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Research Project: Acoustic and Geophysical Technology Development for Improving Assessment and Monitoring of Erosion and Sediment Transport in Watersheds

Location: Watershed Physical Processes Research

Title: Installation of Impact Plates to Continuously Measure Bed Load: Elwha River, Washington, USA

item HILLDALE, ROBERT - Bureau Of Reclamation
item CARPENTER, WAYNE - University Of Mississippi
item GOODWILLER, BRADLEY - University Of Mississippi
item CHAMBERS, JIM - University Of Mississippi
item RANDLE, TIMOTHY - Bureau Of Reclamation

Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2014
Publication Date: 11/19/2014
Citation: Hilldale, R., Carpenter, W., Goodwiller, B., Chambers, J., Randle, T. 2014. Installation of impact plates to continuously measure bed load: Elwha River, Washington, USA. Journal of Hydraulic Engineering. 141(3). 06014023.

Interpretive Summary: Sediments are a global-scale pollutant whose yield has been estimated at 20 billion tons per year and there have been ongoing Federal Interagency Sedimentation Conferences (FISC) to showcase research and progress in the field with the most recent held in 2015. Furthermore, the results of corrective actions on fluvial systems, assessment of soil erosion losses, and reservoir sedimentation (in conjunction with dam removal) can be determined using suspended and bedload sediment data. However, accurate measurements of sediment flux are difficult to obtain since sediment load is highly variable in both time and space. In many streams, the majority of sediment moves during flood events caused by a few large storms per year. These floods are unpredictable and frequently occur at night, making the collection of physical sediment samples difficult and sometimes dangerous. Manual techniques yield samples that are widely spaced in time, small in number, and flow intrusive. To improve the current state of sediment measurement technology, acoustic measurement systems can be used to detect sediment and bedload flux with a high degree of both spatial and temporal resolution. Non-invasive techniques that have been used to measure gravel transport in particular include bottom tracking (passive), magnetic sensors (passive), radio frequency (RF) tracking (active), and acoustic emission (passive). The work presented in this manuscript examines the use of kinetic energy impact plates instrumented with geophones or accelerometers to monitor bedload movement of gravel or sand after the removal of two large dams on the Elwha River. This paper describes the specifics of the Elwha impact plate system and the ongoing process to collect bed-load measurements for system calibration. That is, as the gravel strikes the plates it generates a vibration signal which is captured by the data collection system. To first approximation , there is an increase in the acoustic energy captured that correlates with an increase in gravel transport. However, the relationship is complex and ongoing data analysis should provide and improved understanding of the phenomena. This work expands the state of the art for monitoring gravel bedload movement across other watersheds and should provide an added tool for water management professionals.

Technical Abstract: In 2008 and 2009, a series of bed load impact plates was installed across a channel spanning weir on the Elwha River, Washington. This is the first permanent installation of its kind in North America and one of the largest anywhere. The purpose of this system is to measure coarse bed load during and after the removal of Elwha and Glines Canyon Dams. It is estimated that 21''million'm3 of sediment have accumulated behind both dams, with 45–50% of the total accumulated volume expected to be eroded through natural processes. The impact plate system consists of 72 plates installed at a diversion weir downstream from both dams and 5 km upstream from the river mouth. Of the 72 plates, 46 are instrumented with a geophone and 26 with an accelerometer. Collection of physical bed-load data for calibration of the geophone plates has begun, with additional measurements to be collected in the future. This paper describes the specifics of the Elwha impact plate system and the ongoing process to collect bed-load measurements for system calibration. Read More: