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Contrasting styles of swell-driven coastal erosion: examples from KwaZulu-Natal, South Africa

Published online by Cambridge University Press:  21 May 2010

A. M. SMITH ,
A. A. MATHER ,
S. C. BUNDY ,
J. A. G. COOPER ,
L. A. GUASTELLA ,
P. J. RAMSAY  and
A. THERON
A. M. SMITH*
Affiliation:
School of Geological Sciences, University of KwaZulu-Natal, Durban 4001, South Africa
A. A. MATHER
Affiliation:
Coastal and Catchment Policy, Co-ordination and Management, eThekwini Municipality, P.O. Box 680, Durban, 4000, South Africa
S. C. BUNDY
Affiliation:
Sustainable Development Projects cc, P.O. Box 1016, Ballito 4420, South Africa
J. A. G. COOPER
Affiliation:
Centre for Coastal and Marine Research, School of Environmental Sciences, University of Ulster, Cromore Road, Coleraine BT52 1SA, Northern Ireland
L. A. GUASTELLA
Affiliation:
Bayworld Centre for Research & Education (BCRE), 5 Riesling Rd, Constantia 7806, South Africa
P. J. RAMSAY
Affiliation:
Marine Geosolutions, 105 Clark Rd, Glenwood, Durban, 4001, South Africa
A. THERON
Affiliation:
Coast & Ocean Competency Area, CSIR, P.O. Box 320, Stellenbosch, 7599, South Africa
*
*Author for correspondence: [email protected]
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Abstract

During 2006–2007, the KwaZulu-Natal coast of South Africa was exposed to several large swell events (Ho > 3 m), near the peak of the lunar nodal cycle, causing shoreline recession. The largest swell (Hs = 8.5 m) struck the coast on the March equinox (18th–20th) and generated a strong storm-return flow. Observations made before, during and after record dramatic coastal erosion (shoreline recession of up to 40 m and substantial property damage). This swell event removed the semi-continuous nearshore bar system and ‘conditioned’ the coast such that lesser subsequent swell events accomplished much greater amounts of coastal erosion than expected (up to 100 m at certain erosion hotspots) because waves reached the coast without significant energy dissipation. Subsequent bar generation rebuilt the inshore bars within six months. The styles of erosion during the March ’07 event and other 2007 swells were markedly different. Lesser swells are focused by headlands and result in megarip development and activation of erosion hotspots. The March ’07 event still-water level was raised (equinoctial spring high tide and a storm surge of 0.33–0.45 m) to a level that rendered most headlands (and erosion hotspots) ineffective and resulted in laterally extensive erosion of soft shorelines. Results record cumulative effects of successive swell events on coastal behaviour that proved to be critical in enabling erosion to proceed at rapid rates after the coast had been initially destabilized. Unlike hurricanes and tsunamis, surges associated with swell events are relatively minor and therefore extensive erosion is linked with high lunar tides. There is circumstantial evidence that swell-induced erosion follows the broad 18.6 yr lunar nodal tidal cycle when the chances of large swells coinciding with high water levels are increased.

Keywords

coastal erosionmegariphigh swelldisequilibrium coastlinestorm-return flow
Type
Original Article
Information
Geological Magazine , Volume 147 , Issue 6 , November 2010 , pp. 940 - 953
Copyright
Copyright © Cambridge University Press 2010

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References

Allan, J. C. & Komar, P. D. 2002. Extreme storms on the Pacific Northwest Coast during the 1997–98 El Niño and 1998–99 La Niña. Journal of Coastal Research 18, 175–93.Google Scholar
Anderson, D. & Mead, S. 2009. Multi-purpose reefs for coastal protection and amenity enhancement, St Francis Bay, South Africa. Abstracts, IMPR Conference, Jeffery's Bay, May 2009, p. 33.Google Scholar
Backstrom, J. T., Jackson, D. W. T. & Cooper, J. A. G. 2009. Shoreface morphodynamics of a high-energy, steep and geologically constrained shoreline segment in Northern Ireland. Marine Geology 257, 94–106.CrossRefGoogle Scholar
Begg, G. W. 1978. The Estuaries of Natal. Natal Town & Regional Planning Commission Report, vol. 41, The Town & Regional Planning Commission, P/B 9038, Pietermaritzburg, 3200, 657 pp.Google Scholar
Böning, C. W., Dispert, A., Visbeck, M., Rintoul, S. R. & Schwarzkopf, F. U. 2008. The response of the Antarctic Circumpolar Current to recent climate change. Nature Geoscience 1, 864–9.CrossRefGoogle Scholar
Bosman, C., Smith, A. M. & Uken, R. 2008. A Sigmoidal Shoreface-Connected Ridge Field: Aliwal Shelf, KZN, South Africa. South African Marine Science Symposium: Our Changing Seas. University of Cape Town, Cape Town 29th June–3rd July 2008, Symposium Guide & Book of Abstracts, p. 13.Google Scholar
Bromirski, P. D., Flick, R. E., Cayan, D. R. & Graham, N. 2004. California Coastal Sea Level and Wind Wave Variations During the Historical Record. From Climate to Economics: Anticipating Impacts of Climate Change in California. California Climate Change Centre, Annual Climate Change Conference, June 9–10, 2004, Abstracts.Google Scholar
Castelle, B., Le Corre, Y. & Tomlinson, R. B. 2008. Can the Gold Coast beaches withstand extreme events? Geo-Marine Letters 28, 23–30.CrossRefGoogle Scholar
Cooper, J. A. G. 1991 a. Shoreline Changes on the Natal coast: Mkomanzi River mouth to Tugela River mouth. Natal Town & Regional Planning Commission Report vol. 77. The Town & Regional Planning Commission, P/B 9038, Pietermaritzburg, 3200, 57 pp.Google Scholar
Cooper, J. A. G. 1991 b. Shoreline Changes on the Natal coast: Tugela river mouth to Cape St Lucia. Natal Town & Regional Planning Commission Report vol. 76. The Town & Regional Planning Commission, P/B 9038, Pietermaritzburg, 3200, 57 pp.Google Scholar
Cooper, J. A. G. 1994. Shoreline Changes on the Natal coast: Mtamvuna River mouth to the Mkomazi River mouth. Natal Town & Regional Planning Commission Report, vol. 79, The Town & Regional Planning Commission, P/B 9038, Pietermaritzburg, 3200, 53 pp.Google Scholar
Cooper, J. A. G. 2001. Gemorphological variability among microtidal estuaries from the wave-dominated South African coast. Geomorphology 40 (1–2), 99–122.Google Scholar
Cooper, J. A. G., Jackson, D. W. T., Navas, F., McKenna, J. & Malvarez, G. 2004. Identifying storm impacts on an embayed, high-energy coastline: examples from western Ireland. Marine Geology 210, 261–80.CrossRefGoogle Scholar
Dolan, R. & Hayden, B. 1981. Storms and shoreline configuration. Journal of Sedimentary Petrology 51, 737–44.Google Scholar
Elliot, T. 1986. Siliciclastic Shorelines. In Sedimentary Environments & Facies (ed. Reading, H. G.), pp. 155–88. Oxford: Blackwells.Google Scholar
Elsner, J. B., Kossin, J. P. & Jagger, T. H. 2008. The increasing intensity of the strongest tropical cyclones. Nature 455, 92–5.CrossRefGoogle ScholarPubMed
Ematek. 1992. Durban Offshore Wave Recording Quarterly Progress Report: Winter 1991. Confidential CSIR Report EMAS-D 92001.Google Scholar
Finkl, C. W. 2004. Leaky valves in littoral sediment budgets: loss of nearshore sand to deep offshore zones via chutes in barrier-reef systems, southeast coast of Florida, USA. Journal of Coastal Research 20, 605–11.CrossRefGoogle Scholar
Flemming, B. W. 1981. Factors controlling shelf sediment dispersal along the south-east African continental margin. Marine Geology 42, 259–77.CrossRefGoogle Scholar
Gallagher, E. L., Elgar, S. & Guza, R. T. 1998. Observations of sandbar evolution on a natural beach. Journal of Geophysical Research 103, 3203–15.Google Scholar
Garland, G. & Moleko, L. 2000. Geomorphological impacts of Inanda on the Mgeni Estuary, north of Durban, South Africa. Bulletin of Engineering, Geology & Environment 59, 119–26.CrossRefGoogle Scholar
Gratiot, N., Anthony, E. J., Gardel, A., Gaucherel, C., Proisy, C. & Wells, J. T. 2008. Significant contribution of the 18.6 year tidal cycle to regional coastal changes. Nature Geoscience 1, 169–72.CrossRefGoogle Scholar
Guastella, L. A. & Rossouw, J. 2009. Coastal Vulnerability: Are Coastal Storms Increasing in Frequency and Intensity along the South African Coast? Abstracts, IMPR Conference, Jeffery's Bay, May 2009, p. 10.Google Scholar
Guastella, L. A., Smith, A. M., Mather, A. A. & Bundy, S. C. 2008. Post March 2007 Marine Storm Erosion of KZN Beaches. South African Marine Science Symposium: Our Changing Seas. University of Cape Town, Cape Town 29th June–3rd July 2008, Symposium Guide & Book of Abstracts, p. 44.Google Scholar
Hemer, M. A., McInnes, K., Church, J. A., O'Grady, J. & Hunter, J. R. 2008. Variability and trends in the Australian wave climate and consequent coastal vulnerability. CSIRO. Final Report for Department of Climate Change Surface Ocean Wave Variability Project, 119 pp.Google Scholar
Hydrographic Research Unit. 1968. Longshore sediment transport at the Izotsha River mouth near Port Shepstone. Sediment Dynamics Division, Coastal Engineering and Hydraulics, National Research Institute for Oceanology Council for Scientific and Industrial Research. CSIR Report C/SEA 8635.Google Scholar
List, J. H., Farris, A. S. & Sullivan, C. 2003. Large-scale response of foreshore slope to storm events. Proceedings of Coastal Sediments 2003. World Scientific Publishing Corporation and East Meets West Productions, Corpus Christi, TX, 1 CD-ROM.Google Scholar
Loureiro, C., Ferreira, Ó. & Cooper, J. A. G. 2009. Contrasting morphologic behaviour at embayed beaches in Southern Portugal. Journal of Coastal Research Special Issue 56, 83–7.Google Scholar
Mather, A. A. 2007. Linear and non-linear sea-level changes at Durban, South Africa. South African Journal of Science 103, 509–12.Google Scholar
Mather, A. A. 2008. Sea Level Rise for the East Coast of Southern Africa. COPDEC VII, 2008, Dubai, UAE.Google Scholar
McNinch, J. E. 2004. Geologic control in the nearshore: shore-oblique sandbars and shoreline erosional hotspots, Mid-Atlantic Bight, USA. Marine Geology 211, 121–41.CrossRefGoogle Scholar
Moes, H. & Rossouw, M. 2008. Considerations for the utilization of wave power around South Africa. Workshop on Ocean Energy, Centre for Renewable and Sustainable Energy Studies, Stellenbosch, 21 February 2008, Abstracts.Google Scholar
Morton, R. A. & Sallenger, A. H. 2003. Morphological Impacts of Extreme Storms on Sandy Beaches and Barriers. Journal of Coastal Research 19 (3), 560–73.Google Scholar
Oost, A. P., De Haas, H., Jensen, I. F., Van den Boogert, J. M. & De Boer, P. L. 1993. The 18.6 yr nodal cycle and its impact on tidal sedimentation. Sedimentary Geology 87, 1–11.CrossRefGoogle Scholar
Phinn, S. R. & Hastings, P. A. 1995. Southern Oscillation Influences on the Gold Coast's summer wave climate. Journal of Coastal Research 11, 946–58.Google Scholar
Pilkey, H. & Cooper, J. A. G. 2004. Society and Sea Level Rise. Science 303, 1781–2.CrossRefGoogle ScholarPubMed
Rossouw, J. 1984. Review of existing wave data, wave climate and design waves for South Africa and South West African (Namibian) coastal waters. CSIR Report T/SEA 8401, Stellenbosch, 66 pp.Google Scholar
Ruessink, B. G., Pape, L. & Turner, I. L. 2009. Daily to interannual cross-shore sandbar migration: Observations from a multiple sandbar system. Continental Shelf Research 29, 1663–77.CrossRefGoogle Scholar
Ruggiero, P., Komar, P. D., McDougal, W. G., Marra, J. J. & Beach, R. A. 2001. Wave Runup, Extreme Water Levels and the Erosion of Properties Backing Beaches. Journal of Coastal Research 17, 407–19.Google Scholar
Sallenger, A. H. Jr, Krabill, W., Brock, J., Swift, R., Manizade, S. & Stockdon, H. 2002. Sea-cliff erosion as a function of beach changes and extreme wave runup during the 1997–1998 El Niño. Marine Geology 187, 279–97.Google Scholar
Schoonees, J. S. 2000. Annual variation in the net longshore sediment transport rate. Coastal Engineering 40, 141–60.CrossRefGoogle Scholar
Shand, R. D., Hesp, P. A. & Shepherd, M. J. 2004. Beach cut in relation to net offshore bar migration. Journal of Coastal Research, Special Issue 39, 334–40. ICS 2004 (Proceedings) Brazil.Google Scholar
Short, A. D. 1999. Handbook of Beach and Shoreface Morphodynamics. John Wiley and Sons, 379 pp.Google Scholar
Short, A. 2002. Large Scale Behavior of Topographically Bound Beaches. In Coastal Engineering 2002: Solving Coastal Conundrums (Volume 3) (ed. Smith, J. M.), pp. 3778–86. Proceedings of the 28th International Conference, Cardiff, Wales, 7–12 July 2002.Google Scholar
Short, A. D., Trembanis, A. & Turner, I. L. 2001. Beach oscillation, rotation and the southern oscillation, Narabeen Beach, Australia. In Proceedings International Conference on coastal Engineering, Sydney, pp. 2439–52. American Society of Civil Engineers.Google Scholar
Smith, A. M., Guastella, L. A., Bundy, S. C. & Mather, A. A. 2007. Combined Marine Storm and Saros Spring–high Tide Erosion Event, March 19–20, 2007: A Preliminary Assessment. South African Journal of Science 103, 274–6.Google Scholar
Theron, A. K. 2007. Analysis of Potential Coastal Zone Climate Change Impacts and Possible Response Options in the Southern African Region. Proceedings IPCC TGICA Conference: Integrating Analysis of Regional Climate Change and Response Options; Nadi, Fiji, June, pp. 205–16.Google Scholar
Thevenot, M. M. & Kraus, N. C. 1995. Longshore sand waves at Southampton Beach, New York: observation and numerical simulation of their movement. Marine Geology 126, 249–69.CrossRefGoogle Scholar
Thom, B. G. & Hall, W. 1991. Behavior of beach profiles during accretion and erosion dominated periods. Earth Surface Processes and Landforms 16, 113–27.CrossRefGoogle Scholar
Thornton, E. B., Humiston, R. & Birkemeier, W. 1996. Bar-trough generation on a natural beach. Journal of Geophysical Research 101, 12097–110.CrossRefGoogle Scholar
Thornton, E. B., MacMahan, J. & Sallenger, A. H. Jr. 2007. Rip currents, mega-cusps, and eroding dunes. Marine Geology 240, 151–67.CrossRefGoogle Scholar
Tinley, K. L. 1971. Determinants of Coastal Conservation: Dynamics and diversity of the environment as exemplified by the Moçambique Coast. Proceedings of Symposium: Nature Conservation as a form of Land Use. Gorongoza National Park, 13–17 September, 1971, pp. 125–53. South African Regional Committee for the Conservation and Utilisation of Soil.Google Scholar
Tucker, M. E. & Wright, P. V. 1990. Carbonate Sedimentology. Oxford: Blackwell Scientific Publications, 482 pp.CrossRefGoogle Scholar
Zaloumis, A. 2007. St Lucia Opens its Mouth Again. African Wildlife 61, 36–7.Google Scholar