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1. www.usgs.gov › extensometers-and-compactionExtensometers and Compaction | U.S. Geological Survey - USGS.gov

   www.usgs.gov › extensometers-and-compaction

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   Extensometers measure the compaction and expansion of the aquifer system, providing depth-specific data that can help CAWSC scientists better understand the rate, extent, and at what depths in the system subsidence is occurring.

2. www.usgs.gov › centers › california-water-scienceUSGS Scientists Explain How Aquifer Compaction is Measured

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   The Porterville extensometer is located near the Friant-Kern Canal which has been negatively impacted by differential land subsidence (differing amounts of subsidence across the landscape) and can now only transmit about 40% of the water it was designed to transmit.

3. www.usgs.gov › news › extensometer-hunters-searchingExtensometer Hunters: Searching for Long-Lost Technologies in ...

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   Mar 16, 2017 · While a few days in the San Joaquin Valley might not be the same as three years aboard the starship Enterprise, California Water Science Center scientists searching the Valley for lost technologies had no less of an exploration ahead of them during a July 2016 field trip to the area.

4. data.cnra.ca.gov › eu › datasetLocation of 24 extensometers used to measure compaction in ...

   data.cnra.ca.gov › eu › dataset

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   This digital dataset describes the location of 21 extensometers used for observations of subsidence in the Central Valley Hydrologic Model (CVHM). The Central Valley encompasses an approximate 50,000 square- kilometer region of California.

   • Contact Email: ccfaunt@usgs.gov
   • Publisher: U.S. Geological Survey

   • Contact Name: U.S. Geological Survey

5. data.cnra.ca.gov › dataset › measured-compaction-forMeasured compaction for 24 extensometers in the Central Valley

   data.cnra.ca.gov › dataset › measured-compaction-for

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   This digital dataset contains the compaction data for 24 extensometers used for observations in the Central Valley Hydrologic Model (CVHM). The Central Valley encompasses an approximate 50,000 square-kilometer region of California.

   • Contact Email: ccfaunt@usgs.gov
   • Publisher: U.S. Geological Survey

   • Contact Name: U.S. Geological Survey

6. data.usgs.gov › datacatalog › dataUSGS Science Data Catalog

   data.usgs.gov › datacatalog › data

   This digital dataset describes the location of 21 extensometers used for observations of subsidence in the Central Valley Hydrologic Model (CVHM). The Central Valley encompasses an approximate 50,000 square- kilometer region of California.

7. People also ask

   Where are extensometer stations located?

   • A relatively dense network of extensometer stations has been established in metropolitan areas experiencing significant land subsidence. Two major examples are Houston, Texas, USA and Shanghai, China.

   3.4 Borehole Extensometer – Land Subsidence and its Mitigation

   books.gw-project.org/land-subsidence-and-its-mitigation/chapter/borehole-extensometer/

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   When was the first borehole extensometer installed?

   • The first borehole extensometer was installed in 1955 by the United States Geological Survey in the San Joaquin Valley, California, USA (Poland, 1984). Since then, extensometer technology has seen progressive improvement, playing an important role in relating land subsidence to the compaction of confined aquifer systems.

   3.4 Borehole Extensometer – Land Subsidence and its Mitigation

   books.gw-project.org/land-subsidence-and-its-mitigation/chapter/borehole-extensometer/

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   How accurate is an extensometer?

   • The instrumental precision heavily depends on the actual extensometer implementation, but a nominal deformation resolution of 0.01‑0.1 mm can be achieved over a 200‑1000 m depth (Riley, 1986).

   3.4 Borehole Extensometer – Land Subsidence and its Mitigation

   books.gw-project.org/land-subsidence-and-its-mitigation/chapter/borehole-extensometer/

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   What is an extensometer used for?

   • They are used to measure the change in the distance between the land surface and a subsurface benchmark situated at the bottom of a deep borehole. If the subsurface benchmark is established below the base of the compacting aquifer system or in the bedrock, the extensometer can be used as the stable reference for local geodetic surveys.

   3.4 Borehole Extensometer – Land Subsidence and its Mitigation

   books.gw-project.org/land-subsidence-and-its-mitigation/chapter/borehole-extensometer/

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   Can a borehole extensometer be used for geodetic surveys?

   • If the subsurface benchmark is established below the base of the compacting aquifer system or in the bedrock, the extensometer can be used as the stable reference for local geodetic surveys. The first borehole extensometer was installed in 1955 by the United States Geological Survey in the San Joaquin Valley, California, USA (Poland, 1984).

   3.4 Borehole Extensometer – Land Subsidence and its Mitigation

   books.gw-project.org/land-subsidence-and-its-mitigation/chapter/borehole-extensometer/

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   How deep is a borehole extensometer?

   • The borehole extensometers, which were designed according to the sliding‑joint casing type, span a depth down to 936 m (Yu et al., 2014). Shanghai is the first city in China where land subsidence was investigated and monitored, being one of the country’s most densely populated and developed areas.

   3.4 Borehole Extensometer – Land Subsidence and its Mitigation

   books.gw-project.org/land-subsidence-and-its-mitigation/chapter/borehole-extensometer/

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8. books.gw-project.org › borehole-extensometer3.4 Borehole Extensometer – Land Subsidence and its Mitigation

   books.gw-project.org › borehole-extensometer

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   Two major examples are Houston, Texas, USA and Shanghai, China. The Houston‑Galveston area is an extreme example of subsidence hazards, a problem that affects many other USA metropolitan areas, for example: Los Angeles, California; Sacramento, California; and New Orleans, Louisiana.