Estimation of Bankfull Discharge in the Lower Yellow River

Abstract

Bankfull discharge is highly correlated with bankfull elevation. The main channels and bankfull elevations in multi-thread sections are ambiguous and need additional indicators to define. Thus, two additional indicators (maximum width and effective width coefficient) were adopted to estimate the bankfull elevation of both multi- and single-thread cross-sections. Three geometric-criterion based definitions of bankfull elevation (minimum width-depth ratio, abruptly changing-point of wetted area to top channel width ratio, first maximum Riley bench index) were selected to estimate bankfull elevation. Typical cross-sections selected were the Huayuankou and Lijin cross-sections in the Lower Yellow River. More than 300 cross-sectional datasets of the Huayuankou and Lijin were collected to calibrate the value of effective width coefficient. Second, calibrated coefficients were verified by various applications, estimating the variation of sectional bankfull discharge in floods, estimating the variation of sectional bankfull discharge along a river reach, and estimating annual variation of reach-scale bankfull discharge. Third, sensitivities of physical parameters were further analyzed. Calculation and analysis showed that the effective width coefficient was necessary for estimating bankfull elevation in multi-thread cross-sections, and these three definitions could be adapted to estimate the bankfull elevation when coupled with these two indicators. Besides, the key point of this method was defining the maximum width and effective width coefficients, as other factors have limited effects on estimating bankfull discharge. Analyses can also provide information for field survey refering to the balance between time consuming and detailed measurements.