Stream Quantification Tool—A Quantitative Approach to Stream Mitigation

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.