Planet808: O'ahu Expert Says There's No Way Around Sea Level Rise

Nov 8, 2019

Some very high tides are expected later this month, Nov. 25 to Nov. 28. Hawai‘i’s last "king tide" event happened at the end of July. Combined with a freak south swell, ocean levels rose over three feet and reached their highest point of the year so far. One water expert explains how Honolulu will cope with rising sea levels.

Barry Usagawa, 34 years at the Honolulu Board of Water Supply, now as Water Resources Program Administrator he is working on O'ahu's Watershed management Plans and the One Water framework that unites government and community efforts on behalf of a whole water system, mauka to makai.
Credit Noe Tanigawa / Hawai'i Public Radio

Barry Usagawa is water resources program administrator for the Honolulu Board of Water Supply. We’re catching him just after a learning trip to four inundated cities on the East Coast.

“We were lucky in that when we were in Miami and Charleston, it was a king tide, which is the highest tide of the year. So it was a dry day, no rain, and they’re driving through one foot of water.”

That’s sea level rise. Usagawa, and other Hawai‘i scientists and public officials were on a mission to discover best practices in cities that already cope with flooding.

“That’s what I was there for,” says Usagawa. “I wanted to understand, how did they lift their streets because we're going to have to do that in a couple of decades.”

Usagawa points out it’s not just water pipes, sewage lines, drainage, power, and telecommunications that are under the streets.

“We visited an area on Purdy Street in Miami where they lifted it about 3.7 feet. They installed new drain pipes and are routing all the drain pipes to these huge storm water pumps that pump the water out at high tide. All their electronics are elevated above flood levels, and they’re designing their buildings with flexible first floors.”

That means designing buildings with first floors that operate as usual now but could be abandoned later. Sidewalks are raised as well, with ramps running between the different levels.

Usagawa says the areas most in danger for water inundation on O‘ahu is the urban core, Waikīkī to Mapunapuna, and Makiki and lower Kalihi Streams.

There are already seasonal wave runups that threaten luxury hotels. It’s common to have a room of sandbags to keep sand and water at bay. Usagawa says older hotels in Waikīkī have underground parking lots that flood with the tide. He says there’s a pump going almost continuously in Kāhala to keep that area from flooding.

And there’s beach erosion, with some homes on the North Shore, at Rocky Point, where backyards are collapsing into the beach.    

This is not going to get better. Hawai‘i is looking at sea level rise over 3 feet by 2050 and 6 feet by the end of the century.  

Usagawa says, on the mainland, none of the municipalities they visited did anything before they had to.  Two flooding incidents a month appears to be about when people get more willing to pay for mitigation.  And this will be expensive. Until then, planning and coalition-building across departments and constituencies are key.  

“I was at the Ala Wai flood mitigation alternative meeting last night at Ala Wai golf course,” says Usagawa. “And they had a whole host of ideas from the community, just thinking about it. Underground storage, green infrastructure, things we were already kind of thinking about, but they also are.

"It was very motivational, there was a lot of momentum. The thing is to pick the best of the ideas and give it a try.”

Usagawa says people in Hawai‘i seem more generally aware of sea level rise, and Hawaiian culture is a strong base for moving forward because it involves values and personal responsibility to the community.

“Sea level rise is so huge we have to work together,” says Usagawa. “There’s no way around that.”

Currently, water management plans for all eight O‘ahu land use districts are in production, and Usagawa is working on the primary urban center version now.  He says these watershed management plans are the best tool to get us to sustainability.

In addition, Usagawa is developing the Board of Water Supply’s One Water concept, looking at the whole hydrologic system in the watershed and linking agencies and partners in its care.

Usagawa says what’s urgent now is adaptation guidance for development, to prepare for what scientists know is coming.

There is some good news: even with a population increase, we are pumping less water out of our aquifer now than we were in 1990, about 12 million gallons a day less. The savings are thanks to water re-use, water-saving fixtures, and consumer awareness.