Modelling a torrential event in a river confluence

Torrential floods characterized by extremely high discharges and sediment transport rates are common in Mediterranean areas. Few field data is available for such floods due to sudden increase in water discharges and short flood duration. This paper presents the field data collected during a major flood event in a 90° confluence of two torrential rivers of the Mediterranean area. A two-dimensional model was used to describe the flow characteristics at the confluence. The influence on water levels of the torrential character of both rivers and some morphological processes as the tributary mouth gravel bar has been assessed. Although channel roughness coefficients and sediment deposits influence final water surface elevations they have lesser effect than the discharge ratio between main and tributary rivers.