1. Peak Water Levels Rise Less Than Mean Sea Level in Tidal Channels Subject to Depth Convergence by Deepening.
- Author
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Leuven, Jasper R. F. W., Niesten, Iris, Huismans, Ymkje, Cox, Jana R., Hulsen, Lamber, van der Kaaij, Theo, and Hoitink, A. J. F.
- Subjects
SEA level ,ABSOLUTE sea level change ,WATER levels ,FLOOD risk ,TIDE-waters - 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. Plain Language Summary: Many urban deltas are becoming deeper, often due to dredging for navigation purposes. A larger channel depth decreases friction, leading to amplification of the tide (higher peak water levels). At the same time, climate projections predict accelerated Sea‐Level Rise (SLR). SLR also increases the channel depth, thereby amplifying the tide. However, it is unknown to which extent SLR and channel deepening increase peak water levels. Here, we use a validated model of the Rhine‐Meuse Delta to study the effect of SLR and channel deepening on peak water levels. Results confirm that local dredging of the channel increases peak water levels. The larger depth at the mouth increases the convergence of cross‐sectional channel area in landward direction. This convergence is known to increase the tidal amplitude in landward direction, also known as tidal amplification. In contrast, peak water levels do not rise on par with SLR when the current deepened bed level is maintained. This is because the landward reduction in channel area diminishes with SLR. Nevertheless, future low water levels are predicted to be equal to present‐day high water levels, while the tidal range slightly reduces. This will have consequences for flood risk, freshwater availability, navigation and ecology. Key Points: Channel deepening can immediately amplify tides, which over the course of time may partially be counteracted by sea‐level rise (SLR)In depth‐convergent artificially deepened channels, SLR reduces tidal amplificationThe reduction in tidal amplification causes the peak water levels to rise less than mean sea level [ABSTRACT FROM AUTHOR]
- Published
- 2023
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