HYDRODYNAMIC DRIVERS OF SEDIMENT TRANSPORT ACROSS A FRINGING REEF

Willem Bodde, Andrew Pomeroy, Ap van Dongeren, Ryan Lowe, Jaap van Thiel de Vries

Abstract


Coral reefs are highly valuable ecosystems, which are under an increasing number of environmental pressures. Sedimentation and sediment transport patterns are among key physical drivers of coral reefs, so it is important to improve our understanding of these poorly studied dynamics on reefs. To this purpose, flume experiments were performed on a scaled fringing reef in the laboratory facilities of Deltares in Delft. The objective was to improve the understanding of hydrodynamic and sediment transport processes across fringing reefs. The water depth and bed roughness were shown to have influence on many processes such as short wave breaking, infragravity (IG) wave generation, IG wave transformation, reef flat seiching, wave-induced setup and wave reflection. The measurements showed that long waves dominate over the short waves at the back of the reef flat. The flow velocities in the rough cases were lower than those in the smooth cases as a result of the bed friction. Analysis of the third order velocity moment and the bed level changes indicates that both the short and the long waves play a role, but that the long waves appear to be the dominant factor in sediment transport and bed profile development - especially close to the beach. Bed roughness affected the shape of a swash bar, which was more pronounced for the smooth than for the rough cases. This demonstrates that the dominance of long waves in a fringing reef lagoon results in different sediment dynamics than, for example, on a regular sandy beach.

Keywords


fringing reef, sediment transport, infragravity waves, flume experiment, hydrodynamics, morphodynamics, seiching, bed friction, wave setup

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References


Baldock, T.E. (2012). Dissipation of incident forced long waves in the surf zone—Implications for the concept of “bound” wave release at short wave breaking. Coastal Engineering, 60(0), 276-285. doi: 10.1016/j.coastaleng.2011.11.002

Bodde, W.P. (2013). Sediment transport in a fringing reef environment: Analysis using laboratory experiment and numerical modelling. MSc Thesis, TU Delft, Delft.

Dean, R., & Dalrymple, R. (1991). Water wave mechanics for scientists and engineers. World Sci entific, Advanced Series on Ocean Eng, 2.

Ferrario, F., Beck, M. W., Storlazzi, C. D., Micheli, F., Shepard, C. C., & Airoldi, L. (2014). The effectiveness of coral reefs for coastal hazard risk reduction and adaptation. Nature communications, 5.

Hearn, C.J. (1999). Wave-breaking hydrodynamics within coral reef systems and the effect of changing relative sea level. Journal of Geophysical Research, 104(C12), 30007-30019.

Holthuijsen, L. H. (2007). Waves in oceanic and coastal waters. Cambridge University Press.

Komar, P. (1998). Beach Processes and Sedimentation (2nd ed.). Upper Saddle River, N.J.: Prentice-Hall.

Lee, T.T., & Black, K.P. (1978). The energy spectra of surf waves on a coral reef. Paper presented at the Proceedings of the International Conference on Coastal Engineering.

Longuet-Higgins, M. S., & Stewart, R. W. (1962). Radiation stress and mass transport in gravity waves, with application to ‘surf beats’. Journal of Fluid Mechanics, 13(04), 481-504.

Longuet-Higgins, M. S., & Stewart, R. W. (1964). Radiation stresses in water waves; a physical discussion, with applications. In Deep Sea Research and Oceanographic Abstracts (Vol. 11, No. 4, pp. 529-562). Elsevier.

Lowe, R.J., Falter, J.L., Bandet, M.D., Pawlak, G., Atkinson, M.J., Monismith, S.G., & Koseff, J.R. (2005). Spectral wave dissipation over a barrier reef. Journal of Geophysical Research, 110(C4), C04001.

Lowe, R.J., Falter, J.L., Koseff, J.R., Monismith, S.G., & Atkinson, M.J. (2007). Spectral wave flow attenuation within submerged canopies: Implications for wave energy dissipation. Journal of geophysical research, 112(C5), C05018.

Lowe, R. J., Falter, J. L., Monismith, S. G., & Atkinson, M. J. (2009). Wave-driven circulation of a coastal reef-lagoon system. Journal of Physical Oceanography, 39(4), 873-893.

Lowe, R. J., & Falter, J. L. (2014). Oceanic Forcing of Coral Reefs. Annual Review of Marine Science, 7(1).

Monismith, S. G. (2007). Hydrodynamics of coral reefs. Annu. Rev. Fluid Mech., 39, 37-55.

Munk, W.H., & Sargent, M.C. (1948). Adjustment of Bikini Atoll to ocean waves. Trans. Am. Geophys. Union, 29, 855-860.

Pomeroy, A., Lowe, R., Symonds, G., Van Dongeren, A., & Moore, C. (2012). The dynamics of infragravity wave transformation over a fringing reef. Journal of Geophysical Research: Oceans (1978–2012), 117(C11).

Roelvink, D., Reniers, A., Van Dongeren, A., Van Thiel De Vries, J., Mccall, R., & Lescinski, J. (2009). Modelling storm impacts on beaches, dunes and barrier islands. Coastal Engineering, 56(11), 1133-1152.

Roelvink, D., & Stive, M. (1989). Bar-generating cross-shore flow mechanisms on a beach. J. Geophys. Res, 94(C4), 4785-4800.

Rocha, M.V., Michallet, H., Silva, P.A., Abreu, T., & Barthélemy, E. (2013). Nonlinearities of short and long waves across the shoaling, surf and swash zones: Physical model results. Proceedings Coastal Dynamics 2013.

Storlazzi, C.D., Field, M.E., Bothner, M.H., Presto, M., & Draut, A.E. (2009). Sedimentation processes in a coral reef embayment: Hanalei Bay, Kauai. Marine Geology, 264(3), 140-151.

Symonds, G., Huntley, D.A., & Bowen, A.J. (1982). Two-Dimensional Surf Beat: Long Wave Generation by a Time-Varying Breakpoint. Journal of Geophysical Research, 87(C1), 492-498.

Van Dongeren, A.R., A.J.H.M. Reniers, J.A. Battjes and I.A. Svendsen (2003). Numerical modeling of infragravity wave response during Delilah. Journal of Geophysical Research, 108, (C9), 3288, doi:10.1029/2002JC001332.

Van Dongeren, A., Lowe, R., Pomeroy, A., Trang, D.M., Roelvink, D., Symonds, G., & Ranasinghe, R. (2013). Numerical modeling of low-frequency wave dynamics over a fringing coral reef. Coastal Engineering, 73, 178-190. doi: 10.1016/j.coastaleng.2012.11.004

Van Dongeren, A., Wenneker, I., Roelvink, D., & Rusdin, A. (2007). A Boussinesq-type wave driver for a morphodynamical model. Proceedings of the Coastal Engineering Conference, 3129-3141.

Young, I.R. (1989). Wave transformation over coral reefs. Journal of Geophysical Research, 94(C7), 9779-9789.




DOI: https://doi.org/10.9753/icce.v34.currents.37