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<br />cannot be balanced. A water surface elevation equal to the elevation <br />which came closest to balancing (plus 0.1 ft.) will be adopted. It is then <br />up to the program user to determine the appropriateness of the assumed water <br />surface elevation and start the computation over again at that cross section <br />if required. <br /> <br />(2) It is important for the user to study carefully the flow pattern <br />of the river where levees exist. If. for example, a levee were open at both <br />ends and flow passed behind the levee without overtopping it, IEARA equals <br />o or blank should be used. Also, assumptions regarding effective flow areas <br />. may change with changes in flow magnitude. Where cross section elevations <br />i outside the levee are considerably lower than the channel bottom, it may be <br />necessary to set IEARA equal to 10 to confine the flow to the channel. <br /> <br />m. Interpolated Cross Sections. Sometimes it is necessary to insert <br />cross sections between those specified on the GR cards because the change <br />in velocity heads between cross sections is too great to accurately determine <br />the hydraulic gradient. Variable HVINS on card Jl is used to specify when <br />interpolated cross sections should be used. This variable specifies the <br />maximum change in velocity head allowed between cross sections. If this <br />value is exceeded, up to three interpolated cross sections will be generated <br />between given cross sections (depending on the magnitude of 6HV/HVINS - 1). <br />If HVINS is left blank or equal to zero, the computer will suppress, interpolated <br />cross sections. Interpolated cross sections should be ommitted when computing <br />several profiles on the same stream in order to use exactly the same cross <br />sections. Interpolated cross sections are identified on the output by section <br />numbers of 1.01, 1.02, and 1.03. <br /> <br />n. Distance Between Cross Sections. It was pointed out previously that <br />the cross section number, SENCO on card Xl, is used for identification purposes <br />only. The actual distance between cross sections used in the computation is <br />specified on card Xl as variables XLOBL, XLOBR and XLCH for the left overbank, <br />right overbank. and channel, respectively. Normally these three values will <br />be equal. There are, however, conditions where they will differ, such as at <br />river bends, or where the channel meanders considerably and the overbanks <br />are straight. Where the distance between corss sections for channel and over- <br />banks are different, a discharge~eighted reach length is determined based on <br />the discharges in the main channel and left and right overbank segments of the <br />reach. The discharge used for each segment is an arithmetic average of the <br />discharges determined for that segment at cross sections at each end of the <br />reach. <br /> <br />o. Transition Losses. Expansion or contraction of flow due to changes <br />in the channel cr~ss section is a common cause of energy losses within a <br />reach. Whenever this oecurs, the loss may be computed by specifying on card NC <br />the expansion and contraction coefficients as variables CEHV and CCHV respective- <br />ly. The coefficients 'are multiplied by the absolute difference in velocity heads <br /> <br />7 <br />