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Figure 6. Diagram showing the method used in converting historic Platt map channel widths to <br />widths perpendicular to the channel. Procedure: 1. Center line down the channel was drawn. <br />2. A line perpendicular to the center line was drawn from one corner where the section line crossed <br />the channel to the opposite bank to form a right triangle (b). 3. The bank of the river, opposite that <br />corner is considered parallel to the center line (a). 4. The length of c is known from the survey <br />notes. 5. Angle B is measured. 6. The formula c sin B • b is used to determine the perpendicular <br />width of the channel, which is b. <br />Figure 7. Representation of across-section of the Duchesne River identifying the <br />geomorphic surfaces measured in 1995 field width measurements. <br />20 <br />Low elevation inner banks <br />