Most natural rivers, especially in their downstream reaches, consist of a deep and narrow main channel flanked by one or two shallow, complex and vegetated floodplains. Those floodplains provide increased storage for flood waves and protection for towns and cities along the river corridor. Groynes are hydraulic structures that protect against bank erosion, maintain water level by deflecting flow direction, and ensure navigation safety. Groynes constructed on large scale floodplains play important roles in high flood attenuation and protection; however, they add complexity to the system. The...