Akimoto Lake - Multi-purpose Dam

Multi-purpose Dam

In August 1989, the Inner Bandai area experienced heavy torrential rains. The water level at Akimoto Lake, as well as Lake Onogawa and Lake Hibara, had rapidly risen, and the entire river basin sustained major damage. Akimoto Lake has a drainage pumping station at the center of the dam that is used to discharge excess lake water, but the torrential rains outpaced the station's ability to pump water, making it impossible to regulate the water level properly. More water than could be handled under water use regulations was being discharged, and the Nagase River eventually flooded, causing even more damage to the surrounding region.

Fukushima Prefecture, shaken by how quickly the river overflowed, drew up new flood prevention plans for the Inner Bandai tri-lake area. Because of the nearby Bandai-Asahi National Park, environmental protection concerns prevented the construction of levees or dikes. It was decided that a multi-purpose dam would be built to facilitate unspecified water utilization, flood control for Lake Hibara, Lake Onogawa and Akimoto Lake, as well as a normal stream level for the Nagase River; work began at the Inner Bandai tri-lake area in 1997 under the Comprehensive River Development Project.

The practice of damming natural lakes for flood prevention and water usage is performed nationwide, with some of the more prominent examples being Lake Biwa, the Seta River Wash Weir, Lake Kasumigaura and the Hitachi River floodgate, which are all under direct control of the Ministry of Land, Infrastructure, Transport and Tourism, and others like Lake Chūzenji/Chūzenji Dam in Tochigi Prefecture and Yogo Lake/Yogo Dam in Shiga Prefecture, which are controlled at the prefectural level. Natural lakes in Fukushima Prefecture that are dammed include Lake Inawashiro and the Jyūryoku Bridge floodgate. Lake Hibara now features a 3.4 meter-high gravity dam, Lake Onogawa has a 4.9 meter-high fill dam, and Akimoto Lake—in addition to its earth dam—now has a gravity dam with an emergency floodgate on its left bank, making it a combined dam. Facilities such as dams, weirs and flood gates enable flood prevention and water usage for natural lakes and marshes, and can be referred to as "water level regulation facilities." While places like Akimoto Lake are in fact lakes, they are classified as dams under river-related regulations.

Due to the fact that each is less than 15 meters in height, they are technically classified as weirs under river law, but they provide valuable service in the form of flood prevention and hydroelectricity generation among the Nagase River, Akimoto Lake and the other Inner Bandai tri-lake area lakes. Work was completed on the secondary dam in 1999, and control over regulation of water levels that had been performed by Tokyo Electric Power Company was thereafter done directly by Fukushima Prefecture's Inawashiro office of civil engineering.