15 - Sandy beaches in estuaries and bays

Abstract

Sandy beaches in estuaries and bays are distinct from open-coast beaches in that they are partially or fully sheltered from ocean waves. The sheltering increases the importance of other sources of wave energy such as infragravity waves that propagate into bays and estuaries with less dissipation than swell, combined with locally generated wind waves. Moreover, tidal translation and currents may become important and contribute to beach erosion and deposition. In this chapter, we review the importance of sandy beaches in estuaries and bays, and introduce the geological setting and oceanographic conditions that determine where they form and what they look like. We consider the variety of terminology that has been used to describe them (e.g. fetch-limited, low-energy or sheltered beaches) and discuss the relatively limited number of studies on their morphodynamics. We also include a case study from Botany Bay, Sydney, Australia. We conclude that sandy beaches in estuaries and bays should be recognised as a distinct class of beach (’bay and estuary beaches’, or BEBs) that has notable contrasts with open-ocean beaches that are dominated by ocean waves.