Apparent shear stress-based method on an inclined interface plane for predicting discharge in straight compound channels

Xiaonan Tang

doi:10.1016/j.mex.2019.05.027

Abstract

Accurately predicting flow discharge in a compound river channel becomes increasingly important for flood risk management and river eco-environment design. This paper proposes a new general approach based on the concept of the apparent shear stress at an inclined interface plane between main channel and floodplains. The new approach with a diagonal plane is applied with a wide range of the author’s experimental data and the data available in the literature, which include 59 datasets. Among them, 27 are homogenous channels of symmetric channels (22 datasets) and asymmetric channels (5 datasets) whereas 32 are heterogeneously roughened channels of symmetric channels (22 datasets) and asymmetric channels (10 datasets). It was found that the new approach improves the accuracy of discharge compared with the DCM for all datasets. The predicted total discharge for straight homogeneous channels has a mean absolute percentage error (MAPE) of 5%, whereas the MAPE error is about 6.7% for heterogeneously roughened channels.•A general approach of discharge prediction is presented based on apparent shear stress on an inclined interface.•Both zonal and total discharge can be calculated using the proposed method.•The predicted results are compared with 59 sets of experimental data along with the DCM.

Highlights

For the convenience of reference in the subsequent context, the sketched cross-sections of both symmetric and asymmetric compound channels are shown in Fig. 1, where H, h and hf are the flow depth of main channel, bankfull, and floodplain, respectively. b and bf are the widths of the main channel bottom and floodplain, respectively; Sc and Sf are the side slopes of the main channel and floodplain, respectively
The inclined dotted green line is an angel of β with the vertical line that starts from the intersect point between the main channel and floodplain, whereas u is the angel between the diagonal line and the vertical dash line
The new method is described as follows: Based on the streamwise force balance of each part of channels per unit length separated by the vertical line, it follows rgAcSo 1⁄4 rf cU2c Pc þ Nf tahf ð1Þ

Summary

Method details

For the convenience of reference in the subsequent context, the sketched cross-sections of both symmetric and asymmetric compound channels are shown in Fig. 1, where H, h and hf are the flow depth of main channel, bankfull, and floodplain (subscript f), respectively. b and bf are the widths of the main channel bottom and floodplain, respectively; Sc and Sf are the side slopes of the main channel and floodplain, respectively. The apparent shear stress (ta) on the vertical interface plane between main channel and its floodplain can be evaluated by the zonal velocities in each zone, as used by Huthoff et al [1], Yang et al [2,3] and Tang [4] and given by ta 1⁄4. Eq (17) is obtained by Tang [5]

Detailed procedures of calculation

Results

Conclusion