Abstract
A laboratory experiment on alongshore currents is conducted for two plane beaches with slopes 1:40 and 1:100 to investigate the instability of alongshore currents. The dye release experiment is also performed synchronously in surf zone. Complicated and strongly unstable motions of alongshore currents are observed in the experiment. To examine the spatial and temporal variations of the shear instabilities of longshore clearly, dye batches are released in surf zone. The deformation of the dye patch is observed efficiently and effectively with charge coupled device (CCD) system. Some essential characteristics of the shear instability are validated from the results of image analyses of the temporal variation of the dye patch. The influences of alongshore currents, Stokes drift, large-scale vorticity and the shear instabilities on the transport of dye are analyzed using the collected images. The spatial structure of the instabilities of longshore currents is studied by analyzing collected images of the dye patch. And the phase velocity of the meandering movements is obtained through measuring the movement distances of the oscillations of dye patch in alongshore direction with time. The results suggest that the propagation speed of the shear instability is approximately 50%–75% of maximum of mean alongshore currents for irregular and regular waves. The calculated propagation speed using a linear instability analysis theory is compared with the experimental results. The comparison shows agreements between them.
Similar content being viewed by others
References
Allen J S, Newberger P A, Holman R A. 1996. Nonlinear shear instabilities of alongshore currents on plane beaches. Journal of Fluid Mechanics, 310: 181–213
Bowen A J, Holman R A. 1989. Shear instabilities of the mean longshore current: 1. Theory. Journal of Geophysics Research, 94(C12): 18023–18030
Gan Jianping, Li Li, Wang Dongxiao, et al. 2009. Interaction of a river plume with coastal upwelling in the northeastern South China Sea. Continental Shelf Research, 29(4): 728–740
Kirby J T, Ozkan-Haller H T, Haller Merrick C. 2006. Seiching in a large wave flume. Coastal Engineering 2006, San Diego: World Scientific publishing, 1159–1171
Noyes J T, Guza R T, Elgar S, et al. 2004. Field observations of shear waves in the surf zone. Journal of Geophysics Research, 109: C0103, doi: 10.1029/2002JC001761
Oltman-Shay J, Howd P A, Birkemeier W A. 1989. Shear instabilities of the mean longshore current: 2. Field observations. Journal of Geophysics Research, 94(C12): 18031–18042
Ou Suying, Zhang Hong, Wang Dongxiao, et al. 2009. Dynamics of the buoyant plume off the Pearl River Estuary in summer. Environmental Fluid Mechanics, 9(5): 471–492
Ozkan-Haller H T, Kirby J T. 1999. Nonlinear evolution of shear instabilities of the longshore current: a comparison of observations and computations. Journal of Geophysics Research, 104(C11): 25953–25984
Peregrine D H. 1995. Vorticity and eddies in the surf zone. Coastal Dynamics’95, Gydnia: American Society of Civil Engineers, 460–464
Peregrine D H. 1998. Surf zone currents. Theoretical and Computational Fluid Dynamics, 10: 295–309
Putrevu U, Svendsen I A. 1992. Shear instability of longshore currents: a numerical study. Journal of Geophysics Research, 97(C5): 7283–7303
Ren Chunping, Zou Zhili. 2009. Laboratory study and analysis of the instabilities of alongshore currents. Acta Oceanlogica Sinica, 28(4): 1–11
Reniers A J H M, Battjes J A, Falqués A, et al. 1997. A laboratory study on the shear instability of longshore current. Journal of Geophysics Research, 102(C4): 8597–8609
Slinn D N, Allen J S, Newberger P A, et al. 1998. Nonlinear shear instabilities of alongshore currents over barred beaches. Journal of Geophysical Research, 103(C9): 18357–18380
Takewaka Satoshi, Misaki Shoichiro, Nakamura Takashi. 2003. Dye diffusion experiment in a longshore current field. Coastal Engineering Journal, 45(3): 471–487
Tiessen M C H, Van Leeuwen S M, Calvete D, et al. 2010. A field test of a linear stability model for crescentic bars. Coastal Engineering, 1: 41–51
Wang Dongxiao, Hong Bo, Gan Jiangping, et al. 2010. Numerical investigation on propulsion of the counter-wind current in the northern South China Sea in winter. Deep-Sea Research: Part I. Oceanographic Research Papers, 57(10): 1206–1221
Zhao Hui, Tang Danling, Wang Dongxiao. 2009. Phytoplankton blooms near the Pearl River Estuary induced by Typhoon Nuri. Journal of Geophysical Research, 114: C12027, doi:10.10292009JC005384
Zou Z L, Wang S P, Qiu D H, et al. 2003a. Longshore currents of random waves on different plane beaches. China Ocean Engineering, 17(2): 265–276
Zou Z L, Wang S P, Qiu D H, et al. 2003b. Longshore currents of regular waves on different plane beaches. Acta Oceanologica Sinica, 22(1): 123–132
Author information
Authors and Affiliations
Corresponding author
Additional information
Foundation item: The National Natural Science Foundation of China under contract Nos 50479053 and 10672034; the Program for the Changjiang Scholars and the Innovative Research Team in the University of China; the Shanxi Province Natural Science Foundation for Young Scholar of China under contract No.2011021025-1.
Rights and permissions
About this article
Cite this article
Ren, C., Zou, Z. An experimental study of the spatial structures of the instabilities of longshore currents on plane beaches. Acta Oceanol. Sin. 31, 32–45 (2012). https://doi.org/10.1007/s13131-012-0251-7
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s13131-012-0251-7