FLOW STRUCTURE ON GROINS DURING FLOOD EVENT AND MORPHOLOGICAL EVOLUTION OF TOPOGRAPHY

Abstract

Morphological evolution of the topography of the reach with groins is investigated using a numerical model solving the two-dimensional shallow water equations in this study. A flood event is represented to discuss the dischargedependent change of the interaction between flow structure and sediment transport. The primary flow is meandering according to alternate or multiple bars formed in the channel during low-water and medium-water periods, and it is found that deposition of the fine sand and silt on vegetated area between groins is affected by the meander of primary flow. During a high-water period, on the contrary, the primary flow follows the large-scale topography of the river so that flow on the flood plain is also straightforward according to the large-scale channel form. This straightforward flow on the flood plain, formed between groins, induces three-dimensional flow structure (longitudinal vortex), develops streak go through the groins longitudinally, and forms the rib-shaped topography on the flood plain. This ribbed bathymetry is highly interacting with sediment transport not only within the flood plain but also between the channel and the flood plain.