HGSD began groundwater regulation in 1976 near Texas’s Gulf Coast, where subsidence was most prevalent. By the 90s, this area met its regulatory requirements and fully transitioned to alternative water supplies, like treated surface water, to meet 90% of its water demand, ultimately ceasing subsidence near the coast. As the region grew, subsidence shifted more inland to areas that heavily relied on groundwater as their primary water source, leading to conversion requirements for northern Harris County and the creation of the Fort Bend Subsidence District.
Both subsidence districts work together to reduce reliance on groundwater to prevent further subsidence within their jurisdictions; however, regional collaboration is vital to mitigation efforts because the Gulf Coast Aquifer, an aquifer system that compacts when too much groundwater is removed from it, is shared by several neighboring counties.
While HGSD’s regulatory authority is limited to Harris and Galveston counties, it does not limit its subsidence science and research to just these areas and proudly supports neighboring counties with data and resources that can be used to protect our shared aquifer.
To effectively stop subsidence in our region, we must:
- Reduce reliance on groundwater through regulation that allows the sustainable use of our groundwater resources,
- Support long-term regional water planning that provides alternative water supplies to meet our growing water demand, and
- Utilize conservation best practices to make each drop of water go further and protect our natural resources for generations to come!
Subsidence is the gradual sinking of the land caused by subsurface movement. Our region’s distinct experience with subsidence is due to groundwater withdrawals from the Gulf Coast Aquifer System, a multilayered groundwater reservoir made up of layers of sand, silt, and clay that compact when too much groundwater is removed. The process is slower than that of other hazards; however, once this subsidence occurs, it is irreversible and has significant impacts, including:
- permanent loss of land elevation (i.e., Brownwood Subdivision in Baytown, Texas)
- damage to important infrastructure like homes, buildings, pipelines, roads, and bridges
- disruption to the natural flow and drainage patterns; and
- contributing to increased flood risks
To prevent further subsidence, the Harris-Galveston Subsidence District works diligently to reduce reliance on groundwater through groundwater regulation and water conservation.
Illustration of subsidence in a Gulf Coast aquifer as a result of groundwater withdrawals producing a decrease in the potentiometric surface (the groundwater level). Source: Kasmarek, M.C., Ramage, J.K., and Johnson, M.R., 2016, Water-level altitudes 2016 and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction 1973–2015 in the Chicot and Evangeline aquifers, Houston-Galveston region, Texas: U.S. Geological Survey Scientific Investigations Map 3365, pamphlet, 16 sheets, scale 1:100,000, http://dx.doi.org/10.3133/sim3365.
The most effective way to stop subsidence in our region is to reduce reliance on groundwater through groundwater regulation and convert to alternative water sources for our primary water supply. In areas where groundwater withdrawals have been reduced, subsidence rates have also been reduced. In areas that heavily rely on groundwater, subsidence rates continue to rise.
HGSD applies a science-based Regulatory Plan that establishes guidelines for groundwater withdrawals through a well-permitting process to reduce reliance on groundwater. The plan segments Harris and Galveston counties into three regulatory areas. Each area has conversion goals to reduce groundwater withdrawals to a specified percentage and to supply the majority of its water demand through alternative sources by a designated timeline. The plan uses a science-based adaptive management strategy that factors water demand and population growth, availability of alternative water supplies, subsidence modeling, and regulatory scenarios to determine conversion requirements.
The plan is regularly reviewed through a multi-agency effort called the Joint Regulatory Plan Review and is backed by the best available science to ensure its effectiveness in preventing further subsidence in Harris and Galveston counties.
Additionally, water conservation efforts help to further reduce reliance on groundwater. The District has several water conservation programs, including a grant program to fund local water conservation projects, a school program to educate our future water users and decision-makers, and a platform for water conservation tools, tips, and resources available online at smarteraboutwater.org.
Our region’s subsidence problem is a direct result of our reliance on groundwater from the Gulf Coast Aquifer System, which is simply not built to support large volumes of withdrawal. However, now that we know the cause, we can work together to prevent further subsidence by reducing reliance on groundwater through:
- Science-driven groundwater regulations that allow groundwater to supply water demand at a volume that does not further cause subsidence.
- Sustainable regional water planning that provides alternative water supplies to meet growing demand.
- Water conservation efforts that protect our natural resources and help us use our water supplies more efficiently.
Because subsidence occurs slowly over time, it is difficult to see its impact until the damage is already done. Once subsidence occurs, it is irreversible and has contributed to significant impacts on the greater Houston area, including:
- permanent loss of land elevation (i.e., Brownwood Subdivision in Baytown, Texas)
- damage to important infrastructure like homes, buildings, pipelines, roads, and bridges
- faulting
- disruption to the natural flow and drainage patterns; and
- contributing to increased flood risks
Our region’s first recorded subsidence occurred back in 1918 near Baytown, Texas. As the area grew, so did water demand, and subsidence became more of a concern; some areas sank over 9 feet within four decades, prompting the creation of the Harris-Galveston Subsidence District in 1975 to regulate groundwater near the coast. By the 90s, this area worked hard to diversify its water supplies, bringing in alternative water sources like treated surface water to meet its water demand and reduce reliance on groundwater, which resulted in stabilized subsidence rates. However, subsidence in our region has moved more inland as groundwater continues to be a primary water source until alternative water supplies become available.
Brownwood Subdivision in 1944 to 2002. Slide the arrows to see the impact of subsidence.