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What is Land Subsidence?
Subsidence is one of the most varied forms of ground failure, ranging from borad regional lowering of the land surface to local collapse.
The principal causes of land subsidence are:
- aquifer-system compaction,
- drainage of organic soils,
- underground mining,
- natural compaction,
- sinkholes, and
- thawing permafrost.
Why is Land Subsidence Important to UNESCO?
Land subsidence can have significant local or regional impacts. The practical impact depends on the specific form of the surface deformation.
- Regional lowering may aggravate the flood potential or permanently inundate an area, particularly in coastal or riverine areas.
- Local collapse may damage buildings, roads, and utilities and either impair or totally destroy them.
Subsidence is more hazardous to property than to life, because of the typically low rates of lowering. It has caused few casualties. Subsidence, however, increases the potential for loss of life in flood-prone areas by increasing the depth and size of areas susceptible to flooding.
What is the UNESCO
Working Group on Land Subsidence?
The UNESCO Working Group on Land Subsidence enhances the scientific understanding and technical knowledge required to identify and characterize hazards related to natural and anthropogenic land-level lowering.
The Working Group promotes and facilitates the international exchange of information regarding the design, implementation and evaluation of risk assessments and mitigation measures, and the definition of resource-management strategies that support sustainable development in areas vulnerable to land-level lowering.
The mission of the United Nations Educational, Scientific, and Cultural Organization (UNESCO) is to contribute to the building of peace, the eradication of poverty, sustainable development and intercultural dialogue through education, the sciences, culture, communication and information.
Recognizing that land subsidence is globally prevalent and that much of the subsidence is related to hydrological processes affected by human development of local land and water resources, “Land Subsidence” was included in the United Nations Educational, Scientific and Cultural Organization (UNESCO) programme of the International Hydrological Decade, 1965-1974. During the Decade, UNESCO organized the 1st International Symposium on Land Subsidence in Tokyo in 1969. In 1975 land subsidence was retained under the framework of the International Hydrological Programme (IHP) as subproject 8.4 "Investigation of Land Subsidence due to Groundwater Exploitation," and UNESCO formed the associated Working Group on Land Subsidence.
The first Working Group, of which Laura Carbognin (Honorary Chairperson) is the only original member still active in the present group, was chaired by the late Joe Poland, USA (affectionately referred to as "Mr. Land Subsidence" and the "Saviour of Venice"), and comprised the late Soki Yamamoto, Japan, Germán Figueroa Vega, Mexico, the late José da Costa, UNESCO, and the late Ivan A. Johnson, USA, past chairman. The first goal of the UNESCO Working Group was to produce a guidebook to serve engineers, geologists and hydrologists confronting land subsidence problems, particularly in developing countries. The volume1 was published by UNESCO in 1984, and since then the UNESCO Working Group has become the recognized leader in promoting global land subsidence studies, and collaborating with other international scientific organizations to coordinate and host international symposia on land subsidence about every five years.
Since the 1st International Symposium on Land Subsidence, 7 more international symposia on land subsidence have been convened through cooperation of UNESCO with the International Association of Hydrological Sciences (IAHS), and several other agencies and organizations. The proceedings of each of the symposia and the companion publications comprise numerous scientific papers covering the various types of subsidence identified throughout the world. The documents constitute a rich source of research and case studies on subsidence attributed to anthropogenic and natural processes, the development and use of measurement tools such as extensometers, global positioning systems (GPS) and more recently, interferometric aperture radar (InSAR), and the development of mathematical methods and models to simulate flow and aquifer deformation.
- Poland, J. F., ed. () Guidebook to studies of land subsidence due to ground-water withdrawal. United Nations Educational, Scientific and Cultural Organization, Paris, Studies and Reports in Hydrology 40, 305 p., app. A-E., http://unesdoc.unesco.org/$other/unesdoc/pdf/065167eo.pdf, accessed .
What Does the UNESCO Working Group on Land Subsidence Do?
Recent activities of the working group have included:
- Coordination of the Ninth International Symposium on Land Subsidence.
- Advising UNESCO on land subsidence issues and priorities.
- Publication of the proceedings of the Eighth International Symposium on Land Subsidence (EISOLS.)
The Working Group on Land Subsidence develops long- and short-term strategic plans to guide its work in support of UNESCO's mission. The strategic plan is revised annually to respond to changing needs andresources.
Near-term strategies, 2012-2013
- Evaluate regional focus and develop coordination with existing UNESCO IHP Centers and Chairs.
- Summer School Courses (1-2 weeks) focusing on developing countries and oriented to specific topic such as modeling, laboratory measurements, interferometry, and in situ instrumentation.
- Technical Meeting (Workshops) on narrow topics for example land subsidence in coastal areas, subsidence mitigation, etc.
- Planning Ninth International Symposium on Land Subsidence (NISOLS.)
- Coordinate with other UNESCO Regional Offices, IAHS, National IHP Committee Representatives, and other organizations.
Long-term strategies, 2013-2015
- Increase interdisciplinary linkages with other UNESCO programs such as IGCP (International Geological Correlation Programme). Working Group goal is to improve the use of land subsidence science in policy and decision making for managing water and other natural resources.