Modeling the Morphological Responses of the Yellow River Delta to the Water‐Sediment Regulation Scheme: The Role of Impulsive River Floods and Density‐Driven Flows

Abstract

Morphological evolution of river deltas depends to a large extent on river discharges, which are usually highly unsteady due to natural hydrological cycles and anthropogenic regulations. However, it is unclear that how and to what extent the discharge fluctuations influence the delta morphology. In this study, we focus on the morphological response of the Yellow River Delta to the Water‐Sediment Regulation Schemes, which generate impulsive floods and deliver high sediment load within a short time. Tracking the fate of fluvial sediment released by 10 historical events reveals that 51.3%, 19.7%, and 17.8% of fluvial sediment are deposited in the delta front, the subaerial delta and the prodelta, respectively. Hypopycnal and hyperpycnal flows occur alternately during different phases of the regulation schemes, and the latter contribute to 32% of the deposition volume with 10% of the duration. To explore the effects of river discharge schematizations on delta evolution, numerical experiments are conducted to compare models forced by unsteady and constant discharges, with the latter being a common practice in delta morphology modeling. We show that the constant‐discharge simplification fails to capture the highly‐depositional hyperpycnal flows, leading to dramatic underestimation of river mouth depositions. In addition, we demonstrate that including the 3D flow‐sediment interactions are critical in reproducing the correct plume structures, bed surface sediment compositions and deposition patterns. Our study highlights the importance of proper river discharge schematizations and full consideration of flow‐sediment interactions in modeling deltas affected by episodic river floods and high suspended sediment concentrations.

Reservoir Mud Releasing May Suboptimize Fluvial Sand Supply to Coastal Sediment Budget: Modeling the Impact of Shihmen Reservoir Case on Tamsui River Estuary

“…A value of f mor = 10 was adopted herein, based on sensitivity tests over a range of values. These techniques were not used in Stage 1 as typhoon events demand a more detailed account of the processes involved (Luijendijk et al, 2017; G. Wu et al., 2023).…”

“…Several factors not considered in the present study warrant incorporation in future research. (a) Density currents, caused by salinity intrusion and SSC stratification during low flows, would confine sediment transport to the nearbottom range and deposition to a shorter distance (Wang et al, 2010;G. Wu et al, 2023).…”

Yellow River Basin Management under Pressure: Present State, Restoration and Protection II: Lessons from a Special Issue

“…Numerous scholars have systematically researched the characteristics, causes, patterns, and development trends of water-sediment changes in the Yellow River, laying an essential scientific foundation for its governance and development [27,28]. With the development of the economy and society, coupled with the impact of climate change, the balance of the water-sediment relationship faces escalating challenges [29]. In response to this evolving scenario, the following research areas are imperative: (a) establishing a more comprehensive and refined water-sediment monitoring system to explore the integrated use of remote sensing, ground monitoring, sensor networks, and numerical simulation methods to achieve the high spatiotemporal resolution monitoring of hydrological elements and sediment movement within the basin; (b) furthering research on the interaction mechanisms between water and sediment under climate change and human activities [30] to dynamically simulate the interaction process between water and sediment under climate change and strengthen research on the impact of human activities on the water-sediment relationship, particularly factors like urbanization, agricultural development, and industrialization; (c) constructing a multi-level and multi-dimensional water-sediment balance threshold system for the Yellow River Basin, as different balance states exist for water-sediment processes in the Yellow River during various periods and under diverse boundary conditions, making it essential to determine indicators and thresholds for coordinated water-sediment regulation across the entire basin under the demand of high-quality development; (d) conducting special research on intelligent water-sediment regulation technology and decision-making systems [31], including the development of multi-objective joint optimization scheduling technology for water and sediment, the construction of intelligent models to simulate and regulate the water-sediment evolution, and the building of a decision support system for the comprehensive management of river channels and beaches.…”

Evolution of tidal flats in the Yellow River Qingshuigou sub-delta: spatiotemporal analysis and mechanistic changes (1996-2021)

“…This has led to a decrease in sediment inflow from the river to the tidal flats at these particular locations. Nevertheless, it is worth noting that relevant studies have shown (Bi et al, 2014;Ji et al, 2020;Wu et al, 2023) that sediments from the Yellow River estuary can still reach and extend to the tidal flats near the estuary. Sediment transport processes, including littoral and tidal currents, can distribute sediments along the shoreline, allowing sediments to accumulate and expand the tidal flat area far from the estuary.…”

“…Reclamation activities have shifted the land boundary of tidal flats seaward through reclamation and landfilling, resulting in a reduction In the current estuary section of the Qing8 lobe, the sea boundary of delta tidal flats moves under the combined influence of the river sediment discharges and marine hydrodynamics forces. On the other hand, in the abandoned estuary of Qingshuigou lobe, there is no direct input of sand from the river, and sediment recharge from the existing estuary to the abandoned estuary is limited by the blocking effect of the estuarine tidal shear front and the convex dike (Ji et al, 2020;Li et al, 2021;Ji et al, 2022;Wu et al, 2023). Therefore, changes in the tidal flat area at the sea boundary of the abandoned estuary of the Qingshuigou lobe are primarily controlled by marine hydrodynamics forces.…”