The Dynamics of the Estuary – River Plume Interface

We present a series of laboratory experiments re-visiting the dynamics of the interface between the estuary and the river plume. The experiments consist of a long river channel that discharges into an ocean basin, allowing the Froude number at the river mouth to adjust naturally instead of being prescribed. The experiments focus in particular on the spreading and mixing dynamics near the river mouth and in the near-field plume. We observe a variation in plume spreading as the plume lift-off point is forced beyond the river mouth in high discharge (Froude number, Fr) conditions. Our observations suggest that this is associated with the transition in mixing dynamics between the bottom-attached plume and the near-field plume beyond the lift-off point. At very high Fr the plume becomes jet-like and the spreading profiles are insensitive to Fr. We consider the implications of this final transition to the high Fr jet for river plume dynamics in high flood conditions.