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Weighting factors. (ref. Fig. 3) for the depth and velocity ranges used in the matrix are enclosed in brackets. The upper numerals in the matrix refer to the surface area of the stream per 500 feet of reach which possesses that combination of depth and velocity (ref. Table 1), while the numerals in parenthesis refer to the equivalency in weighted usable area (WUA. = C,A,). 1 1 1 Note that in this example the total surface area per 500 feet of reach (2913 ft2), has been equated to 381 ft2 of surface area possessing most suitable depth-velocity conditions, Using the IFG's hydraulic simulation models, one can readily generate velocity depth matricies for unobserved streamflow rates passing through the study site, With these new velocity-depth values at hand, the compilation procedure is repeated to obtain weighted usable area values for the stream- flows being simulated. As a result, weighted usable area can be displayed as a function of streamflow for each life history stage of the target species (Fig. 4). Given the necessary streamflow records, weighted usable area may be presented as a function of mean monthly flow rates, Such a display facilitates comparison of changes in habitat potential between average and drought year conditions (Fig. 5), or demonstrating impacts of streamflow withdrawal (diversion) on a selected life history phase (Fig, 6).- For purposes'of project planning, one may find it desirable to compare weighted usable area fluctuations under pre and post project conditions, Figure 7 presents such a time series comparison of anticipated trends and fluctuations in weighted usable area. In this example, weighted usable area values attributable to September streamflow conditions are compared. However, weighted usable area values for any critical period could serve as a basis for such a comparison, 38