Okutadami Dam

The Okutadami Dam (奥只見ダム) is a concrete gravity dam on the Tadami River, 26 km east of Uonuma on the border of Niigata and Fukushima Prefectures, Japan. The primary purpose of the dam is hydroelectric power generation and it supports a 560 MW power station which is the largest conventional hydroelectric power station in Japan. The dam also forms the second largest reservoir in Japan, next to that of the Tokuyama Dam.

Background
Construction on the dam began and its original 390 MW power station was commissioned 2 December 1960. The rest of the project was complete in 1961. Between 1999 and 2003, the power station was expanded, adding 200 MW in installed capacity. In addition, a 2.7 MW generator was added to ensure a flow of 2.5 m3/s downstream for environmental purposes. Along with the same power plant upgrade, a second Kaplan turbine-generator was added to the 83 m tall Otori Dam's power station downstream at 37.21472°N, 139.21389°W. This generator has an 87 MW capacity in addition to the existing 95 MW unit, for an installed capacity of 182 MW.

36 houses were submerged.

Design
The Okutadami Dam is a 157 m tall and 475 m long concrete gravity dam with a structural volume of 1636000 m3. Sitting at the head of a 595 km2 catchment area, the dam creates a reservoir with a 601000000 m3 capacity of which 458000000 m3 is active (or "useful") storage. The reservoir has a surface area of 1150 ha. The power station is underground and located on the right bank of the river next to the dam's abutment. It consists of two caverns, one for the original power station and another adjacent for the expansion. After being received by the dam's intake, water supplied to the original power plant travels down three penstocks 185 - 189 m in length before reaching an individual 120 MW Francis turbine-generator. The 200 MW Francis turbine-generator receives water via a 280 m long penstock. After water is processed through the generators, it travels down two tailrace tunnels before being discharged over 3 km downstream at the upstream edge of the Otori Reservoir.

Access
 Minami Echigo Kankō Bus ( Okutadami Dam Line and Express Okutadami Dam Line )

 Aizu Bus  (Nakayama Tōge and Oze Line - No.011)
 * Ginzan Daira bus stop
 * For Urasa Station
 * It takes to 2h35m from Tokyo Station to Urasa Station.
 * It takes 1h40m from Niigata Station to Urasa Station.


 * Ozeguchi bus stop
 * For Oze-Oike bus stop or Numayama toge bus stop
 * When passengers want to go to Aizukōgen-Ozeguchi Station you must transfer onto route bus at Numayama Tōge bus stop or Oze-Oike bus stop.
 * It takes 2h40m from Asakusa Station to Aizukōgen-Ozeguchi Station, when you use Tobu Limited Express Revaty Aizu.