HIGH FREQUENCY MONITORING OF SWASH HYDRO-MORPHODYNAMICS ON A REFLECTIVE BEACH (GRAND POPO, BENIN): A NEW METHOD

Raimundo Ibaceta, Rafael Almar, Jean-Pierre Lefebvre, Trinity Mensah-Senoo, Wahab Sowah Layrea

Abstract


A new remote sensing video-based method for measuring rapid variations of the bed elevation and free-surface in the swash zone is tested on a steep reflective beach at Grand Popo. The key assumption is that the free-surface has a distinguishable optical signature with respect to the bed level. This new set up enables a high frequency description of the wave transformation, dissipation and reflection in the swash zone as well as the variations of the bed evolution at the wave-by-wave scale. At a more integrated scale, a good correlation is found between the offshore reflected energy measured by an ADCP, the incident offshore wave characteristics and the swash local morphology, suggesting the importance of the swash dynamics on the energy reflection mechanism.

Keywords


video pole technique; remote sensing; image processing; swash zone hydrodynamics; low tide terrace; incoming and outgoing wave energy; shore face rapid evolution

Full Text:

PDF

References


Almar R., Cienfuegos R., Gonzalez E., Catalán P., Michallet H., Bonneton P., Castelle B and Suarez L., 2012. Barred-beach morphological control in infragravity motion. Proceedings of the International Conference on Coastal Engineering, 1-6 July 2012, Santander, Spain.

Almar R., Hounkonnou N., Anthony E., Castelle B., Senechal N., Laibi R., Mensah-Senoo T., Degbe G., Quenum M., Dorel M., Chuchla R., Lefebvre J.P., du Penhoat Y., Layrea W.S., Zodehougan G., Sohou Z., Addo K., Ibaceta R. and Kestenare E., 2014a. The Grand Popo beach 2013 experiment, Benin, West, Africa: from short timescale processes to their integrated impact over long-term coastal evolution”. Proceedings of the International Coastal Symposium 2014, Durban, South Africa.

Almar R., Catalán P., Ibaceta R., Blenkinsopp C., Cienfuegos R., Villagrán M., Aguilera J.C. and

Castelle B., 2014b. Swash zone based reflection during energetic wave conditions at a dissipative beach : toward a wave-by-wave approach. Proceedings of the 34th Conference on Coastal Engineering, Seoul, South Korea.

Almar, R., Bonneton P., Bonneton N., Lefebvre J.P., Dinh V.U., Nguyen T.V., Le T.B., Nguyen V.D., 2014. Swash hydro-morphodynamics at the low-tide terrace beach during post-typhoon recovery period, Nha Trang bay, Vietnam. 19th IAHR-APD 2014 Congress. 21-24 September 2014, Water Resources University, Hanoi, Vietnam

Ardhuin F. and A. Roland. 2012. Coastal wave reflection, directional spread, and seismoacoustic noise sources. Journal Of Geophysical Research-oceans, 117(C00J20), 16pp.

Battjes, J.A., 1974. Surf similarity. Proceedings of the 14th International Conference of Coastal Engineering (American Society of Civil Engineers),466-480

Blenkinsopp C., M. Mole, I. Turner, W. Peirson. 2010. Measurements of time-varying free-surface profile across the swash zone obtained using an industrial LIDAR. Coastal Engineering 57 (2010).1059-1065.

Blenkinsopp C., Turner I., Masselink G. and Rusell P. 2011. Swash zone sediment fluxes: field observations. Coastal engineering, Vol. 58(1), 28-44.

Blivi A., Anthony E. and Oyédé L. 2002. Sand barrier development in the bight of Benin, West Africa. Ocean and Coastal Management, 45, 185-200.

Brocchini M., and Baldock T. 2008. Recent advances in modelling swash zone dynamics: Influences of surf-swash interaction on nearshore hydrodynamics and morphodynamics. Reviews of Geophysics, Vol. 46, No. 3.RG3003

Butt T. and Rusell P. 2000. Hydrodynamics and cross-shore sediment transport in the swash-zone of natural beaches; a review. Journal of Coastal Research 16 (2), 255-268.

Castelle B., Almar R., Dorel M., Lefebvre J.P., Senechal N., Anthony E., Chuchla R. and du Penhoat Y. 2014. Flash rip dynamics on a high-energy low-tide-terraces beach (Grand Popo, Benin, West Africa), Proceedings of the 13th International Coastal Symposium, Durban, South Africa.

Elfrink B. and Baldock T. 2002. Hydrodynamics and sediment transport in the swash zone: a review and perspectives. Coastal Engineering 45 (3-4), 149-167.

Elgar, S., Herbers, T.H.C. and Guza R.T., 1994. Reflection of ocean surface gravity waves from a natural beach, J. Physical. Oceanogr., 24(7), 1503-1511

Ibaceta R., Almar R., Lefebvre J-P., Mensah-Senoo T., Laryea W.S., Castelle B., Senechal N., du Penhoat Y., Laibi R. and Hounkonnou N.. 2014. A new high frequency remote sensing based method: application to the swash zone of a very high reflective beach under high energetic conditions (Grand Popo, Benin), Actes des XIIIèmes Journées Nationales Génie Côtier - Génie Civil, Dunkerque 2014, Paralia Editions.

Iribarren C. and Nogales C., 1949. Protection des Ports. XVIIth International Navigation Congress, Section II, Communication,pp. 31-80.

Masselink G., and Puleo J., 2006. Swash-Zone Morphodynamics. Continental Shelf Research, Vol. 26, 661-680.

Masselink G., Russell P., Turner I and Blenkinsopp C., 2009. Net sediment transport and morphological change in the swash zone of a high-energy sandy beach over tidal cycle and swash event time scales. Marine Geology 257, 18-35.

Senechal N., Laibi R., Almar R., Castelle B., Biausque M., Lefebvre J.P., Anthony J., Dorel M., Chucla R., Hounkonnou N. and du Penhoat Y., 2014. Observed destruction of a beach cusp system in presence of a doublecoupled cusp system : the example of Grand Popo, Benin. Proceedings of the International Coastal Symposium 2014, Durban, South Africa.

Turner I.L., Rusell P. and Butt T., 2008. Measurement of wave-by-wave bed levels in the swash zone. Coastal Engineering 55 (12), 1237-1242.

Vousdoukas M.I., Kirupakaramoorthy T., Oumeraci H., de la Torre M., Wubbold F., Wagner B., Schimmels S., 2014. The role of combined laser scanning and video techniques in monitoring wave-by-wave swash zone processes, Coastal Engineering 83, 150-165, ISSN 0378-3839.




DOI: https://doi.org/10.9753/icce.v34.currents.36