Physical and numerical modeling of overbank flow with a groyne on the floodplain

This paper focuses on both physical and numerical modeling of flow in the vicinity of a groyne, blocking off the floodplain of an asymmetric compound channel, and perpendicular to the main flow direction. Experiments were conducted in a laboratory flume and in a small-scale model. Various lengths of groyne d were used in both the laboratory flume and the small-scale model. Water levels, ve-locity field and spreading of the recirculation zone behind the obstacle were measured for five flow configurations. The influence on the flow parameters of aspect ratio d/B (where B is the total width of the channel), of total discharge Q and of relative depth ratio hr were examined. Particularly, a hydraulic disjunction may occur between the subcritical flow and the supercritical flow respectively located up-stream and immediately downstream the obstacle, depending on the values of discharge Q and aspect ratio d/B. Flows were simulated with the 2D-H program RUBAR 20 (Cemagref). Two simple turbu-lence closures that are often used by engineers were tested: a constant eddy viscosity and the Elder's model u*, h. Simulations are compared to experimental measurements, focusing on the streamwise profiles of water level and discharge distribution across the channel, and on the spreading of the recir-culation zone. The influence of the turbulence model on flow parameters is then investigated.