hypopycnal flow At a river mouth, a flow of river water that is less dense than the water in the basin receiving it. The river water is buoyant and flows above the basin water. This is typical of the situation where a river enters the sea, because of the difference in density between fresh and salt water. Compare HOMOPYCNAL FLOW, and HYPERPYCNAL FLOW.

hypopycnal flow The flow developed at the mouth of a delta where the fresh water from the river flows as a buoyant plume over the denser salt water. The salt water will ride under the fresh water and enter the river channel as an upstream-tapering wedge.