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cipants would find such a depth usable. Point "D" indicates the pre- <br />ferred or safety maximum and "E" indicates the physical maximum. <br />If the Y axis is changed from a desirability scale to a probability <br />scale, with 1.0 on top and 0 on the bottom, the "probability-of-use" may <br />be read off the Y axis. <br />If Figure 2 represents a probability-of-use curve for an activity <br />in a region where the resource is experiencing capacity use, then the <br />following assumptions can be stated: <br />I. Areas having depths less than "A" or greater than "E" will <br />have no use. <br />2. Areas having depths equal to "C" will be experiencing capacity <br />use. <br />3. Areas having depths equal to "B" and "D" will be experiencing <br />50 percent of the use of area "C." <br />Appendix A sets forth the depth and velocity criteria in tabular <br />and graphic forms and defines depths and velocities in terms of desir- <br />ability as follows: <br />Optimum Depth or velocity usable by all; probability-of- <br />use or weighting, factor 1.0 <br />Acceptable Depth or velocity between safety limit and optimum; <br />probability-of-use.or weighting factor 0.5-0.99 <br />Marginal Depth or velocity between physical and safety <br />limits; probability-of-use or weighting factor <br />0.01-0.49 <br />Unacceptable Depth or velocity unusable; probability-of- <br />use or weighting factor 0.0 <br />Appendix B shows the probability-of-use curves which are developed <br />from the depth and velocity criteria. <br />APPLICATION <br />There are situations where the single cross section method or the <br />incremental method is best suited to do instream flow studies. <br />The single cross section approach is best suited to situations <br />where: <br />12 <br />