Fundamental Considerations on the Influences of Large Boulders to the Flow Resistance in Boulder-bed River

In boulder-bed streams, large boulders jutting through the river bed play important roles in resistance to flow.This paper deals with the drag force and the structure of flow around hemispherical roughness elements, which are models of large boulders. The separation length and the drag coefficient for a hemipherical roughness element were experimentally studied in the flows with various Froude number, spacings of roughnesses, or relative depth.