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.• <br /> <br />edge of reeds, and riparian vegetation nearest water's edge. Where the vegetation was <br />not present, a ridge of newly-deposited sediment that created a break in slope was <br />identified as the low elevation inner bank. The high flood debris was identified by a drift <br />line along the bank or by a small scarp that was created from high flow events. The top <br />of high bank was the top of obvious cut banks or the edge of corresponding surfaces <br />covered with saltcedar, russian olive, and cottonwood trees. <br />Field measurements were made in October and November 1995. In many cases, <br />channel change has been so great that channel widths could not be precisely repeated. <br />Present-day measurements were made by extending the section lines from the historic <br />platt maps through the present-day channel. Measurements were made where the <br />channel crossed the same quarter-section line as the original measurements in a <br />straight channel reach or inflection point between two bends nearest the point <br />intersecting the original surveyed line. At each cross-section, width measurements of <br />each geomorphic surface were made with a tape measure perpendicular to the channel. <br />Present-day width measurements of each surface were compared to historic widths. <br />Field surveys were made at two Geological Survey gaging stations to determine <br />the recurrence of inundation of the four geomorphic surfaces. In December 1995, a <br />longitudinal profile up and downstream from each gage was developed from surveys using <br />a theodolite. Elevations were related to a fixed datum. The slope of each geomorphic <br />surface (water surface width, low elevation inner bank, high flood debris, and top of <br />high bank) was estimated by linear least squares regression and the point where each <br />line intersected the gaging station rating relation was determined. The corresponding <br />discharge was determined from the rating relation. The frequency of inundation of each <br />geomorphic surface was then determined using the annual flood series recurrence data. <br />21 <br />