Water Quality Modeling and TMDL Development for the Illinois River Watershed
Client:USEPA Office of Science and Technology and EPA Region 6, Dallas, TX
Funding:EPA Region 6
Background
The Illinois River is a multi-jurisdictional tributary of the Arkansas River, approximately 100 miles (160 km) long, between the states of Arkansas and Oklahoma. The Illinois River begins in the Ozark Mountains in the northwest corner of Arkansas, and flows west into northeastern Oklahoma. Upon entering Oklahoma, the river flows southwest and then south through the mountains of eastern Oklahoma, until it enters the reservoir Tenkiller Ferry Lake, also known as Lake Tenkiller. The upper section of the Illinois River is a designated scenic river and home to many native species of bass with spring runs of white bass. The lower section, below Tenkiller dam, is a designated year-round trout stream, stocked with rainbow and brown trout.
Several segments of the Illinois River are currently on the State of Oklahoma’s 303(d) list for Total Phosphorus (TP), while the main stem Illinois River in Arkansas is not listed for TP. However, three tributaries to the Illinois River in Arkansas (Osage Creek, Muddy Fork, and Spring Creek) are 303(d) listed for TP. The State of Oklahoma identified that the likely causes of pollution of the Illinois River are domestic wastewater and poultry farm runoff.
The Illinois River, USA
The objective of this project is to develop a scientifically robust and defensible watershed model to determine reductions in phosphorus loads needed to meet water quality standards in both states, Arkansas and Oklahoma. This watershed model will serve as a tool for sound technical decisions on appropriate point and nonpoint source controls to meet those standards. Ultimately, the intent is development of a tool that can lead to scientifically sound TMDLs and a basin-wide water quality restoration plan.
Approach
Six technical tasks will be completed under this project: 1) Quality Assurance Project Plan (QAPP) Development, 2) Data Compilation and Assessment, 3) Development of a GIS Database of Land Uses and Other Relevant Geospatial Data, 4) Water Quality Model Development, 5) TMDL Development and 6) Addressing Public Comments and Amending the TMDL (as needed). Currently, the project is in its second of three years of funding. The first three tasks have been completed, and the fourth (water quality model development) is underway.
AQUA TERRA performed an extensive data compilation and developed an assessment report to describe and document the extent and results of these data gathering efforts, compare this accumulated data and information to the data requirements for watershed and waterbody modeling in the IRW, and thereby identify any critical data gaps, or deficiencies, which might impact, or ultimately inhibit, water quality model development for the Illinois River watershed. In addition, this report allows the designated State Points-of-Contact (POCs), other state and federal agencies, and other stakeholders to assess and evaluate whether any relevant data and information has not been identified and is still outstanding.
AQUA TERRA has also provided a GIS database to Region 6 for the Illinois River Watershed. The database includes coverages used for previous modeling studies; relevant coverages contained in the USEPA BASINS modeling system; and supplemental coverages provided by State liaisons.
Ongoing work for the project is resulting in development of a Simulation Plan that provides a roadmap and a communication tool for both the WAM and stakeholders as it describes the study objectives, the available data, water quality constituents and land uses, calibration/validation procedures and targets, and potential scenarios for assessment. Review of the Simulation Plan by technically-strong stakeholders will substantiate (and potentially refine) the modeling approach that is performed.
US EPA’s Hydrological Simulation Program – FORTRAN (HSPF) is being used to develop the watershed model for the Illinois River Basin, and the Environmental Dynamics Fluid Computations (EFDC) Model is being used to develop the lake model that will be used to simulate Tenkiller Ferry Lake.
