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Hydraulic Response to Changes in Discharge: The reach selected to evaluate thresholds <br />for coarse sediment transport in the 15 mile reach is located about 2 km downstream of the Corn <br />Lake State Wildlife Area and the highway 141 bridge. The reach is relatively straight (Fig. 20) <br />with a prominent bar along the left (south) side of the main channel (also shown in the cover <br />photo). The majority of the study reach would be characterized as run habitat; there is a short <br />section of riffle habitat in the middle of the reach, and a relatively deep pool at the lower end of <br />the reach (Fig. 20). A secondary channel/backwater occurs along the south bank. The average <br />bankfull channel width is 127 in and the average gradient is 0.0020 m/m. <br />Water-surface elevations were surveyed through the study reach at eight different <br />discharges ranging from 37 to 396 m3/s. These measurements were used with data from the <br />cross sections surveys to determine changes in wetted area of the channel and to calibrate the <br />roughness coefficient in the gradually varied flow model. Table 4 summarizes some of the basic <br />data from measurements at various discharges. <br />Figure 20. Delineation of in-channel habitats within the RM 176 study reach. <br />45