Research on river channel change in medium-sized alluvial fan rivers by comparative investigations of aerophotos: a case study of the Toyosawa River in Iwate Prefecture

摘要

The Toyosawa River, Iwate Prefecture, is one of medium-sized alluvial tan rivers in Japan. There are many rivers with similar size in the Tohoku Area, such as the Shizukuishi River, the Sagae River and etc.. These rivers were in almost natural states until the end of the Second World War. Dykes and river bank protections have been gradually constructed and those rivers have changed into compound cross section channels with high water channels. Comparative investigations of many aerophotos taken at interval of nearly tell years from around 1947 make clear not only the above artificial changes but also the natural changes of river channels caused by flood in the Toyosawa River. Natural river changes occur with river bank erosions and disasters Their locations have close relations to the main courses of flood and colliding banks m each period estimated the formations of alternate bars. The actual states of bank erosions and disasters are checked precisely by field surveys Through these studies, we will be able to predict the locations of colliding banks more accurately and to prevent bank disasters.