CSDMS 2013 annual meeting poster Jun Cheng
Cross-shore and Vertical Distribution of Turbulence Kinetic Energy in the surf zone generated by plunging breakers
Ping Wang, The University of South Florida Tampa Florida, United States. pwang@usf.edu
Abstract:
Breaking waves, especially plunging breakers, generate intense turbulence and is crucial in dissipating incident wave energy, suspending and transporting sediment in the surf zone. Therefore quantifying breaking-induced turbulence kinetic energy (TKE) is essential in understanding surf zone processes. Surf zone hydrodynamic data collected at the Large-scale Sediment Transport Facility (LSTF) at the U.S. Army Engineer Research and Development center were used here. One LSTF case, with irregular waves (3 s peak period), is examined here. This case resulted in dominantly plunging type of breaker. Waves and currents were measured simultaneously at 10 cross-shore locations and throughout the water column, with a sampling rate of 20 Hz. In order to separate orbital wave motion from turbulent motion, an adaptive moving average filter is developed, involving a 5-point moving average, with additional 3-point moving average at sections with more fluctuations. This adaptive moving average filter is able to maintain more wave energy as compared with the results from 7-point moving average, while resolve more turbulence energy as compared with the result from 5-point moving average.
The TKE was calculated based on the resolved turbulence. Large TKE was generated at the water surface associated with wave breaking and dissipated rapidly downward. The TKE decreased nearly one order of magnitude downward within 15 cm. The TKE reached a minimum value at approximately 50%-80% of the water depth, and increased towards the bottom due to the generation of bed-induced turbulence. The TKE flux during wave crest and tough indicate that, at the bottom and middle layers of the water column, the TKE is transported dominantly onshore, while for the top layer, it is transported mostly offshore.
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