Estuarine Front Formation and Propagation

Front conditions associated with estuarine saline wedges are investigated both theoretically and experimentally. It is deduced theoretically that two distinct front types should exist in a salt wedge estuary, namely wave fronts and St. Venant fronts. When the salt wedge is advancing in its ambient fluid on the flood tide a wave front exists characterized by a vertical wall of water. On the ebb flow however, when the salt wedge is retreating in its ambient fluid a St. Venant front should occur characterized by zero depth at the front. Experiments confirmed that these two front types do occur, but due to stability constraints, their frontal flow conditions are different from that predicted by theory. It is deduced that the fronts of all salt wedges effectively end at the critical flow section and that this should be the front criterion upon which a mathematical model of a salt wedge estuary is based.