Introduction of current subsidence maps
Earth observation technologies (radar satellite) can be used to derive soil subsidence indicators for urban (paved) and rural (non-paved) areas. The main cause of upper soil subsidence in rural areas is peat oxidation/clay settlement as a result of the water management pursued, in which the groundwater level is kept well below the surface level. In urban areas, the main cause is the compression of soft layers by the deposited loads (particularly sand deposits and pavement). In urban/built-up areas, other key causes of soil subsidence, in addition to the weight on the soil, are (thick) foundation layers that put pressure on the subsoil.
Many factors can affect the quality of satellite measurements, especially in rural areas. That is why an average of 150 images have been used over a period of several years in order to compile a statistically substantiated relative soil subsidence indicator for each sub-area. Additional research is needed to filter out other interferences. Validation has shown that with respect to rural areas (particularly a large number of peat and clay areas), the soil subsidence indicators produce relevant signals. In other areas (e.g., sandy soils), however, soil subsidence has been identified by the radar at locations where it is not expected. The validation report on the indicator maps is available here .
The maps can provide insight relating to the topics of drought and waterlogging, by identifying locations prone to soil subsidence, along with its degree and spread. In urban areas, the soil subsidence indicators are added to the currently available model-based soil subsidence prediction maps (see “Soil Subsidence Prediction Maps” tab). However, improved maps for both urban and rural areas, covering the whole of the Netherlands, are expected in the years ahead.
Why is this topic important?
Soil subsidence in urban and rural areas ensues from a wide range of factors, the most important of which is human intervention and the climate. By reference to the aforementioned causes of soil subsidence in various conservancy areas, the indicator maps can provide information on the spread and the extent of soil subsidence, thus enabling assessment of measures (e.g., the impact of water level management - MLGL and the duration of low groundwater levels – but also the impact of land level raising and the construction of foundation layers).