Record-breaking rains

Uonuma River at Horinouchi

Shinano River at Ojiya

Ohkozu Bunsui at Watabe

Shinano River at Kamo City

Agano River at Maoroshi

Agano River at Yokogoshi

During July 28-30, the Niigata and Fukushima regions were attacked by record-breaking storms as a rainy season type weather pattern developed pushing cooler air from the north into hot and humid air from the south. The result was explosive storms and record rainfall intensities. Over the 3 days, 619mm of rainfall was recorded in Kamo City, with 290mm recorded in a single day on July 29. That's equivalent to twice the average July rainfall in just 3 days! Examples of record rainfall intensities are 94mm/hr in Kamo City and 121mm/hr in Tokamachi. All this rain led to record-breaking high water levels in most of the rivers of the Niigata plains, and several rivers burst their banks flooding nearly 9000 homes and businesses.

Above I have given several examples of stage hydrographs showing record high water levels, including the Uonuma River which is a tributary of the Shinano River, the Ohkozu diversion channel which reduces flooding on the lower Shinano River, and the Agano River. Even though the Ohkozu diversion channel was diverting record amounts of flow into the Japan Sea, the lower Shinano River still suffered flooding in some low-lying areas. Fortunately the river levees were built up to a higher level after the last major flood of 2004, and this must have reduced the flood damage on this occassion.

Ohkozu diversion channel upper sill (July 30)

Ohkozu diversion channel entering the Japan Sea (July 30)