USGS, Tacoma

USGS, Tacoma

Established in 1879, the U.S. Geological Survey (USGS) is an organization that monitors and analyzes the health of the environment of the United States.

The Project

The U.S. Environmental Protection Agency and the National Park Service were concerned that the decommissioning of dams on the Elwha River would create an environmental threat due to the levels of sediment that had accumulated since the dams were originally installed in 1913 and 1927. They partnered with the USGS to develop and implement a decommissioning plan that would mitigate the environmental impact through “deconstruction hold periods” based on the monitored sediment load, allowing for the decommissioning of the dams without harming the existing aquaculture.

Challenge

To reduce the impact of increased sediment concentration on migrating fish, and to accommodate sediment-transport management targets established by the U.S. Department of the interior, this team needed a reliable and robust sensor to measure turbidity data. The data would then be used to calculate suspended-sediment levels during the dam decommissioning and subsequent restoration of the river.

Solution

Following standard USGS guidelines, the team chose to use turbidity as a surrogate for suspended-sediment concentrations. FTS DTS-12 turbidity sensors were selected for this project, and the units were installed upstream and downstream of the dams, within protective pipes to allow turbidity measurement in actively flowing parts of the river channel while mitigating debris build-up around the sensor face or on the mounting hardware.

The team found early on that the DTS-12 was an easy-to-install, robust sensor. Their examination during routine calibration checks found that the wiper system was effective and no abrasions on the optical face of the sensor were observed, and the team was able to acquire the data required for this project. The DTS-12 is the “last sensor standing”, as alternative units proved to be unsuitable for this harsh environment.

Now that the dams have been completely removed, the turbidity data is available for use by the science partners in the National Parks Service and Coastal Marine Geology.

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