Case Study: The Galgeplaat, The Netherlands
The Galgeplaat tidal flat is located in the Eastern Scheldt, a former estuary in the Netherlands. This is an important area for foraging birds, especially shorebirds, but is suffering from erosion. Galgeplaat was one of a number of pilot projects launched to investigate the effectiveness of erosion mitigation. In 2008, 130,000 m 3 of sediment was added to an area of 150,000 – 200,000 m 2 . The sediment was obtained from maintenance dredging in the tidal channels Brabantsche Vaarwater and Witte Tonnen Vlije. The sediment was less than 7% mud and was coarser than the surrounding, undisturbed sediment. After placing the sediment, the average nourishment height of the area was 0.65 m. The initial plan was for the placed sediment to supply sand to the surrounding area. However, it did not spread much within the first two years. It was speculated that placing the sediment at a more dynamic location with varied topography would encourage the sediment to spread (Borsje et al. , 2012). The sediment volume decreased by 10% after four years, which equates to an erosion rate faster than the surrounding environment. The sediment buried, and killed, a lot of the benthic macrofauna in the area, which in turn reduced the amount of time birds spent foraging. However, biological recovery began straight away. Recovery of invertebrates was highest at locations that were wet for a longer period of the tidal cycle. Two years after the sediment was placed, the overall average invertebrate biomass at Galgeplaat reached similar values to a reference site and the amount of time spent foraging by birds increased to the level before sediment addition. Eurasian Curlews Numenius arquata and Oystercatchers Haematopus ostralegus returned to the site but other shorebirds, such as Red Knot Calidris canutus , Bar-tailed Godwit Limosa lapponica , Grey Plover Pluvialis squatarola and Dunlin Calidris alpina did not, despite the abundance of food.
Sources: Borsje et al. (2012); van der Werf et al. (2015)
5. Other sources of information
Documents
Managing dredged-material islands for birds in the USA: Golder W., Allen D., Cameron S. & Wilder T. (2008) Dredged Material as a Tool for Management of Tern and Skimmer Nesting Habitats . Technical note: ERDC TN-DOER-E24. U.S. Army Engineer Research and Development Center: Vicksburg, USA. http://hdl.handle.net/11681/8757 Guidance on working with dredged material in coastal environments: Manning W., Scott C. & Leegwater E. (2021) Restoring Estuarine and Coastal Habitats with Dredged Sediments: A Handbook. Environment Agency: Bristol, UK. Available at:
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