North Central Texas Water Quality
Using simulation models to identify potential contaminant sources
By Clint Wolfe
Water quality in North Central Texas reservoirs is a growing concern. Six of the major reservoirs in the Trinity River Basin managed by Tarrant Regional Water District (TRWD) now serve 1.6 million people across 11 counties and are expected to serve 2.66 million by 2050.
TRWD has been concerned about the recent water quality issues caused by point and nonpoint source pollution in the Watershed. The District initiated efforts in 1998 to address water quality issues, developing a water quality monitoring program to collect data for these reservoirs and their associated watersheds for nearly 40 parameters. TRWD has made a notable effort to understand the mechanisms of how the pollutant loads reach the reservoirs and the hydro-dynamics taking place within the reservoirs.
The Texas Water Resources Institute is collaborating with TRWD to study water quality protection and improvements in area reservoirs with regard to problems of sediment and nutrient loading. Sediment loading affects capacity and water clarity while excessive nutrient loading results in algae growth that impacts water treatment and recreational use.
This four year study will focus on one reservoir annually, beginning with Cedar Creek Reservoir. Eagle Mountain, Richland-Chambers, and Bridgeport reservoirs will be studied in subsequent years.
The group plans to develop and use simulation models to identify potential contaminant sources, estimate the potential costs and benefits of best management practices (BMPs) to reduce contaminant loading and develop plans to improve water quality.
A team of Texas Agricultural Experiment Station researchers, Texas Cooperative Extension specialists and agents, Spatial Sciences Laboratory personnel, as well as the consulting firms of Alan Plummer Associates, Inc and Espey Consultants, Inc, will assist TRWD in obtaining data for the development and implementation of a watershed management plan.
Key objectives of this project include: assisting TRWD by assembling information on water quality and pollution loads for its reservoirs and their watersheds, analyzing the biophysical and economic feasibility of alternative management practices and structures, identifying key stakeholders in those watersheds and among the clients of TRWD, holding public meetings to educate stakeholders and clients in each watershed about their water quality and its protection and providing public educational programs to help achieve water quality goals.
Because of the complexity of the hydrologic processes that take place in watersheds, it is highly desirable that several complex models be used in an integrated strategy to fully capture the impact of point and nonpoint source loadings on the water quality of the region. While some limited water quality modeling has been done in the region, this project represents one of the first comprehensive efforts to utilize a series of models to provide a thorough assessment of point and nonpoint source pollutants of all watersheds and to determine the effectiveness of proposed management measures to address water quality concerns.
The Soil Water Assessment Tool, or SWAT model, developed by the United States Department of Agriculture-Agricultural Research Service (USDA-ARS) will be used to simulate watershed processes and pollutant loads from subwatersheds. SWAT was selected for this study because of its capabilities to appropriately represent landscape processes and agricultural management. Major components of the model include hydrology, weather, erosion, soil temperature, crop growth, nutrients, pesticides and agricultural management. Additionally, SWAT has the ability to predict changes in sediment, nutrients such as organic and inorganic nitrogen and organic and soluble phosphorus, pesticides, dissolved oxygen, bacteria and algae loadings from different management conditions in large ungauged basins.
Loading estimates from subwatersheds using SWAT will be input into the QUAL2E steady state in-stream dynamic model to simulate water quality in river and stream segments. QUAL2E has built-in options to depict the major reactions of nutrient cycles, algal production, benthic and carbonaceous oxygen demand and atmospheric reaeration. Outputs from these models will drive the Water Quality Analysis Simulation Program (WASP) model to simulate reservoir water quality.
Spatial Sciences Laboratory personnel will lead SWAT watershed modeling efforts while Espey Consultants, Inc will lead QUAL2E and WASP modeling efforts.
This project will also develop a database of wastewater plants in the region as well as management strategies for these facilities. Alan Plummer Associates, Inc will lead tasks related to wastewater treatment plants.
“The goal of this project is to accommodate varied activities such as a growing population and increased urbanization without sacrificing water quality,” said Clint Wolfe, research assistant and project manager at the Texas Water Resources Institute. Watershed management is the first, and often most cost-effective step to ensure a safe and reliable public water supply.”
Watershed management is a holistic approach defined by hydrologic boundaries and integrates water quality impacts from both point and nonpoint sources. Key objectives of watershed management plans include identifying potential contaminant sources, evaluating costs and benefits of implementing management plans and/or constructing facilities to reduce loadings and producing useful watershed planning tools.
Information gathered from this research study will allow TRWD and cooperating agencies to use scientifically based methods to not only identify sources for water quality impairment, but also to evaluate the costs and benefits of addressing these sources by developing and implementing a watershed management plan.
The U.S. Environmental Protection Agency and the U.S. Department of Agriculture Natural Resources Conservation Service are funding the project.
