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 Building with Nature Guideline > Projects > Tidal flat nourishment - Galgeplaat, NL

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Tidal flat nourishment - Galgeplaat, NL

Location: Oosterschelde (Eastern Scheldt), the Netherlands

Date: 2008-2012

Involved parties: Deltares, IMARES, Rijkswaterstaat, NIOZ (former NIOO-CEME), EcoShape 

Technology Readiness Level: 9

Environment: Estuaries, Sandy shores

Keywords: Benthic ecology, tidal flat restoration, estuary protection, measures against erosion, biodiversity, morphology, hydrodynamic model

Building with Nature designTraditional design

The nourishment on the Galgeplaat was designed in a circular shape. First a protective bund of sand of approximately 1 m high was built, forming a ring with a diameter of 450 m. This ring was filled with sand during the flood phase of the tidal cycle and spread by bulldozers during the ebb phase. This allowed for a controlled construction of the nourishment, as an increase in the concentration of suspended matter had to be avoided because of nearby commercial mussel beds.  

Traditional working methods, while effective from a technical perspective, provide less control over the spreading of fine sediments than the work method implemented in this project, with the perimeter of sand. 


Tidal flats are valuable habitats and are important for coastal protection. The total area of tidal flats is decreasing worldwide due to various problems like sea level rise, coastal squeeze, subsidence by gas extraction and erosion initiated by man made constructions. The construction of a storm surge barrier and compartmentalization dams in the Eastern Scheldt in the 1980s is one example of a man made structure that resulted in a change in hydrodynamic conditions of the Eastern Scheldt estuary and hence the sediment equilibrium. As a result, channels are filling in and tidal flats inside the estuary are eroding. Nourishing tidal flats with sediment might be a promising solution to mitigate these effects. 


To test this approach, a small area of the Galgeplaat, a tidal flat in the Eastern Scheldt, was nourished in 2008 with 130.000 m3 sand dredged from adjacent channels over a total area of 150.000 m2. The processes of sediment distribution on the flats and benthic recolonization are coupled and interact with each other. Therefore the design challenge is to find an optimum to reduce the initial impact of the nourishment on the benthic fauna, while optimizing the distribution of the sand over the tidal flat by wind and waves and the subsequent recovery of benthic life.

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Planning and design

Primary purpose of the Galgeplaat pilot was to investigate whether nourishment can compensate the erosion of a tidal flat. Furthermore, the pilot offers the opportunity to gain a better insight into the biological and morphological development of an intertidal flat and the relationship between biotic and abiotic parameters. This will help improving the design of new measures with respect to the mitigation of the ongoing erosion of tidal flats in estuaries like the Eastern Scheldt in the future.

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From August to September 2008 130,000 m³ of sand was deposited on the Galgeplaat in a low circular mound, creating a kind of sand reservoir (figure 9).

First, a protective ring of sand was built, approximately 1 m high with a diameter of 450 m. The ring was made by bulldozers with sediment taken from the flat itself. At the south east side an opening was created for discharging excess water during the nourishment operation. At the inner side of the opening a settling-basin was excavated, in order to reduce the content of suspended matter in the effluent. The opening was oriented towards the nearby channel (Brabantsche Vaarwater).

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Operation and Maintenance

 The development of the nourishment and its impact on the morphological and biological processes has been and will be further monitored for several years, primarily by Rijkswaterstaat. Additionally Building with Nature has taken extra samples of the benthic macrofauna and has installed an Remote monitoring of bio -and morphological developments - ArgusBio for morphological imaging and close-up images of birds, and other ecological features like the presence of algal mats and microphytobenthos. 

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Lessons Learned

Several lessons-learned have been obtained on the field of morphology, ecology dynamics and (predictive) modelling 

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