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with fence posts or rebar that also serve as local elevation control points. Measurements <br />were made by fixing a steel or kevlar tag line between the endpoints and measuring depth at <br />3.05-m intervals. The echo-sounding transducer was mounted on a pole attached to a raft; <br />boat position was held under the tagline by the boat operator using oars or an outboard <br />motor. The echo sounder was operated by a second person on the boat who labeled tag- <br />line marks on the paper trace. Accuracy was evaluated by repeating measurements with the <br />total station for those points where water depth was less than 1.5 m. The standard <br />deviation of the 4 passes was calculated and was typically less than the thickness of the line <br />used to plot the bed profile. Large errors in measured depth occurred only where depth <br />changed rapidly or where bed material was primarily large rocks and boulders. Water- <br />surface elevations were surveyed at the time of each cross-section measurement and again <br />during a mapping trip in July 1996. Characteristics such as bed and bank material, high- <br />water marks, and locations of distinct geomorphic surfaces were noted and surveyed at <br />each site. The precise location of each cross section was recorded on aerial photographs <br />(1:5000 scale) and topographic maps. The coordinate survey data were reduced into <br />distances and elevations relative to the reference pins. The discharge at the time of <br />measurement was determined from records for the U.S. Geological Survey stream gaging <br />station at Green River, Utah (station number 09315000). <br />Cross sections were established on or as near as feasible to river mile markers as <br />located by Belknap (1994), so as to create a systematic sample of channel types and bed <br />materials. Waves in rapids cause many difficulties in measuring the bed, and cross <br />sections were generally not surveyed in rapids. Cross sections were established in small <br />riffles, zones of strong downstream flow, pools and recirculating eddies. <br />Mapping <br />Surficial geology of the river corridor was mapped in each of the four study reaches <br />to establish the distribution of geomorphic features and determine the composition of bank