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.