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<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 /> <br />3.5 <br /> <br />SUPERELEY A TION ANALYSIS <br /> <br />Often, water surface elevation differences (superelevation) are seen across cross-sections. This <br />effect is primarily due to the wide variation of velocities and momentum between the channel <br />banks. The result is a higher water surface elevation at the outside bank. In the case of the Elk <br />River, it was anticipated that Section 5 could experience superelevation due to the sharp <br />meander bend seen at this location. Superelevation at Cross-section 5 was computed using the <br />100-year discharge of 5,365 cfs, based on the following equation (from the FHW A Hydraulic <br />Engineering Circular, No. 20): <br /> <br />!iZ = (ro-ri) y2jgrc <br /> <br />Where: <br /> <br />!iZ = the difference in water surface elevation between banks; feet <br />Y = the average velocity; feet/second <br />ro = radius of the outside bank; feet <br />rj = radius of the inside bank; feet <br />rc = radius of the center of the stream; feet <br />g = acceleration of gravity; 32.2 feet/second <br /> <br />Based on this equation, the resulting water surface elevation of the west bank would be <br />approximately 1.9 feet higher than the water surface elevation of the east bank for the 100-year <br />discharge. The impact of the superelevation on the overall flood depth would be fairly <br />localized. There may also be locations along the bend where flow would exceed the channel <br />bank before the additional 1.9 feet of depth due to superelevation would be reached. A copy of <br />these calculations is provided in Appendix F. <br /> <br />22 <br />