The Longitudinal Profile of a Prograding River and Its Response to Sea Level Rise

Abstract

River longitudinal profile, a key morphological characteristic of the river channel, is subject to river mouth progradation. Given the increasing influence of human activities and climate change on this critical downstream control, understanding its effects on the evolution of the longitudinal profile is imperative. A general theoretical framework is proposed to quantify the relevant effects, which is tested by numerical experiment and compared with field, numerical and laboratory data from the literature. The results suggest the existence of a critical ratio of accommodation space to sediment supply of approximately 0.5, above which the typical concave upward profile tends to form. Further analyses show that sea level rise tends to increase the concavity of the longitudinal profile of a river with a relatively low equilibrium bed slope and progradation rate. Plain Language Summary As a key feature of a river, the bed level along the river, i.e., the river longitudinal profile, affects flooding, navigation, etc., and thus greatly influences human societies and natural ecosystems. However, the effects of the seaward progradation of a river mouth on the evolution of the river longitudinal profile are still unclear. Given the increasing influence of human activities and climate change on this critical downstream control, understanding these effects becomes imperative. A new theoretical framework incorporating the effects of river mouth progradation on the evolution of a river longitudinal profile is developed and tested by numerical experiments, field observations, and numerical and laboratory data from the literature. The results show that the seaward progradation of a river mouth could potentially lead to the formation of a concave river longitudinal profile. Specifically, we found that there exists a critical condition in which the sediment supply is insufficient to balance the seaward progradation of the river mouth, causing the typical concave upward longitudinal profile to form. The proposed theoretical framework further suggests that sea level rise tends to increase the concavity of the longitudinal profile for river with a relatively low equilibrium bed slope and progradation rate.

System‐Wide Effects of Local Bed Disturbance on the Morphological Evolution of a Bifurcating Channel Network

“…The simulated equilibrium bed levels with either symmetric or asymmetric equilibrium configurations of the river bifurcations were adopted for further simulations with local disturbance of channel deepening (see Figure 2). Notably, in this study, the equilibrium configuration of a single channel is characterized by a linear longitudinal profile given by the water depth D 0 and channel bed slope S 0 (Blom, Arkesteijn, et al., 2017; Gao, Li, et al., 2020). Therefore, the water levels and bed levels are identical for scenarios with constant β 0 , that is, S1‐1 to S1‐5 for β 0 = 25 and S2‐1 to S2‐5 for β 0 = 33.33, as shown in Figure 4.…”

“…With fixed channel width, the evolution of longitudinal profile of river channel under human interventions or natural changes has become the main focus (Blom, Arkesteijn, et al., 2017; Gao, Nienhuis, et al., 2020; Wang et al., 2008; Ylla Arbós et al., 2023; Zheng et al., 2022). This is basically built upon the in‐depth understanding of the equilibrium longitudinal profiles of river channels thus far (Blom et al., 2016; Chang, 1986; Ferrer‐Boix et al., 2016; Gao, Li, et al., 2020). The morphological evolution of the river channel always proceeds toward an equilibrium longitudinal profile (Jansen et al., 1979), that is, a combination of water depth and slope that can exactly transport the upstream supplied sediment to the downstream, as initially proposed by Mackin (1948).…”

A Tale of Two Deltas: Dam-Induced Hydro-Morphological Evolution of the Volta River Delta (Ghana) and Yellow River Delta (China)

“…To quantify the annual mean discharge on the morphodynamics of the two waveinfluenced river deltas, we calculated the fluvial dominance ratio R, which is defined as the ratio of annual fluvial sediment supply (Q r ) and the combined annual maximum possible alongshore sediment transport away from the river mouth (Q s,max ) [9,62]. The fluvial dominance ratio R has been used to define deltaic morphological evolution in previous studies [9,63,64]. River deltas are considered wave-dominated if R < 1 and river-dominated if R > 1 [62].…”

Centennial Channel Response to Climate Change in an Engineered River

“…Field and modeling studies on channel response to interventions are abundant (e.g., Arkesteijn et al., 2021; Czapiga et al., 2022; Gao et al., 2020; Surian & Rinaldi, 2003; Verhaar et al., 2011; Zaprowski et al., 2005). Large‐scale studies of channel response to overall climate change are scarce, and do not typically address the relative magnitude of climate‐related and intervention‐related changes.…”