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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Volume 6, issue 1 | Copyright
Earth Surf. Dynam., 6, 187-201, 2018
https://doi.org/10.5194/esurf-6-187-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 07 Mar 2018

Research article | 07 Mar 2018

Establishing a sediment budget in the newly created “Kleine Noordwaard” wetland area in the Rhine–Meuse delta

Eveline Christien van der Deijl, Marcel van der Perk, and Hans Middelkoop Eveline Christien van der Deijl et al.
  • Faculty of Geosciences, Universiteit Utrecht, the Netherlands

Abstract. Many deltas are threatened by accelerated soil subsidence, sea-level rise, increasing river discharge, and sediment starvation. Effective delta restoration and effective river management require a thorough understanding of the mechanisms of sediment deposition, erosion, and their controls. Sediment dynamics has been studied at floodplains and marshes, but little is known about the sediment dynamics and budget of newly created wetlands. Here we take advantage of a recently opened tidal freshwater system to study both the mechanisms and controls of sediment deposition and erosion in newly created wetlands. We quantified both the magnitude and spatial patterns of sedimentation and erosion in a former polder area in which water and sediment have been reintroduced since 2008. Based on terrestrial and bathymetric elevation data, supplemented with field observations of the location and height of cut banks and the thickness of the newly deposited layer of sediment, we determined the sediment budget of the study area for the period 2008–2015. Deposition primarily took place in channels in the central part of the former polder area, whereas channels near the inlet and outlet of the area experienced considerable erosion. In the intertidal area, sand deposition especially takes place at low-lying locations close to the channels. Mud deposition typically occurs further away from the channels, but sediment is in general uniformly distributed over the intertidal area, due to the presence of topographic irregularities and micro-topographic flow paths. Marsh erosion does not significantly contribute to the total sediment budget, because wind wave formation is limited by the length of the fetch. Consecutive measurements of channel bathymetry show a decrease in erosion and deposition rates over time, but the overall results of this study indicate that the area functions as a sediment trap. The total contemporary sediment budget of the study area amounts to 35.7×103m3year−1, which corresponds to a net area-averaged deposition rate of 6.1mmyear−1. This is enough to compensate for the actual rates of sea-level rise and soil subsidence in the Netherlands.

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To study the effectiveness of river delta restoration, we used field observations and elevation data to quantify the magnitude and spatial patterns of aggradation and erosion in a restored wetland in the Rhine-Meuse delta. Erosion and aggradation rates decrease over time, but aggradation compensates for sea-level rise and soil subsidence. Channels in the centre had aggraded, whereas the inlet and outlet eroded. Furthermore, sediment is in general uniformly distributed over the intertidal area.
To study the effectiveness of river delta restoration, we used field observations and elevation...
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