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<br />Lesson 2 <br /> <br />Basic Hydraulics - Participant Workbook <br /> <br />If the typical cross-section is improperly subdivided, a discontinuity <br />(known as a switchback) in the stage-discharge curve may appear. A <br />switchback can occur. <br /> <br />In a switchback, the discharge appears to decrease with an associated <br />increase in elevation. With a minor increase in water depth, there is a <br />large increase of wetted perimeter. Simultaneously, there is a small <br />increase in cross-sectional area This results in a net decrease in the <br />hydraulic radius. The combination of the lower hydraulic radius and <br />the slightly larger cross-sectional area, may cause a discontinuity in <br />the discharge or conveyance. <br /> <br />. More subdivisions within the cross-sections should be used in order <br />to avoid this discontinuity. <br />. The cross-section usually should be subdivided with respect to both <br />vegetation and geometric changes. <br /> <br />2.10. WATER SURFACE PROFILES <br /> <br />STREAM BACKWATER PROFILE <br /> <br /> <br />2.33 Stream Backwater Profile <br /> <br />A. When a uniform flow assumption and the application of Manning's equation is <br />not appropriate, the gradually varied flow water suriace profile must be <br />calculated. <br /> <br />B. A gradually varied water suriace profile can be estimated by the standard <br />step-backwater method of channel analysis. Gradually varied flow is a type of <br />non-uniform flow in which the area of the stream cross-section changes so <br />slowly that the energy losses can be computed for various reaches in the <br />same manner as for uniform flow. Therefore, apply the step-backwater <br />method when uniform flow cannot be assumed. <br /> <br />2.20 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />