United States Department of Transportation
i
A Temperature-Based Monitoring System for Scour and Deposition at Bridge Piers
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2017-05-01
[PDF-1.66 MB]
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Abstract:Stream flows around a bridge pier can be fast and highly turbulent causing large shear stresses that may mobilize streambed sediment resulting in scour around bridge foundations. Scour is the leading cause of bridge failure in the USA because it compromises bridge structural stability. However, streambed surface elevation may decrease (sediment scour) or increase (deposition of sediment) depending on local upstream sediment transport and water flow conditions. Consequently, yearly or biyearly measurements of streambed elevations may not provide an accurate evaluation of the scour risk at bridges. Current techniques are too expensive, difficult to install or provide only maximum scour. Thus, this project tests a low-cost and simple methodology to monitor streambed elevation changes continuously. The method uses the naturally occurring oscillations of stream water temperature as a tracer. As the water temperature signal propagates through the sediment, it undergoes advection dispersion and diffusion, which change the phase and amplitude of the original signal (stream water temperature). The proposed method detects changes in local streambed elevation from paired analysis of the phase and amplitude of instream and in-sediment water temperature signals. Our test at five Idaho bridges in five different watersheds proves that the method is robust. The method detects streambed elevation changes and maximum scour, which are verified with time series of ground-surveyed streambed elevations and scour chains, respectively.
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