Modeling the Future: Water Quality Project Advances at Possum Kingdom Lake
The Brazos River Authority has reached the first major milestone in its Possum Kingdom Lake Water-Quality Modeling Project - the most comprehensive effort of its kind in BRA history.
In May, water sampling activities in the lake began as a way of establishing a data baseline for the model to be developed so it can predict how changes in land use might impact water quality. Algae are being analyzed in greater detail than ever before in BRA history, along with other parameters, such as nutrients, bacteria, and physical characteristics, that are routinely monitored by the river authority.
“Our goal is to create a modeling tool that will enable us to assess how changes around the lake may impact water quality” said Tiffany Malzahn, environmental and compliance manager for BRA. “We feel that we’re off to a good start.”
Algae specimens will be analyzed by a Baylor University laboratory while others will be handled by BRA’s laboratory. Sampling locations and depths were selected to capture both the main body of the lake as well as coves, and additional sampling will follow storm events.
The project was launched in late 2024 to better understand how future development around the lake could affect its exceptionally high water quality. Many lakes and rivers in the state are murky because of shallow topography while Possum Kingdom Lake is clearer because of the deep limestone canyon that holds the reservoir.
The project involves a dual-model approach that ties two models together to allow scientists and decision-makers to evaluate how changes in land use may influence water quality over time.
One component—a watershed model—will examine land-use changes, such as the conversion of ranchland into residential developments, and their impact on the water quality of the runoff that flows into the lake. The runoff will be assessed for nutrients, salinity, sediment, and bacteria, among other constituents. The other model component—a lake model—will look at nutrient patterns, river inflows, water levels, temperature fluctuations, and other variables to predict lake impacts.
“We want confirmation that we can recreate the historical record – which will give us confidence that the model can accurately predict what happens to water quality when changes occur,” said Tim Osting of Hazen and Sawyer, the engineering firm carrying out the project for BRA. “Those changes could include new development, a water plant near the lake or natural changes like an unusual storm or drought.”
Over the past year, the project team has:
- Reviewed data to identify strengths and gaps in available information
- Selected water sampling sites and parameters
- Developed a work plan that was peer reviewed and refined through input from BRA, a scientific review committee, and key stakeholders.
After a baseline is established, then the combined model will be tested and refined to ensure it can accurately simulate known events—such as the severe drought conditions that occurred between 2012 and 2015.
By September, about 50 percent of the initial lake model and watershed development should be completed.
The project team anticipates that by late summer or early fall, the models will be sufficiently developed to begin sharing calibration and initial results with the science review committee and stakeholders.
Through this forward-looking effort, the BRA is equipping the region with the tools needed to balance growth and conservation—helping ensure that Possum Kingdom Lake remains a vital resource for generations to come.