Fukuji Dam

The Fukuji Dam (福地ダム) or Fukuchi Dam is a rock-fill embankment dam on the Fukuchi River 2.5 km northeast of Higashi, Okinawa Prefecture, Japan. The purpose of the dam, the tallest in Okinawa, is water supply and flood control.

Background
Under the Ryukyu Domestic Water Corporation, the U.S. Army Corps of Engineers began constructing the dam in 1969. After the United States Civil Administration of the Ryukyu Islands returned administration of Okinawa back to Japan in 1972, construction became the responsibility of the Japanese government. The dam was completed in 1972, and the auxiliary spillway in December 1974. The dam was later raised to accommodate an improved intake and an additional 2.4 m in water elevation. This additional work was completed in 1991.

Design
The dam is a 92 m tall and 260 m long rock-fill embankment type with a structural volume of 1622000 m3 and a crest elevation of 90 m. The dam sits at the head of a 32 km2 catchment area and its reservoir has a surface area of 3 km2. The reservoir's capacity is 55000000 m3 while 52000000 m3 serves as active (or "useful") capacity. The dam is equipped with a drum gate-controlled chute spillway. On the eastern edge of the reservoir, 6.3 km east of the dam, there is an auxiliary spillway at 26.6375°N, 128.23667°W. This spillway is a siphon-type and operates automatically to help drain the reservoir during flooding. It has a 900 m3/s capacity and discharges directly into the Pacific Ocean.