Implementing New Acoustic Monitoring Techniques in the Trinity River

Science Center Objects

Accurate river-sediment data is fundamental to planning and managing river restoration efforts on the Trinity River, and throughout the world’s waterways. The USGS has developed a “hydrophone” that enables scientists to listen to sediment particles as they move along the riverbed in order to inexpensively and reliably record near-continuous sediment-bedload-transport data. For this study, scientists will use this technology in the design of a permanently installed acoustic-sediment-monitoring gage on the Trinity River.

Problem

Dam operations on the Trinity River have changed sediment distribution in the river, which has contributed to ecosystem and native salmon declines. The Trinity River, located in Northern California, has historically been a habitat for large salmon populations. Since 1960, Lewiston Dam operators have regulated river discharge to supply water to the Central Valley Project and to lakes, reservoirs, and rivers that provide water to the Central Valley. River discharge regulation, sediment trapping in upstream reservoirs, and sediment coarsening downstream of the dam have degraded aquatic habitat, and contributed to native salmon population declines. To reverse these declines, the U.S. Bureau of Reclamation (BOR) began the Trinity River Restoration Program (TRRP) to restore the habitat and promote naturally spawning salmon.

Submerged hydrophone near bank of the San Joaquin River

Submerged hydrophone 

A critical component of the TRRP is sediment (bedload) transport management through strategic gravel replenishment. Sediment transport monitoring helps resource managers understand gravel injection impacts on the Trinity River’s ecosystem. Hydrophonic bedload data can help BOR and USGS adequately address sediment transportation concerns raised in the TRRP.

Objective

o better understand the effects of sediment replenishment and transport in the Trinity River, the USGS will build a permanent acoustic-based bedload monitoring gage to collect data during spring restoration flow releases from Lewiston Dam. The gage will be installed on the Trinity River at the town of Lewiston, California. The USGS will install hydrophones at this site, which will collect periodic audio samples. These data will be used to estimate total bedload transport rate or bedload transportation rates.

In 2015 and 2016, the USGS used acoustic forms of measurement to evaluate sediment transport in temporary locations throughout the Trinity River. Through measuring the sound of sediment as it moves though a study area, USGS is able to use that data to create an acoustic-based sediment-rating curve, which relates the acoustic energy of the bedload to transport rates. Because the measured sound is directly physically linked to bedload transport, acoustic monitoring has proven to be more accurate than discharge measurements, particularly at sites like Lewiston Dam, near where gravel replenishment is occurring.

A permanent monitoring station will allow USGS and BOR to collect continuous bedload data that can be used to meet critical components of the Trinity River Restoration Plan.

Plan

To meet project objectives, the USGS will design and build an equipment enclosure at the Lewiston site on the Trinity River. This gage will record acoustic data during the spring 2017 flood releases at Lewiston Dam at 15-minute intervals. These acoustic data will be downloaded periodically and processed using signal analysis tools.

Map of the Trinity River study area illustrating the locations of USGS streamgages and acoustic bedload gages.

Map of the Trinity River study area illustrating the locations of USGS streamgages and acoustic bedload gages.

While an acoustic-based sediment rating curve has already been established at this site using 2016 data, additional measurements are needed to periodically check and validate the rating curve. Therefore, BOR and its partners will collect a small number of additional bedload measurements during the 2017 flood releases. Once processed, the acoustic data and bedload estimates will be published online and freely available to the public.

Beyond providing more accurate, direct data, this method of bedload monitoring is less expensive, and provides near-continuous measurements. The frequency of these measurements can help answer critical management questions raised by the TRRP. This project in the Trinity River allows USGS to implement this technology into a permanent monitoring station. This innovative science could be used nationwide to help resource managers across the country better understand the effects of water and habitat management on ecosystem health.