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PROBABILITY-OF-USE CURVES <br />All of the curves constructed by IFG have been developed from <br />information available in the literature and when available with, ex- <br />tensive utilization of unpublished data from agency files. Two basic <br />types of information were used in the construction of these curves; that <br />derived from field observations with directly measured hydraulic param- <br />eters, and that derived from descriptions of fish distribution with <br />general descriptions of-the habitat, and with hydraulic parameters <br />calculated from the stream description. Methods of analysis of this <br />information varied according to the format in which the information was <br />presented. <br />CURVE UNITS <br />All curves are in English units, except the substrate curves. <br />Depths are given in feet, velocities in feet per second, and tempera- <br />tures in degrees Farenheit. <br />Substrates were categorized by a modified Wentworth particle size <br />scale, when possible (Table 2). In most cases, the field data contained <br />only a descriptor of the bottom type (i.e., gravel, rubble, etc.) rather <br />than a size range. These substrate types were coded as shown in Table 1. <br />Table 1. Substrate Codes Used for Curve Construction. <br />1 Plant detritus <br />2 Mud <br />3 Silt <br />4 Sand <br />5 Gravel <br />6 Rubble <br />7 Boulder <br />8 Bedrock <br />Notice that a mixture of two different (but adjacent) substrate <br />types may be described by this code. <br />For example, a numeric code value of 5.5 refers to a bottom which <br />is composed of a 50:50 mixture of gravel and rubble. A value of 4.2 <br />would refer to a substrate which is 80% sand and 20% gravel, whereas <br />4 <br />