8251 - Laserfiche WebLink

Home Browse Search

Draft Final Completion Report to UDWR for Contract #93-1070. Amendment 3 27 Enumeration of Bars The long-term behavior of the channel and bars were noted from the GIS maps. For summarizing the overall behavior of bars, each bar was classified as a mid-channel bar. or as a point or bank-attached compound bar. While some discharges may dissect bank-attached compound bars, only a small portion of the flow was carried by chute channels at discharges that do not overtop the bars. GIS Statistics Statistics were generated from each GIS coverage in order to determine total area of each classified polygon and the total length of perimeter enclosing each polygon classification for each sampling date. As shown below, the contacts between geomorphic units were surrogates for topographic elevation contours. The different pseudo- topographic geomorphic units are used to simulate the river condition for those discharges greater than the one flow that occurred at the particular time of each photo. Areas and perimeters were calculated for each pseudo-topographic elevation by melding all lower "elevation" polygons into a singie polygon. then calculating the resulting polygon's area and perimeter. ihe latter calculation indicates how the topographic complexity of each bar, indicated by the area and shoreline of each pseudo-topographic elevation. changed during summer low flow and from year-to-year. It was possible to examine the following questions from the GIS statistics: (1) Was a greater portion of the channel occupied by an equivalent discharge in 1992 than 19931; and (2) Did the area of high elevation white sand increase with the passage of the 1993 flood? We also assessed the possibility of using a remotely sensed metric to predict the area of available habitat. The "shoreline development" index of Wetzel (1983) was employed as a complexity index. This index was used to compare the length of the shoreline to the area of water and indicate the degree of convolutedness of the shoreline edge (Fig. 13). While developed for lake and reservoir systems, this type of index was appropriate for discerning shoreline convolutedness for this alluvial system. Rivers are linear systems, so the length of the reach greatly influences this calculated complexity index. If reaches of river of different lengths are compared, normalization must be applied to this non-dimensional complexity index. Comparison of indices for reaches of the same length of similar width or comparison of changes to a single reach. such as the 10-km study reach. over time required no normalization. ~