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(Fig. 7). The cans were filled with clean gravel > 32 mm in size. At various times after the peak <br />in the annual hydrograph the cans were retrieved, emptied of fine sediment, and replaced. <br />Conditions limited us from retrieving cans in flows more than -0.5 m deep. Samples taken from <br />the traps were subsequently sieved at 1/2 phi intervals. <br />A <br />B <br />Figure 7. Traps used to monitor the movement of sand. Photo on the left (a) shows a trap prior <br />to runoff; photo on right (b) shows the same trap after runoff. Ruler is 15 cm in length. <br />Cobble and Gravel: Estimates of discharges required to mobilize cobble- and gravel-sized <br />sediment were made by coupling several equations for flow and sediment transport, calibrated <br />with the aid of field data from the study reach near RM 176. Spot measurements of water- <br />surface elevations were made at each of the cross sections in the study reach at eight different <br />discharges ranging from 37 to 394 m3/s. The water-surface measurements were used with cross <br />section data to calibrate a one-dimensional hydraulic model to determine variations in flow <br />properties, including channel roughness (Manning's n), mean velocity, U, and average boundary <br />shear stress, z. Other measures of flow conditions, such as wetted perimeter, P, and water <br />surface area, AS, were obtained as part of this process. <br />17