Study on Artificial Methods of Sandbar Flushing Against Blockages at the Mouth of a Floodway

Blockages at the mouth of floodways due to a sandbar need to be flushed away to have a proper function of a floodway. This study examined the methods of effective flushing of sand blockages at a floodway mouth by using iRIC model simulations. The site of the study is the floodway of Hojo River, Tottori, Japan, which is divided from the main river by a diversion rubber dam at 2.25 km upstream from the mouth. The conditions for flushing the sandbar were investigated by simulating the formation of an artificial notch on the sandbar, discharge from a diversion dam, and a combination of the two. The simulation results confirmed that the sandbar flush progresses rapidly if the water level at the river mouth is even slightly higher than the top of the sandbar (or the bottom height of the notch), and the importance of the relationship between the sandbar height and the river mouth water level. Further the effects on the main river and upstream of the diversion dam due to the rapid flow change associated with the discharge from the diversion dam were also analyzed. From these analyses, the conditions for effectively and efficiently eliminating river mouth blockage by artificial sandbar flushing are summarized.