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<br />Substrate and temperature may also be incorporated into this analysis <br /> <br />following similar procedures. If the temperature associated with the above <br /> <br />combination of depth and velocity were 750 F, it would have a weighting factor <br /> <br />of 1.0; were the substrate sand, the numeric index would be 4 and its <br /> <br />associated weighting factor 0.80. The composite weighting for that combina- <br /> <br />tion of depth, velocity, temperature, and substrate would be (0.37 x 0.80 x <br /> <br />1.0 x 0,80) or 0.24, <br /> <br />Weighted usable area lS defined as the total surface area having a <br /> <br />certain combination of hydraulic conditions, multiplied by the composite <br /> <br />weighting factor for that combination of conditions. This calculation is <br /> <br />applied to each cell within the multidimensional matrix and is then summed, <br /> <br />This habitat index in its simplest form is described in equation 1. <br /> <br />n <br />WUA = L <br />i=l <br /> <br />C.A. <br />1 1 <br /> <br />(1) <br /> <br />where: <br /> <br />WUA = weighted usable area <br /> <br />Ci = composite weighting factor for usability <br /> <br />A, = surface area of a cell <br />1 <br />n = total number of cells within the simulated stream reach. <br /> <br />This procedute roughly equates the total surface area of the simulated <br /> <br />reach to an equivalent area of optimal (preferred) habitat. For example, if <br /> <br />1,000 square feet of surface area had the aforementioned combination of depth, <br /> <br />velocity, temperature, and substrate it would have the approximate habitat <br /> <br />value of 240 square feet of optimum habitat (1000 ft2 x 0.24). <br /> <br />An example of a two-dimensional matrix (depth and velocity) is presented <br /> <br />~ <br /> <br />ln Table 2, <br /> <br />36 <br />