Preliminary Findings from the Next Regional Water Planning Tool

On Tuesday, December 14, the U.S. Geological Survey released the preliminary findings for the new Gulf Coast Land Subsidence and Groundwater (GULF)-2023 model that illustrates the ongoing issue of compaction and subsidence in the Houston region.

Subsidence occurs at the surface when the aquifer compacts or sinks in on itself when the water is removed or lowered. The GULF-2023 model takes water use data, aquifer water level and subsidence measurements, and other research data and historical literature to simulate groundwater flow and compaction within the aquifers.

Preliminary Findings from the Model

Historically, subsidence has been a serious problem in the region since the early 1900s. Subsidence is caused when there is significant groundwater withdrawal from the aquifer, causing damage to infrastructure and private property. It also makes areas more prone to flooding.

“The model simulates the impacts of groundwater use on aquifer water levels and subsidence using observed data and cutting-edge model to recreate observed conditions since 1906,” Dr. Tina Petersen said. “This robust methodology confirms that water use is the key factor in determining the rate of compaction and subsidence.”

The model illuminates which aquifers are compacting and contributing to the observed subsidence. For example, the USGS provided preliminary results showing about a third of subsidence observed in the Spring Creek watershed can be attributed to compaction in the Jasper aquifer due to groundwater withdrawal. The Jasper aquifer is the primary source of groundwater throughout most of Montgomery County.

The modeling approach uses an ensemble, or collection of models, to provide greater information about model predictions and assess the likelihood of the subsidence results in the greater Houston area and Gulf Coast aquifer system.

General Manager Mike Turco emphasized that while the model is an improvement to the previous 2010 model, the understanding of the relationship between groundwater use and subsidence hasn’t changed – stress the aquifer, water levels go down, compaction occurs and subsidence is seen at the surface.

“This model will give us better insight into where compaction is occurring and its improved resolution will provide an important tool for the region to evaluate future water management strategies,” Turco said.

The Collaborative Planning Process

The new GULF-2023 model helps illuminate the historical threat of subsidence throughout the Houston region, using input from the local, state, and national levels.

“The new model is going through a very rigorous peer-review process conducted by the USGS,” Dr. Petersen shared.

“One of the goals of this study is to reproduce the observed subsidence in the Houston area” USGS Supervisory Hydrologist John Ellis said.

In Harris, Galveston, and Fort Bend counties, current regulations and future planned reductions in groundwater use are in place to prevent too much groundwater from being removed from the region’s aquifer. The model is being developed as part of an ongoing regulatory review process being conducted by both the Harris-Galveston and Fort Bend Subsidence Districts. This model will also update the Texas Water Development Board Groundwater Availability Model (GAM) for the northern portion of the Gulf Coast Aquifer System.

“Updated groundwater availability models are essential to water supply planning and ensuring that water managers have the best available tools to effectively manage this important resource,” said John Dupnik, Deputy Executive Administrator of Water Science and Conservation at the Texas Water Development Board. “Developing the GULF-2023 model is a significant step in a very collaborative process that the Texas Water Development Board is pleased to be part of.”

The finalized model report will be available later in 2022 and relies on coordination between multiple entities.

“Although the model is funded locally, we are collaborating with the Texas Water Development Board, a vital state agency charged with water planning for the state of Texas, and the USGS, a trusted national science agency,” Turco said.

How the Model Impacts Regional Water Planning Efforts

Going forward, the GULF-2023 model will be used to evaluate potential regulatory policies to address future water use, climate change, and their impacts on subsidence.

“This model calibration is an important milestone for our planning process,” Dr. Petersen shared. “The model agrees with what’s been observed in the past century and will help predict the effects of subsidence for the next century.”