Ko‘olau volcano started its life as a seamount above the Hawaiian hotspot around 4-million years ago. It broke sea level some time prior to 2.9-million years ago.
About 2-million years ago, much of the northeast flank of Ko‘olau volcano was sheared off and material was swept more than 140-miles north of O‘ahu and Moloka‘i onto the ocean floor (named the Nu‘uanu Avalanche) – one of the largest landslides on Earth.
Following a period of dormancy, Ko‘olau eruptions about 1-million years ago (known as the Honolulu Volcanic Series) created landmarks such as Diamond Head, Hanauma Bay and Punchbowl Crater. Ko‘olau’s eroded remnants make up the Ko‘olau Mountain Range.
About 6,000 years ago and before the arrival of the Hawaiians, Kawainui (“the large [flow of] fresh water”) and Ka‘elepulu (“the moist blackness”) were bays connected to the ocean and extended a mile inland of the present coastline. This saltwater environment is indicated by inland deposits of sand and coral.
A sand bar began forming across Kawainui Bay around 2,500 years ago creating Kawainui Lagoon filled with coral, fish and shellfish. The Hawaiians probably first settled along the fringes of this lagoon.
Gradually, erosion of the hillsides surrounding Kawainui began to fill in the lagoon with sediments.
About 500 years ago, early Hawaiians maintained the freshwater fishpond in Kawainui; the fishpond was surrounded on all sides by a system of canals (‘auwai) bringing water from Maunawili Stream and springs to walled taro lo‘i.
In 1750, Kailua was the political seat of power for the district of Ko‘olaupoko and a favored place of the O‘ahu chiefs for its abundance of fish and good canoe landings.
Kawainui was once the largest cultivated freshwater fishpond on Oahu. Rimming the wetland are numerous heiau (temples.)
Farmers grew kalo (taro) in the irrigated lo‘i (fields) along the streams from Maunawili and along the edges of the fishponds. Crops of dryland kalo, banana, sweet potato and sugarcane marked the fringes of the marsh. Fishermen harvested fish from the fishponds and the sea.
In the 1880s, Chinese farmers converted the taro fields of Kawainui to rice, but abandoned their farms by 1920. Cattle grazed throughout much of Kawainui.
The marsh drains into the ocean at the north end of Kailua Beach through Kawainui Canal (Oneawa Channel.)
The marsh attracts migratory seabirds and is home to four species of endangered waterbirds: the Hawaiian stilt (aeʻo), the Hawaiian coot (ʻalae keʻokeʻo), the Hawaiian gallinule (ʻalaeʻula) and the Hawaiian duck (kōloa maoli).
In 1979, the US National Registrar for Historic Places issued a “Determination of Eligibility Notification” finding that Kawainui Marsh area is eligible for listing in the National Register for Historic Places.
According to the determination, “Kawainui Marsh is important as a major component of a larger cultural district which would include … the ponding/wet agricultural area … remains of extensive terracing systems, ceremonial sites, burial sites, and habitation areas associated with this agricultural complex”.
In 2005, the Kawainui and Hāmākua Marsh Complex was designated as a Wetlands of International Importance and added to the Ramsar List (Ramsar site no. 1460.)
The Convention on Wetlands (Ramsar, Iran, 1971) – called the “Ramsar Convention” – is an intergovernmental treaty that embodies the commitments of its member countries to maintain the ecological character of their Wetlands of International Importance and to plan for the “wise use”, or sustainable use, of all of the wetlands in their territories.
Kawainui Marsh also functions as a flood storage basin to protect Kailua. As part of flood control measures, the Oneawa Canal and levee started in 1950 and were completed a few years later. When flood waters over-topped the levee and flooded Coconut Grove in the December 31, 1987-January 1, 1988 flood, the levee was raised and floodwall added.
Projects are underway to restore waterbird habitat, as well as care for some of the historic sites. DLNR has plans for visitor center and trails around the wetland – they have been on the books for a long time, it would be nice to see those community visions come to fruition.
Lots of good work is being done by lots of dedicated folks in helping to restore Kawainui Marsh, including ‘Ahahui Mālama I Ka Lōkahi (led by Doc Burrows,) Kailua Hawaiian Civic Club and others.
When I was a kid, we referred to this area as the “swamp” – many of the old maps referred to it as such. Auto parts shops lined the road at its edge; the dump was nearby. Times have changed.
The image shows a 1951 aerial photo of the Kailua area, with Kawainui Marsh centered in the image (photo from UH-Mānoa and USGS.) In addition other images and maps of Kawainui are included in a folder of like name in the Photos section on my Facebook page.