Impacts Of Engineered Diversions And Natural Avulsions On Delta-Lobe Stability

Reduced sediment supply and rising sea levels are driving land submergence on deltas worldwide, motivating engineering practices that divert water and sediment to sustain coastal landforms. However, lobe response following channel abandonment by diversions has not been constrained by field-scale studies. Herein, avulsion and engineered diversion scenarios are explored for the Huanghe delta (China), where three lobes were abandoned in the last 40 yr. Two lobes were completely cut off by diversions, and one naturally by an avulsion. Shoreline retreat rates are strikingly different: similar to 400 m/yr for diverted lobes and similar to 90 m/yr for avulsed lobe. We hypothesize that this variability is linked to vegetal cover across lobes, and therefore the capacity to buffer hydrodynamic reworking of shoreface sediment. Furthermore, the vegetal cover is related to lobe salinity and elevation, which vary by abandonment style. We offer this as a case study to inform about the efficacy of future delta diversions.Plain Language Summary Sediment and water diversions are an important tool to combat land loss of deltaic coastlines. However, nourishment of drowned coastal land typically requires diverting water and sediment away from another region of the coast, potentially resulting in additional land loss. This study finds that the stability of shorelines facing reduced sediment supply is dependent on elevation before sediment loss, freshwater supply, and vegetation coverage. These findings have implications for future sediment and water diversions, by informing strategies that optimize land preservation.