Near-Miss at Wahiawā Dam as Kona Low Triggers Hawaiʻi’s Worst Flooding in Decades

Phones started buzzing in the dark just before dawn on Oʻahu’s North Shore.

“Imminent dam failure,” the alert warned. “Evacuate immediately. Move to higher ground.”

Outside, water was already rising around homes in Haleʻiwa and Waialua. Streets had turned to brown rivers. Power was out in some neighborhoods, and the main highway north was disappearing under a roiling flood.

Upstream, at a 120-year-old earthen dam above the town of Wahiawā, the water in the reservoir locals call Lake Wilson was pushing toward a level state officials had quietly identified as the trigger for a worst-case scenario.

The dam did not collapse. By late Friday, the water had receded. But the hours between midnight and late morning on March 20 were the closest Hawaiʻi has come in years to a catastrophic dam failure—an outcome engineers, regulators and nearby residents have warned about for decades.

Hawaiʻi’s worst flooding in more than 20 years

The powerful Kona low that parked near the islands last week produced Hawaiʻi’s worst flooding in more than 20 years, Gov. Josh Green said. At least 230 people were rescued from rising waters on Oʻahu, thousands were under evacuation orders, and damage statewide could exceed $1 billion, the governor said.

“The storm is going to have a very serious consequence for us as a state,” Green told reporters Friday, adding that costs could include major damage to airports, schools, roads, homes and a hospital on Maui. He said there were no confirmed deaths and about 10 people had been treated for hypothermia.

The most frightening hours unfolded on Oʻahu, where a narrow band of heavy rain stalled overnight over the island’s north and central sections. The National Weather Service recorded 8 to 12 inches of rain in parts of Oʻahu and nearly 16 inches at Mount Kaʻala, the island’s highest peak, over a 24-hour period. Forecasters issued a rare flash flood emergency for northern Oʻahu, warning of a “particularly dangerous situation” and urging people to seek higher ground.

As the rain hammered the island, Kamehameha Highway on the North Shore and parts of Farrington Highway on the west side closed under floodwaters and debris. Longtime residents described the flooding on Kamehameha Highway as the worst they had seen in decades. Isolated pockets of Haleʻiwa and Waialua were effectively cut off.

Honolulu firefighters, ocean safety crews and the Hawaiʻi National Guard pulled people from flooded homes and vehicles using boats, high-water trucks and helicopters. Among the rescues was an airlift of 72 children and adults from a youth retreat at Our Lady of Keaʻau, a Catholic camp on Oʻahu’s west coast.

A dam long flagged as “high hazard potential”

Amid the rescues, emergency managers were watching one gauge closely: the water level behind Wahiawā Dam.

The earthen dam, built in 1906 to irrigate sugar plantations, impounds the Wahiawā Reservoir above the town and feeds Kaukonahua Stream, which runs down to Waialua and Haleʻiwa. State regulators classify the dam as “high hazard potential,” meaning failure would likely cause loss of life. A state dam inventory warns that more than 2,500 people live in areas that could be inundated in a worst-case breach.

Engineering reports going back to the 1970s have repeatedly flagged the structure’s spillway as undersized for extreme rain events. In earthen dams, overtopping is one of the primary paths to catastrophic failure.

Overnight Thursday into Friday, the water level rose from about 79 feet to 84 feet at the dam, according to state and local data cited by officials. Emergency planners have identified 84 feet as the point at which downstream evacuation orders should be triggered. Some technical analyses have suggested a breach could become likely several feet higher.

By early morning Friday, water was pouring over the spillway at an estimated 1,500 gallons per second.

A predawn scramble: “LEAVE NOW”

At 3:42 a.m., Honolulu’s Department of Emergency Management sent a warning for parts of the North Shore, urging residents to evacuate or move to the highest level of their homes and warning them not to retreat into attics without a way to access the roof.

At 5:35 a.m., as floodwaters rose, a sterner message went out: “LEAVE NOW.” The alert covered low-lying areas of Waialua and Haleʻiwa and cited “extremely dangerous flooding” and rising levels at Wahiawā Dam.

Just before 8:30 a.m., emergency officials issued the most alarming notice yet: an “imminent dam failure” alert tied directly to Wahiawā. Sirens sounded. Some residents received multiple, overlapping text alerts as cellular networks strained. Social media posts quickly spread claims that the dam had already failed, even as city officials and local television stations said it had not.

By midday, gauges below the dam showed the water had peaked above the evacuation threshold and begun to fall. Governor Green said late Friday the reservoir level had receded, though he warned the dam remained a concern if additional heavy rain bands moved over the island.

Mayor Rick Blangiardi called the damage on the North Shore “catastrophic” and said there was “no question” that the flooding had devastated the area. At the same time, he said officials were “confident” in the stability of Oʻahu’s dams, while acknowledging that uncertainty about how much more rain could fall added to the risk.

Dole Food Co., which owns the dam and the reservoir, said in statements that Wahiawā Dam remained stable during the storm and operated as designed. The company said employees monitored the structure and that a portable flood barrier installed for the rainy season was in place to help manage high inflows.

Decades of warnings—and a transfer still unresolved

State records show concerns about the dam’s safety have been circulating for decades.

The former Waialua Agricultural Co. built the dam in the early 20th century to support sugar cane. It failed once, in 1921, and was rebuilt. As the plantations gave way to housing and diversified agriculture, development filled in downstream floodplains.

State dam safety inspectors have issued multiple deficiency notices to Dole since at least 2009 over the inadequacy of the spillway and other safety concerns. In 2019, the state fined the company $20,000 for failing to complete required improvements.

A 2023 submittal to the state land board again described Wahiawā as a high-hazard dam and stated that failure “will result in probable loss of human life.” The document said the dam was not yet in full compliance with current safety standards.

Facing mounting regulatory pressure and warning that it could not afford major upgrades, Dole proposed that the state acquire the dam, reservoir and associated irrigation system. The Legislature approved that plan in 2023, authorizing the state to take ownership and appropriating roughly $26 million—about $5 million to acquire the spillway and $21 million to repair and enlarge it.

Dole’s own consultants had estimated the core spillway work at about $20 million, according to public records. At the same time, Dole plc, the parent company, reported $155 million in net income in 2023, its highest profit since going public two years earlier.

Once the acquisition was authorized, state land officials eased the threat of escalating penalties against Dole, shifting the focus to completing the transfer and planning repairs. A key Board of Land and Natural Resources vote to finalize the acquisition was scheduled for the same week as the storm but was postponed when the Kona low hit, leaving ownership and responsibility in flux as water rose.

A familiar risk across aging plantation-era infrastructure

The near emergency at Wahiawā comes 20 years after the Ka Loko Dam on Kauaʻi failed in 2006, killing seven people and destroying homes. That disaster led to stricter state regulation of private dams. More recently, heavy rains in March 2021 triggered evacuations below Kaupakalua Dam on Maui, again raising questions about aging plantation-era infrastructure.

Hawaiʻi has 132 regulated dams, many built for sugar cane irrigation and now serving new purposes in a warmer, wetter climate. A recent infrastructure report card described several as being in poor or unsatisfactory condition.

Gov. Green declared an emergency March 9 under state law, activating the Major Disaster Fund and authorizing deployment of the Hawaiʻi National Guard as forecasters warned of prolonged heavy rain and strong winds from a Kona low from March 10 to 15. As the threat persisted, he extended the proclamation and temporarily suspended certain procurement, labor and environmental review laws, including statutes governing dams and flood control, to speed response and repairs.

On the ground, the consequences have been felt most acutely in communities like Haleʻiwa, Waialua, Mokulēʻia and Wahiawā—rural, working-class areas already pressured by housing costs, coastal erosion and tourism. Residents described wading through chest-deep water, rescuing livestock and watching as homes filled with mud. One shelter at Waialua High and Intermediate School, running on generators, had to be evacuated itself as concerns about the dam mounted; 186 people and 45 dogs were bused to facilities on higher ground.

As crews began the slow work of clearing roads and assessing damage this weekend, officials warned that more heavy rain could still arrive and that the full scope of losses would take time to tally.

Wahiawā Dam held this time. For people living downstream, the question now is whether the close call will finally accelerate long-promised repairs—and whether Hawaiʻi can move quickly enough to shore up similar structures before the next Kona low stalls over the islands.