The central sea clay area (the polders)
The third type of sea clay area consists of polders. These polders can be situated on both old and young sea clay.
Polders on old sea clay
Around 1550, North and South Holland had some natural lakes in the peat scenery. These lakes became increasingly larger because of the dredging of the peat and erosion, resulting in a loss of valuable soil. To prevent this, the lakes needed to be impoldered.
The impoldering started by building a dike around the lakes. This dike was called a ring dike. Around the dike, a ring canal was dug, so that the water from the polder could be filtered off. The first polders were completed with the help of windmills. In 1852, electric draining was used for the poldering of the Haarlemmer Lake. This technique had progressed in 1930, with electric and diesel drains being used for the impoldering of the the Wieringer lake. With the polders impoldered, the old sea clay would sink to the bottom. The parcellation is modern and orthogonal in the polders on old sea clay and the scenery is rather flat.
Polders on young sea clay
The youngest polders are the IJssel lake polders, of which the bottom consists of young sea clay. The parcellation in these areas is straight and large-scaled. Soil usage in this area is highly varied and the ground water level is controlled through very effective drainage techniques.