Scour‐depth Prediction Under Armoring Conditions

A simple procedure is proposed to predict scour depth on an alluvial bed having graded materials under certain flow conditions that can produce an armor layer at the bed surface. The procedure is based on calculation of an active or mixing layer that supplies the fine particles to the sediment load transported by the flow and from where all the heavier and larger particles, not transportable under the flow conditions, collect at the bed surface and gradually form the armor layer. The procedure is validated in both laboratory and field conditions. It predicted scour depths in the Little and Mayer's experimental flume and in the Missouri River, downstream from Gavins Point Dam, as expected. The procedure can serve as a useful tool for practicing engineers in making conservative estimates of scour depths downstream of hydraulic structures and in new unlined canals and in selecting materials for canal beds and banks.