Flooding of tunnelled ocean outfalls

Model studies were undertaken of the flooding of the Sydney deepwater outfalls with seawater following the cessation of effluent discharge. It was found the time taken to flood the tunnels was three to five times that based on the development of a friction-gravity controlled maximal exchange flow in the tunnel. The experiments suggest that the flooding of tunnelled outfalls is a complex process which is controlled by the geometry of the riser section and in particular the elevations of the diffusers.