As humans continue to inhabit coastal and naturally swampy areas, the need to drain surface and subsurface water can cause significant sinking of local land. Subsidence occurs when upper layers of ground shift downward to replace the empty space left after drainage. Many urban areas are subsiding due to withdrawal of ground water or other fluids (oil, natural gas). For certain types of aquifers, if the subsidence process goes on for long enough, permanent loss of porosity may occur, leaving little or no opportunity for the natural recharge of ground water.

Mexico City has sunk roughly nine meters in the last century with an annual rate of sinking as high as 38 cm/year. Damage has plagued the city’s infrastructure, including building foundations, wells, streets and the sewer system. Flooding has become a problem as the city now lies six feet below nearby Lake Texcoco. This rapid subsidence is due to the fact that ground water is withdrawn faster than it is replenished, and the rocks on which the city is built – clay, sand and gravel- easily compress when the liquid is drained.

Other areas, including parts of New Orleans, are subsiding due to the drying out and decomposing of organic-rich soils that were originally marsh deposits, subsequently drained to facilitate urban development. Drainage of ground water often causes the aeration of soil, allowing the oxidation of its organic components, such as peat. This decomposition process may cause significant land subsidence as the topsoil compresses and consolidates as a result of increased effective stress. Under these types of conditions, subsidence can become a gradual and sustained occurrence with damaging effects on local homes, economy, and wild life. Measures must be taken in order to monitor and keep the process under control.

Interferometric Synthetic Aperture Radar (InSAR) is a technique using multiple SAR images in sequence to determine minute changes on the ground. This approach has been demonstrated to measure surface subsidence and rebound in response to aquifer discharge and recharge in regions, such as Los Angeles, Las Vegas, Houston and other cities, dependent on subsurface water.