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<br />, <br /> <br />In order to evaluate the effect of these physical changes upon <br />a streams des i rabil ity for recreation, it is necessary to <br />develop an information base for each recreation activity. <br />Such an information base should identify a relationship <br />between depth and velocity of the water, and the desirability <br />of such water for each recreation activity. The information <br />base, called recreation criteria, has been developed and is <br />set forth in the following pages. <br /> <br />--;':':'. . <br />:;~::::;~~::::: . <br /> <br />3. <br /> <br />Composite Probabil ities-of-Use. Determination of the proba- <br />bility-of-use for an activity on a certain area of water <br />requires multiplying the probability-of-use for the depth by <br />the probabil ity-of-use for the velocity. For example, from <br />Figure 1 the probability-of-use for the depth of 2.6 feet is <br />0.9. The probabil ity-of-use for the velocity of 6 feet per <br />second is 0.24. The composite probability-of-use for a depth <br />of 2.6 feet and a velocity of 6 feet per second, is 0.216 (0.9 <br />x.0.24). Theprobability-of-use is also the weighting factor <br />for calculation of the weighted usable surface area. <br /> <br />" <br /> <br />4. Wei ghted Usab 1 e Surface Area. The wei ghted usab 1 e surface <br />area equates an area of low desirability to an equivalent area <br />of optimal desirability. For example, if 1,000 square feet of <br />surface area had a composite probability-of-use of 0.216 (see <br />above) it would have a weighted usable surface area of 216 <br />square feet (total surface area times compos i te probabil ity- <br />of-use). These 1,000 square feet of surface area would be <br />considered to have the same recreation potential as 216 square <br />feet of surface area having optimum depths and velocities. <br /> <br />An example of a matrix is shown in Table 3. ln each cell of the <br />matrix, the upper number refers to the surface area of a stream having a <br />depth ve 1 ocity combi nat i on as i ndi cated. The numbers in parentheses <br />refer to the weighted usable surface area. <br /> <br />, <br /> <br />-~' <br /> <br />6 <br /> <br />I- <br />i <br />