Abstract
Due to the heavy rainfall caused by Typhoon No. 19 in 2019, precipitation was recorded at 300-400mm in the Saku District of the upper Chikuma River on October 12. The highest water level ever observed was recorded at 12.46m at the Tategahana Water-Level Observatory located at the middle reaches of the Chikuma River at 3:20 the next day. As a result, the dike collapsed 70m section in the Hoyasu District of Nagano City (approximately 4km from the upper reaches of the Tategahana Water-Level Observatory), and the ensuing floodwaters flowed onto the inland bank. Residential houses were washed away and completely destroyed. At the Shinkansen vehicle center located in the low-lying area of the floodplain, 120 vehicles comprising 10 compositions were flooded to seat level and considered a total loss. Inundation damage of 100-400cm occurred in the former town office area and in the new residential area in the Toyono District, caused by the floodwaters that flowed over the dike for the Asakawa River (a branch of the Chikuma River) from the Akanuma District. The inundation area in the northern region of Nagano City (Naganuma, Toyono, Furusato) encompassed approximately 934ha and almost coincided with over 2m of flood inundation assumption areas. Furthermore, there were 1,034 buildings completely destroyed, 285 buildings large-scale partially destroyed, and 360 buildings partially destroyed, 292 buildings part destroyed for a total of 1,971 buildings.
