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<br />30 <br /> <br />The program then calls a subroutine, for calculation of flow conditions <br /> <br />at the section, which is based upon sectional properties and the <br /> <br />assumption of steady flow. <br /> <br />Discharge Parameters at Section Control <br /> <br />Sectional properties will exert a direct influence upon flow <br /> <br />characteristics in a control section, where the flow in the section <br /> <br />is not influenced by stream geometry in adjacent sections. Flow <br /> <br />characteristics in such a section are determined by cross-sectional <br /> <br />parameters. Such parameters are well defined for measuring devices <br /> <br />such as critical flow flumes and wiers, but they are defined in an <br /> <br />empirical way for natural streams. For example, at established <br /> <br />stream gaging stations, discharge and water surface elevation (stage) <br /> <br />are measured periodically to establish the empirical stage-discharge <br /> <br />relation. The present problem is to describe sufficient cross-sectional <br /> <br />parameters to allow mathematical expression of the empirical stage- <br /> <br />discharge relationship in natural streams. To satisfy this requirement, <br /> <br />the following equation is proposed: <br /> <br /> Q = C ARm (3-1) <br /> s <br />where Q = discharge <br />C section coefficient <br /> s <br /> A hydraulic area <br /> H = depth <br /> m = hydraulic exponent <br />