Abstract Natural, moderately loosely packed sands can only erode from the surface of the bed after an increase in pore volume. Because of this shear dilatancy, negative pore pressures are generated in the bed. In cases of low permeability, these negative pressures are released relatively slowly, which retards the maximum rate of erosion. This effect is incorporated in a new, analytically derived, pickโup function that can explain the observation of gradual retrogressive failure of very steep subaqueous slopes, sometimes more than 5โm high, in fine nonโcohesive sands. This process, termed โbreachingโ in the field of sediment dredging, may produce large failures in sand bars or river banks. The analytical function that describes the breaching process in fine sand is incorporated in a oneโdimensional, steadyโstate numerical model of turbidity currents describing the spatial development of flow. This model is applied to simulate a large โflushingโ event in Scripps Submarine Canyon, Pacific coast of California. Breach retrogradation and the successive evolution in time of the resulting turbidity current in the canyon are predicted in a sequence of discrete steps. Predicted velocities are compared with values measured during a flushing event. Implications for the interpretation of deepโwater massive sands are discussed.