Long-term influence of maritime access works on the distribution of cohesive sediments: analysis of historical and recent data from the Belgian nearshore area (southern North Sea)

Long-term changes in the cohesive sediment distribution of the Belgian-Dutch nearshore zone (southern North Sea) are related to human activities (port construction, deepening of navigation channels, disposal of dredged sediments) and to natural variability, due to tides and meteorological effects. Results are based on the combined analyses of recent and historic (100 years ago) sediment sample information and bathymetric maps. Data processing was based mainly on field descriptions of the samples (consolidation, thickness) and on bathymetric maps of 1866-1911. Results indicate that the distribution of fresh mud and suspended sediment has changed during the last 100 years, due mainly to maritime access works. Most of the present deposition of thick layers of fresh mud (> 30 cm) has anthropogenic causes. The results further indicate that erosion of older Holocene mud has increased in recent times and, as a consequence, higher amounts of fine-grained sediments are being released into the southern North Sea today.