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Water Quality Modeling and TMDL Development for the Illinois River Watershed

Client:USEPA Office of Science and Technology and EPA Region 6, Dallas, TX

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.

The Illinois River, USA

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 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.

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

The project was divided under six technical tasks: 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 final of three years of funding. The first four tasks have been completed, and the fourth task is currently under review.

AQUA TERRA performed 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 Illinois River Watershed (IRW), and thereby identify any critical data gaps or deficiencies which might impact or ultimately inhibit water quality model development for the IRW. 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.

Illinois River Watershed Model Area

AQUA TERRA 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. AQUA TERRA developed a Simulation Plan that provided a roadmap and a communication tool for both the EPA Work Assignment Manager and stakeholders that 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 substantiated and refined the modeling approach.

US EPA’s Hydrological Simulation Program – FORTRAN (HSPF) was used to develop the watershed model for the Illinois River Watershed. The model was calibrated for the simulation period of 2001-2009 and validated for the period of 1992-2000. Following the calibration and validation, a future model scenario is being developed using the land use data from 2011 (NLCD 2011).

The outputs from the HSPF model for the Illinois River Watershed are being used to provide boundary conditions for the Environmental Fluid Dynamics Computations (EFDC) Model that is being used to develop the lake model to simulate Tenkiller Ferry Lake.

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