NWDTW 2024

The salt dilution method is a global, time-tested approach for measuring streamflow. It is achieved by adding a known mass of sodium chloride (NaCl) to a stream, allowing it to mix through a reach, and measuring NaCl dilution via changes in specific conductance. A vast majority of USGS streamflow measurements rely on velocity-area methods, which depend on quasi-laminar flow where accuracy of measurements across the channel can be degraded in turbulent conditions. The salt dilution method is ideal for measuring turbulent streams, but the method is seldomly used by the USGS. With support from the SAWSC Science Advancement & Program Development Challenge, the salt dilution method was tested in diverse streams throughout North Carolina and Georgia. The method proved effective at many of the streams with turbulent characteristics such as bends, steep gradients or other features that encourage lateral mixing. Additionally, recent advancements in field instrumentation for measuring salt dilution via changes in specific conductance have reduced the mass of NaCl required in the stream and allow for real-time streamflow and uncertainty calculations. The project concluded that USGS programs could consider it as a reliable option at difficult-to-measure, turbulent streams. This presentation will introduce the salt dilution method to those unfamiliar with it. The audience will (1) learn to recognize site conditions favorable as well as those unfavorable for the salt dilution method, (2) learn salt dilution calculation theory, and (3) learn the basic salt dilution measurement field processes developed and assessed during the SAWSC Science Advancement & Program Development Challenge.