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<br />protecting benthic macro invertebrates. For a discussion of effects of the sediment release <br /> <br />on benthic macroinvertebrates see reports by R. Zuellig, B. Kondratieft~ and H. Rhodes. <br /> <br />Methods <br /> <br /> <br />Channel surveys were conducted along the study reach in October 1996, March <br /> <br /> <br />1997 after the experimental discharge, and again in September 1997 after snowmelt <br /> <br /> <br />runoff had receded. During all surveys, channel cross sections were surveyed and the <br /> <br /> <br />thickness of sediment accumulation was determined by probing with a steel rod down to <br /> <br /> <br />the original cobble or boulder channel bed. Repeat surveys were compared to determine <br /> <br /> <br />the amount of scour and fill occurring between field outings. Grab samples were <br /> <br /> <br />collected of sediments within marginal bars of the riffles and within the pools for grain <br /> <br /> <br />size analysis, <br /> <br /> <br />A sampling cross section was also established in a riffle at Cross Section 17 <br /> <br /> <br />(Figure I). From 22 February to 3 September 1997 the cross section was sampled <br /> <br /> <br />weekly, During the sno\\iTIlelt peak (May to June) the sampling frequency was increased <br /> <br />to twice a week, Flow depth and velocity were measured, and suspended and bedload <br /> <br /> <br />samples were collected at distinct intervals along the cross section. These data served as <br /> <br /> <br />input for the sediment transport models; specifically. sediment and water rating curves, <br /> <br /> <br />bed material gradation. and starting water surface elevations. <br /> <br />Sediment Transport Modeling <br /> <br /> <br />One-dimensional sediment transport models are computer programs that simulate <br /> <br /> <br />the hydraulics of\\<1ta flow and sediment movement in rivers, Sediment transport <br /> <br /> <br />models have been developed solely for alluvial rivers. or those with channel bed and <br /> <br /> <br />banks composed of erodible material. Within the last decade, sediment transport models <br /> <br /> <br />have been gaining popularity outside engineering circles, and are recognized as useful <br /> <br /> <br />predictive tools to assess channel recovery after a variety of perturbations, and to evaluate <br /> <br /> <br />magnitude and duration of flows that might effectively flush sediments through a channel <br /> <br />system. particularly where critical aquatic habitat has been affected (Wick, 1997). <br /> <br /> <br />For this project. sediment transport models HEC-6 and GSTARS 2.0 were <br /> <br />selected to simulate scour and deposition within pools. The criteria used to evaluate the <br /> <br />6 <br />