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 results provide an adequate picture of the impact of nourishment operations. But the conclusion is that more research is needed if we want to combine sand nourishment and nature development in the future,” Deltares said.
From 2009 to 2015, Deltares led a research program 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 studies in the dunes on the coasts of Holland and the Wadden Sea, on the beach and under 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 field measurements in the dunes indicate that drifting sand affects the soil and vegetation well behind the first row of dunes.
The drifting sand comes mainly from the beach and the amount is determined by the presence, or absence, of openings in the foredunes, regardless of whether there has been sand nourishment.
A study of the water table in the dunes of Ameland also indicated that minor sand nourishment operations do not have a significant impact on the water table in adjacent dunes.
This conclusion does not, incidentally, apply to major nourishment projects such as the Sand Motor and the Hondsbossche dunes, where the water table has been affected.
Nourishment and benthos
No direct evidence was found on Ameland suggesting effects on benthos associated with the composition of the sand used for nourishment.
Sand nourishment does result in a sharp fall in benthos numbers.
The time that the benthos needs to recover from any disruption resulting from nourishment depends on factors that include the physical conditions in a particular location.
Various studies, including those on Ameland, also indicate that the benthos in a sandy dynamic environment such as the shallow foreshore recovers within 2 to 3 years.
Long-term research for the entire Dutch coast
To see whether the conclusions apply to the entire Dutch coast, more research will be required using the same temporal and spatial scales.
Rijkswaterstaat and ten nature organisations therefore signed a covenant on 3 November at the Seventh National Delta Conference in Apeldoorn.
The organizations will now look annually to see whether and how the findings can be applied to combine coastal protection and nature development better. Unanswered questions will be addressed by Deltares and Imares.
The covenant will continue until the end of 2022.