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Cross-sectional area (A) - the area of the cross section containing <br />water, normal to the direction of flow. <br />Computed as width X mean depth of cross <br />section. <br />Wetted perimeter (P) - the distance along the bottom and sides of <br />a channel cross section, in contact with <br />water. Roughly equal to the width + 2 times <br />the mean depth. <br />Hydraulic radius (R) - the ratio of the cross sectional area to <br />the wetted perimeter, R = A/P. For wide <br />shallow channels, R approximates the <br />hydraulic depth. <br />Hydraulic slope (S-h) the change in elevation of the water surface <br />between two cross sections, divided by the <br />distance between the cross sections. <br />Bottom slope (So) - the change in the average elevations of the bed <br />between two cross sections, divided by the <br />distance between them. <br />Thalweg slope - the change in the elevation of the bed, measured <br />at the point of maximum depth (y), divided by the <br />distance between cross sections. <br />Energy slope (Se) - change in total energy (potential and kinetic) <br />.available, divided. by the distance between <br />cross sections. See discussion of Bernoulli's <br />equation in the next section. <br />Channel roughness (n) - a coefficient of resistance to flow <br />caused by particle friction and <br />channel features. <br />Uniform Flow and Varied Flow - Uniform Flow by definition means <br />that the depth of low is the same at every <br />section of the channel. Thus, the hydraulic, <br />energy, and bottom slopes are parallel. If the <br />flow is varied, the depth of flow changes along <br />the length of the channel. Varied flow is <br />classified as either rapidly or gradually <br />varied, depending on the distance within which <br />the change in depth occurs. Rapidly varied flow <br />is manifest- in an abrupt change in depth, result <br />i ng in hydraulic jumps, hydraulic drops, and <br />related phenomena. The criterion for uniform or <br />varied flow is change in depth with respect to <br />space. <br />Steady flow and Unsteady Flow - Flow in an open channel is said to <br />be steady if the depth of flow does not change or <br />can be assumed constant over a specified time <br />interval. The flow is unsteady if.the depth <br />changes with time. <br />Sub-critical, Critical, and Supercritical Flow - In any body of <br />moving water both inertial and gravity forces are <br />acting on the water body. The effect of gravity <br />