Multibeam Sponsors

Welcomes you to the Icebreaker Party

Monitoring of silt content in sediments off the Dutch Coast

Koos de Vries1, Johan de Kok2, Ronald Koomans1, John de Ronde2, Marcel Rozemeijer3

Silts, present in sand extraction sites, can potentially mobilize in the water column and result in increased turbidity of the North Sea. The main knowledge gap in assessing this potential risk is the capacity to buffer silts in the sandy sediments. To assess this buffering potential, Rijkswaterstaat started a campaign to monitor the concentration and variation of fines in the sediments off the Dutch Coast.

We monitored the concentration of fines in the sediment along 3 cross-shore tracks, ranging from 0-9 km off the coast, with the Medusa system and by taking sediment samples. The Medusa system results in continuous measurements of the silt content of sediments along a line, the samples have been used for validation purposes.

In the period September 2009 – Oktober 2010, 6 campaigns have been conducted. Measurements show that, although the silt content is very low (<5%), the silt content can vary strongly on small spatial scales. Temporal variations show how the silt content along the entire profile of the December 2009 measurements is almost twice the concentration of the September 2009 measurements. When the profiles with silt concentrations are compared to the daily average wave height before the measurements, the silt contents appear to increase with declining wave height.

In the presentation we will show the methodological developments and we will present the results of 6 measurement campaigns.

1)      Medusa Explorations BV, Groningen, The Netherlands,, tel: 0031-(0)50 5770280

2)      Deltares, Delft

3)      Waterdienst, Rijkswaterstaat, Lelystad