BOISE, Idaho — Scientists with the U.S. Geological Survey are applying acoustic technology to better estimate the types and amounts of sediment in northern Idaho’s Kootenai River. An improved understanding of how the river transports sediment is critical to ongoing efforts by the Kootenai Tribe of Idaho to restore river habitat.
Sediment promotes natural stream changes that provide habitat and food for fish. However, sediment that accumulates in the spawning habitat of the endangered Kootenai River white sturgeon can smother the fish’s eggs.
To improve sediment estimates, USGS scientists deployed acoustic Doppler velocity meters at three sites on the Kootenai River near Bonners Ferry. The submerged devices emit sound pulses into the river at specific frequencies, similar to sonar. The sound pulses reflect off sediment suspended in the water. Scientists use the strength of the return signal, called backscatter, to calculate the amount of sediment particles.
USGS hydraulic engineer Molly Wood compared the results of the acoustic monitoring with traditional sediment sampling methods and statistical models, called sediment transport curves, that are based on streamflow. During the study, total suspended-sediment and fine sediment concentrations were driven primarily by contributions from tributaries flowing into the Kootenai River between Libby Dam and the study area. Concentrations were highest during rain-on-snow events in those tributary watersheds. These and other results of the study are documented in a newly published report.
“The use of acoustic technology is improving how we monitor sediment nationwide,” said Wood. “These monitoring sites in the Kootenai River let us track high sediment transport through critical habitat reaches.”
Susan Ireland, director of the Tribe’s Fish and Wildlife Department agreed. “The USGS has provided the Tribe with river and sediment monitoring for many years. The information they provide us is important for designing and evaluating our river restoration work.”
The acoustic monitoring proved its value in early December when an atmospheric river brought significant rainfall to the Pacific Northwest. “The rain caused substantial erosion in the watershed,” said Wood. “Using the acoustic technology, we were able to estimate and track unusually high sediment concentrations.”
The report “Sediment Transport and Evaluation of Sediment Surrogate Ratings in the Kootenai River near Bonners Ferry, Idaho, Water Years 2011–14” is available online through the USGS Publications Warehouse.