On Discharge Computations in Non-Symmetrical Trapezoidal Compound Channel

The complexity of flow area determination in compound channels may lead to errors in flow estimation. Although the uniform flow formulae, such as Manning’s equation, are widely used to determine flows through open channels having simple cross-sections, this may lead to considerable errors in the case of compound channels. This paper evaluates various alternatives to account for flood plain conveyance in non-symmetrical trapezoidal compound channel cross-section. Evaluations are based on applying several traditional discharge estimation methods to a field data aiming at determining the best interface plane arrangement leading to flow estimation for different flow depths. Six interface and one other standard method for computing discharge in open channels were compared. Each interface method uses a particular arrangement of imaginary interface planes to artificially sub-divide the compound flow field into homogeneous zones. These methods are named for the particular interface plane arrangement adopted. The standard method does not involve interface planes. Computed discharges were compared and evaluated by applying various statistical measures to determine the degree of goodness-of-fit between computed and observed discharges. In terms of overall performance, the weighted extended side slope method proved to correctly predict the discharge. However, the vertical interface planes method produced the most accurate computations among the methods tested for the non-symmetrical trapezoidal compound channel cross-sections under consideration.