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The river outflow case is meant to test XBeach for the combined effects of a river outflow and a steady wave-driven longshore current on the sediment transport and the morphological evolution. Though purely hypothetical, this case contains many salient features of real-life applications, such as longshore currents through open side-boundaries and exchange of water and sand through a gap in a closed boundary. Thus, the formulation of open boundary conditions is also tested here.

The initial topography consists of a plane beach (slope 1:50), which is interrupted by a 75 m wide river mouth with a water outflow of 150 $m^3/s$. The bottom contours are straight and parallel to the shoreline, except for a shallow submerged channel in line with the river.

The computational grid is rectangular, with 56 nodes in the x-direction (cross-shore) and 111 nodes in the y-direction (longshore), with a uniform grid spacing of 15 m. The waves are irregular and long-crested, with a root-mean-square height of 2m at a water depth of 13.5m. The direction of wave incidence is 30 degrees with respect to the shore-normal. The peak wave period is 8s. The bed material is uniform sand of 250$\mum$, with a settling velocity of 0.031m/s.

In this figure the bathymetry is shown after approxiately 4 days; arrows indicate the sediment transport vectors. plotted for every cross-shore cell and every third longshore cell. When functioning correctly, we see a channel that has turned towards the north and striaght contour lines downstream of the channel.

${tools.image('River_Outflow/default/', 'fig1.eps', 'Final bathymetry')}
