HR: 0800h
AN: OS11A-0496    [Abstracts]
TI: Pressure Gradients on a Barred Beach
AU: * Shin, S
EM: shinsu@engr.orst.edu
AF: Oregon State University, O.H. Hinsdale Wave Research Laboratory 202 Apperson Hall Oregon State University, Corvallis, OR 97331-2302 United States
AU: Suzuki, T
EM: suzutk@mb.infoweb.ne.jp
AF: Oregon State University, O.H. Hinsdale Wave Research Laboratory 202 Apperson Hall Oregon State University, Corvallis, OR 97331-2302 United States
AU: Boylston, W
EM: wboylsto@bowdoin.edu
AF: Bowdoin College, Physics and Astronomy Department Bowdoin College 8800 College Station, Brunswick, ME 04011-8488 United States
AU: Cox, D T
EM: dan.cox@oregonstate.edu
AF: Oregon State University, O.H. Hinsdale Wave Research Laboratory 202 Apperson Hall Oregon State University, Corvallis, OR 97331-2302 United States
AB: Pressure gradients generated by free surface oscillation and wave breaking are examined. With the purpose of defining when and how pressure gradients most significantly create instability, Madsen (1974) proposed that the critical value of normalized pressure gradient needed for sand bed instability was 0.5. Cox et al. (1991) conducted a laboratory experiment and suggested that the occurrence probability of the momentary landward and seaward failure might occur at the steep rear face of near-breaking and breaking random waves. The laboratory experiment was conducted at O.H. Hinsdale Wave Research Laboratory of Oregon State University in a 104 m long by 3.7 m wide by 4.6 m high concrete-walled large wave flume equipped with a flap-type wavemaker. In this experiment, a bar was installed on a 1/36 slope beach area with rough impermeable bottom slope. 4 pressure transducers, 2 three-component Acoustic Doppler Velocimeters and 3 wave gages were installed on the movable cart and 6 wave gages were directly fixed on the flume. Nine positions (2 for offshore, 4 on the bar, and 3 for onshore) were chosen to understand how pressure gradients behave as waves propagate across barred beaches. Both regular and irregular wave conditions were involved in the measurements. For the analysis, pressure gradients are calculated from four sensors to obtain better estimates and are compared with water surface elevation and velocity. In regular wave case, phase-averaged quantities (i.e., water surface elevation, pressure gradients, and acceleration) are used to discuss the relationship to maximum pressure gradient. Exceedance probabilities of pressure gradients are considered at each cross-shore location using irregular wave data to evaluate the critical value for bed instability on barred beach. Also, large but rare pressure gradients are compared with acceleration to figure out their relationship. Funding for Research Experience for Undergraduates (REU) was provided by the National Science Foundation. The O.H. Hinsdale Wave Research Laboratory was partially supported by the NSF as part of the George E. Brown NEES program.
DE: 4546 Nearshore processes
DE: 4558 Sediment transport
DE: 4560 Surface waves and tides (1255)
DE: 3094 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting