Calibration of Bed Load Impact Sensors for Surrogate Sediment Measurement
Project ID: 115
Principal Investigator: Robert Hilldale
Research Topic: Sediment Management and River Restoration
Funded Fiscal Years: 2012, 2013 and 2014
Keywords: bed load impact sensor, surrogate sediment measurement, bed load discharge
A series of bed load impact sensors has been fabricated and installed on the Elwha River in WA (Science and Technology proj. # 6499). The purpose of the bed load impact sensors is to continuously measure bed load passing the site, which is downstream of the Elwha and Glines Canyon Dams. These dams are slated for removal beginning in September, 2011. The bed load measurements will be part of the sediment monitoring program being conducted by the Bureau of Reclamation during and after dam deconstruction.
Recent progress on the bed load impact sensors was accomplished in May, 2011, when we completed writing software for sampling and processing the data and PCs, and related hardware were installed (Science and Technology proj. # 9562). The bed load impact plate system was op-checked and is currently collecting data, although there is no field calibration.
A field calibration is needed to make the system fully operational. The calibration will require the collection of physical bed load samples deploying a pressure difference bed load sampler (Elwha or Toutle River-2) from a raft. These data need to be collected over a range of discharges to provide a valid calibration.
Two research questions will be addressed by this research. 1.) Are bed load impact sensors a viable surrogate method for continuously measuring bed load transport? 2.) How much and at what rate is bed load passing a site downstream of two dams that are to be removed?
Need and Benefit
There are two benefactors for this research, one is more immediate and narrow in scope, the other serves the broader interest of advancing the technology of bed load measurements. The immediate benefactor is the Elwha River Restoration Project, who will be monitoring sediment during and after dam removal.
In a broader context, the sediment transport community will benefit from the advancement of a surrogate technology to continuously measure bed load. An advancement such as this would be a significant step forward in understanding the transport of bed material in a gravel bed river. We'll also gain a good understanding of the fate of the coarse reservoir deposits during and after dam removal, which will be the largest controlled release of sediment through dam removal in North America.
Accurate measurement of bed load is very difficult due to logistical issues related to the movement and capture of the coarsest fractions of coarse sediment constituting the bed material of a river. Generally, the coarsest fraction of a river's bed material is only mobilized during flood events, making it very difficult and potentially dangerous to place a sediment sampler on the bed of a river to collect a timed sample. Moreover, this methodology only results in a discrete sample occurring over approximately one or two minutes at each location across the river, providing an incomplete picture of the nature of bed load movement (< 1% of the total bed load is actually measured). This incomplete understanding of bed load has confounded researchers and has hindered the complete understanding and modeling of sediment transport.
The primary product of the proposed research will be a calibrated bed load impact sensor system. The results of this research will be shared through a minimum of a completion report, Science and Technology Bulletin, and a scientific paper presented at an appropriate conference. Two conference papers have already been presented on this topic, co-authored by the PI. Upon completion of the calibration and after appropriate evaluation this research will be submitted to an appropriate, peer-reviewed professional journal.
This information was last updated on August 1, 2014
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