Subsidence due to peat decomposition in the Netherlands, kinematic observations from radar interferometry

The western part of the Netherlands has a typical Dutch landscape with drained peat meadows in polders below sea level. The area is used in concert for agriculture, recreation, residence, and nature conservation. Water levels are being artificially controlled in the area. Large areas of this region are fen-meadows that consist of wet pasture lands with drained peat soils alternated by natural and artificial lakes, ditches, reed swamps and quaking fens. The current fen-meadows have originated from the drainage of a large peat system dating back from 1800 B.C. To keep the land suitable for agricultural use, the peat area has been drained deeper in recent decades. This drainage has resulted in a subsidence of the soil and as a result the polders with fen-meadows are now 1-2 m below sea level. In between the fen-meadows, deep polders with a clay soil are found. These deep polders used to be large lakes, which have been reclaimed in the 17th century for agricultural use. Presently, these polders are 2-6 m below sea level. The observation of subsidence of wetlands is notoriously difficult using conventional geodetic techniques, due to the absence of fixed benchmarks. Here we show that analyses from persistent scatterer interferometry (PSI) can be used to infer subsidence rates of several millimeters per year, using coherent targets identified in the area. These results are obtained over the Green Heart, an open area surrounded by a horseshoe-shaped ring of cities, Randstad Holland. The derived subsidence rates will be interpreted and related to processes in the shallow subsurface. This paper presents preliminary results of the investigation.