Wageningen Marine Research aanvaardt geen aansprakelijkheid voor gevolgschade, noch voor schade welke voortvloeit uit toepassingen van de resultaten van werkzaamheden of andere gegevens verkregen van Wageningen Marine Research. Opdrachtgever vrijwaart Wageningen Marine Research van aanspraken van derden in verband met deze toepassing. Alle rechten voorbehouden. Niets uit deze uitgave mag weergegeven en/of gepubliceerd worden, gefotokopieerd of op enige andere manier gebruikt worden zonder schriftelijke toestemming van de uitgever of auteur.
<p>Coastal defences such as dikes are increasingly pressured by climate change. Increasing storm surge, extreme rainfall and periods of draught requires evermore strengthening of dikes to maintain flood risk standards. Conventional dike strengthening (i.e., heightening and/or widening) will be either structurally or financially unfeasible. Therefor, engineers are exploring other, more sustainable, methods to ensure future flood safety. A promising method is incorporating tidal marshes in the coastal defence system. Tidal marshes reduce dike loads by wave attenuation, increase bio diversity and ecology and under the right circumstances are able to grow with sea level rise. Moreover, in case of dike failure, resulting in a dike breach and inundation of the hinterland, tidal marshes have been shown to reduce breach erosion rates. This reduction positively affects flood risk. However, in order to quantitatively estimate the effect, dike breach models need to also model tidal marsh erosion. In this study we tested a mature tidal marsh, in-situ, in winter conditions under high flow velocities (up to 2.5 m/s) to measure the erosion and estimate erodibility. We measured little erosion, order millimeters after a cumulative 2-2.5 hours. Small-scale experiments, such as the Jet Erosion Test, showed high resistance to erosion (85-140 Pa) and large varying erodibility (6.5-45 cm<sup>3</sup>/N&#183;s). By estimating the shear stresses acting on the soil during the experiment we compare the data with the small-scale results. The comparison gives insight in whether the small-scale experiment results can be accurately translated to full-scale erosion. Also, the experiment showed which (erosion) mechanisms are important for tidal marshes during a dike breach.</p>
<p>Nature-based&#160; strategies,&#160; such&#160; as&#160; wave&#160; attenuation&#160; by&#160; tidal&#160; marshes,&#160; are&#160; increasingly &#160;proposed&#160; as&#160; a&#160; complement&#160; to&#160; mitigate&#160; the&#160; risks&#160; of&#160; failure&#160; of&#160; engineered&#160; flood&#160; defense &#160;structures such as levees. However, recent analysis of historic coastal storms revealed smaller&#160; dike&#160; breach&#160; dimensions&#160; if&#160; there&#160; were&#160; natural,&#160; high&#160; tidal&#160; marshes&#160; in&#160; front&#160; of&#160; the &#160;dikes.&#160; Since&#160; tidal&#160; marshes&#160; naturally&#160; only&#160; experience&#160; weak&#160; flow&#160; velocities&#160; (~0-0.3&#160; ms<sup>-1 </sup>during&#160; normal&#160; spring&#160; tides),&#160; we&#160; lack&#160; direct&#160; observations&#160; on&#160; the&#160; stability&#160; of&#160; tidal&#160; marsh &#160;sediments&#160; and&#160; vegetation&#160; under&#160; extreme&#160; flow&#160; velocities&#160; (order&#160; of&#160; several&#160; ms<sup>-1</sup>)&#160; as&#160; may &#160;occur&#160; when&#160; a&#160; dike &#160;behind&#160; a&#160; marsh&#160; breaches.&#160; As&#160; a&#160; first&#160; approximation,&#160; the&#160; stability&#160; of &#160;a tidal marsh sediment bed and winter-state vegetation under high flow velocities were tested in a flume. Marsh monoliths were excavated from <em>Phragmites australis</em> marshes in front of a dike along the Scheldt estuary (Dutch-Belgian border area) and installed in a 10 m long flume test section. Both sediment bed and vegetation responses were quantified over 6 experimental runs under high flow velocities up to 1.75 ms<sup>-1</sup> and water depth up to 0.35 m for 2 hours. These tests showed that even after a cumulative 12 hours exposure to high flow velocities, erosion was limited to as little as a few millimeters. Manual removal of the aboveground vegetation did not enhance the erosion either. Present findings may be related to the strongly consolidated, clay- and silt-rich sediment and <em>P. australis</em> root system in this experiment. During the flow exposure, the <em>P. australis</em> stems were strongly bent by the water flow, but the majority of all shoots recovered rapidly when the flow had stopped.&#160; Although&#160; present&#160; results&#160; may&#160; not&#160; be&#160; blindly&#160; extrapolated&#160; to&#160; all&#160; other&#160; marsh &#160;types, they do provide a strong first indication that marshes can remain stable under high flow conditions, and confirm the potential of well-developed tidal marshes as a valuable extra&#160; natural&#160; barrier&#160; reducing&#160; flood&#160; discharges&#160; towards&#160; the&#160; hinterland,&#160; following&#160; a&#160; dike &#160;breach. These outcomes promote the consideration to implement tidal marshes as part of the overall flood defense and to rethink dike strengthening in the future.</p>
Wageningen Marine Research accepts no liability for consequential damage, nor for damage resulting from applications of the results of work or other data obtained from Wageningen Marine Research. Client indemnifies Wageningen Marine Research from claims of third parties in connection with this application.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.