Morphodynamic variability of surf zones and beaches: A synthesis

Natural beaches may be grouped into several beach types on the basis of breaker height (H b ), wave period (T), high tide sediment fall velocity (w s ) and tide range (TR). These four variables are quantified by two dimensionless parameters: the dimensionless fall velocity (Ω= H b /w s T) used by WRIGHT and SHORT (1984) to classify micro-tidal beaches, and the relative tide range (RTR = TR/H b ) introduced in this paper. The value of the dimensionless fall velocity indicates whether reflective, intermediate or dissipative surf zone conditions will prevail. The relative tide range reflects the relative importance of swash, surf zone and shoaling wave processes. A conceptual model is presented in which beach morphology (beach type) may be predicted using the dimensionless fall velocity and the relative tide range, whereby the mean spring tide range (MSR) is used to calculate the relative tide range. The model consists of the existing micro-tidal beach types, which as RTR Increases, shift from reflective to low tide terrace with and finally without rips; from intermediate to low tide bar and rips and finally ultra-dissipative; and from barred dissipative to non-barred dissipative and finally ultra-dissipative. Using this model, all wave-dominated beaches in all tidal ranges can be classified.

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The Effect of Tide Range on Beach Morphodynamics and Morphology: A Conceptual Beach Model

Short term variability in delta form and process can be partly explained by the relative strength of hydraulic parameters such as river discharge, discharge variability, wave energy flux and tidal range. However, the calibre or grain size is also important. The amount, mode of transport and grain size of the sediment load delivered to a delta front have a considerable effect on the facies, formative physical processes, related depositional environments and morphology of the deltaic depositional system. The available grain size influences (1) the gradient and channel pattern of the fluvial system on the delta plain; (2) the mixing behaviour of sediment as it discharges into the ambient basin waters at the river mouth; (3) the type of shoreline, whether reflective or dissipative, and its response to both wave energy and tidal regime; and (4) the deformation and resedimentation processes on the subaqueous delta front. Long term aspects of deltaic sedimentation, including a few generalized relationships between sediment supply and physiographic setting, are briefly introduced. The need for further detailed research on modern and ancient deltaic dispersal systems is emphasized, and specific suggestions are given for future research.

Variability of deltaic processes in terms of sediment supply, with particular emphasis on grain size

Wave, beach and dune interactions in southeastern Australia

To investigate the influence of marine macrophyte wrack subsidies on community structure, relationships between community attributes, including species richness, abundance, and biomass of macrofauna and abundance of shorebirds, and a variety of factors, including the standing crop of wrack and beach morphodynamics, were examined on 15 exposed sandy beaches on the southern California coast. The beaches sampled were primarily modally intermediate morphodynamic types, and three were groomed regularly. Species richness, abundance, and biomass of the macrofauna were high compared to values reported for similar beach types in other regions and were not predicted by morphodynamics or other physical factors. Overall species richness and abundance, and the species richness, abundance, and biomass of wrack-associated fauna and selected taxa were significantly correlated with the standing crop of macrophyte wrack. Wrack-associated macrofauna, such as amphipods, isopods, and insects, made up an average of >37% of the species on ungroomed beaches and comprised 25% or more of the total abundance on half of those beaches. The abundance of two shorebird species, plovers that forage using visual cues, was positively correlated with the standing crop of wrack and with the abundance of wrack-associated invertebrates. Significant differences in community structure, including depressed species richness, abundance, and biomass of macrofauna, especially for wrack-associated taxa, were associated with beach grooming and provided strong evidence for the bottom-up effects of wrack subsidies. Grooming also reduced the prey available to vertebrate predators, such as shorebirds. Substantial ecological effects of the large-scale disturbance and removal of organic material, food resources, and habitat are associated with beach grooming. These results suggest that macrophyte wrack subsidies strongly influence macrofaunal community structure, higher trophic levels, and ecological processes on exposed sandy beaches. The supply of macrophyte wrack should be considered as a factor in ecological studies of exposed sandy beaches, particularly where macrophyte production is high.

The response of macrofauna communities and shorebirds to macrophyte wrack subsidies on exposed sandy beaches of southern California

Morphodynamics of reflective and dissipative beach and inshore systems: Southeastern Australia

This paper examines sandy beach types that exist in wave environments ranging from low ( 2.5m). Three basic beach types — reflective, intermediate and dissipative, composed of six beach states have been identified. Each beach state can be classified by its wave-sediment characteristics. In addition, the paper discusses the environmental conditions required to produce each beach state, and their associated morphology; surfzone circulation and dynamics; mode and scale of sediment exchange and erosion; and spatial and temporal variability.

L.D Wright

Papers

Morphodynamic variability of surf zones and beaches: A synthesis

Morphodynamics of reflective and dissipative beach and inshore systems: Southeastern Australia

Physical Variability of Sandy Beaches

Dynamics of a high-energy dissipative surf zone

Morphodynamics of a macrotidal beach