NUUANU, OAHU (HawaiiNewsNow) - Board of Water Supply and Fire Department crews have lowered water levels at a Nuuanu dam that quickly rose amid torrential rains.
Earlier in the day, the Board of Water Supply warned that as many as 10,000 residents might have to be evacuated if water levels continued to rise.
The board later said that warning was issued in an abundance of caution and that there was never any immediate danger of the dam failing.
But they also stressed that more rains could spur bigger concerns, and urged residents to familiarize themselves with the reservoir's risks.
Heavy rains from Tropical Storm Olivia overnight and into Thursday quickly pushed up water levels in the reservoir, prompting crews to dial up efforts to pump water from the dam. Through the day, crews were pumping water from the dam at 800 gallons a minute.
Less than an hour after the Board of Water Supply issued its warning about possible evacuations, U.S. Sen. Brian Schatz sent a tweet about 11:15 a.m. that evacuations wouldn't be necessary and that pumps had lowered water levels. The city and Board of Water Supply later echoed that message.
Ernest Lau, manager and chief engineer at the Board of Water Supply, said in a news conference Thursday that evacuations would be ordered if water levels in the dam get within 1 foot of its banks.
At its highest level, water was about 5 feet from the top of the dam, or about 1 1/2 feet from the reservoir's spillway.
Over the course of the morning, crews were able to decrease the water levels in the dam by about 2 to 3 inches.
Nuuanu reservoir no. 1, just off the Pali Highway, is a 33-foot-high earthen dam. Its hazard classification is "high," which means a dam failure could result in significant economic losses.
Lau said the dam, which is much smaller than Nuuanu reservoir no. 4 (the dam that residents used to be able to fish in), dates back to 1905 and holds about 23 million gallons of water.
While officials stressed evacuations were not likely, the city did release a map of the evacuation area should the dam fail.
The evacuation area stretches from Nuuanu to Iwilei.
The Board of Water Supply started pumping water from the dam early in the week, and called in the Fire Department to help on Thursday.
Onlookers said the episode underscored the need for dam oversight and proper maintenance.
The state Department of Land and Natural Resources, which has a dam safety program, said it's monitoring the work at reservoir no. 1 along with reservoir water levels statewide.
More than 100 dams in Hawaii are considered high hazard, but only Nuuanu reservoir no. 1 came close to exceeding its capacity in the heavy rains from Olivia.
While Tropical Storm Olivia didn't make landfall on Oahu, the island did get torrential rains from the tropical cyclone. The National Weather Service said in the 24 hours that ended at 10 a.m. Thursday, Upper Nuuanu got 8 inches of rain.
Some residents who live near Nuuanu reservoir no. 1 said they didn't even know the dam was in their community. Others said they saw the water being pumped from the reservoir, but had no idea the situation was so serious.
"We saw the water," said Nuuanu resident Alvin Chung. "They were actually dumping the water out with hoses. I've seen that before. I didn't know it was this bad."
Resident Stephanie Furuno said the whole episode is "kind of scary, especially not being prepared for it or even knowing what could happen."
If evacuations were ordered, here's the area (in red) that would be affected:
This story will be updated.