LONG-TERM COASTAL EVOLUTION MODELLING OF LONGSHORE BARS

  • Bárbara Marinho
  • Carlos Coelho
  • Magnus Larson
  • Hans Hanson

Abstract

An extended version of a numerical model introduced by Larson et al. (2013) to simulate long-term cross shore material exchange for the subaqueous portion of the profile has been developed. Efforts have focused on improving the model to better account for beach systems consisting of two bars (inner and outer bar), as well as simulating the feeder response over time of nearshore dredged material bars, intended to function as beach nourishment. The theory for the evolution of a single-bar to a two-bar system was modeled, considering an inner and an outer bar, where the outer bar is of primary interest with the purpose of predicting the behavior of placed dredged material. The cross-shore sediment transport rate is based on the evolution equation for the bar system response to the hydrodynamic forcing by reference to its equilibrium condition, where the change in the bar volume is based on a set of wave criteria, describing the onset of a new breaking zone when the outer bar forms. Empirical formulas are employed for the bar equilibrium volume and for coefficients determining the bar response rate. In this study, a description of the extended model and the results from the model component validation at two different sites in USA (Duck, North Carolina, and Cocoa Beach, Florida) are presented. Duck measurements have detected that some bars form in the nearshore and move all the way offshore (eventually deflating by non-breaking waves). At the same time, it was equally observed that a lot of inner bars formed in shallow water do not move offshore but remain as inner bars all the time. According to this, the developed model considers that the inner bar will not become the outer bar, but material previously dedicated to the inner bar will be available for the outer bar. Overall, the present study demonstrates the potential for using rather simple models, based on the definition of an equilibrium state that is compared to the current state and the magnitude of offshore wave forcing to drive the changes in the profile. The methodology employed here allowed to quantitatively reproduce the main trends in the subaqueous beach profile response in a long-term perspective as a function of the bar volumes disequilibrium, the magnitude of the incident wave height and the dimensionless fall velocity to move the sand with a time varying forcing.

References

Aleman, N., Certain, R., Robin, N., Barusseau, J. (2017). Morphodynamics of slightly oblique nearshore bars and their relationship with the cycle of net offshore migration, Marine Geology, Volume 392, 41-52 pp.

Almar, R., Castelle, B., Ruessink, B., Sénéchal, N., Bonneton, P., Marieu, V. (2010). Two- and three-dimensional double-sandbar system behavior under intense wave forcing and a meso-macro tidal range. Cont. Shelf Res. 30 (7), 781-792.

Andrassy, C. J. (1991). Monitoring of a Nearshore Disposal Mound at Silver Strand State Park. Proceedings Coastal Sediments '91, American Society of Civil Engineers, pp 1970-1984.

Barnard, P.L., Hanes, D.M., Lescinski, J., Elias, E. (2006) Monitoring and modeling nearshore dredge disposal for indirect beach nourishment, Ocean Beach, San Francisco. Proceedings 30th Coastal Engineering Conference, ASCE, 4192-4204.

Bodge, K. (1994). Performance of nearshore berm disposal at Port Canaveral, Florida. Proceedings, Dredging'94, American Society of Civil Engineers (ASCE) Specialty Conference, Orlando, Florida; November 13-16, 10 p.

Bouvier, C., Balouin, Y., Castelle, B. (2017). Nearshore bars and nearshore dynamics associated with the implementation of a submerged breakwater: topo-bathymetric analysis and video assessment at the Lido of Sète beach. Proceedings Coastal Dynamics 2017, Helsingør, Denmark, Paper no.22, 10 p.

Dean, R. (1987). "Coastal Sediment Processes: Toward Engineering Solutions," Proceedings Coastal Sediments '87, American Society of Civil Engineers, pp 1-24.

Howd, P. A., Birkemeier, W. A. (1987). Beach and Nearshore Survey Data: 1981-1984 CERC Field Research Facility, Technical Report CERC-87-9, Coastal Engineering Research Center, US Army Engineer Waterways Experiment Station, Vicksburg, MS.

Larson, M., Kraus, N.C., (1989). SBEACH: Numerical model for simulating storm-induced beach change, Report 1: Empirical foundation and model development. Technical Report CERC-89-9. U.S. Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, Vicksburg, MS.

Larson, M., Kraus, N.C., (1992). Analysis of cross-shore movement of natural longshore bars and material placed to create longshore bars. Technical Report DRP-92-5. U.S. Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, Vicksburg, MS.

Larson, M., Hanson, H., Kraus, N., Newe, J. (1999). Short- and Long-Term Responses of Beach Fills Determined by EOF Analysis. Journal of waterway, Port, Coastal, and Ocean Engineering, 285-293.

Larson M., Hanson H., Palalane J., (2013). Simulating cross-shore material exchange in long-term coastal evolution models. Proceedings Coastal Dynamics 2013, Arcachon, France, 1037-1048 pp.

Larson, M., Hanson, H. (2015). Model of the evolution of mounds placed in the nearshore. Journal of the Integrated Coastal Zone Management, 15 (1): pp 21-33.

Larson, M., Palalane, J., Fredriksson, C., Hanson, H., (2016). Simulating cross-shore material exchange at decadal scale. Theory and model component validation. Coastal Engineering, 116, 57-66.

Marinho, B., Coelho, C., Larson, M., Hanson, H. (2017a). Short- and long-term responses of nourishments: Barra-Vagueira coastal stretch, Portugal. Journal of Coastal Conservation, Springer, 22(3), 475-489 pp.

Marinho, B., Coelho, C., Larson, M., Hanson, H. (2017b). Simulating cross-shore evolution towards equilibrium of different beach nourishment schemes. Proceedings Coastal Dynamics 2017, Helsingør, Denmark, Paper no.121, 15 p.

Marinho, B., Coelho, C., Larson, M., Hanson, H. (2018). Monitoring the Evolution of Nourished Beaches Along Barra-Vagueira Coastal Stretch, Portugal. Ocean & Coastal Management, 157, 24-39 pp.

Palalane, J., Fredriksson, C., Marinho, B., Larson, M., Hanson, H., Coelho, C., (2016). Simulating cross-shore material exchange at decadal scale. Model application. Coastal Engineering, 116, 57-66.

Price, T.D., Ruessink, B.G., (2011). State dynamics of a double sandbar system. Continental Shelf Research. 31 (6), 659-674. http://dx.doi.org/10.1016/j.csr.2010.12.018.

RóżyÅ„ski, G. and Lin, G. (2015). Data-Driven and Theoretical Beach Equilibrium Profiles: Implications and Consequences. Journal of Waterway, Port, Coastal, and Ocean Engineering, Volume 141(5), 17p.

Ruessink, B., Kroon, A. (1994). The behavior of a multiple bar system in the nearshore zone of Terschelling, The Netherlands: 1965-1993. Marine Geology, 121, pp 187-197.

Ruessink, B., Terwindt, J. (2000). The behavior of nearshore bars on the time scale of years: a conceptual model. Marine Geology, 163, pp 289-302.

Ruggiero, P., Kaminsky, G., Gelfenbaum, G., Cohn, N. (2016). Morphodynamics of prograding beaches: A synthesis of seasonal- to century-scale observations of the Columbia River littoral cell, Marine Geology 376, 51-68 pp.

Splinter, K., Turner, I., Reinhardt, M., Ruessink, G. (2018). Rapid adjustment of shoreline behavior to changing seasonality of storms: observations and modelling at an open-coast beach. Earth Surface Processes and Landforms, 42 (8), 1186-1194 pp.

Smith, E., D'Alessandro, F., Tomasicchio, G., Cailani, J. (2017). Nearshore placement of a sand dredged mound. Coastal Engineering, 126, pp 1-10.

Sunamura, T., Maruyama, K. (1987). Wave-induced geomorphic response of eroding beaches - with special reference to seaward migrating bars. Proceedings of Coastal Sediments'87, ASCE, 884-900 pp.

Swart, R., Ribas, F., Ruessink, G., Simarro, G., Guillén, J. (2017). Characteristics and dynamics of crescentic bar events in an open, tideless beach. Proceedings Coastal Dynamics 2017, Helsingør, Denmark, Paper no. 192, 12 p.

Walstra, D., Ruessink, G. (2017). Recent insights into inter-annual sandbar dynamics. Proceedings Coastal Dynamics 2017, Helsingør, Denmark, Paper no.13, 12 p.

Published
2018-12-30
How to Cite
Marinho, B., Coelho, C., Larson, M., & Hanson, H. (2018). LONG-TERM COASTAL EVOLUTION MODELLING OF LONGSHORE BARS. Coastal Engineering Proceedings, 1(36), papers.97. https://doi.org/10.9753/icce.v36.papers.97

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