According to the Harris-Galveston Subsidence District (HGSD), land subsidence is the sinking of the earth’s surface due to subsurface (underground) movements. Land subsidence occurs when large amounts of groundwater have been excessively withdrawn from an aquifer. The clay layers within the aquifer compact and settle, resulting in lowering the ground surface in the area from which the groundwater is being pumped.
Over time, as more water is removed from the area, the ground drops and creates a cone. Once the water has been removed from the sediment, it cannot be replaced. For example, only about 5.3 million acre-feet of the total rainfall “recharge” Texas aquifers each year. However, in 1996 approximately 9.9 million acre-feet of groundwater were pumped, resulting in a net loss of 4.6 million acre-feet of groundwater.
Land subsidence can lead to many problems, including changes in elevation; damage to structures such as storm drains, sanitary sewers, roads, railroads, canals, levees and bridges; structural damage to public and private buildings; and damage to wells. Most commonly, though, subsidence is known for causing an increase in the potential for flooding.
Because of the growing awareness and concern of subsidence-related problems, the 1975 Texas legislature created the HGSD. Their mission is “to control subsidence and manage groundwater resources in Harris and Galveston Counties through regulation of groundwater withdrawal, conservation, and cooperation with surface water suppliers to assure adequate future supplies of water for beneficial uses.”
The United States Geological Survey maintains 14 borehole extensometers in the Houston-Galveston area. The goal of these extensometers is to measure compaction from different aquifers. HGSD has a number of CORS sites that are used to monitor subsidence. CORS (Continuously Operating Reference Station) sites continuously measure subsidence around the clock.
One of HGSD’s CORS sites is located in The Woodlands. Last month, HGSD worked alongside SJRA to get the CORS site up and running. Below are some pictures of the HGSD’s CORS site on SJRA property.
Before installation
After installation
John Yoars, Woodlands MUD #36 Director, Mike Turco, General Manager, Harris Galveston Subsidence District, and Matt Corley, Customer Service & Compliance Manager, San Jacinto River Authority visit the newly installed CORS site
One of the major river authorities in Texas, SJRA’s mission is to develop, conserve, and protect the water resources of the San Jacinto River basin. Covering all or part of seven counties, the organization’s jurisdiction includes the entire San Jacinto River watershed, excluding Harris County. For additional information on SJRA visit our website at www.sjra.net, like SJRA on Facebook @SanJacintoRiverAuthority, follow us on Twitter @SJRA_1937, find us on Instagram @sanjacintoriverauthoritySJRA, or connect with us on LinkedIn @San Jacinto River Authority.
Featured in Dock Line Magazine.
