Equilibrium scour in rivers with sandbeds
Severe floods caused extensive scour along sand-bedded rivers in Natal during 1984 and 1987. Recorded information on the extent of scour as well as peak flood discharges was analysed in an attempt to develop criteria which could be used to predict scour depths in future. Contrary to expectations, all the indications are that laminar rather than turbulent boundary layer conditions prevail when equilibrium scour depths are approached. By deforming their beds through the formations of dunes and other bed formations, the sediment transporting capacity of rivers is decreased. This means that rivers have a built-in mechanism through which excessive scour is prevented when extreme floods occur.