An Experiment on Levee Breach Caused by Overflow with a Full-scale Levee Model in the Tokachi Rivers Chiyoda Experimental Channel
Frequent disasters brought by typhoons and localized torrential rain in recent years have raised concerns over the risk of large-scale disasters caused by river flooding. Among such disasters, damage caused by levee breach can be particularly devastating. It is said that over 80% of previous levee breaches have stemmed from the phenomenon of overflow.
As the mechanism behind levee breach caused by overflow remains largely unknown, its clarification is expected to lead to improvements in related resources such as the accuracy of hazard maps.
With the aim of understanding this mechanism, the Civil Engineering Research Institute for Cold Region and the Hokkaido Regional Development Bureau of the Ministry of Land, Infrastructure, Transport and Tourism have conducted experiments on levee breach caused by overflow using the full-scale Chiyoda Experimental Channel in the Tokachi River since FY 2008. In FY 2010, such an experiment was performed with the inundation area shown in Fig. 1.
Some of the findings from the experiment are summarized below:
There are five steps in the progress of levee breach width increase after the onset of overflow (Fig. 2):
Step 1: After the onset of overflow, there is no increase in levee breach width without a significant rise in flood discharge.
Step 2: The levee breach width gradually increases in the upstream and downstream directions as flood discharge begins to rise.
Step 3: The levee breach width increases rapidly with sharp rises in flood discharge.
Step 4: The levee breach width increase becomes moderate with rising flood discharge at an almost constant rate.
Step 5: The levee breach width increase stops.
In FY 2011, further experiments will be conducted using levees with various soil properties and shapes.
(Contact: River Engineering Research Team,CERI)