Dynamic adjustments in bankfull width of a braided reach

Remarkable channel degradation has occurred in a braided reach of the Lower Yellow River owing to the recent operation of Xiaolangdi reservoir, and downstream progressive incision has caused a significant process of channel widening. For the 104 km long braided reach, the dynamic adjustments in bankfull channel widths were investigated at both the section scale and reach scale, based on post-flood cross-sectional profiles surveyed annually from 1999 to 2013. It was found that the bankfull width at one section increased by up to 2887 m (296% increase) over 14 years, with an increase in the reach-scale bankfull width of 666 m (59% increase) in the braided reach. Fluvial erosion intensity was identified as a key factor influencing the variation in bankfull width, based on a comparison of various fluvial and non-fluvial factors controlling channel widening. Empirical relationships were developed, in the form of simple power functions, between these bankfull widths and the previous four-year average fluvial erosion intensity during flood seasons at the hydrometric station of Huayuankou. It is concluded that the significant increase in bankfull width was prominent in the channel evolution of the braided reach, which resulted in a major loss of floodplains.