Search

Beachrocks are a common characteristic of tropical and subtropical coastlines. It is known that they have a substantial influence on beach morphodynamics and they are commonly utilised as indicators of palaeo‐sea levels. At the same time, facies variability in beachrocks is understudied and their effect on shoreline evolution is poorly understood. At Mission Rocks on the KwaZulu‐Natal coastline of South Africa a narrow beach with isolated sand patches occupies low points of an otherwise continuous 3 m thick, raised shore platform of sandy and gravelly beachrocks. These beachrocks are in the process of disintegrating into megagravel deposits through chemical and mechanical weathering in a wave‐dominated, high‐energy setting. The breakdown is potentially slowed by a contemporary, fast‐forming beachrock facies, that blankets the surface and fills fractures and potholes within the older platform. The accumulation and cementation of this recent beachrock is the focus of this study. The beachrock is dated by historical evidence to post‐World War II. Data from field observations, petrographic and geochemical methods reveal that the cementing agents of the beachrock were precipitated from marine water in a phreatic setting despite its position above the intertidal zone. Not only does this facies have implications for the interpretation of palaeo‐beachrock as a sea‐level indicator, it also raises further questions regarding modelling of coastal erosion of beaches associated with outcrops of beachrock. [ABSTRACT FROM AUTHOR]

This perspective examines case examples, primarily from the U. S. Carolinas and Alabama, that illustrate some of the flaws of four federal programs of the last 50 years (National Flood Insurance Program, U. S. Coastal Barrier Resources Act, Coastal Area Management Act, Stafford Disaster Relief Act), as well as general reasons for state and local regulation failures. The latter include: variances that undercut the regulatory intent by the tyranny of small decisions, emergency dispensations, and compensatory mitigation; allowances for ‘temporary’ shore-hardening structures that become permanent; establishing control lines that are not adjusted to shifting shorelines; over-simplifying (one-size-fits-all) and misapplying (importing inappropriate strategies) regulations; conflicting jurisdictional boundaries; and the political instability of regulatory laws. Political-legislative realm failures include: 1) generalized laws do not match the complexity of coasts; 2) legislators lack the foresight to provide funding for regulatory monitoring/enforcement/penalties; 3) legislative bodies lack continuity of visions or goals for the future (e.g., overturn or weaken prior regulatory legislation); and 4) politicians are subject to conflicts of interest (e.g., affluent coastal land owners; pro-development lobbies). The political-legislative disconnect from the reality of Nature, and failure to use longer-term projections of erosion rates, sediment supply, and effects of sea-level rise, are the most frequent culprits in regulatory failure. New starting points for sound regulatory coastal management are better-informed politicians with the will to enact laws based on science that reflect natural variability, and laws that are unflawed by variances or over simplification. Regulations need to have continuity, proper funding, and enforcement. [ABSTRACT FROM AUTHOR]

Nearshore bars play a pivotal role in coastal behaviour, helping to protect and restore beach systems particularly in post-storm conditions. Examination of bar behaviour under various forcing conditions is important to help understand the short- to medium-term evolution of sandy beach systems. This study carried out over a nine-week period examines, the behaviour of three intertidal bars along a high energy sandy beach system in northwest Ireland using high-frequency topographic surveys and detailed nearshore hydrodynamic modelling. Results show that, in general, there was onshore migration for all the bars during the study period, despite the variability observed between bars, which was driven mostly by wave dominated processes. Under the prevailing conditions migration rates of up to 1.83 m day−1 and as low as 0.07 m day−1 were observed. During higher wave energy events the migration rates of the bars decelerated in their onshore route, however, under lower wave energy conditions, they quickly accelerated maintaining their shoreward migration direction. Tidal influence appears to be subordinate in these conditions, being restricted to moderating the localized wave energy at low tides and in maintaining runnel configurations providing accommodation space for advancing slip faces. The study highlights the intricate behavioural patterns of intertidal bar behaviour along a high energy sandy coastline and provides new insights into the relative importance of wave and tidal forcing on bar behaviour over a relatively short time period. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The 550 km-long KwaZulu-Natal coast broadly divides into a bedrock-framed southern section and northern coastal plain section, each of approximately equal length. Seven types of coastal dune are identified on this coast: estuary barrier dunes; mainland beach foredunes; prograded beachridge dunes; headland bypass dunes; transverse dune fields; parabolic/migrating dunefield; and climbing dunes. The development and distribution of the various dune forms is more strongly controlled by the geological setting, than the aerodynamic regime. [ABSTRACT FROM AUTHOR]

Abstract: The equilibrium planform concept (EPC) for bayed beaches has achieved wide currency in coastal morphodynamics. The north coast of Ireland comprises a series of discrete headland-embayment beaches within which waves and currents recycle a finite sediment volume. It is therefore an ideal setting in which to explore the applicability of the concept. Application of the approach to 9 embayment beaches on the north coast of Ireland provides some insights into the application of the concept. The planform of some beaches does correspond to that predicted while others do not. Those whose measured planform does not correspond to the predicted planform can be interpreted through, (a) difficulty in identifying the wave diffraction point, (b) disequilibrium on the beach (sediment scarcity or excess), (c) geological control of beach morphology. The subjectivity in selecting the diffraction point renders alternative explanations difficult and reduces the utility of the approach on natural shorelines, where significant irregularities render identification of such points difficult. [Copyright &y& Elsevier]

High-energy events (extratropical storms, tsunamis, and hurricanes), sediment supply variability, and sea-level rise are regarded as major drivers of coastal geomorphic behavior. In this paper we document a 170 yr record of cyclic coastal changes that occur independently of such external drivers. In a geologically constrained situation with no external sediment input, two end-member morphological configurations (attractors) are identified between which the system alternates. Although neither configuration is stable, the system as a whole exhibits century-scale equilibrium. Our findings present a hitherto unreported form of decadal scale self-adjustment in a coastal system that has occurred under a stable sea level with a consistent wave and tidal regime. [ABSTRACT FROM AUTHOR]

In Ireland, coastal zone management has proceeded largely in an ad hoc manner and is based on sectoral legislation covering issues such as fishing, water quality, coastal protection, etc. Within this framework there exists a plethora of national and local institutions whose responsibility is divided between the marine and terrestrial sub-zones of the coastal zone. This paper presents results from a survey of local government approaches in 16 coastal local authorities to 2 aspects of coastal zone management, viz. coastal protection and application of the national legislation contained in the Foreshore Acts. The approaches of three local authorities are highlighted to illustrate that management, while based on the same legislative and administrative framework, varies considerably between local authorities. While changes in the administrative structure of local government are on-going it is important that the current problems of legal ambiguity and administrative uncertainty are clarified in order to provide a more consistent approach to coastal protection in Ireland. [ABSTRACT FROM AUTHOR]

Coastal sand dunes on the western seaboard of Ireland display a range of diverse morphologies that has largely developed after initial emplacement. Modification of the initial dune structure through natural and human processes has led to a complex and chaotic geomorphology within the dunes. Aerial photography and morphological mapping shows that a number of features exist that have not previously been recorded in the literature. The dune features recorded indicate that dune systems continue to evolve in a temporally erratic way once initial emplacement has taken place. Small pockets within the dunefield become disturbed then revegetate and stabilise. With each period of activity the height and angular nature of the dune forms decrease. Surface geomorphology potentially reflects various stages in an evolutionary pathway that ultimately results in a machair (sandy dune plain) topography. [ABSTRACT FROM AUTHOR]

Abstract: Very large boulders (mega-clasts) are found on some coasts. The size and position of the boulders has been used to suggest that contemporary marine processes, acting within their normal spatial and energy range, are unlikely to have moved them. Explanations for the presence of such boulders include transport by infrequent very high-energy marine processes (storms or tsunamis), mass movement from backing cliffs, transport by ice, or exhumation from glacial deposits. This paper advances an alternative explanation which does not involve transport by any of the marine or glacial processes, or gravity. It is proposed that, in a very specific geological and topographic setting, large boulders are exhumed in situ by storm waves acting on heavily weathered jointed basalts. Eventually wave action liberates residual blocks from the deeply weathered matrix. These liberated boulders will be mobile only if they lie within wave competence, and the larger ones will remain as stationary residuals. The same in situ weathering processes, followed by removal of the friable matrix material debris by wave action, also progressively round the boulders. Consequently, despite their appearance of being transport-rounded, the larger boulders have not transported at all. In specific locations, the assumption that the presence, and rounding, of such large clasts in the shore zone can be attributed to marine transport can lead to erroneous interpretations of very high-energy storm wave (or tsunami) activity. [Copyright &y& Elsevier]

Abstract: Experiments carried out at Magilligan Strand on the north coast of Ireland suggest that topographic steering of offshore winds is an important facet of the aeolian sediment transport system at this location. A five-day study (18–22 June 2005) investigated the pattern of airflow over the foredune while simultaneously collecting data on sediment flux. A simple instrument setup was used to characterise the airflow: a sonic anemometer was placed at the dune crest, with another on the mid-beach. Horizontal traps, electronic and integrating, measured sediment flux on the supra-tidal beach. Results show that offshore wind flow deviated from its original direction in the lee of the dune (seaward of foredune). The change in direction was not a simple steering of flow to a singular new direction, but rather flow separation resulting in turbulent multidirectional flow — including reversal. Traps located at the foot of the dune scarp recorded sediment transport during events forced by offshore winds. Data from sediment traps, wind and observational evidence have been used to argue that sedimentation was occurring in this zone. When budgeting for sediment movement within beach–dune systems it is important to take into account the effect of secondary airflow patterns during offshore winds and their role in constructive processes of foredune formation, particularly in post-storm recovery. [Copyright &y& Elsevier]