The Harris-Galveston Subsidence District Board of Directors approved the District’s 2020 Annual Groundwater Report on Wednesday, May 12, 2021.

The District’s 45th edition of the report covers four main topics: climate data, groundwater use within the District, aquifer water levels, and updated subsidence rates. Each of these topics are compared to data from previous years, providing context on the impact that changes in water use and water sources can have on the occurrence and magnitude of subsidence.

“Monitoring subsidence, as well as groundwater use and aquifer water levels, allow the District to measure the effectiveness of its Regulatory Plan,” Deputy General Manager Dr. Tina Petersen said. “The change in water-level in the Chicot/Evangeline aquifers since 1977 clearly shows the impact of District regulation on the aquifers.”

Within the District’s three regulatory areas, Harris and Galveston counties withdraw groundwater from the Gulf Coast Aquifer System, including the Chicot/Evangeline aquifers. Since 1976, the District has worked with water users near the coast and then inland to switch from primarily groundwater to alternative sources of water in an effort to prevent subsidence.

“The District’s subsidence monitoring efforts include a GPS network with more than 250 GPS stations across multiple counties,” Project Chief Ashley Greuter said. “We also have research projects incorporating remote sensing techniques to broaden the coverage of changes in the land-surface elevation over time in the greater Houston-Galveston region.”

A Few Takeaways from the Report

  • On average, climate stations measured precipitation values lower than normal in 2020. Scholes Field in Galveston measured 15 inches under normal 29-year benchmark.
  • Groundwater use in the Houston region made up about 60 percent of total water use in 1976. In 2020, the percentage has dropped to 21 percent and a nine percent decrease in pumpage from 2019.
  • Most of the current groundwater use occurs in Regulatory Area Three where the conversion to alternative water supply will not be completed until 2035. Water-levels continue to be significantly lower than the historical benchmark, declines of nearly 370 feet in the Chicot/Evangeline aquifers.
  • The annual rates of subsidence observed in Regulatory Areas One and Two are generally stable, since both areas have reached their full regulatory conversion level (1990 and 1995, respectively) and Chicot/Evangeline water-levels have risen up to 242 feet.
  • Subsidence rates are generally above 0.5 centimeters (cm) per year throughout Regulatory Area Three as this area is still undergoing conversion.

“Our mission is to prevent future subsidence and mitigate its impacts, such as infrastructure damage and potential flooding impacts,” Dr. Petersen said. “The District gathers this data and creates this report so we, as a region, can make more informed decisions about groundwater use and aid in building a more resilient community.”

To view the full report and the executive summary, visit the Annual Groundwater Reports section. For more information on the District’s other ongoing research projects, click here.