Preprints
https://doi.org/10.5194/egusphere-2024-283
https://doi.org/10.5194/egusphere-2024-283
02 Feb 2024
 | 02 Feb 2024
Status: this preprint is open for discussion.

Exploring the Tidal Response to Bathymetry Evolution and Present-Day Sea Level Rise in a Channel-Shoal Environment

Robert Lepper, Leon Jänicke, Ingo Hache, Christian Jordan, and Frank Kösters

Abstract. Intertidal flats and salt marshes in channel-shoal environments are at severe risk from drowning under sea level rise (SLR) ultimately ceasing their function in coastal defense. Earlier studies indicated that these environments can be resilient against moderate SLR as their mean height is believed to correlate with tidal amplitude and mean sea level. Recent morphological analyses in the German Wadden Sea on the Northwestern European Shelf contradicted this assumption as mean tidal flat accretion surpassed relative SLR; indicating that nonlinear feedback between SLR, coastal morphodynamics, and tidal dynamics played a role. We explored this relationship in the German Wadden Sea’s channel-shoal environment by revisiting the sensitivity of tidal dynamics to observed SLR and coastal bathymetry evolution over one nodal cycle (1997 to 2015) with a numerical model. We found a proportional response of tidal high and low water to SLR when the bathymetry was kept constant. In contrast, coastal bathymetry evolution caused a spatially-varying hydrodynamic reaction with both increases and decreases of tidal characteristic patterns within few kilometers. An explorative assessment of potential mechanisms suggested that energy dissipation declined near the coast which we related to decreasing tidal prism and declining tidal energy import. Our study stresses the fact that an accurate representation of coastal morphology in hind- and nowcasts and ensembles for bathymetry evolution to assess the impact of SLR are needed when using numerical models.

Robert Lepper, Leon Jänicke, Ingo Hache, Christian Jordan, and Frank Kösters

Status: open (until 06 Apr 2024)

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  • RC1: 'Comment on egusphere-2024-283', Anonymous Referee #1, 03 Mar 2024 reply
Robert Lepper, Leon Jänicke, Ingo Hache, Christian Jordan, and Frank Kösters
Robert Lepper, Leon Jänicke, Ingo Hache, Christian Jordan, and Frank Kösters

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Short summary
Coastal environments are often sheltered by intertidal flats and salt-marshes. These environments are at severe risk from drowning under sea level rise. Recent analyses in the Wadden Sea demonstrated tidal flats grew faster than the local mean sea level contrary to expectation. We found that tidal high and low water increased proportionally with SLR while coastal bathymetry evolution caused spatially-varying tidal adaptation with sharp increase-decrease edges at the coast.