Modeling water quality and developing a Total Maximum Daily Load for the Illinois River Watershed.

Project Details

Environmental Protection Agency's Office of Science and Technology (Subcontractor to Michael Baker International).

2015 - Present

Arkansas and Oklahoma


The Illinois River is a multi-jurisdictional tributary of the Arkansas River and is approximately 100 miles long between the states of Arkansas and Oklahoma. The Illinois River begins in the Ozark Mountains in the northwestern corner of Arkansas and flows west into northeastern Oklahoma. The river flows southwest through Oklahoma 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 and is stocked with rainbow and brown trout.

Several segments of the Illinois River are currently on the state of Oklahoma’s Clean Water Act, Section 303(d) list for Total Phosphorus (TP) levels, including three tributaries in Arkansas (Osage Creek, Muddy Fork, and Spring Creek). The main stem Illinois River in Arkansas is not listed for TP. The  state of Oklahoma identified the likely causes of pollution of the Illinois River are domestic wastewater and poultry farm runoff.

The project’s objective is to develop a scientifically robust and defensible watershed model to determine reductions in phosphorus loads needed to meet water quality standards in Arkansas and Oklahoma. This watershed model tool will aid decision makers in sound technical decisions on appropriate point- and nonpoint-source controls to meet those standards. The ultimate goal is to develop a tool that can lead to scientifically sound Total Maximum Daily Loads (TMDLs) and a basin-wide water quality restoration plan.

The project was divided into 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.

The US Environmental Protection Agency’s (EPA) HSPF model is being used to develop the watershed model for the Illinois River Basin, and the EFDC model is being used to develop the lake model that will be used to simulate water quality conditions within Lake Tenkiller. RESPEC performed extensive data compilation and developed an assessment report to describe and document the extent 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 identify any critical data gaps or deficiencies that might impact or inhibit further water quality model development. Additionally, this report allows the designated state Points-of-Contact (POCs), other state and federal agencies, and stakeholders to assess and evaluate whether any relevant data and information have not been identified and are still outstanding. The final project and model reports have been submitted, approved by the EPA, and are undergoing a formal peer review.

A GIS database was provided to Region 6 for the Illinois River Watershed. The database includes coverages used for previous modeling studies, relevant coverages contained in the US EPA BASINS modeling system, and supplemental coverages provided by state liaisons. A Simulation Plan was created as a reference and  a communication tool for the EPA Work Assignment Manager and stakeholders that describes the study objectives, the available data, water quality constituents and land uses, calibration and validation procedures and targets, and potential scenarios for assessment. The Simulation Plan was reviewed by stakeholders with a strong technical background who substantiated and refined the modeling approach.