Hydraulic Parameters Controlling Bedform Migration on an Intertidal Sand Body

Abstract

Bedform migration on an intertidal sand body in the Minas Basin, Bay of Fundy, is controlled by time-velocity asymmetry of tidal currents and by water depth. Dune migration occurs during ebb tide, whereas sand wave migration occurs during flood tide. Bedform migration is limited to short periods ranging from 40 min to 1.5 hrs, which coincide with maximum velocity phases of time-velocity profiles. Normal bottom-current velocities are achieved rapidly after sand body submergence and high water stage. Initiation of bedform migration occurs during both a subsequent decrease in bottom-current velocity and a later sharp increase to maximum bottom-current velocities. Dune migration takes place in water depths greater than those required for sand wave migration. This contrasts with water depth relations predicted from empirical formulae relating bedform wave length and wave height to depth of fluid flow. Representation of intertidal bedform migration variables on a depth-velocity-particle-size diagram shows excellent agreement with similar data obtained from experimental studies.