Morphodynamic Classification Research Articles

Morphodynamic classification of sandy beaches in low energetic marine environment

Morphodynamic classification of beaches has achieved widespread acceptance in both geological and geomorphological literature. In this sense, the present work classifies twelve Mediterranean low energetic beaches according to the dimensionless fall parameter ( Ω) parameter in the Island of Mallorca. Propagation of 44 yr of wave data as well as a detailed sediment study allows to provide probabilities for morphodynamical beach state on an annual and seasonal basis. Consequently, beaches in Mallorca fall between three major categories which are (a) truly reflective, (b) reflective skewed to intermediate and (c) intermediate beaches. The Mallorcan beach position in the morphodynamical scheme is close related to the physiographical and geological framework. Comparison of observed values with those obtained in the analysis leads that for gross beach classification there is agreement between predicted and real state. However on a seasonal classification, mainly during summer, there is no agreement between the predicted state and the real one. As the model does not incorporate the role of summer sea breezes, beach reflective states are highlighted. Real beach configurations correspond to more energetic wave dynamic conditions and to intermediate state scenarios.

Barrier Island Morphodynamic Classification Based on Lidar Metrics for North Assateague Island, Maryland

In order to reap the potential of airborne lidar surveys to provide geological information useful in understanding coastal sedimentary processes acting on various time scales, a new set of analysis methods are needed. This paper presents a multi-temporal lidar analysis of north Assateague Island, Maryland, and demonstrates the calculation of lidar metrics that condense barrier island morphology and morphological change into attributed linear features that may be used to analyze trends in coastal evolution. The new methods proposed in this paper are also of significant practical value, because lidar metric analysis reduces large volumes of point elevations into linear features attributed with essential morphological variables that are ideally suited for inclusion in Geographic Information Systems. A morphodynamic classification of north Assategue Island for a recent 10 month time period that is based on the recognition of simple patterns described by lidar change metrics is presented. Such morphodynamic classification reveals the relative magnitude and the fine scale alongshore variation in the importance of coastal changes over the study area during a defined time period. More generally, through the presentation of this morphodynamic classification of north Assateague Island, the value of lidar metrics in both examining large lidar data sets for coherent trends and in building hypotheses regarding processes driving barrier evolution is demonstrated.

Coastal dunes: sensitive or not?

This paper introduces a classification of coastal dune systems into two main morphodynamic classes, namely retentive and transgressive dune systems. Retentive systems include coastal dune types where sand accumulation within vegetation is dominant over other processes. In this category we include such morphological types as hummock dunes, foredunes, and retention ridges, including sub-environments such as precipitation ridges that form the landward boundary of transgressive dunefields. Transgressive systems include those coastal dune types where sand transport is dominant over other processes, and the dunes are unvegetated and mobile. In this category we include such morphological types as parabolic dunes, reversing transverse dunes, barchans, seif dunes, transgressive sheet dunefields and headland-bypass dunefields. Components of the two main morphodynamic types of coastal dune systems range in sensitivity from sensitive to robust. Retentive dune systems, being vegetated, are sensitive and fragile. Mobile dunes that form the major component of transgressive dune systems are robust and resilient. This morphodynamic classification is particularly useful because the two types of dune systems have diametrically opposed sensitivities and hence different management requirements.

Eolian dune types preserved in the Tensleep Sandstone (Pennsylvanian-Permian), north-central Wyoming

The Tensleep Sandstone is one component of an erg system that prograded southward out of north-central Wyoming from Middle Pennsylvanian to Early Permian time. Each erg advance was temporarily interrupted by regional marine transgression. Interpretation of dune types deposited in these ergs is developed from an analysis of the relative proportions of eolian stratification types comprising foreset strata, geometry and relationships of bounding surfaces, and paleodispersal patterns. Two basic morphologic dune types are inferred: simple dunes and compound crescentic dunes. The simple dunes are dominant and are subdivided into 1–2 km wavelength and 1.0 km saddle-spacing slightly crescentic, and 0.1–0.2 km wavelength straight-crested subtypes based on their first-order bounding surface geometries. Foresets are composed of grainfall and wind-ripple strata; avalanche strata are rare. The compound crescentic dunes had wavelengths of 0.5–1 km and saddle spacings of 0.8 km. Foresets are dominated by avalanche and wind-ripple strata. A morphodynamic classification of the dune types is inferred from considerations deduced from paleodispersal patterns and comparison with paleocirculation models. The simple dunes were demonstrably oblique to some elements of the wind field and less oblique to others. The compound crescentic dunes had a predominantly transverse configuration.

Wave, beach and dune interactions in southeastern Australia

A morphodynamic classification of surfzones, beaches and dunes of the microtidal, low- to high-energy southeast Australian coast is presented. The first section (A: Waves and beaches) briefly deals with the transformation of deep-water wave energy as it crosses the shelf, nearshore and surfzone. Depending on the deep-water wave characteristics and shelf and inshore morphology, resultant breaker wave energy may be high, moderate or low, and the accompanying beach surfzone morphodynamic state in fine to medium sand beaches either dissipative, intermediate or reflective. Dissipative beaches have wide surfzones with shore parallel bar(s) and channel(s) and predominantly shore-normal circulation; intermediate beaches are characterised by rip circulation, crescentic-transverse bars and megacusps; and reflective beaches by a barless surfzone and steep, cusped or bermed beach. Each beach form has a characteristic level of beach stability, zone of sediment storage and mode of beach and dune erosion. Landward aeolian sediment transport of swash-deposited sand (Section B) is dependent on the subaerial beach topography and the aerodynamic flow regime across that topography. Characteristic profile shapes are ascribed to each beach type (dissipative, intermediate and reflective). Aeolian sand transport rates are potentially highest on dissipative beaches, moderate on intermediate beaches and lowest on reflective beaches. These rates determine the potential size of foredunes which are correspondingly largest on dissipative beaches and smallest on reflective beaches. The combination of mode and frequency of beach/dune erosion, rates of aeolian sand transport, and foredune volume and morphology provide an explanation of the nature and morphology of landward-occurring, large-scale dune systems. Dissipative beaches are frequently characterised by large-scale transgressive dune sheets; intermediate, by a trend from large-scale parabolic dune systems (high-wave energy) to small-scale blowouts (low-wave energy); and reflective beaches by minimal dune development.