Morphodynamics of a macrotidal ridge and runnel beach

The topography, currents, waves, and sediment dynamics of a macrotidal ridg e and runnel beach were monitored from April 24 to May 4, 1997 in order to characterise the morphodynamics of this beach type under fair-weather and s torm conditions. Sand tracer experiments show moderate longshore and cross- shore transport components while profile surveying highlights a remarkably stable system. These trends are not in agreement with the current pattern, which is dominated by an essentially tidally driven longshore component. Th e stability of the ridges reflects the high rates of migration of the break er/swash zone in response to the important vertical tidal excursion across a wide, low-gradient beach. ((C) Academie des sciences / Elsevier, Paris.).