A Positive Feedback Between Sediment Deposition and Tidal Prism May Affect the Morphodynamic Evolution of Tidal Deltas

Abstract

Tidal deltas are fragile systems whose morphology can be easily impacted by variations in water and sediment fluxes caused by natural and human processes. Here we explore the relation between tidal prism and sediment dynamics in tidal deltas using the recent evolution of the Yangtze River estuary, China, as an example. Using the numerical model Delft3D, we examine how changes in delta morphology can trigger variations in tidal signal, suspended and bed load transport, and how these could ultimately cause additional morphological changes. Our results show that a positive feedback between sediment deposition and tidal prism dominates the morphodynamic evolution of the delta. Accretion of the shoals in the delta front increases the dissipation of tides and decreases the tidal prism leading to weaker tidal flows. This reduction in tidal currents lowers the sediment flushing capacity of the system, promoting deposition on the shoals and tidal dissipation. This positive feedback potentially traps more sediment in the delta topset and possibly offsets the decrease in sediment load triggered by the construction of upstream dams, often present in tidal deltas.

A nonlinear relationship between marsh size and sediment trapping capacity compromises salt marshes’ stability

“…Regional effects are crucial when evaluating coastal interventions under the management of multiple agencies. Though many studies have focused on local marsh dynamics, less attention has been paid to how changes in marsh areal extent might drive large-scale variations of hydrodynamic and sediment transport processes (Donatelli et al, 2018a;Zhang et al, 2018). Donatelli et al (2018b) studied the influence of salt marsh deterioration on the sediment budget in Barnegat Bay-Little Egg Harbor estuary (New Jersey, USA) and showed the existence of a positive feedback between marsh erosion and the decrease in the trapping efficiency of the marsh and the whole tidal system.…”

On the morphology of radial sand ridges

“…In coastal tidal environments, tidal prism, its related peak velocity and shear stresses are crucial to sediment transport and hence morphodynamic evolution (Donatelli et al, 2018; Zhang et al, 2018b). To explore the connections between tidal prism, peak velocity, and the morphology of the RSRs in China we have carried out a morphometric analysis of bathymetry, hydrodynamic and sediment transport simulations in an idealized fan‐shaped basin, and high‐resolution simulations with the real bathymetry and tidal forcing.…”

“…During the post‐glacial rise in sea level large‐scale sand banks formed in many inner‐ and mid‐shelves (Dyer and Huntley, 1999). These deposits are constantly reworked by tides and waves, and bottom topography adapts to physical processes at the decadal timescale (Zhang et al, 2018b). The feedback between channel incisions and flow redistribution in the RSRs is an example of how tidal hydrodynamics rework sediments and thus sculpt coastal landscapes.…”

Tropical Cyclones Significantly Alleviate Mega‐Deltaic Erosion Induced by High Riverine Flow

“…However, it is still debatable whether different deltaic areas are eroding or depositing during and after TCs. Previous work suggests that summer typhoons cause large‐scale erosion in the Changjiang deltaic front (Hu et al, 2009; Yang et al, 2003; Zhang et al, 2018), while winter storms evacuate alluvial sediments deposited in the northern part of Changjiang Delta and transfer the eroded material to deeper channels (Wan et al, 2014). Extreme storms and riverine floods might also cause large‐scale erosion and deposition in the subaqueous delta (Dai et al, 2014), but for the inner part of the Changjiang Estuary, such a study has not been carried out.…”