ABSTRACT
The levee is a hydraulic structure installed along a river so that the damage does not occur by preventing over-topping of river water. Due to the recent climate change, localized heavy rain and flash flood occur frequently, the water level of the river often increases rapidly. So risks of levee overtopping are increasing. The slope of levee was eroded by river flow generated due to levee overtopping and the eroded section is expanded to crown of levee. When the crown of levee is breached, the breach cross section becomes large, the river water flows into the land rapidly and the magnitude of damage increases, so the degree of breach development is very important. Therefore, in this study, when the levee is breached, the Froude number of river and levee breach were analyzed through hydraulic experiment. The hydraulic model of levees is the crown width of 0.3 m and the height of 0.3 m. The slope is 1:2. And the scale of hydraulic model experiment is 1/10. The length of the experimental channel was 16.0 m in total, the 4 m section in the middle part of channel was made of mobile phase material. The material of mobile phase is a sand. The conditions of Froude number at channel are set to 0.15, 0.20, 0.25, 0.30 and 0.35 respectively. Breach width was measured indirectly because direct measuring was impossible. Progress of breach width was measured by image processing recorded by digital camcorder. For all Froude number, the breach width was increased with time increasing. Breach width was expressed stepped graph because bottom of the levee was breached firstly and top of the levee collapsed at a time. This phenomenon is general characteristic of levee breach. As a results of experiment, the levee breach speed also was maximum when Froude number was 0.3. Through this study, it was confirmed that the levee breach speed is different along the flow of the river. Because the breach width is closely related to the breach flow, this result will be used as an important basic material in order to understand the magnitude of the damage due to levee breach. In the future, if additional experiments considering various material of levee will proceed, which can be more accurate damage predictions.
