Erosion of Sand from a Gravel Bed

Abstract

AbstractCleaning of fine sediment out of gravel streambeds has become an important method to restore affected stream habitats. Introducing the increased flows needed to entrain fine sediments without eroding the coarser fractions of the bed and potentially destroying its usefulness as a habitat requires careful selection of flow strength. Toward this end, a series of flume experiments was conducted on the entrainment of sand from immobile gravel beds to determine the depth to which the sand could be eroded without the gravel being mobilized. A series of steady flows was imposed on three gravel beds filled with sand with median sizes of 0.2, 0.3, and 0.9 mm. The shear stress of the series of flows ranged from just above the critical shear stress for initiation of motion of the sand up to 0.9 times the critical stress of the 36.1-mm gravel. The experiments continued until the rate of fine sediment exiting the channel was very small. It was found that the cleanout depth of the sand was reasonably predicted b...