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g) Velocity: Linear distance water moves per second. Curve Break Analysis Curve breaks are defined as the rate of greatest change in a variable with declining flow and were determined for all seven variables from all selected cross sections. Rate of maximum change was calculated by fitting a line to the x and y coordinates (Figure 3.2) and selecting the largest regression residual (the largest difference between the curve and the line). Curve breaks were calculated by mesohabitat type (runs, riffles, and pools) in all strata. To prevent over-representation of any given riffle among clusters, a single cross section was selected from riffles where more than one cross section was measured. Typically the cross section selected was the widest or shallowest part of the riffle measured. For each riffle cross section, the values for each of the seven variables were plotted against a range of flows from 1 to 300 cfs. The maximum range of 300 cfs was selected because it represents the median flow during the baseflow period for the period of record. Figure 3.2. Example of curve break flow (i.e., approximately 80 cfs) representing the point at which flows decline at the greatest rate relative to the decrease in a given stream profile variable (i.e., wetted width). In most cases there were multiple cross sections for each run. In general, cross sections through run mesohabitats were placed above the riffle/run transition (tail), at the narrowest and at the widest part of the run. This placement was used to represent different habitat qualities of each run. For example, the tail of a run may have characteristics more similar to riffles while the upper reach may have characteristics more similar to pools. Typically, only one pool cross section was surveyed per cluster. 43