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Stream Quantification Tool—A Quantitative Approach to Stream Mitigation

Nov 7, 2019 | Engineering, Environmental, News

Under Section 404 of the Clean Water Act (CWA), activities such as water resources projects (e.g. dam construction), mining projects, and infrastructure developments require a permit before dredged or fill materials can be discharged into wetlands or “waters of the United States.” As part of the permitting process, permit applicants must identify and implement measures to avoid or minimize impacts to aquatic resources. A new spreadsheet-based calculator, called the Stream Quantification Tool (SQT), is steadily being adopted by Army Corps Districts throughout the United States for certain CWA 404 permitting projects to better quantify stream impacts and inform mitigation measures.

Historically, stream function and potential impact has been difficult to quantify. In the absence of quantification tools, more qualitative stream assessment methods have generally been used to describe changes in stream function. The SQT’s quantitative-based approach provides a more objective, verifiable, and repeatable result for characterizing changes in stream function. 

In 2014, the Environmental Defense Fund and an organization called Stream Mechanics developed the SQT based on the Stream Functions Pyramid Framework. The SQT uses an array of indicators, including pertinent hydrology, hydraulics, geomorphology, physicochemical, and biology data to calculate the difference between a stream’s existing condition and its forecasted post-project condition in terms of functional loss (debit) or functional lift (credit). The SQT results can then be used to identify necessary mitigation activities, which can in turn be incorporated into a CWA Section 404 permit application.

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While primarily associated with permitting efforts, the SQT may provide additional benefits. The tool can help stakeholders develop function-based project goals; select project sites based on restoration potential; and develop assessment approaches, monitoring plans, and performance standards that align with project objectives. 

The SQT’s guidance provides standard procedures for collecting data to characterize stream function along a given project reach. Collected data are then used as inputs to the SQT calculator. The tool contains several worksheets, with the “Quantification Tool” serving as its primary powerhouse. This worksheet accepts user inputs regarding a stream’s existing and proposed function and provides outputs that can be used to calculate debits from proposed impacts, as well as credits from mitigation or restoration activities.

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While the SQT is not required by all Army Corps Districts for CWA 404 permitting, several states have adopted it and mandate its use. States that are implementing and regionalizing the SQT include: North Carolina, South Carolina, Tennessee, Wyoming, Colorado, Michigan, Georgia, and Minnesota.

Training is not required to use the tool, but practitioners are expected to have a foundational understanding of the Stream Functions Pyramid Framework and have the familiarity and expertise to perform the required field assessments.

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