Flume Construction and RFID Tracking Techniques for Fluvial Sediment Transport Studies
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Sediment transport studies incorporating radio frequency identification (RFID) tracers are becoming a key component in understanding sediment transport dynamics due to the data they provide on spatial and temporal variability. This technique involves inserting small glass cylindrical transponders into stones then seeding those stones in the river bed. Existing methods of using RFID tracers involve either manually sweeping the channel bed after a hydrologic event or placing a series of fixed antennas along the channel to detect when sediment containing a RFID tracer passes that point. The first method is limited because it does not correlate the hydrodynamic conditions with the movement of the sediment, while the second method is limited by spatial resolution afforded by the fixed antennas. The goal of this research is to develop a flume with the capacity to accurately measure sediment inputs, transport, and export in real time. This is accomplished by automating the sediment supply, using a sediment trap with a light table to monitor sediment leaving the flume, and implementing an RFID sediment tracking system to provide real time tracking of the movement of individual clasts over the course of an experiment. A tilting flume with sediment supply and capture systems was designed and built with an integrated RFID tracking system to enable sediment transport experiments to be conducted in the flume while continuously tracking the position of RFID tagged sediment. The RFID tracking system, located under the floor of the flume, consists of a carriage containing the antennas, tuners, multiplexing RFID readers, batteries, and rollers to enable the carriage to roll along the flanges of the beam supporting the flume. The carriage is transported back and forth the length of the flume using cogged belts and pulleys powered by a DC motor and controlled by a PLC with limit switches. The identification of RFID tags detected by the carriage is transmitted Bluetooth to a stationary computer that also receives carriage position information from a laser range finder. Validation tests were conducted with vertically oriented RFID tags to establish the detection range and accuracy of estimating RFID tag positions. When no steel cross members were present, an RFID tag could be detected up to 21 cm above the flume floor with streamwise position estimation accurate within 1 cm. When steel cross members or multiple RFID tags were present, the detection range and position estimation accuracy decreased. Further refinement to this technique could be achieve by experimenting with different antenna designs which may provide a larger detection range and by using different type of PIT tags to enable tracking of smaller sized sediment. The developed flume and tracking system will allow us to obtain new and better information about sediment transport which should improve fundamental understanding and aid in the design of channel restoration projects.