SCOUR RATE FORMULA

In alluvial streams bed scour often occurs if the sediment load is less than the capacity of the flow. Two types of scour are identified, namely local scour and channel bed scour. Many studies have been devoted to local scour but very few to the channel bed scour. Channel bed scour can be further classified according to their causes as flood scour, downstream reservoir scour, hyperconcentrated flow scour and channelized river scour. The scour depth depends on the scour rate and duration of scour. More than 100 experiments were conducted to investigate the laws of scour rate. It is found that the scour rate is proportional to the stream power of flow and the steeper the slope and the finer the cohesionless sediment, the higher the scour rate will be. A scour rate formula, the first of its kind, is proposed in the paper, which is proved valid for unsteady flow scour.