Abstract
This paper describes the flow resistance (or bed roughness) due to lush vegetation in the Asahi River during the flood event which occurred in September 2011. First, we investigated the vegetation condition based on the field observations in the floodplain of the river, and simply classified a variety of flourishing vegetation into three categories by using previous reports and handbooks. Secondly, the distributed Manning’s roughness coefficients in the floodplain were inversely estimated by using a data assimilation approach with the water level data gained longitudinally during the flood. The results showed that the roughness is closely related with the category or type of dominant vegetation in the floodplain, and is likely to decrease slightly during the flood because the vegetation is bent, broken and washed-out.
