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Advancing Urban Stream Restoration/Enhancement Practices for Compensatory Mitigation Credits
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2024-04-01
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[PDF-3.72 MB]
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Edition:Final Report May 2022- July 2024
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Abstract:Tennessee Department of Transportation Research is required to provide compensatory mitigation credits per Section 404 of the Clean Water Act and Tennessee’s Aquatic Resource Alteration Permit program when aquatic resource losses occur from highway construction. The Tennessee Stream Quantification Tool (TN SQT V.1) was created in 2019 to generate debits from impacts and credits from proposed restoration. After implementation of the TN SQT V.1 practitioners and TDOT staff identified multiple issues with its use mostly in urban streams. Research for this project used Beaver Creek in Knox County as a case study to compare the TN SQT V.1 with a revised version (TN SQT V.2) that better supports mitigation credit generation from the restoration of urban streams. The TN SQT V.2 was improved through a reduction in overall parameters to be assessed in the field and providing alternative parameters for those requiring bankfull indicators when none are present. The Beaver Creek case study found that the existing condition scores between the two SQT versions resulted in an 11% increase in mitigation functional feet credits with the use of V.2 compared with V.1. A second component of this research project advanced the design of pool-riffle sequences, particularly useful for urban stream restoration. The pool depth prior to a riffle should be at least 1 meter. Overall, this project demonstrated that there is potential to obtain mitigation credits in urban streams on public lands, and that due to hydromodification it is suggested the use of an ecohydraulic approach can improve restoration.
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