Abstract
In natural rivers, there often happen the flows which bed roughness changes abruptly by some reasons. Around the section of abrupt change, river bed or bed protection structures may be scoured or eroded by the action of high shear stress, which is caused by development of the internal boundary layer. There are generally two types of flow, that is, smooth to rough bed flow, and rough to smooth bed flow. It is found that these two types of flow are not of same property, by the results of experiments. Based on some assumptions wich are derived from the experimental results, bed shear stress and internal boundary layer thickness can be calculated by applying the momentum equation to the control volume of internal boundary layer. This method can simulate the flow conditions in the wind tunnel and open channel.
