IWRA Proceedings

AbstractThis work was part of the IMPLIT project (“Impact of extreme events (storms and sea surges) linked to climatic change, on the French coastal Mediterranean hydro-systems”) developed within the framework of the GICC program (“Management and impact of climatic change”) (Ministry of Ecology and Sustainable Development). The objective of the Rhone delta hydrosystem modelling task was to analyse hydraulic management constraints of the “Ile de Camargue” in extreme hydro-climatic conditions; to develop a simplified and adaptive simulation tool for hydrologic and hydraulic functioning of the Vaccarès lagoon system, in order to provide decision support for flood management and prospective. An analysis of existing hydro-climatic data was made (precipitations, wind, flood discharges and management of Camargue drainage basins; Rhone river floods at Beaucaire, effects of wind on lagoon water levels), in order to derive crisis scenarios used for simulations. After calibration and validation on autumn-winter periods (September to March) 2003-2004 and 2005; simulations were made with a conceptual model, combining observed data (wind, evaporation, sea level) and forcing by drainage hydrographs from the North delta flooded area (1993 or 1994 flood event type). Impact of additional works: drainage pumping station on the basin, increased capacity for discharge by gravity to the sea; with sea level rise, were also simulated, using scenarios based on data from 1996-97, 2002 and 2003, corresponding to the last major floods of the Rhone river. Statistical analysis of maximum annual discharge shows that the last strong flood of the Rhone river in 2003 may have only a 50 year return period, revisiting former risk analysis knowledges. The simulations made with the simplified model (developed with Vensim TM) show that in order to maintain water levels in the lagoon under 0,5 m NGF less than 20 days after a flood, new management rules and hydraulic works must be made.