Probabilistic Description of Sediment Plume Requirements at the Øresund Fixed Link Dredging Project

In an increasing number of dredging contracts, environmental requirements concerning sediment plumes have to be met. The required frequency of measurements to check if the actual turbidity or concentration of suspended solids complies with the limits, varies largely per contract. When measurements are taken continuously the probability that the limits are exceeded without registration by measuring are small, but continuous measurement methods are very expensive. The objective of this study is to optimise the number of measurements at a location, i.e. the number of ship crossings through a sediment plume, given the costs and the accuracy of the turbidity measurements, by a statistical data analysis. Data from the O/resund Fixed Link project in the Baltic Sea is used for the case study. Turbidity was measured 24 hr/day throughout this project. The measurements of one day, 15 January 1996, were used for the data analysis. The measurements were carried out from a vessel that sailed perpendicular across the sediment plume, at a distance of 200m from the dredger, collecting current and turbidity data. Upstream turbidity was measured for baseline values.