Coastal Subsidence: Causes, Mapping, and Monitoring

Subsidence is a widespread phenomenon in what is named low laying areas, particularly important along several littorals because the coastal system consists of beaches and coastal wetlands. Ground subsidence has many causes that can be divided into two broad categories; shallow causes due to, for example, peat oxidation, compaction and groundwater extraction, and deep causes due to, for example, tectonic phenomena and effects of mining and extraction activities (gas, salt). Although subsidence can be a direct hazard (e.g. landslides, sinkholes), more commonly it is the associated hazards that are exacerbated by subsidence, which are a greater threat to human land use. Subsidence is generally under-acknowledged as a geohazard, indeed subsidence is generally too slow for human perception and effects are often invisible, at least before structural damage appears. This makes subsidence an insidious threat, which may proceed undetected for decades, e.g. having significant cumulative effects on flood risk or the integrity of water defences and infrastructure. Supported by advancements in space-based technologies and combining multi-sensor space-borne remote sensing (Synthetic Aperture Radar and optical) to estimate the variability and associated uncertainties the aim of this part of the book is to describe the causes of coastal subsidence, mapping and monitoring techniques including satellite-based methods. Different sites will be considered as example of relevant processes and monitoring techniques in subsidence areas.