Backwater Curves

Abstract

The transition curves of a nearly uniform flowstate or, in general, the free surface profiles in open channels are designated backwater curves. They provide, for steady flow, the most general surface profile under a given discharge for specified boundary conditions. Usually, their computation is lengthy but they are required if backwater and drawdown effects have to be determined. Chapter 8 presents a simplified method to determine backwater curves. It is based on a differential equation which can be solved exactly. Therefore, no convergence criterion with regard to the length of the calculation step is needed. The procedure is detailed by describing the computational scheme and explained with examples. Apart from the circular section, the egg-shaped and the horseshoe sections as well as the rectangular section are also considered. Finally, the effect of the non-hydrostatic pressure distribution on the discharge is discussed.