Morphology and Formation of an Holocene Coastal Dune Field, Bruce Peninsula, Ontario

This paper describes a dune field on the gently-sloping Lake Huron shoreline of the Bruce Peninsula, Ontario. The inland boundary is marked by a prominent dune ridge 60 m wide and up to 30 m high, which extends parallel to the shoreline for about 19 km, and was formed about 5000 years BP near the end of the Nipissing transgression. The islands and rock reefs which protect the modern shoreline were submerged under the higher lake levels, giving rise to a relatively straight, exposed beach from which sediment was supplied for building the dune ridge. Dunes formed between this ridge and the modern shoreline during the post-Nipissing regression decrease in height and continuity, reflecting decreased sediment supply associated with regression and reduced wave exposure as the offshore islands emerged. The sequence described here supports previous conclusions that transgressions are associated with periods of coastal dune formation and instability.On fait ici la description d'un champ de dunes situé sur le rivage faiblement incliné de la péninsule de Bruce, au lac Huron. La limite intérieure est caractérisée par une chaîne de dunes de 60 m de large et jusqu'à 30 m de haut qui s'étend parallèlement au rivage sur une longueur de 19 km; elle a été formée il y a 5000 ans BP, presque la fin de la transgression de Nipissing. Les îles et les écueils rocheux qui protègent le rivage actuel étaient alors immergés sous des niveaux lacustres supérieurs, permettant ainsi la formation d'une plage découverte relativement rectiligne qui a fourni le sable nécessaire à l'édification de la chaîne de dunes. La formation, au cours de la régression post-Nipissing, de dunes moins hautes et plus dispersées, entre la chaîne de dunes et le rivage actuel, témoigne d'une faible alimentation en sédiments associée à la régression et d'une moindre exposition aux vagues en raison de l'émersion des îles. La séquence décrite ici corroborent les conclusions antérieures selon lesquelles les transgressions correspondent à des périodes de formation et d'instabilité des dunes littorales.Dieser Aufsatz beschreibt ein Dùnenfeld, das am schwach abfallenden Ufer des Huron-Sees, Bruce-Halbinsel liegt. Die Grenze zum Landinnern ist hervorgehoben durch eine Kette von Dunen, die 60 m breit und bis zu 30 m hoch sind, und die sich parallel zum Ufer ùber eine Lange von 19 km ausdehnt; sie wurde vor 5000 Jahren v.u.Z. gebildet, fast am Ende der Transgression von Nipissing. Die Insein und die Felsklippen, die das heutige Ufer schùtzen, waren damais unter den hôheren Seen-Niveaus untergetaucht, so dass ein offener, relativ gerader Strand entstehen konnte, der den fur den Aufbau der Dunenkette notwendigen Sand lieferte. Wàhrend der Regression post-Nipissing haben sich zwischen der Dunenkette und dem heutigen Uferweniger hohe und mehr verstreute Dùnen gebildet, welche Zeugnis von einer schwachen Sediment-Zufuhr abgeben, in Verbindung mit der Regression und einem geringeren Einfluss der Wellen wegen des Auftauchens der Insein. Die hier beschriebene Sequenz bestàtigt frùhere Schlussfolgerungen. denen zufolge die Transgressionen mit Perioden der Bildung und Instabilitàt von Kùstendùnen in Verbindung gebracht werden

Sediment Budget Controls on Foredune Height: Comparing Simulation Model Results with Field Data

The form, height and volume of coastal foredunes reflects the long-term interaction of a suite of nearshore and aeolian processes that control the amount of sand delivered to the foredune from the beach versus the amount removed or carried inland. In this paper, the morphological evolution of foredune profiles from Greenwich Dunes, Prince Edward Island over a period of 80 years is used to inform the development of a simple computer model that simulates foredune growth. The suggestion by others that increased steepness of the seaward slope will retard sediment supply from the beach to the foredune due to development of a flow stagnation zone in front of the foredune, hence limiting foredune growth, was examined. Our long-term data demonstrate that sediment can be transferred from the beach to the foredune, even with a steep foredune stoss slope, primarily because much of the sediment transfer takes place under oblique rather than onshore winds. During such conditions, the apparent aspect ratio of the dune to the oncoming flow is less steep and conditions are not favourable for the formation of a stagnation zone. The model shows that the rate of growth in foredune height varies as a function of sediment input from the beach and erosion due to storm events, as expected, but it also demonstrates that the rate of growth in foredune height per unit volume increase will decrease over time, which gives the perception of an equilibrium height having been reached asymptotically. As the foredune grows in size, an increasing volume of sediment is needed to yield a unit increase in height, therefore the apparent growth rate appears to slo

Scale-dependent perspectives on the geomorphology and evolution of beachdune systems

Despite widespread recognition that landforms are complex Earth systems with process-response linkages that span temporal scales from seconds to millennia and spatial scales from sand grains to landscapes, research that integrates knowledge across these scales is fairly uncommon. As a result, understanding of geomorphic systems is often scale-constrained due to a host of methodological, logistical, and theoretical factors that limit the scope of how Earth scientists study landforms and broader landscapes. This paper reviews recent advances in understanding of the geomorphology of beach-dune systems derived from over a decade of collaborative research from Prince Edward Island (PEI), Canada. A comprehensive summary of key findings is provided from short-term experiments embedded within a decade-long monitoring program and a multi-decadal reconstruction of coastal landscape change. Specific attention is paid to the challenges of scale integration and the contextual limitations research at specific spatial and/or temporal scales imposes. A conceptual framework is presented that integrates across key scales of investigation in geomorphology and is grounded in classic ideas in Earth surface sciences on the effectiveness of formative events at different scales. The paper uses this framework to organize the review of this body of research in a 'scale aware' way and, thereby, identifies many new advances in knowledge on the form and function of subaerial beach-dune systems. Finally, the paper offers a synopsis of how greater understanding of the complexities at different scales can be used to inform the development of predictive models, especially those at a temporal scale of decades to centuries, which are most relevant to coastal management issues. Models at this (landform) scale require an understanding of controls that exist at both ‘landscape’ and ‘plot’ scales. Landscape scale controls such as sea level change, regional climate, and the underlying geologic framework essentially provide bounding conditions for independent variables such as winds, waves, water levels, and littoral sediment supply. Similarly, an holistic understanding of the range of processes, feedbacks, and linkages at the finer plot scale is required to inform and verify the assumptions that underly the physical modelling of beach-dune interaction at the landform scale

High-angle wave instability and emergent shoreline shapes : 2. Wave climate analysis and comparisons to nature

Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): F04012, doi:10.1029/2005JF000423.Recent research has revealed that the plan view evolution of a coast due to gradients in alongshore sediment transport is highly dependant upon the angles at which waves approach the shore, giving rise to an instability in shoreline shape that can generate different types of naturally occurring coastal landforms, including capes, flying spits, and alongshore sand waves. This instability merely requires that alongshore sediment flux is maximized for a given deepwater wave angle, a maximum that occurs between 35° and 50° for several common alongshore sediment transport formulae. Here we introduce metrics that sum over records of wave data to quantify the long-term stability of wave climates and to investigate how wave climates change along a coast. For Long Point, a flying spit on the north shore of Lake Erie, Canada, wave climate metrics suggest that unstable waves have shaped the spit and, furthermore, that smaller-scale alongshore sand waves occur along the spit at the same locations where the wave climate becomes unstable. A shoreline aligned along the trend of the Carolina Capes, United States, would be dominated by high-angle waves; numerical simulations driven by a comparable wave climate develop a similarly shaped cuspate coast. Local wave climates along these simulated capes and the Carolina Capes show similar trends: Shoreline reorientation and shadowing from neighboring capes causes most of the coast to experience locally stable wave climates despite regional instability.This research was funded by the Andrew W. Mellon Foundation and NSF grants DEB-05-07987 and EAR-04-44792

Event‐scale dynamics of a parabolic dune and its relevance for mesoscale evolution

Parabolic dunes are wide-spread aeolian landforms found in a variety of environments. Despite modelling advances and good understanding of how they evolve, there is limited empirical data on their dynamics at short time-scales of hours, and on how these dynamics relate to their medium-term evolution. This study presents the most comprehensive dataset to date on aeolian processes (airflow and sediment transport) inside a parabolic dune at an event-scale. This is coupled with information on elevation changes inside the landform to understand its morphological response to a single wind event. Results are contextualized against the medium-term (years) allowing us to investigate one of the most persistent conundrums in geomorphology, that of the significance of short-term findings for landform evolution. Our field data suggested three key findings: 1) sediment transport rates inside parabolic dunes correlate well with wind speeds rather than turbulence; 2) up to several tonnes of sand can move through these landforms in a few hours; 3) short-term elevation changes inside parabolic dunes can be complex and different from long-term net spatial patterns, including simultaneous erosion and accumulation along the same wall. Modeled airflow patterns along the basin were similar to those measured in situ for a range of common wind directions, demonstrating the potential for strong transport during multiple events. Meso-scale analyses suggested that the measured event was representative of the type of events potentially driving significant geomorphic changes over years, with supply-limiting conditions playing an important role in resultant flux amounts