Influence of harbour construction on mud accumulation in the Scheldt estuary

Abstract

The bottom sediments of the turbidity maximum area of the Scheldt estuary were mapped in 1999 using echo sounding, sidescan sonar and grain-size analyses of bottom sediments. Four sediment types, sand, muddy sand, sandy mud and mud were recognised. Mud, with very little sand, occurs mainly in the access channels to the sluices giving access to the harbour docks of Antwerp. The sediments of the main channel have a sandier texture. One might conclude that the total mud stock in the middle estuary has increased, both between 1964–1986 and 1986–1999, but on the contrary the mud supply from the river, the mud stock in the river channel and the mud supply to the lower estuary have all decreased. The increase in the mud stock in the area as a whole was completely at the expense of mud deposition in the access channels to the sluice gates giving access to the harbour of Antwerp. The mud stock in the river channel decreased over the years because of a decreasing mud supply from the river. The mud stock in the river channel shows variations that are directly related to fluctuations in the river load. When the suspended matter decreased during a certain year the supply of silt and clay particles decreased correspondingly and the resuspension-deposition mechanism caused a relative increase of the sand fraction in the bottom sediments in that year.