <br /> <br />become obvious that the mesh has to be refined in someway. If the mesh is altered in any <br /> <br />significant way, hotstart files cannot be used and the step down process must be started again <br /> <br />using a flat water surface elevation. <br /> <br />HABITAT A V AILABILITY <br />On September IS, 1999, at a flow of 287 cfs, aerial photographs were flown at a scale <br /> <br />of 1"=600'. The aerial photography included the survey site and the representative reach <br /> <br />section described for the fish sampling. Aerial photos were qualitatively used to compare <br /> <br />habitat availability in the surveyed study sites to longer sections of the river. The images of <br /> <br />the sites were rectified using ground control points and the Imagine software package. These <br /> <br />images were then registered in the Surface Modeling Software (SMS) and were used for <br /> <br />reference in creating the finite element mesh. Aerial photography for the IS-Mile Reach <br /> <br />were purchased from Mesa County. The county rectified the photo with highly precise UTM <br /> <br />coordinates. The IS-Mile Reach photographs were taken on September 30 and October I, <br />1997 at a flow of3000 cfs. <br /> <br />26 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />IhI <br />I <br />I <br />I <br />I <br />