A method to estimate flooding frequency of backwaters in the Chikuma River, Nagano central Japan. Ecol. Civil Eng. 2(1), 63-72, 1999

Backwaters in rivers are important habitats for plants and animals. The flooding frequency on backwaters is an important parameter to define the character of the waters. However, methods for estimation of the flooding frequency have not been developed. In this paper we proposed a practical method to estimate flooding frequency of backwaters with an example studied in the Chikuma River. Flooding frequency of the backwaters in the Chikuma River was estimated based on the map with contour lines at every 0.25 m. Assuming the water elevation rise to 0.25 m, 0.5 m, the water was estimated to run into the backwaters through the lower part of river terrace. When the water elevation rise to 0.75 m, flooding situation changed drastically. The flooding stream was estimated to occur on the river terrace and many backwaters was inundated. The important point was that flooding frequency at the backwater was not dependent on the backwater elevation.