Kawai Nui Marsh

Kawai Nui Marsh Flood Control Project is located in Kailua on the windward coast of the island of O‘ahu. The project was authorized under Section 205 of the Flood Control Act of 1948, as amended, at a total cost of $5,918,000 (Federal: $4,143,000; non-Federal: $1,775,000). The original flood control project was constructed by USACE in August 1966 to protect the community of Kailua from flooding. The project included a trapezoidal channel (9,470 feet long and 80 to 110 feet wide); an earth levee (6,850 feet long); a stub groin (50 feet long); a shore revetment (50 feet long); a silt basin (370 feet long); and drainage outlets.

Over the years, vegetation within the marsh created a dense mat that affected the hydraulics of the marsh causing the project to be overtopped during the January 1988 storm. As a result, the levee height was raised, and a concrete floodwall was installed in 1997. The floodwall has a maximum height of four feet and is 6,300 feet long extending from Kailua Road on the south to the Oneawa outlet channel on the north. The levee fills 1.8 acres of wetland fringe and provides a higher level of flood damage reduction to a larger part of Coconut Grove, which has more than 2,000 structures.

The local sponsor is the City and County of Honolulu, Department of Facility Maintenance (City). Maintenance for the levee and marsh was transferred from the City to the State of Hawai‘i Department of Land and Natural Resources (DLNR) as part of an agreement to allow construction of the Kawai Nui Marsh Ecosystem Restoration Project in the marsh headwaters.