Impacts of Riverine Floods on Morphodynamics in the Yellow River Delta

Abstract

The geomorphological stability and ecological environment of megadeltas worldwide are of vital importance for their sustainable development. Deltaic hydro-morphodynamics is extremely sensitive to high riverine flow due to reduced sediment supply. However, the morphological evolution and response of deltas under high riverine flow have remained inadequately quantified. As one of the typical megadeltas, the Yellow River Delta (YRD), is becoming increasingly sensitive to environmental changes and intensified human interventions. In this study, a numerical model and field data were used to investigate the hydrodynamic changes and morphodynamic evolution induced by extreme river discharge in the YRD. The numerical experiments with different runoff scenarios reveal that high-energy riverine floods can cause significant hydrodynamic changes in bed shear stresses, water levels, and flow velocities, particularly in the abandoned river mouth. Moreover, it enhances the ebb-dominated tidal asymmetry, which considerably intensifies fluvial sediment resuspension and transport processes. The results also show high-energy riverine floods in the flood seasons trigger severe erosion in the Yellow River submerged delta, with a net erosion volume reaching −0.07 × 108 m3/yr. The hydrodynamic increment in the abandoned river mouth is more significant, and therefore, severe erosion occurs, with the maximum erosion thickness reaching 7 m. These findings highlight the role of high riverine floods on the hydro-sediment dynamics of large river deltas under a sediment starvation condition.

Detecting the magical yellow-blue demarcation off the Yellow River Estuary from the space

“…It could be found that at low water and sediment discharge (29 June, 1 July 2018, and 24 June and 15 July 2022), the YBDLs were mainly distributed within 10 km around the two river distributary mouths, while during floods (16-21 July 2018, 25 June -5 July 2022), the YBDL could extend significantly seaward (>20 km). This was because not only could flooding processes provide large amounts of sediment, but high-energy riverine floods could alter the hydrodynamic conditions in the estuary, allowing the estuarine turbidity plume to diffuse more widely (Ji et al, 2020;Fu et al, 2023). However, it was worth noting that there was a distinct difference in the YBDL distributions during these two floods.…”

“…After 2018, the WSRS was implemented again and differed from the previous WSRS processes by discharging more runoff and sediment to the sea (Figure S2). In addition, several major flood events occurred during the flood seasons of 2020 and 2021 because of the extreme rainfall in the basin (Figure S3) (Fu et al, 2023). The rapid delivery of high-energy runoff and enormous amounts of sediment into the sea would not only reshape the estuarine morphology, but also inevitably have a profound impact on the spatiotemporal dynamics of YBDL (Li et al, 2021a;Li et al, 2022a;Lu et al, 2022).…”