Heavy rain from Tropical Storm Olivia filled Nuuanu Reservoir #1 to dangerous levels Thursday.
The Board of Water Supply said the water level rose four to five feet overnight, and by Wednesday morning, the reservoir was about 1.5 feet below the spillway.
In the event the dam overflows, officials say roughly 10,000 residents would need to evacuate.
One resident who lives next to the reservoir tells us he’s not too worried.
“I feel pretty good about it not overflowing,” said resident Craig Hayashi.
“All these years, we haven’t had any threat or high levels of flooding, and I know the back terrain has changed a lot, so the water comes down differently, but that reservoir has been dormant for a long time, so it’s been low, and the Board of Water has always been draining or siphoning before storms to keep the level low,” Hayashi continued.
Some residents knew about the risk, but most others did not.
“This whole area is a flood plain and like I said, when you move in there, you should know that and there’s a chance that it floods,” said Doug Bowers.
“Today was the first day that I have ever seen that map, and I lived in this area for two and a half years,” said Joseph Reinhart.
After seeing first-hand how Waolani Stream can swell up, Reinhart says he’s been prepared to take his dogs and head to safety.
“I actually want to look into what is the evacuation plan? When I heard today that I could possibly be evacuated, my first question was, what am I supposed to do? Where am I supposed to go, other than get out of the area?” he asked.
The utility had been monitoring and siphoning excess water from the reservoir since the beginning of the week, however, officials say the passing of Olivia brought a deluge of rain that exceeded siphoning capacity.
“Out of an abundance of caution,” BWS and Honolulu Fire Department personnel were deployed at the dam with extra water pumps Thursday to lower the reservoir level and prevent risk of overflowing.
“We’re taking preemptive actions. This is not a reactive one,” said Roy Amemiya, city managing director. “Additionally, the reservoir that we are working on is a much smaller dam than what you may be accustomed to, the one that everybody goes fishing for catfish, which is Reservoir #4.”
“The water has not even reached the spillway, and the spillway is a normal part of a reservoir like this. It allows the safe release of water from the reservoir when the levels behind the dam reach a certain point,” explained Ernest Lau, BWS manager and chief engineer. “You don’t want to have a dam like this, which is an earthen dam, where the water levels go above top of the dam itself and start to go over the dam.
“This is not a dam breach situation right now. We’re nowhere close to that,” Lau stressed. “We’re just trying to keep the water levels lower than spillway, because once water goes over the spillway, then you’ll start to experience more flooding downstream, because water has to go someplace and it’ll go makai downstream.”