7245 - Laserfiche WebLink

Home Browse Search

1. Field Measurements The data collected at the Ouray site consists of seven transects, three sets of water surface elevations with concurrently measured discharges, and one set of velocity distribution measurements. Three of the seven transects represent side channel backwater. A side channel backwater is defined as a secondary channel or fingerlike projection, depending on the flow, commonly occurring behind a sandbar or island. 2. Model Calibration The IFG4 program was used to calculate the stage-discharge relationship for the first transect. The mean error for the three measured versus predicted discharges was 8.2 percent (National Ecology Center, 1987). The stage- discharge equation for the first transect was used to calibrate the water surface profile (WSP) program. During the initial calibration of measured versus predicted water surface elevations using a constant n value, a range of 0.01 to 0.34 of a foot was the best fit achievable (National Ecology Center, 1987). Transect seven consistently had the greatest difference in measured versus predicted water surface elevations. Therefore, since this transect did not cross the side channel backwater and was not critical to the simulation, it was dropped. Supsequent calibration runs resulted in reducing the differences in measured versus predicted water surface elevations to a range of 0.01 to 0.16. A variable Manning's n was plotted and inserted in the WSP calibration input file. The production run for WSP was made for a range of flows from 1000 to 10000 cfs. The WSEI4S program was used to insert water surface elevations into the IFG4 input files on the WSL cards. To simulate the backwater, the input files were split into a low flow and high flow range. From the WSP production run it was determined that the water surface elevation that matched the invert elevation of the upstream inlet (91.42 ft.) occurred at a discharge of 3200 cfs. Therefore, the simulation was split ~t this point. In order to evaluate the side channel habitat, the three stations that cross the side channel backwater were "tagged" by changing the substrate values from 2, 3, and 4 to 12, 13, and 14 and concurrently changing the substrate suitability curve. Thus 12, 13, and 14 were made to have an index value of 1.0, while 2, 3, and 4 were changed to 0.0. Consequently, the habitat would be usable only if the depth and velocity criteria were met. In addition, the n values were increased to 99.9 at these three stations, thus causing the velocities to be 0.0. 35