9493 - Laserfiche WebLink

Home Browse Search

FINAL REPORT, November 2003 High-flow Requirements for the Duchesne River points representing control point locations for each scene, then linking the actual control point locations to their proper specified coordinates and moving them to their proper coordinates with Arc/Info's "adjust" command. This command causes the program to apply a polynomial interpolation based on the displacement specified for the control points to reposition all features in the coverage. This procedure has the potential to significantly reduce the reported RMS error associated with distortion of the original photographs. However, we have no basis to determine the final positional accuracy of the rubber-sheeted coverage. In the case ofthe 1948 coverage, we conservatively estimate that it reduced the initial RMS error by 50 percent. This coverage then has an estimated RMS error of approximately 17 m. Portions of cadastral survey maps from 1875 and 1882 were also digitized using intersections of section lines as control points. The resulting coverage shows the approximate river bank location in the late 19th century. Analvsis of Geographic Data The study area was divided into 19 subreaches between 0.5 - 2.7 kIn in length, measured down the valley axis (Figure 2). These subreaches were established to facilitate the analysis and reporting of longitudinal patterns of channel form and adjustment. Subreach boundaries were drawn normal to the channel to the extent permitted by temporal changes in channel configuration. Metrics of channel change were obtained for each subreach, and areas of similar channel behavior were identified. Subreach metrics include subreach channel width, areas of erosion and deposition, volumes of gravel erosion and deposition, and changes in gravel storage. Channel Width Two width metrics were defmed for each subreach: low-flow channel width and floodway channel width. The low-flow channel was defined as the region comprised of the water surface and low bars. Dividing the area of this region within a subreach by the channel length within the subreach yielded the average low-flow channel width for the subreach. The floodway channel was defined as the low-flow channel plus adjacent high bars, i.e., it is the near- channel area that is essentially free of vegetation. Width of the floodway channel was computed by dividing the area of water plus both high and low bars within each subreach by the channel length within the subreach. The channel length used in these computations was measured along the centerline of the floodway channel for each photo series analyzed, and varied from year to year with changes in channel pattern. The area of a 10-km-long secondary channel that was 15