title: Transect based analysis versus area based analysis to quantify shoreline displacement: spatial resolution issues.
abstract: Field surveys, aerial photographs, and satellite images are the most commonly employed sources of data to analyze shoreline position, which are further compared by area based analysis (ABA) or transect based analysis (TBA) methods. The former is performed by computing the mean shoreline displacement for the identified coastal segments, i.e., dividing the beach area variation by the segment length; the latter is based on the measurement of the distance between each shoreline at set points along transects. The present study compares, by means of GIS tools, the ABA and TBA methods by computing shoreline displacements recorded on two stretches of the Tuscany coast (Italy): the beaches of Punta Ala, a linear coast without shore protection structures, and the one at Follonica, which is irregular due to the presence of groins and detached breakwaters. Surveys were carried out using a differential global positioning system (DGPS) in RTK mode. For each site, a 4800-m-long coastal segment was analyzed and divided into ninety-six 50-m-long sectors for which changes were computed using both the ABA and TBA methods. Sectors were progressively joined to have a length of 100, 200, 400, and 800 m to examine how this influenced results. ABA and TBA results are highly correlated for transect distance and sector length up to 100 m at both investigated locations. If longer transects are considered, the two methods still produce good correlated data on the smooth shoreline (i.e. at Punta Ala), but correlation became significantly lower on the irregular shoreline (i.e., at Follonica).
authors.affiliation: Departamento de Ciencias de la Terra, Facultad de Cuiencias del Mar y Ambientales, Universitad de Cádiz, Poligono Rìo San Pedro s/n, 11510, Puerto Real, Càdiz, Spain. giorgio.anfuso@uca.es.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Anfuso
authors.affiliation: Department of Geography, Ben-Gurion University of the Negev, P.O. Box 653, 84105, Beer Sheva, Israel.
authors.forename: Dan
authors.initials: D
authors.lastname: Bowman
authors.affiliation: Curtin University Sustainability and Policy Institute, Curtin University, Kent Street, Bentley, WA, 6102, Australia.
authors.forename: Chiara
authors.initials: C
authors.lastname: Danese
authors.affiliation: Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via Micheli 6, 50121, Florence, Italy.
authors.forename: Enzo
authors.initials: E
authors.lastname: Pranzini
mesh_terms: D001493:Bathing Beaches / Q000706:statistics & numerical data*; D004784:Environmental Monitoring / Q000379:methods*; D040362:Geographic Information Systems; D005843:Geography; D007558:Italy; D063809:Satellite Imagery / Q000379:methods*
keywords: Beach erosion; Beach survey; Shore protection; Shoreline evolution