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EPA's Region 6 Office

Serving: Arkansas, Louisiana, New Mexico, Oklahoma, Texas, and 66 Tribal Nations

Illinois River Watershed Illinois River Watershed | Region 6 Water Programs | US EPA

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 (Washington County) and flows west into northeast Oklahoma. Once the Illinois River enters Oklahoma, it then flows southwest and south through the mountains of eastern Oklahoma into Tenkiller Ferry Lake. The Illinois River in Oklahoma is currently on the 303(d) list for total phosphorus, while tributaries to the Illinois River (e.g. Osage Creek, Muddy Fork, and Spring Creek) in Arkansas are also on the 303(d) list for total phosphorus.

Illinois River Wateshed geographical map

Project Updates

Current Phase – Watershed and Lake Calibration/Validation Modeling

The calibration/validation modeling is complete for both Illinois River and Lake Tenkiller. The purpose of the calibration/validation modeling is to ensure a scientifically sound modeling system is developed to represent the entire Illinois River Watershed. Calibration modeling was performed using data obtained from the time period of 2001 to 2009, whereas data obtained from the 1992 to 2000 period of record was used for validation purposes. Calibration and validation of the Illinois River Watershed models was achieved by considering qualitative and quantitative measures, involving both graphical comparisons and statistical tests.

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Events and Activities

NEW: Modeling complete. September 2015

Technical Memorandum-Procedures and Methodologies for the Sensitivity and Uncertainty Analyses for Illinois River Watershed and Tenkiller Ferry Lake, Oklahoma describes the model sensitivity analysis and uncertainty analysis performed for Illinois River Watershed HSPF model and Tenkiller Ferry Lake EFDC model.
Final SA UA Technical Memo_08_07_2015

The Response to Statement of Findings explains the findings from the two peer reviewers based on their evaluation of the final reports developed by U.S. EPA contractors for the Agency’s Illinois River Watershed (IRW) TMDL Modeling Program.
Response to Statement of Findings- Final_8_4_2015

The Final Watershed Lake Model Main Report contains the Final Setup, Calibration, and Validation for Illinois River Watershed Nutrient Model and Tenkiller Ferry Lake EFDC Water Quality Model.
Final-Watershed Lake Model_Main Report 08_07_15

Appendices to the Final Watershed Lake Model Main Report


Calibrated Modeling Files

To obtain the calibrated modeling files contact:

Taimur A. Shaikh, Ph.D
Water Quality Protection Division
EPA Region 6

Archived Information

The Cherokee Nation hosted an informational meeting on November 14, 2013, at 6 pm.  At the meeting, EPA updated the public on the Illinois River Watershed Modeling and TMDLs development project.  The meeting was held in the Cherokee Casino, located at 2416 Hwy 412 in Watts, Oklahoma 74964.  The meeting included presentations on the Illinois River Watershed Modeling effort to date and a question and answer session. 

The Arkansas Department of Environmental Quality hosted an informational meeting on November 8, 2012.  At the meeting, EPA provided status updates on the Illinois River Watershed Modeling and TMDLs Development project.  The meeting was held in Springdale, Arkansas.  Information from this meeting is listed below.

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You will need Adobe Acrobat Reader, available as a free download, to view these files. See EPA's PDF page to learn more about PDF, and for a link to the free Acrobat Reader.

Technical Workgroup Meeting/Conference Calls

January 17, 2013 Conference Call

November 8,2012 Springdale, AR Technical Meeting

Core Group Meeting/Conference Calls

October 3, 2012 Conference call

August 24, 2012 Conference call


November 14, 2013 Meeting

November 8, 2012 Meeting

April 26, 2012 Meeting

May 19, 2011 Meeting

January 6, 2011 Meeting

September 14, 2010 Meeting

February 4, 2010 Meeting

November 20, 2009 Meeting - Project Kickoff Meeting

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Conference Call Minutes

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Drafts and Comments

Project QAPP (Quality Assurance Project Plan)

Data Gap Report

Model Selection Report

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Modeling QAPP

Simulation Plan

GIS Data

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Final Documents


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Watershed Based Plans

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