Roger Pelnard-Considère

Bio: Roger Pelnard-Considère is an academic researcher. The author has contributed to research in topics: Groyne. The author has an hindex of 2, co-authored 2 publications receiving 158 citations.

Essai de théorie de l'évolution des formes de rivage en plages de sable et de galets

Abstract: Model tests on beach movement under wave action have shown that for small angles of wave incidence the transport is proportional to this angle Under these conditions it is possible to determine analytically how the shape of the beach will alter in case when, on a straight coastline, a long structure has been built which completely eliminates beach movement for a certain length of time Some model tests have well confirmed this theory, which does not, however, apply to the "shadow zone"of the structure, not to the case of short structures

Essai de théorie de l’évolution des formes de rivage en plages de sable et de galets

Abstract: Les mesures, faites au modele, du charriage de sable le long d'une plage sous l'action de la houle ont montre que pour des incidences faibles le transport est proportionnel a cette incidence. Dans ces conditions, il est possible de determiner analytiquement les formes successives du rivage dans le cas ou sur une cote rectiligne on vient etablir un ouvrage de grande longueur arretant totalement le charriage pendant un certain temps. Quelques essais en modele ont permis une bonne verification de cette theorie qui ne s'applique pas toutefois dans la zone «d'ombre » creee par l'ouvrage, ni dans le cas d'ouvrages tres courts epis habituels).

High‐angle wave instability and emergent shoreline shapes: 1. Modeling of sand waves, flying spits, and capes

Abstract: [1] Contrary to traditional findings, the deepwater angle of wave approach strongly affects plan view coastal evolution, giving rise to an antidiffusional “high wave angle” instability for sufficiently oblique deepwater waves (with angles between wave crests and the shoreline trend larger than the value that maximizes alongshore sediment transport, ∼45°). A one-contour-line numerical model shows that a predominance of high-angle waves can cause a shoreline to self-organize into regular, quasiperiodic shapes similar to those found along many natural coasts at scales ranging from kilometers to hundreds of kilometers. The numerical model has been updated from a previous version to include a formulation for the widening of an overly thin barrier by the process of barrier overwash, which is assumed to maintain a minimum barrier width. Systematic analysis shows that the wave climate determines the form of coastal response. For nearly symmetric wave climates (small net alongshore sediment transport), cuspate coasts develop that exhibit increasing relative cross-shore amplitude and pointier tips as the proportion of high-angle waves is increased. For asymmetrical wave climates, shoreline features migrate in the downdrift direction, either as subtle alongshore sand waves or as offshore-extending “flying spits,” depending on the proportion of high-angle waves. Numerical analyses further show that the rate that the alongshore scale of model features increases through merging follows a diffusional temporal scale over several orders of magnitude, a rate that is insensitive to the proportion of high-angle waves. The proportion of high-angle waves determines the offshore versus alongshore aspect ratio of self-organized shoreline undulations.

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

Abstract: [1] 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.

A model integrating longshore and cross-shore processes for predicting long-term shoreline response to climate change

Abstract: We present a shoreline change model for coastal hazard assessment and management planning. The model, CoSMoS-COAST (Coastal One-line Assimilated Simulation Tool), is a transect-based, one-line model that predicts short-term and long-term shoreline response to climate change in the 21st century. The proposed model represents a novel, modular synthesis of process-based models of coastline evolution due to longshore and cross-shore transport by waves and sea level rise. Additionally, the model uses an extended Kalman filter for data assimilation of historical shoreline positions to improve estimates of model parameters and thereby improve confidence in long-term predictions. We apply CoSMoS-COAST to simulate sandy shoreline evolution along 500 km of coastline in Southern California, which hosts complex mixtures of beach settings variably backed by dunes, bluffs, cliffs, estuaries, river mouths, and urban infrastructure, providing applicability of the model to virtually any coastal setting. Aided by data assimilation, the model is able to reproduce the observed signal of seasonal shoreline change for the hindcast period of 1995–2010, showing excellent agreement between modeled and observed beach states. The skill of the model during the hindcast period improves confidence in the model's predictive capability when applied to the forecast period (2010–2100) driven by GCM-projected wave and sea level conditions. Predictions of shoreline change with limited human intervention indicate that 31% to 67% of Southern California beaches may become completely eroded by 2100 under sea level rise scenarios of 0.93 to 2.0 m.