Application of the independent subsections method for the estimation of the rating curve in the compound channel – a case study

Abstract

The independent subsections model (ISM) was developed for the steady uniform and non-uniform flow computations in compound channels with constant and variable channel widths. It was thoroughly tested against experimental data in different compound channel layouts. Since the existing set of equations is derived for the simple compound channel geometry, this paper aims at: 1) extending the model to arbitrary geometries, 2) adding the term that accounts for the influence of emergent rigid floodplain vegetation into momentum equations and 3) at validating the method against available floods data from one river gauging station. Comparison with the recorded data has shown that the optimal value for the model parameter ψt = 0.10 is greater than that obtained for the canal with smooth floodplains. Partial head losses due to vegetation are two orders of magnitude greater than the friction loss for H* > 0.25 when they are calculated with the formula for the volume drag force caused by an array of emergent rigid vegetation, proposed by Nepf,. The head loss due to a drag grows faster with the increase in floodplain submergence ratio on the floodplain with the constrained width. In the presence of vegetation on the floodplains, the head loss caused by mass exchange due to non-prismaticity of the compound channel does not depend on the floodplain width. This component of the head loss is balanced with the sum of head losses due to turbulence diffusion and vegetation drag.