International - Special Land Subsidence 2020

To develop a land subsidence monitoring system for cultivated peatlands four measuring techniques are applied in the north-eastern part of The Netherlands, including spirit levelling, extensometery, LiDAR and InSAR. The desired monitoring system should be able to capture long-term spatial and temporal subsidence trends at mm-scale accuracy. Preliminary levelling and extensometry results demonstrate seasonal and shorter-term dynamics with a total vertical movement of up to 35-40 mm in one-year time. A longer (multiple years) monitoring and experimenting period is needed to be able to determine long-term net subsidence (or uplift), and to optimize the subsidence monitoring system for peatlands.

In the Netherlands, subsidence of peat and clay soils due to (artificial) lowering of the groundwater table and loading of soft soils causes extensive damage. The topic is a major concern to homeowners and public authorities but an integrated risk assessment is currently lacking. In this paper, we propose a modular methodology for the systematic countrywide assessment of two subsidence-related damage mechanisms to buildings: timber pile rot due to low groundwater levels and differential settlement of buildings on shallow foundations. Application of the approach is expected to support private and public decision-making on coping strategies e.g. in awareness raising and evaluating interventions.

For the dike strengthening project Krachtige IJsseldijken Krimpenerwaard (KIJK) in The Netherlands two studies have been undertaken for which monitoring data played an important role. The data is used to determine the amount of soil needed to balance the subsidence and to quantify the building settlement due to natural subsidence.

The Delta Plan on Spatial Adaptation (DRA) aims to make the Netherlands climate-proof and water-resilient. Spatial adaptation means changing the public realm so that it can cope with the effects of climate change. As part of the DRA Programme (DPRA), Fugro was commissioned to contribute to a study on active groundwater level management.

In the 21st century, the Netherlands will be faced with four climate-related trends: it will get hotter, it will get drier (in summer), it will get wetter (in winter), and the sea level will rise. The effects and impact of this will be different for each sector. So far, over a hundred climate-related effects have been identified, from the rotting of wooden piles through to roads flooding.

The Geological Survey of the Netherlands maps the Dutch subsurface systematically in 3D. Here we outline the development of GeoTOP, its recent application in subsidence studies, and its use under a newly implemented key register of the subsurface. Recent studies based on GeoTOP confirm that

agricultural areas are more prone to subsidence by peat compression and oxidation than major urbanized areas. Subsidence is greatest in the central delta, a rural region that emits a lot of oxidation-related CO2, contributing to the greenhouse effect. Implementation of GeoTOP in the key register enables governmental stakeholders to make the right subsidence-related decisions.