144 S. Atamturktur and A. Khan refill processes. Although the VTP device is insensitive to the environmental conditions of the channel, it seems to be affected by the floating and accumulated debris in front of the sensor. Debris obstructs the impact of flow turbulence on the vibrating membrane, which reduces the response level of the sensors in the flow. Thus, it can become difficult to accurately distinguish the sensors in the sediment and in the flow. This problem is expected to be more pronounced in shallow depth channels whereas in the case of moderately deep channels, obstruction by debris is expected to be minimal. Rotating the pipe 90ı however is observed to alleviate the problems associated with debris accumulation. Acknowledgements The authors would like to thank the South Carolina Department of Transportation for supporting this work through grant number 1,417. The authors thank Murray Fisher and Md. Nasimul Chowdhury for their contributions in obtaining the experimental results for this study. References 1. Lagasse PF, Clopper PE, Pagán-Oriz JE, Zevenbergen LW, Arneson LA, Schall JD, Girard LG (2009) Bride scour and stream instability countermeasures: experience, selection and design guidance. Hydraulic engineering circular no.23, 3rd edn. Publication No. FHWA-NHI-09111, U.S. Department of Transportation, Federal Highway Administration 2. Fisher M, Atamturktur S, Khan A (2013) A novel vibration-based monitoring technique for bridge pier and abutment scour. J Struct Health Monitor 12(2):114–125 3. Fisher M, Chowdhury MN, Khan AA, Atamturktur S (2013) An evaluation of scour measurement devices. Flow Meas Instrum 33:55–67
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