The Alenaio Stream Flood Control project is located in the Hilo district on the island of Hawai‘i. Alenaio stream originates approximately 11 miles southwest of Hilo. The project was authorized under Section 101 of the Water Resources Development Act (WRDA) of 1986, and with the completion of the General Design Memorandum (GDM) in March 1990, it was reauthorized in the WRDA of 1990.
The project was physically completed in November 1997 at a total project cost of $15.7 million (Federal: $11.2 million; non-Federal: $4.5 million). The project consists of an 830-foot earthen levee; a 1,790-foot-long rectangular concrete-lined channel (30 to 50 feet wide); a 200-foot-long wedge-shaped concrete-lined entrance transition; three floodwall structures consisting of 640 feet of concrete floodwall and 545 feet of concrete rubble masonry floodwall; four bridges; access roads; and an earthen channel at the mouth connecting the concrete channel to the existing flood plain.
The local sponsor is the County of Hawai‘i, Department of Public Works (DPW). The project provides flood protection to the Hilo community from periodic flooding of Alenaio stream. Flooding was a recurring problem for the 223 residences and 286 commercial businesses located along and adjacent to the stream. To date, the project has prevented more than $48.2 million in projected damages within the project area.