Flooding problems related to land subsidence
For centuries the low-lying peatlands and polders in Friesland, Utrecht and Holland have been drained to keep the land suitable for agriculture. As a result, the peat layers have dried out and decomposed, resulting in significant land subsidence. The land keeps on sinking. During wet periods excess water is drained, but in dry periods land subsidence continues. Flooding risks are increasing because polder boezems (drainage reservoirs) have an increasingly hard time to drain excess water during wet periods. At the same time, summer water shortages are increasing because the boezems cannot keep up with the demand for water during periods of drought.
Clearly, land subsidence is not only an agricultural, but also a cultural-historical, ecological and environmental problem. And it threatens the recreational function of areas such as the ‘Groene Hart’ (the polderland surrounded by Amsterdam, The Hague, Rotterdam, and Utrecht).
In polders that are susceptible to (saline) groundwater intrusion, effective climate buffers can be created by increasing groundwater levels. This will slow down, stop, or even reverse land subsidence, and reduce (saline) groundwater intrusion. Natural peat accumulation and soil formation will raise polder levels by approximately 1 cm per year.
The natural ‘sponge’ function of shallow peat meadows and low-lying peat marshes such as the Naardermeer lake area can be restored, and peat plant communities will return. The increased water retention capacity of these areas will improve the water supply for surrounding agricultural and residential areas. Cultural heritage is preserved, recreational opportunities open up, and marshland habitat becomes available for various bird species, including black tern, bittern, purple heron and great reed warbler.
Agricultural land will have to be converted to create these buffers, but conversion may be more cost-effective than continued farming. ‘Uncoupling’ peat meadows from their polder drainage system will relieve the polder boezems. The water storage capacity thus made available can be used to drain excess water from surrounding agricultural, residential and industrial areas. The water stored in the climate buffer ‘sponges’ is a valuable water reserve during droughts.