LOCAL SCOUR INDUCED BY 3D FLOW AROUND ATTRACTING AND DEFLECTING GROINS

In recent years, groins are set perpendicular to a riverbank, which is called a deflecting groin. However, many old groins in Japan were set at angles to a bank. This type of groin is called an attracting groin of which head is shifted toward downstream. Such groin is not usually used in a submerged situation, because a flow over the groin attacks a bank and erodes it. In this paper, local scour and flow structure around these two kinds of groin are investigated experimentally in nonsubmerged and submerged situations. By comparing the results in the two groin cases, the local scour induced by a three dimensional flow is discussed. It is found that scouring position is changing on the depth of overtopping flow in both cases and that a strong downward flow produces deep scour holes near the head or root of groin.