Miles from Venice
While I am originally from Canada, I’ve been in Houston for nearly five decades and consider myself a Texan. Frustratingly enough, in that time I have been unable to shake an old habit of reading foreign newspapers. In a recent perusal of the British press, I chanced upon a most disconcerting report proclaiming our cherished Houston as the swiftest subsiding metropolis in all of America. It was said that research from multiple sources have estimated “as much as 42% of Houston's land area is subsiding faster than 5 millimeters per year, and 12% is sinking faster than 10 millimeters per year.” Houston is indeed sinking, however we are miles from Venice, both figuratively and literally.
This year marks the 50th anniversary of the Harris-Galveston Subsidence District, established to address Houston’s sinking land issue which once-upon-a-time threatened the region’s viability. The district pro-actively works to mitigate subsidence across the Upper Gulf Coast Aquifer, and it should be noted that it has had measurable success in so doing.
Houston has traditionally relied on aquifers for drinking water, naturally filtered through layers of sand and clay. The key aquifers here are the Chicot, Evangeline, and Jasper. The Jasper recharges mainly in Grimes County, while the Chicot and Evangeline draw recharge from Grimes, Montgomery, Harris, and Galveston Counties. As Houston developed, three factors impaired aquifer recharge. First, groundwater extraction surged. Second, paved surfaces expanded, blocking water infiltration. Third, enhanced drainage systems, built alongside development, sped up stormwater runoff, reducing its time in the watershed. Despite consistent annual rainfall, these changes hindered aquifer replenishment.Aquifers consist of permeable materials like sand and silt beneath clay layers. Clay expands or contracts with water content, while sand and silt maintain volume. When recharge fails, water voids in clay become empty, causing the clay to collapse into these spaces. This consolidates both clay and sand layers, lowering the elevation of overlying strata. Over time, this subsidence reaches the surface.
Coastal areas face heightened risks from subsidence. For instance, Brownwood Subdivision near Baytown, built in the 1940s, was largely submerged by Galveston Bay by 1975 due to sinking land. Recognizing varying risks, the Subsidence District divided its regulatory area into three zones. Area 1, mostly coastal, faces the strictest rules, with groundwater use reduced to under 10% through surface water conversions. Area 2 maintains groundwater at 20% of total use, while Area 3 and non-regulated areas allow up to 40% groundwater reliance, with less aggressive surface water shifts.
The Subsidence District’s 2025 annual report, covering 2020–2024, illustrates that aggressive groundwater reductions in Areas 1 and 2 have significantly curbed subsidence. The focus now shifts to Area 3 and beyond, where transitioning to surface water could further limit subsidence. Data from Areas 1 and 2 suggest that cutting groundwater to 15% of total demand could enhance property protection by minimizing subsidence risks.
The question remains: Where will Houston’s surface water come from to support these reductions? We’ll explore that next time.
Dr. Culp is the most senior hydrologist at Tetra Land Services and has three decades of civil engineering experience. His Ph.D. scholarship studied the effectiveness of structural BMP for the control of storm water pollution in Harris County while performing water quality monitoring and modeling upon selected ponds for the county. Dr. Culp also co-authored the City of Houston stormwater quality management plan. He is one of Texas’s original Certified Floodplain Managers. Recently, Dr. Culp and his staff have developed a series of drainage studies for Industrial and Oil Majors along the Texas Gulf Coast. Dr. Culp is married with two children, and lives on his farm in Southwest Houston.