Peak Water Levels Rise Less Than Mean Sea Level in Tidal Channels Subject to Depth Convergence by Deepening

Abstract

Effects of sea‐level rise (SLR) on future peak water levels in tidal deltas and estuaries are largely unknown, despite these areas being densely populated and at high risk of flooding. While the rates of SLR accelerate, many channels simultaneously experience channel deepening for navigation. With globally decreasing sediment supplies, most channels are at risk of becoming deeper when the rate of SLR accelerates and sedimentation cannot keep pace with SLR. These factors potentially favor amplification of the tides and thereby increase flood risk, but the extent to which they will do so is unknown. Here, we introduce and use a validated model for an artificially deepened multi‐branch delta to get a mechanistic understanding of non‐linear SLR‐effects on peak water levels. Results show that, when the current deepened bed level will be maintained, peak water levels do not rise on par with mean sea‐level. Thus flood risk increases less than what can be expected from the predictions of the mean sea‐level increase. The reason is that SLR causes a proportional reduction in convergence of channel area. This mechanism reduces tidal amplification. Nevertheless, SLR effects extend far beyond the range of present‐day seasonal variations, with future low water levels being equal to present‐day high water levels, while the tidal range slightly reduces. This will have consequences not only for flood risk, but also for freshwater availability, navigation and ecology.

Climate Change Can Intensify the Effects of Local Interventions: A Morphological Modeling Study of a Highly Engineered Estuary

“…Similarly Leuven et al. (2023) find that if the Rotterdam waterway becomes deeper, due to dredging or SLR, tidal amplification reduces. However, in larger estuaries with large tidal ranges near the mouth SLR is likely to amplify tides (Khojasteh et al., 2021).…”

Quantifying Compound and Nonlinear Effects of Hurricane‐Induced Flooding Using a Dynamically Coupled Hydrological‐Ocean Model

“…With the rapid advancements in high-performance computing technology, we expect to conduct hyper-resolution simulations (less than 10 m resolution) in the near future, potentially making the diagonal flow algorithm no longer needed and thus further enhancing the model's computational efficiency. Such a development will enable us to focus on the flooding processes at smaller scales and represent the effect of topographic features such as channel depth and morphology (Familkhalili & Talke, 2016;Gugliotta & Saito, 2019;Leuven et al, 2023;Muñoz et al, 2022;Ralston et al, 2019;Talke et al, 2021).…”

Sea level rise and the drivers of daily water levels in the Sacramento-San Joaquin Delta

“…Water levels and RSLR rates in deltas and rivers are influenced by coastal water level trends and variability, hydrologic changes, spatially varying vertical land motion (VLM), human modifications (e.g., dredging, structures), astronomical tidal variability, tidal evolution, and dynamical interactions between river flow and tides 6 – 13 . For example, RSLR in Shanghai has been strongly influenced by groundwater pumping and resulting land consolidation 14 , 15 .…”