The northern sea clay area (Groningen and Friesland)
Silt marsh shores are common in the sea clay area in the north of the Netherlands. Silt marsh shores originated from old silt marshes that rose strongly through accretion during high storm surges. The storm surges wore away the silt marsh shores through erosion, and the eroded material would wash over the land and form silt marsh shores.
Since silt marsh shores were situated high up, they were an idea place for people to settle. The first people settled there from about 600 years before Christ. However, as described earlier in this chapter about the development of the sea clay scenery, the sea level started to rise again around 500 years before Christ. To ensure the water did not reach their houses, people had to raise their residential land areas by means of clay and sand. This is how terps originated. Terps had to be raised over and over again because of the rising sea level.
Between 300 and 1000 years after Christ, the influence of the sea on the scenery was increased because of different transgressions. The sea regularly flooded the land and left behind a layer of heavy clay. This clay has a lime deficiency and is called ‘knipklei’ in Dutch.
1000 years after Christ, dikes were built north of the silt marsh shores. The terps became places for permanent habitation and more and more sea clay soil was parcellated from the terp villages. Thanks to improved techniques, land was able to created on the seaside from the year 1200. The land reclamation of these young salt marsh soils was stimulated by the wealth of the inhabitants. The owners of the land within the dikes, were entitled to the salt marshes which bordered onto their territory. People would dike in these areas, by which their territory grew. Strip parcellation developed, perpendicular to the dikes. The soil of this new area consisted of sea clay. The silt marsh shores were situated south of this sea clay.
Nevertheless, the effect of the sea was still noticeable after the impoldering: every now and then, much of the newly reclaimed land was lost because of storm surges. The sea caused large crevices in the land, through which some so called sea gulfs developed. The ‘Lauwers sea’ and the ‘Dollard’ are examples of such sea gulfs.
Outside the dikes of the young salt marsh soils, land reclaimation was stimulated by humans. The tide-land during ebb tide was surrounded by osier dams. This allowed the sea water to be held back, and the fertile clay was able to settle. Gradually, the land would silt up and new ground would be reclaimated.
The sea clay of the north of the Netherlands has many different types of parcellation and soil usage. As described earlier, strip parcellation occurs in the ‘knipklei’-area. The wet soils that are situated at a lower level are usually used as grassland. The sandy clay of the salt marsh shores are irregularly parcellated into blocks. These areas, which are situated higher up, were primarily used for cattle breeding in Friesland and for agriculture in Groningen. The fertile sea clay of the young, diked salt marsh soils made a good soil for agriculture.