50 jaar maaivelddaling van veengrasland : ruim vijf decennia (1968-2024) meten op 29 locaties

One of the most feared consequences of deeper drainage of peat soils is the increase in surface level subsidence. Over a period of 50 years, the land subsidence and soil layer profile were measured using subsidence plates at 29 locations in the Netherlands. In this study, the focus was on long-term irreversible land subsidence. This means that only the dataset with the spring measurements has been analyzed. The average surface level subsidence rate of all locations over 1970-2020 is 7 mm/year. There is a large spread around this average, for example, only 2 mm/year is measured in Hoenkoop and on the other hand more than 17 mm/year in Spannenburg and Assendelft. There is a clear relationship between the measured ditch level and the surface level subsidence rate. It is striking that even at high ditch levels (< 30 cm bls), significant surface level subsidence is still measured. By comparing the contribution of the various soil layers to the subsidence of the surface, it becomes clear that about 2/3 of the subsidence takes place in the layers where oxygen can penetrate (< 80 cm bls). In those layers, oxidation and partial shrinkage are the most important processes. In the layers that are always saturated 1/3 of the ground level subsidence still occurs. Partly caused by consolidation and partly by creep.