An Information Entropy-Based Methodology to Construct the Avulsion Threshold in the Tail Reach of the Estuarine Alluvial Plain

Channel avulsion is a natural phenomenon that occurs abruptly on alluvial river deltas, which can affect the channel stability. The causes for avulsion could be generally categorized as topography- and flood-driven factors. However, previous studies on avulsion thresholds usually focused on topography-driven factors due to the centurial or millennial avulsion timescales of the world’s most deltas, but neglected the impacts of flood-driven factors. In the current study, a novel demarcation equation including the two driven factors was proposed, with the decadal timescale of avulsion being considered in the Yellow River Estuary (YRE). In order to quantify the contributions of different factors in each category, an entropy-based methodology was used to calculate the contributing weights of these factors. The factor with the highest weight in each category was then used to construct the demarcation equation, based on avulsion datasets associated with the YRE. An avulsion threshold was deduced according to the demarcation equation. This avulsion threshold was then applied to conduct the risk assessment of avulsion in the YRE. The results show that: two dominant factors cover respectively geomorphic coefficient representing the topography-driven factor and fluvial erosion intensity representing the flood-driven factor, which were thus employed to define a two dimensional mathematical space in which the demarcation equation can be obtained; the avulsion threshold derived from the equation was also applied in the risk assessment of avulsion; and the avulsion threshold proposed in this study is more accurate, as compared with the existing thresholds.