Backwater Curves in Circular Channels

Abstract

Backwater curves in circular sewers and drainage conduits are considered by an explicit approach. The new method is based on simple expressions for uniform and critical flows, and a transformation of the longitudinal coordinate by which the effect of relative uniform flow depth may be incorporated. As a result, the method presented allows the explicit determination of any backwater effect. This is of engineering concern, particularly in large sewer systems where the computational effort may now considerably be reduced. The degree of approximation is analyzed and it is found that the present solution may satisfy the demands in practice. Further, the solution is discussed and referred to the well‐known Bresse and Chow classifications. Considerations regarding basic lengths of backwater curves are presented, including the maximum extension of M‐ and S‐curves. Finally, a computational example illustrates the application of the results, to a grade break involving the transition from sub‐ to supercritical flow.