The characteristic induced length scale produced by a river flow in its outlet is studied. Two experimental methods are compared: a) Physical modeling in laboratory and b) numerical mesoscale diffusion model; under low tidal and realistic seasonal flow conditions from Spring, Summer, Fall and Winter field data from the Ebro delta shelf. The physical laboratory experiences were performed on a five-meter diameter turntable, using the Froude-Rossby similarity. This paper shows complementary results from both methods investigating the vortex characteristic and the dynamics of the flow. The experimental results under rotating conditions show coherent vortex dynamics in the large-meso scale coastal boundary. The numerical model, on the other hand, lacks the mesoscale vortex dynamics and its induced diffusion but gives reasonable flow conditions in the close region (15-20 km) around the river mouth. Both the experiments and numerical simulations show river plume diffusion smaller than D2 α t3.