Under the influence of the tide, the landscape of Saeftinghe is constantly changing as areas erode and build up. Overall, about 30% of the area is composed of a mosaic of sand banks, mud banks and creeks, with the remaining 70% being vegetated with salt marsh plants and grasses. In some areas, century old peat also appears at the surface.
During heavy storms, ferocious waves pound against the steep edges of salt marsh, eating away at the banks, and due to the turbulence of fast flowing storm tides, the silt and sand in the creeks is shifted around. Following severe storms, once the tide has receded, you will see that whole creeks have moved and a wild pattern of wave ripples have been left in the sand. Some steep edges of salt marsh and sand bars will have partially (or completely) gone, and little streams that only a few days earlier were passable on foot, might have been transformed into massive creeks or high sand bars.
Any eroded sand and silt taken up by the tide has to settle again somewhere else. This occurs most readily in areas where the water flows more slowly - predominantly on the inside bend of creeks and in dead-end gullies deep in the salt marsh. The suspended sand particles are much bigger and heavier than silt particles, and therefore settle much quicker in slow flowing water than the suspended silt particles, which require still water in order to settle. This is why you will often find that the edges of creeks are dominated by sandy particles, whereas more clay and silt can be found in the middle of vegetated salt marsh.
Salt Marsh, Levees and Marsh Flats
As time passes, sandbars can turn into salt marsh composed of levees and marsh flats. The creeks are bordered by high sided, sandy banks: levees, which act like small barriers that restrict water flow into the salt marsh. These levees enclose the lower lying marsh flats – silt/clay areas of vegetated salt marsh.
Initially, water floods over the creek banks with every high tide. Each time this happens, a little more sand settles on the levees, and the silt particles precipitate when the water comes to a virtual standstill over the lower marsh flats.
As the levees and marsh flats get higher through the sedimentation process, eventually it might become sufficiently dry for salt marsh plants to start colonising the ground. If this happens, the sedimentation process increases considerably; the growing plants slow down the water flow, making deposition of sediment easier. This results in the salt marsh getting higher and higher, and even more plant species establishing themselves.
Sand Bars and Megaripples
At the entrance to the larger creeks Ijskelder, Hondegat and the smaller Speelmansgat, are massive sand bars. A striking feature of these sand bars are the megaripples: wave ripples in the sand that are created by strong currents and can measure a metre high and several metres wide. The most impressive sand ripple landscape in Saeftinghe is found northeast of the radar tower. Smaller sand ripples can be seen throughout Saeftinghe – the result of changing water currents and the wind.
At several locations, peat banks appear where the sand layer has been eroded on the banks of the Western Scheldt. These peat banks were formed at an earlier time, when Zeeland was completely overgrown. At low tide these peat banks appear above the water as steep black cliffs. Peat can be found under a large part of Saeftinghe, up to several meters thick in some areas, but is only visible around the beaches. From the peat we can read in to Saeftinghe’s history: many thousands of years of seeds, roots, and even whole trees can be found.
Even older than the peat is a sand layer that can be found only at extremely low tides in the mouth of the Ijskelder, underneath the peat. This sand layer is called ‘dekzand’, and is the remnants of an old dune system that dates back to the last Ice Age. It runs directly under the whole area and emerges again at the surface close to Hulst.