Wave-dominated coasts

• Published in: Coastal Evolution pp. 121 - 186
• Main Authors: Roy, P.S., Cowell, P.J., Ferland, M.A., Thom, B.G.
• Format: Book Chapter
• Language: English
• Published: Cambridge University Press 05.01.1995
• Subjects: Earth Sciences; Hydrology, Oceanography & Glaciology
• ISBN: 0521598907; 9780521419765; 052141976X; 9780521598903
• DOI: 10.1017/CBO9780511564420.006

IntroductionWave-dominated sedimentary coasts comprise accumulations of detrital sand and gravel-sized material which undergo high levels of physical reworking, interspersed with periods of burial before finally being deposited as the coastal deposits we see today (Davis & Hayes, 1984). Quite commonly sediments tend to be of clean sand and gravel, often quite well sorted and abraded, containing relatively high proportions of more resistant minerals and rock types such as quartz, chert and heavy minerals. Waves and wave-induced currents are the dominant mechanisms for moving and depositing sand on shorefaces and beaches of the open coast, although winds, river discharge, tidal currents and Ekman flows variously act as transporting agents landward of the beach, in estuaries and seaward of the shoreface. In relation to the shoreface and beach, open coastal types are determined by four factors: (i) substrate gradient, (ii) wave energy versus tidal range; (iii) sediment supply versus accommodation volume (Swift & Thome, 1991); and (iv) rates of sea-level change. At one extreme are steep, high-energy, sediment-deficient coasts that have bedrock cropping out as headlands, with negligible sand at their base and relatively deep water offshore (autochthonous, accommodation-dominated coast of Swift & Thorne, 1991). At the other extreme are low-gradient, low-energy coasts that are typically muddy with a coastal fringe of wetland vegetation. Here, incident wave action is dissipated over very shallow offshore gradients such as those associated with deltaic environments at river mouths (autochthonous, sediment-supply dominated coast of Swift & Thorne, 1991; see Chapter 3). But even here, rare high-energy events such as cyclones can cause episodes of wave reworking leading to the formation of cheniers.