MORPHOLOGY OF SAND ACCUMULATION IN ESTUARIES: AN INTRODUCTION TO THE SYMPOSIUM

Abstract

The morphology of sand deposits in estuaries is determined by the interaction of a number of process variables, including: (a) tidal range, (b) tidal currents, (c) wave conditions, and (d) storm action. Of these, variations in tidal range have the broadest effect in determining large-scale differences in the morphology of sand accumulation. The papers in this symposium have, therefore, been arranged according to differences in tidal range of the areas discussed, following the classification scheme proposed by Davies (4):ICoarse-grained sediment accumulation in estuaries with small tidal ranges (microtidal estuaries: tidal range (T.R.) = 0 − 2 m).Wave action and storm deposition are more important in this class than in any other. Galveston Bay, Texas, is an example of this type of estuary.IICoarse-grained sediment accumulation in estuaries with intermediate tidal ranges (mesotidal: T.R. = 2 − 4 m).Tidal deltas and tidal-current-formed sand bodies increase noticeably in this class. The estuaries of New England, South Carolina, and Georgia are prototypes.IIICoarse-grained sediment accumulation in estuaries with large tidal ranges (macrotidal: T.R. > 4 m).Funnel-shaped, wide-mouthed estuaries that contain linear sand bodies are the most common types occuring in this category. Prototypes are Bristol Bay, Alaska, and the Ord River estuary, Australia.IVWide-mouthed estuaries.This category was created in order to include in the symposium papers covering the large entrances into such major bodies of water as the Baltic Sea and Chesapeake Bay.Much of the emphasis in these papers has been placed on estuaries in the mesotidal category, principally because these are the ones that have been studied most. Despite the fact that mesotidal estuaries show a wide range in morphological and hydrographic characteristics, the sand shoals affiliated with them are remarkably similar from place to place. For example, flood-tidal deltas usually contain the same major components, including a flood ramp, flood channels, ebb shields, ebb spits, and spillover lobes, regardless of the variations in current and wave conditions under which they occur. Similarly, the ebb-tidal deltas, although they are exposed to great variations in open-ocean-wave intensity, are strikingly consistent in morphology.