Flow-separation berms downstream of a hydraulic jump in a bedrock channel

The first direct observation of the development of lateral gravel berms associated with hydraulic jumps in bedrock channels is reported. Cobbles and pebbles were observed being swept through jumps and deposited in the tranquil flow immediately downstream and either side of the V-shaped shock-waves. Field measurements of jumps and geometry, current speed and water depth are found to be consistent both with laboratory data and theoretical considerations. The deposits have significance in constraining flood palaeoflow reconstructions as the presence of berms determines the former location of hydraulic jumps whilst the angle subtended by the berm crestline (with respect to a regular bankline) may be used to estimate the Froude number of the flow.