ON THE BOTTOM SHEAR STRESS DURING LONG WAVE RUNUP AND BACKWASH

Takenori Shimozono, Akio Okayasu, Teppei Mishima

Abstract


Laboratory experiments were performed to examine flow characteristics during runup and backwash of a breaking solitary wave. Boundary layer flows were measured by LDV at two locations landward of the still shoreline under different bed conditions. Temporal variations of the bottom shear stress were estimated from nearbed velocity profiles with different methods. The shear stress determined through the logarithmic fitting roughly agreed with that deduced from a depth-integrated momentum balance during turbulent flow phases. The friction factors during the active phases of the runup and backwash were similar in magnitude except in the leading tip where the value sharply increased. A movable bed experiment was also carried out under the same geometry to discuss relations between the bottom shear stress and sediment transport. The result indicated clear dependencies of bed deformations on the magnitude and duration of the exerted shear stress.

Keywords


bottom shear stress; swash zone; sediment transport; solitary wave

References


Archetti, R. and M. Brocchini. 2002. An integral swash zone model with friction: an experimental and numerical investigation, Coastal Engineering, 45, 89-110.http://dx.doi.org/10.1016/S0378-3839(02)00038-8

Barnes, M.P., T. O'Donoghue, J.M. Alsina, and T.E. Baldock. 2007. Direct bed shear stress measurements in bore-driven swash, Coastal Engineering, 56, 853-867. http://dx.doi.org/10.1016/j.coastaleng.2009.04.004

Cowen, E.A., I.M. Sou, P.L.F. Liu, and B. Raubenheimer. 2003. Particle image velocimetry measurements within a laboratory-generated swash zone, Journal of Engineering Mechanics, 129, 1119–1129. http://dx.doi.org/10.1061/(ASCE)0733-9399(2003)129:10(1119)

Cox, D.T., W.A. Hobensack, and A. Sukumaran. 2001. Bottom stress in the inner surf and swash zone, Proceedings of 27 th International Conference on Coastal Engineering, ASCE, 108–119.

Goring, D.G. 1978. Tsunamis–The propagation of long waves on to a shelf, Rep. KH-R-38, W. M.

Keck Lab., Cal. Inst. of Technol., Pasadena,. Cal.

Kobayashi, N., and A. Lawrence. 2004. Cross-shore sediment transport under breaking solitary waves, Journal of Geophysical Research, 109, C030047.http://dx.doi.org/10.1029/2003JC002084

Petti, M. and S. Longo, 2001, Turbulence experiments in the swash zone, Coastal Engineering, 41, 1-24.http://dx.doi.org/10.1016/S0378-3839(00)00068-5

Puleo, J.A., and K.T. Holland. 2001. Estimating swash zone friction coefficients on a sandy beach. Coastal Engineering, 43, 25–40.http://dx.doi.org/10.1016/S0378-3839(01)00004-7

Raubenheimer, B., S. Elgar, and R.T. Guza. 2004. Observations of swash zone velocities: A note on friction coefficients, Journal of Geophysical Research, 109, C01027.http://dx.doi.org/10.1029/2003JC001877

Yeh, H. H., A. Ghazali, and I. Marton (1989). Experimental study of bore run-up, journal of fluid mechanics, 206, 563-578

Young, Y.L., H. Xiao, and T. Maddux. 2010. Hydro- and morpho-dynamic modeling of breaking solitary waves over a fine sand beach. Part I: Experimental study, Marine Geology, 269, 107-118.http://dx.doi.org/10.1016/j.margeo.2009.12.009


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