Morphodynamics of nearshore rhythmic sandbars in a mixed-energy environment (SW France): I. Mapping beach changes using visible satellite imagery

Abstract This paper presents a new method to analyze the morphology and migration of shallow water sandbanks based on the retrieval of maps from high-resolution Spot satellite imagery. This approach was applied to the study of intertidal ridge and runnel systems and subtidal crescents that border the southwest coast of France. Maps were obtained from 16 Spot images recorded between 1986 and 2000. Ridge and runnel shapes, with regard to a reference level, were delineated using a watercolor reflectance code parameterized and validated with field data. Crescent plan shapes, which appear on the images due to water transparency or breaking-induced foam, were directly extracted. The spatial maps show that, in conformity with field surveys, the mean alongshore spacing of intertidal systems and crescents range from 370 ± 146 m (variability is indicated by standard deviation) to 462 ± 188 m, and from 579 ± 200 to 818 ± 214 m, respectively. Several couples of images also show that ridge and runnel systems and crescents move in the longshore drift direction (southward) by about 2.4–3.1 and 1 m day−1, respectively. Alongshore migration rates of intertidal systems are confirmed by field surveys, whilst crescent dynamics cannot be validated because there is no in situ data available. To complete these measurements, an analysis of the influence of wave climate on both the shape and movements of these rhythmic sedimentary patterns is proposed in a companion paper.

[1]  H. Dupuis,et al.  Morphodynamics of Ridge and Runnel Systems during Summer , 2002, Journal of Coastal Research.

[2]  H. Howa,et al.  Short-Term Morphodynamic Response of a Ridge and Runnel System on a Mesotidal Sandy Beach , 1999 .

[3]  J. Froidefond,et al.  Spatial Variation in Sinusoidal Wave Energy on a Crescentic Nearshore Bar; Application to the Cap-Ferret Coast, France , 1990 .

[4]  Dennis K. Clark,et al.  Atmospheric effects in the remote sensing of phytoplankton pigments , 1980 .

[5]  R. Holman,et al.  Quantitative characterisation of rip dynamics via video imaging , 1999 .

[6]  C. Pattiaratchi,et al.  Morphological evolution of beach cusp morphology and associated swash circulation patterns , 1998 .

[7]  R. Holman,et al.  The spatial and temporal variability of sand bar morphology , 1990 .

[8]  K. White,et al.  Monitoring changing position of coastlines using Thematic Mapper imagery, an example from the Nile Delta , 1999 .

[9]  Didier Tanré,et al.  Second Simulation of the Satellite Signal in the Solar Spectrum, 6S: an overview , 1997, IEEE Trans. Geosci. Remote. Sens..

[10]  Henk Jan Verhagen,et al.  Coastlines of the Southern North Sea , 1993 .

[11]  Giovanni Coco,et al.  A mechanism for the generation of wave‐driven rhythmic patterns in the surf zone , 2000 .

[12]  L. Moore,et al.  Interannual evolution of multiple longshore sand bars in a mesotidal environment, Truro, Massachusetts, USA , 2003 .

[13]  Jean-Marie M. Dubois,et al.  Suivi de l'evolution du trait de cote a partir d'images HRV (XS) de SPOT: Application au delta du fleuve Rouge, Viet-nam , 2002 .

[14]  G. Coco,et al.  Test of self-organization in beach cusp formation , 2003 .

[15]  T. Aagaard.  Multiple-bar morphodynamics and its relation to low-frequency edge waves , 1991 .

[16]  Taejung Kim,et al.  Automatic satellite image registration by combination of matching and random sample consensus , 2003, IEEE Trans. Geosci. Remote. Sens..

[17]  Virginie Lafon,et al.  Méthode d'analyse de l'évolution morphodynamique d'une embouchure tidale par imagerie satellite. Exemple du bassin d'Arcachon (France)Analysis methodology of tidal inlet morphodynamics through satellite imagery. Example: the Bassin d'Arcachon (France). , 2000 .

[18]  David S. Lemberg,et al.  Mapping Stamp Sand Dynamics: Gay, Michigan , 2002 .

[19]  C. Sonu.  COLLECTIVE MOVEMENT OF SEDIMENT IN LITTORAL ENVIRONMENT , 1968 .

[20]  L. Wright,et al.  Morphodynamic variability of surf zones and beaches: A synthesis , 1984 .

[21]  Robert A. Holman,et al.  The statistics and kinematics of transverse sand bars on an open coast , 2000 .

[22]  Andrew D. Short,et al.  Single and Multi-Bar Beach Change Models , 1993 .

[23]  C. Davis,et al.  An empirical algorithm for light absorption by ocean water based on color , 1998 .

[24]  T. O’Hare,et al.  Bar formation due to wave groups and associated long waves , 1994 .

[25]  Miles O. Hayes,et al.  What is a wave-dominated coast? , 1984 .

[26]  Douglas L. Inman,et al.  Edge waves and crescentic bars , 1971 .

[27]  E. Antia.  Rates and Patterns of Migration of Shoreface-Connected Sandy Ridges along the Southern North Sea Coast , 1996 .

[28]  A. Short.  Rip-current type, spacing and persistence, Narrabeen Beach, Australia , 1985 .

[29]  M. Mulrennan.  Ridge and Runnel Beach Morphodynamics: An Example from the Central East Coast of Ireland , 1992 .

[30]  Virginie Lafon,et al.  Determining ridge and runnel longshore migration rate using Spot imagery , 2002 .

[31]  Philippe Bonneton,et al.  Spatial Variability of Wave Conditions on the French Atlantic Coast using In-Situ Data , 2002, Journal of Coastal Research.

[32]  B. G. Ruessink,et al.  Video observations of nearshore bar behaviour. Part 1: alongshore uniform variability , 2003 .

[33]  Robert G. Dean,et al.  Multiple longshore sand bars in the upper Chesapeake Bay , 1985 .

[34]  D. Lyzenga.  Passive remote sensing techniques for mapping water depth and bottom features. , 1978, Applied optics.

[35]  Rodrigo Pedreros,et al.  Application of grain size trend analysis for the determination of sediment transport pathways in intertidal areas , 1996 .

[36]  C. Pattiaratchi,et al.  Morphological evolution of beach cusps and associated swash circulation patterns , 1998 .

[37]  B. Ruessink,et al.  Analysis of observed two- and three-dimensional nearshore bar behaviour , 2000 .

[38]  Virginie Lafon,et al.  SPOT shallow water bathymetry of a moderately turbid tidal inlet based on field measurements , 2002 .

[39]  A. C. Bird,et al.  GEOMETRIC CORRECTION OF SPOT AND LANDSAT IMAGERY: A COMPARISON OF MAP- AND GPS-DERIVED CONTROL POINTS , 1996 .

[40]  L. Prieur,et al.  Analysis of variations in ocean color1 , 1977 .

[41]  Andrew D. Short,et al.  Macro-Meso Tidal Beach Morphodynamics: An Overview , 1991 .

[42]  E. Anthony,et al.  Location and height of intertidal bars on macrotidal ridge and runnel beaches , 2001 .

[43]  Kurt Novak,et al.  Precision rectification of SPOT imagery using the direct linear transformation model , 1996 .

[44]  Donald G. Bailey,et al.  An Inter-Site Comparison of Net Offshore Bar Migration Characteristics and Environmental Conditions , 1999 .

[45]  E. Owens,et al.  Ridge and Runnel Systems in the Magdalen Islands, Quebec , 1977 .