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<br />272 Y.K. CONVERSE ET AL. <br />Table III. Number of electrofishing samples among reaches and shoreline types <br />Reach Shoreline type Total <br /> Bedrock Cobble Debris fan Sand Talus Vegetation <br />I 69 21 92 36 164 63 445 <br />2 27 15 20 7 49 56 174 <br />3 2 2 5 4 12 20 45 <br />Combined 98 38 II7 47 225 139 664 <br /> <br />To account for changes in habitat condition and habitat use with discharge, we used discharge data <br />from two USGS gauge stations. For analysis of physical habitat changes within the study area, discharge <br />data from the gauge station located above the confluence of the LCR were used (station number <br />93831(0). The discharge at this station most closely reflected the actual discharge within the study area at <br />the time of data collection. <br />For analysis of long-term changes in the overall flow regime, data from the gauge station located at <br />Lee's Ferry was used (station number 9380000), because this station maintained the longest period of <br />record. We used the latter data to derive flow duration curves (see Data collection) for pre- and post-dam <br />periods of the Colorado River in Grand Canyon, which allowed us to compare differences in the flow <br />regime since construction of Glen Canyon Dam. <br /> <br />Data collection <br />Geomorphic reaches. To quantify differences in reach geomorphology, the total length of each of the <br />shoreline types and surficial riffle area along the entire 24-km study area was mapped and the mean <br />width-to-depth ratios of each reach was calculated. Surficial riffle area was defined as a relatively shallow <br />area that was characteristically broken or rippled by fast water moving over underlying cobble but that <br />lacked standing waves. The total available shoreline of each type was mapped on mylar overlays of <br />1 :24000 scale aerial photographs. The percentage riffle area in reaches was then mapped and shoreline <br />mapping was verified in the field. The channel transect data of Schmidt and Graf (1990) taken at arbitrary <br />cross sections throughout the study area were used to derive an average width-to-depth ratio for the three <br />geomorphic reaches. <br />Shoreline longitudinal transects. Three habitat variables along 100 m lengths within different shoreline <br />types were quantified. We refer to one set of measurements as a longitudinal transect. At each lO-m <br />interval along a transect, water depth and water velocity were measured (at 0.6 of depth) and the presence <br />of cover types was recorded. We assumed that shoreline structure most strongly influenced channel <br />hydraulic conditions within 2.5 m of the shoreline and, therefore, measured depth, velocity and cover at <br />three distances from shore: 0.5, 1.5 and 2.5 m. The presence of three cover types was recorded: lateral (L), <br />instream (I) and overhead (0) (Table IV). Cover was based on lateral, emergent or overhead shelter from <br />hydraulic or visual exposure. We tallied the presence of each cover type at each point, and then <br />summarized the frequency of cover for each longitudinal transect. Each longitudinal transect comprised <br /> <br />Table IV. Definition of cover types <br /> <br />Cover type Definition <br /> <br />Lateral Any laterally emerging in stream structure that obstructs flow and provides shelter from the main <br />current above, below or beside it <br />Instream Any instream structure emerging vertically from the river bottom that obstructs flow and provides <br />shelter from the current in its wake <br />Overhead Any structure from the shore that hangs above the water in the channel margins <br /> <br />.f) 1998 John Wiley & Sons, Ltd. <br /> <br />Re~ul. Rivers: Res. M~mt. 14: 267-284 (1998) <br />