Small to medium size rivers draining mountainous watersheds are capable of plunging to the ocean floor during large floods. The plunging occurs if the river water becomes heavier than the receiving saline water by transporting an excessive amount of suspended sediment. After plunging to the sea floor, the river water continues to flow as a turbid bottom current. Although infrequent, such events may influence the coastal sediment dispersion and margin architecture in a profound way. One such event is modeled here for the Northern California Margin near the mouth of the Eel River by using a two-dimensional unsteady model. Simulation experiments indicate that the undercurrent has a tendency of flowing towards the adjacent Eel Canyon. However, along-shelf currents may influence the overall development of the underflow by redirection of the flow to other parts of the margin.