(Via: Hawaii News Now)
September 14, 2018
By: Gordon Pang
Honolulu Board of Water Supply officials said Thursday afternoon that there was no danger of Nuuanu Reservoir No. 1 failing and said they notified the public about the possibility of evacuations downstream that morning in an abundance of caution to keep the community informed.
BWS Chief Engineer Ernest Y.W. Lau said water was being pumped from the dam — which is above Oahu Country Club on the Ewa side of Pali Highway — to keep the water level below the dam’s spillway and that the efforts were succeeding.
“This is not a dam breach situation right now. We’re not nowhere close to that,” Lau said Thursday afternoon. “We’re just trying to keep the levels lower than the spillway. Because once water goes over the spillway, then you’ll start to experience more flooding downstream because the water has to go someplace, and it will go makai downstream.”
At about 10 a.m. Thursday, BWS sent out a news release saying that the water was about 18 inches from the spillway and that BWS crews and the Honolulu Fire Department were pumping water to keep the level below the spillway after overnight heavy rain in the aftermath of former Tropical Storm Olivia. The release also said the board was working with city officials on an operations plan “which includes public evacuation notification and sheltering if needed. Approximately 10,000 residents would be affected.” It did not specify what areas would be affected or when.
More than an hour later, BWS and city officials said through social media that there was no immediate need for evacuations.
Lau said at an afternoon news conference that there was never any danger of dam failure or a need for evacuations, and BWS put out a news release after getting inquiries from the media and the community.
At the news conference, city officials distributed a map of the area that would have been affected if an evacuation was needed. The area included a major portion of lower Nuuanu, Chinatown, Aala Park and Iwilei, including Costco and Dole Cannery.
City Deputy Emergency Management Deputy Director Hiroyuki Toiya said his agency was already being contacted by people who had heard “from the rumor mill” that evacuations were already taking place.
“So we wanted to get ahead of that and let people know that we are taking pre-emptive action before the action,” Toiya said. Variables such as the intensity and duration of the storm made it difficult to say when evacuations would have occurred, he said, but “we were still a good ways out from having to pull the trigger on evacuations.”
Lau said evacuations would have been mandatory if the water level got within 1 foot below the top of the dam. The spillway is about 3-1/2 feet lower than the top of the dam, he said.
Since the water reached about 1-1/2 feet from the spillway, that would have meant the water would have needed to rise an additional 5 feet.
In the 24 hours ending at 10 a.m., former Tropical Storm Olivia and its aftermath dumped more than 8 inches on upper Nuuanu, according to a National Weather Service gauge.
The earthen dam, built in 1905, is 33-1/2 feet high and 588 feet long. It has a capacity of 21 million gallons.
BWS had been siphoning the water from the reservoir for several weeks in anticipation of several earlier storms as well as Olivia, city officials said. But when water in the reservoir rose some 4 feet, and siphoning wasn’t removing enough quickly, BWS began using two of its pumps as well as two from the Honolulu Fire Department, they said.
“I just took a conservative, very cautionary approach,” Lau said. Pumping will be used more frequently after this experience, he said, “because we’re going to start trying to lower the water levels even more knowing that we could have an event like this where there are 8 inches of rain in a short period of time in that area.”
Lau said BWS staff is working with the city Department of Emergency Management, tasked with organizing evacuations, to refine its evacuation plans.
Toiya said should there have been a need for an evacuation, it would have occurred long before a spill occurred and that the goal would have been to complete the evacuation in under an hour.
Honolulu police, fire and emergency management personnel would have been dispatched to notify those who live in the immediate area, giving them enough time to evacuate, he said. The media also would have been asked to spread the word, he said.
Lau said the board also is using this episode as an opportunity to improve its communications with the public.
“I think there is an opportunity for greater communication with our communities downstream from these dams about the unlikely failure of a dam and what the evacuation requirements would be,” Lau said.
The reservoirs were first constructed as part of an irrigation scheme for agriculture in the area. Today they’re used primarily for flood control during storms to slow down water making its way to the ocean, Lau said, although there currently is research being done to study their potential for hydroelectric production.
The two Nuuanu dams are among the 130 largest private and public dams in Hawaii that are regulated by the Department of Land and Natural Resources. Each is inspected every two years, said Denise Manuel, an engineer with the DLNR Dam Safety Program.
Each of the dams is required to file an action plan, and Manuel’s agency has been monitoring them during the storms, she said. “I’ve been tracking them continuously statewide,” she said.
Manuel said BWS “did a good job” handling the situation at Nuuanu Reservoir No. 1. “As Ernie said, there was never any risk of a dam failure; it was simply that it was getting to the spillway level.”
Source: Hawaii News Now