Choke-Free Flow in Ovoidal Sewers with Increase in Bed Elevations

The condition of choke-free flow in ovoidal sewers subject to a rise in bed elevation is considered. For a subcritical approach flow with a smooth and gradual transition zone, the maximum limiting rise in bed elevation for ovoidal sewers is determined. Based on a condition of critical flow downstream of the transition zone, the energy and continuity equations are solved numerically to obtain the maximum permissible limits of bed elevation rises and allowable ranges for upstream flow depths. Design graphs are presented for practical use.