In the early 1900s, subsidence was first observed near the Goose Creek Oil Field in Baytown, TX. This was the first documented case where shallow fluid withdrawal (in this case, oil and water) from the unconsolidated sediments of the Texas Gulf Coast resulted in a localized area of surficial fissures and subsidence. Increased oil production and the establishment of the Port of Houston in 1925 led to rapid industrial and, consequently, population growth. The region’s reliance on the groundwater resources of the Gulf Coast Aquifer sustained this growth. However, the community’s need outpaced the aquifer’s ability to safely meet their water demand, and the same mechanism that led to subsidence at Goose Creek Oil Field now resulted in widespread subsidence at rates exceeding 0.1 feet per year.
By the 1940’s, research conducted by local universities, the State of Texas, and the U.S. Geological Survey began to identify the correlation between groundwater withdrawal for municipal, industrial, and agricultural supply and subsidence. Level surveys conducted in the 1940s of National Geodetic Survey benchmarks established just after the turn of the century verified subsidence in the Houston region and further underscored the need to better understand the causal factors.
Although the scientific support connecting groundwater withdrawal and subsidence had been established for many years, it was not until the 1960’s when community leaders began to link the increased frequency and severity of flooding to the ongoing subsidence. The Houston region is essentially flat, with the land sloping generally towards the Gulf of Mexico about 1 foot every mile. Considering the topography, the recurrence of hurricanes and tropical storms, and the consistently high rainfall in the Houston region, flooding was already a concern; land subsidence was beginning to exacerbate the issue. In 1961, Hurricane Carla hit the Houston area, causing flooding on a scale that was beyond what was, in the past, expected from a hurricane of Carla’s size. As a result, local area governments began to analyze the serious and very real impact subsidence could have on the area’s potential economic growth and quality of life, and, just as important, began to determine what exactly could be done about it, and how best to reduce the region’s reliance on groundwater.
By 1973, the City of Galveston, working in cooperation with the City of Houston and the Coastal Water Authority, had begun converting to surface water supplied from Lake Houston, and in May of 1975, the Texas Legislature created the Harris-Galveston Subsidence District, the first political subdivision of its kind in the United States. Authorized as a regulatory agency created to cease ongoing and prevent future subsidence through science-driven groundwater regulation and impactful water conservation programs.
By 1976, the District had begun compiling hydrologic information on the characteristics of the most widely used water-bearing units in the Gulf Coast Aquifer System. The District went on to compile information on water usage and water supply in Harris and Galveston counties, and implemented regulatory procedures associated with the first groundwater regulatory plan. The District designated an area of concentrated emphasis and began working with regional water providers and groundwater users to reduce groundwater withdrawal in the coastal areas. The plan included directives to convert industries on the Houston Ship Channel to surface water supplied from the recently completed Lake Livingston reservoir. As a result of that effort, subsidence rates in the Baytown-Pasadena area were reduced significantly.
As subsidence rates were being reduced to near zero in coastal areas, groundwater levels in inland areas north and west of Houston were rapidly declining due to substantial development and rapid population growth in those regions. As a result, the water level in the Gulf Coast Aquifer declined by more than 100 feet between 1977 and 1997. Because of this increasing threat of subsidence in these areas, the HGSD adopted a series of regulatory plans to reduce groundwater pumpage, and ultimately mandated a reduction to only 20% reliance on groundwater by 2035.
