State officials said today that the Kaupakalua Reservoir and Dam on Maui is slated for removal some time this summer due to its “unsatisfactory” overall condition.

Heavy rains on Monday caused the aging reservoir to swell, and overtop the earthen dam in the Haiku region, resulting in the emergency evacuation of some 150 downstream homes.

Mahi Pono late this morning said that its team monitored waters levels at the reservoir and dam as rainfall continued overnight, and provided hourly update reports to the Maui Emergency Management Agency.

Overtopping ceased in the early evening of Monday, said Mahi Pono. At a visual inspection of the facility at about 10 a.m., chief operating officer Shan Tsutsui saw no signs of re-occurrence.

“At this time, we are not aware any property damage that occurred due to the overtopping,” said Tsutsui in a statement. “However, this does not diminish the damage caused in the surrounding community located mauka of the reservoir by the overwhelming and unprecedented rainfall here on Maui.”

Kaupakalua Dam — an earthen dam built in 1885 – measures 57 feet high and 400 feet long, state officials said, and can hold 68 million gallons of water. It sits on land owned by East Maui Irrigation, which is co-owned by Mahi Pono and Alexander & Baldwin, the state said.

The state Department of Land and Natural Resources says the dam has been the focus of regulators over past years.

On Feb. 18 of last year, DLNR said it sent a notice of deficiency to the dam’s owner, East Maui Irrigation Company and Mahi Pono Holdings Inc., with a compliance schedule for remediation. A week later, on Feb. 24, DLNR said it issued a notice of civil resource violation for “failure to comply” with these remediations by the deadlines.

Specifically, the notice cited “the failure to install a real-time reservoir water level gauge with the readings accessible on the internet by May 30, 2020, as required by state statutes” after one was stolen in 2018.

Due to these deficiencies, DLNR has required Kaupakalua to operate the reservoir empty, and said the owner has complied.

Prior to Monday’s storm, Mahi Pono said the reservoir was empty, and was not being used to collect water for irrigation purposes — and is dry under normal conditions. A valve is kept open to allow water during typical rain events to quickly exit, and continue to flow downstream.

Regarding the notice of deficiency, Mahi Pono said two out of three items related to topography and hydraulics were resolved — and that the third, the water level gauge, is now in the process of being resolved.

Mahi Pono said Tuesday that East Maui Irrigation was already in the process of decommissioning Kaupakalua.

“After commissioning a review and study of the existing reservoir and dam, it was determined that removing the dam and decommissioning the reservoir was the best option,” said Mahi Pono in a statement.

Last October, EMI submitted a permit application to DLNR and the U.S. Army Corps of Engineers for the removal, and is footing all costs. The permit is still pending.

DLNR said of 130 state-regulated dams in Hawaii, 126 are classified as high or significant hazard potential structures due to proximity to people and structures downstream. All regulated dams — except one — now have emergency action plans on file with the state.

“Our Dam and Reservoir Safety Program works continuously with private and public owners of dams and reservoirs to bring them into compliance with all required safety regulations,” said DLNR chair Suzanne Case in a news release. “Yesterday’s overtopping of water over this dam certainly indicates the removal is necessary to protect people and property. We will continue to work with the dam owners around the state to ensure the optimum level of safety and awareness possible.”

Monday’s evacuation was carried out according to the emergency action plan for Kaupakalua, DLNR said.

The National Weather Service said the impacts of the torrential rainfall and flash flooding Monday impacted Maui the greatest.

NWS on Tuesday noted 48-hour rainfall totals that included 19.21 inches in West Wailuaiki on Maui, 12.83 inches at Piihonua on Hawaii island, 10.87 inches at Mount Waialeale on Kauai, and 10.78 inches at Kahana on Oahu.