Variation in reach-averaged bankfull discharge in the Yellow River Estuary in recent years

The Yellow River Estuary (YRE) alternatively experienced channel aggradation and degradation during the period 1990–2016. To study the variation in flood discharge capacity during the process of river bed evolution, bankfull characteristic parameters were investigated on the basis of measured hydrological data and surveyed cross-sectional profiles, which was crucial for comprehending the processes and the key factors to cause these rapid changes. A reach-averaged method was presented in this study in order to calculate the characteristic bankfull parameters in the YRE, and this method integrated the geometric mean using the logarithmic transformation with a weighted mean based on the distance between the two successive sections. The reach-averaged bankfull parameters in the tail reach of the Yellow River Estuary (the Lijin-Xihekou reach) during the period 1990–2016 were then calculated. Calculated results indicated that the adoption of a concept of reach-averaged bankfull discharge was much more representative than the cross-sectional bankfull discharge, and the results also indicated that bankfull discharges decreased during the process of channel aggradation, and increased during the process of channel degradation. Finally, an empirical formula and a delayed response function were established between the reach-averaged bankfull discharge and the previous 4-year average fluvial erosion intensity during flood seasons, and both of them were adopted to reproduce the reach-averaged bankfull discharges, and calculated results showed high correlations (R2 > 0.8) of these two methods.