Estimating the Overbank Flow Discharge using Slope-Area Method

Abstract

The present research proposed an improved slope-area method for estimating the overbank flow discharge. The prediction of conveyance factor has been improved by including the secondary flows effect using the coherence concept. Field measurements of velocity that reached 540 m were taken in a study of the River Dough, south of Kalale City, Iran, during the February 2004 flood. A nonlinear trend was observed between the depth of the relative flood-marks and the amount of predicted discharge error. The slope-area method significantly overestimated the overbank flow rate, especially in nonhomogeneous cross section, where the interaction effects increase progressively with a relative depth of less than 0.2. The overestimated value of 23% was obtained in prediction of the River Dough overbank flow by the slope-area method. The improved slope-area method predicted the flow rate with an error of 2.58% compared to the flood field measurements. The results show agreement between the proposed method prediction and the measured data.