Journal of Coastal Research, Special Issue No. 65, 2013 1224 Sottolichio, et al. Evaluation of the recent morphological evolution of the Gironde estuary through the use of some preliminary synthetic indicators Aldo Sottolichio†, Vincent Hanquiez†, Helene Périnotto†, Laurie Sabouraud†, Olivier Weber† †Universite Bordeaux 1, EPOC Laboratory, UMR CNRS 5805, avenue des Facultes, 33405 Talence - France a.sottolichio@epoc.u-bordeaux1.fr INTRODUCTION Drastic changes of the physical coastal environment are expected in the future under the effect of climate change. They make necessary to better understand its morphology evolution, especially considering that these areas are the habitat for specific ecosystems. Understanding the past evolution of the systems is then an essential step to identify trends and achieve understanding of ecosystem trajectories. Estuaries are complex systems under constant evolution, where habitats are submitted to natural and anthropogenic pressures. Human interventions such as channel dredging, sand excavation, embakment and land reclamation cause significant changes in bathymetry, hydraulic regime and sediment transport patterns (Talke et al., 2009; Juang et al., 2011; Wang et al., 2010). Moreover, in the case of european estuaries, the context of the water framework directive (WFD) implies that a good ecological status must be achieved in 2020. This is conditioned by a good hydromorphological status. To evaluate this, EU members need to generate pratical indicators to describe and evaluate the status of water masses. Estuarine waters are part of the transitional waters that are needed to be evaluated. The indicators are still under development, in particular those concerning the hydro-morpho- sedimentary (HMS) functioning of large turbid estuaries. The recent French project LITEAU-BEEST (2008-2011) focused on the definition on primary synthetic indicators that can be useful to define the ecological status of an estuary (Le Hir et al., 2011). This implies a good knowledge not only on the physical processes in estuaries, but also on the affinity of biological species with parameters of the estuary (Sottolichio et al., 2011). The main french estuaries (Seine, Loire and Gironde) are also the largest and present high levels of turbidity. In the Seine and the Loire estuaries, secular evolution was drastic because there have been intense civil engineering works during the XXth century (see for instance Lesourd et al., 2001). The Gironde estuary, SW France, is the largest estuary of the west Atlantic coast, and also one of the most deeply investigated by numerous sedimentological studies in the past decades (Nichols and Biggs, 1985). Because engineering works were much less intense in the Gironde than in the Seine and in the Loire estuaries, it has been assumed that the Gironde estuary has experienced nonsignificant changes. However, and maybe for this reason, very few studies are available on the recent morphological evolution of the Gironde ABSTRACT Sottolichio, A., Hanquiez, V., Périnotto, H., Sabouraud, L. and Weber, O., 2013. Evaluation of the recent morphological evolution of the Gironde estuary through the use of some preliminary synthetic indicators. In: Conley, D.C., Masselink, G., Russell, P.E. and O’Hare, T.J. (eds.), Proceedings 12 th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 1224-1229, ISSN 0749-0208. Drastic evolution of the physical coastal environment are expected in the future under the effect of climate change. They make necessary to better understand the past morphology evolution, especially considering areas that are the habitat for some specific ecosystems. Moreover, because the context of the water framework directive (WFD), EU members need to generate indicators to evaluate the status of estuarine water masses. To satisfy these two obectives, the recent evolution of the Gironde estuary has been studied by the analysis of bathymetry with GIS. The Gironde is the largest estuary of western Europe, and one of the most turbid. In this study, the analysis extents from 1962 to 1994. Results show that the zone of maximum volume of deposited sediment has migrated continuously towards the upstream portion of the estuary, which is coherent with the decrease of summer river flow and the upstream shift of the turbidity maximum toward the riverine sections. In addition, zones with relative stable and unstable morphology were identified, showing rythmic distribution similarly to those previously recognized through the evolution over 160 years (1825- 1984). This seems to be independent from the fluvial regime, but rather related to the interaction between tidal co- oscillations and estuarine morphology, which is not elucidated yet. Finally, some hydro-morpho-sediemntary (HMS) indicators useful to the WFD have been described : distribution of depths, changes on cross section areas, changes of intertidal areas. They are discussed to discriminate the “natural” and “anthropogenic” contribution to morphological changes observed. ADDITIONAL INDEX WORDS: bathymetry, DEM, sedimentary evolution, macrotidal estuary, long-term changes www.JCRonline.org www.cerf-jcr.org ____________________ DOI: 10.2112/SI65-207.1 received 07 December 2012; accepted 06 March 2013. © Coastal Education & Research Foundation 2013