Further research needed to combine sand nourishment and nature development

Published: 29 November 2016

In recent years (2009-2015), Deltares has studied the impact of sand nourishment on the functioning and the quality of the coastal ecosystem. As a part of Knowledge for Primary Processes – Coastal Management and Maintenance (KPP BenO Kust), Deltares programmed the research questions and commissioned or implemented a range of studies. The research has provided a picture of the local effects of nourishment on benthos in the foreshore, and on dunes, beaches and birds. The upcoming programme will focus on the effects of nourishment at larger temporal and spatial scales.

From 2009 to 2015, Deltares led a research programme looking at the impact of sand nourishment on benthos, animals, fish and shorebirds, and the effect of drifting sand on dune flora and fauna in various locations. The effects were studied in several ways: field measurements in the dunes on the coasts of Holland and the Wadden Sea, on the beach and below the water line water on the coasts of Ameland and Schiermonnikoog, literature studies, model calculations of groundwater levels in the dunes of Ameland, and data analyses and interviews with managers of coasts and dunes.

Effect on dune growth and water tables

The dune field measurements indicate that sand drifts a long way past the first row of dunes. The drifting sand comes mainly from the beach and the amount is mainly determined by the presence, or absence, of openings in the foredunes, regardless of whether there has been sand nourishment. Dune management therefore plays a major role. A study of the water table in the dunes of Ameland showed that nourishment operations had no significant impact on the water table in adjacent dunes. Major sand nourishment projects such as the Sand Motor and the Hondsbossche dunes do affect the water table.

Nourishment and benthos

The study on Ameland shows that benthic populations in a sandy dynamic environment like the shallow foreshore recovered within 2 to 3 years to levels close to those prior to the nourishment operation. This period of time corresponds to the nourishment cycle. Sand nourishment does result in a sharp fall in benthos numbers in the short term. This finding applies to only one location and so it is unclear whether these effects will also be found on the rest of the Dutch coast.

Long-term research for the entire Dutch coast

To see whether the same conclusions apply to the entire Dutch coast, research will be required at larger temporal and spatial scales. Deltares will be teaming up with Wageningen Marine Research over the next five years on this follow-up research. Rijkswaterstaat and ten nature organizations signed a covenant to this effect on 3 November at the seventh National Delta Congress in Apeldoorn. The research programme will continue until the end of 2022.

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