I am trying to run a breakwater simulation in xbeach nonhydrostatic
mode. The breakwater has dimensions 300x30m and the long side is
facing the waves. The breakwater extends 4m above calm water level and
has a slope of 21/10; water depth 17m. All goes well for some time
until instabilities start to appear and xbeach stops because of high
flow velocities. Significant wave height is 1m. Does anyone have any
suggestions how to avoid this?