ABSTRACT
Spur dikes are classified into impermeable and permeable types. The combination of impermeable and permeable spur dikes can create various flow patterns behind them. We call this type of spur dike “hybrid spur dike”. In this study, an outer (in horizontal direction) or upper (vertical direction) part of dike is made permeable. As a permeable dike, pile-group and slit plate types were adopted. Flow structures were measured by using PIV method. In laterally hybrid case, permeable part at the main-flow side decreases the acceleration of the main flow and increases the flow around interfacial region of the spur dike keeping the low velocity near the bank. Staggered arrangement of pile provides milder velocity gradient in lateral direction than in-line arrangement. The effects of slit plate type were compared with the pile group type. In vertically hybrid case, the ratio of permeable part to impermeable part was changed. Pile group at the upper part of the dike increases the velocity behind the dike and reduces the reverse flow region near the bed with an increase of the penetration ratio in vertical direction. The results indicate that the hybrid spur dike can control the flow structure in its vicinity, so the configuration of the permeable part can be selected based on the desired flow pattern.
