How Will Urban Honolulu Deal With the Rising Ocean?

From street level, Waikīkī feels like a dense urban environment packed with invincible structures. But viewed from the air, its vulnerabilities are clear: All that heft is situated on what looks like a low-lying island, buffered on one side by a thin ribbon of sand and on the other by the murky Ala Wai Canal.

The area is remarkably vulnerable to water, like much of Honolulu’s flat urban corridor. Water pours down streams in the Ala Wai watershed during heavy rain, often slipping over the banks of the canal.

When rainfall coincides with king tides – an exceptionally high tide seen in winter and summer – streets can flood from Mō‘ili‘ili to Māpunapuna as seawater inundates the porous ground, lifting the water table to create new wetlands and simultaneously blocking the drainage system.

Then there’s permanent sea level rise. For years, climate scientists have warned that the ocean would swallow more and more coastline as glaciers melt and water expands in a warming climate. The U.N. Intergovernmental Panel on Climate Change predicts a 3- or 4-foot rise by 2100 if global warming stays under 2 degrees Celsius, and a more than 6-foot rise if warming exceeds that mark.

“We know that change is coming to our shoreline, whether we’re prepared or not.”

– Matthew Gonser, Chief Resilience Officer & Executive Director of Honolulu’s Office of Climate Change, Sustainability and Resilience

Chip Fletcher, the associate dean for academic affairs at UH Mānoa’s School of Ocean and Earth Science and Technology and a leading climate scientist, says worst-case scenarios are highly plausible.

What’s more, he says Hawai‘i and other Central Pacific islands can expect additional rise because of “fingerprinting,” a phenomenon that originates with the ice sheets of Greenland and Antarctica and other glaciers. The ice exerts a slight gravitational pull on the water surrounding it. As the ice melts and that pull subsides, distant locations can experience sea level rise that is more than the global average.

“This is not your average thorny problem,” says Fletcher. “Sea level rise is an unsolvable problem that needs to be managed so we can decrease the amount of loss and suffering and damage that we experience.”

On O‘ahu, rising oceans have washed out roads and beachfront homes have collapsed from coastal erosion – costly, painful problems, but isolated. The future will bring much worse.

The Hawai‘i Climate Change Mitigation and Adaptation Commission’s report from 2017 estimates that, statewide, 3.2 feet of sea level rise would displace more than 20,000 people and destroy over $19 billion worth of land and structures, not counting a lot of critical infrastructure.

These human and financial impacts would hit the urban core heaviest, including the epicenter of the state’s tourism sector, Waikīkī. On NOAA’s sea level rise viewer, a 3-foot rise would flood areas near the Ala Wai Canal. At just 4 feet of sea level rise, more than half of Waikīkī would be underwater. At 6 feet, it’s all submerged, along with much of the southern coast.

Waikīkī’s Vanishing Beaches

Like many residents, I hadn’t visited the shoreline between Kaimana Beach and Magic Island in years. It was time to get off Google maps and go see for myself.

The beaches were in worse shape than I expected. Tourists may envision strolling along Waikīkī’s fabled sands, but it’s one of the least walkable stretches on the island – narrow, clogged with people and structures, or literally gone.

Heading west from the Kapahulu groin, a sprawl of sunbathers and gear tossed across the loose, crunchy sand drives me inland to the sidewalk. I finally turn left into the Royal Hawaiian Center that leads to The Royal Hawaiian hotel.

The beachfront is blocked by a fence. Back inside, I soak up the hotel’s calm, stately interiors before heading west to the Sheraton Waikiki. The beach fronting the Sheraton has largely disappeared, and the elevated walkway is shut for safety reasons. I move through the patio area, past an infinity pool lined with sunbathers, then down past a patch of sand and people huddled under a lone tree. Circling the edge of a tiny pocket beach, I finally reach an uncrowded stretch: the seawall straddling the Halekulani Hotel, closed for renovations, and the deep Pacific pressing against it.

Beyond the seawall, waves make the path unpassable. It’s about 2:30 in the afternoon in late July and low tide is at 3:41, so most times of the day would be worse than this.

Nuisance Flooding Could Turn into Permanent Inundation

The UN Intergovernmental Panel on Climate Change predicts a 3- or 4-foot rise by 2100 if global warming stays under 2 degrees Celsius, and a more than 6-foot rise if warming exceeds that mark. The IPCC report released in August 2021 says the world will reach 1.5 degrees Celsius of warming by 2040 or sooner, and it’s irreversible. Under most scenarios, warming will continue through the century, though dramatic cuts to global emissions could stabilize temperatures.

Here’s what that could look like in Waikīkī and the surrounding area:

Map based on the NOAA Sea Level Rise Viewer, updated July 2020,  The viewer shows the scale of potential flooding, but not exact locations. It does not account for future erosion, construction or mitigation efforts. The SLR scenarios are mapped to average high tides and factor in hydrologic connectivity, or how surface and subsurface water connects. | Animation: Amy Ngo

■  Waikīkī at 2 feet of sea level rise  – The first impacts will be flooding, depicted in light orange, at the Ala Wai Golf Course. The deep navy blue is the ocean and the Ala Wai Canal, as well as the convergence of the Mānoa and Pālolo streams flowing into the canal.
■  Waikīkī at 3 feet of sea level rise  – Canal spillage and groundwater inundation become more pervasive. Rising seas enter the permeable rock and push up the water table, creating wetlands and blocking drainage systems.
■  Waikīkī at 4 feet of sea level rise  – Much of Waikīkī, as well as low-lying residential and commercial areas, are regularly submerged. The flood zone grows further at 5 feet of SLR.
■  Waikīkī at 6 feet of sea level rise  – Coastal flooding and groundwater inundation are catastrophic and require dramatic adaptations and even retreat. NOAA says it has a high degree of confidence about the extent of flooding at 6 feet, but less confidence at lower levels of sea level rise.

An Engineered Shoreline

No one with a financial stake in Waikīkī – and that’s nearly everyone in Hawai‘i – is ready to give up the beachfront, a proverbial golden goose. If the beaches were completely eroded, Waikīkī would lose an estimated $2.2 billion annually from tourists going elsewhere, according to a UH Sea Grant College Program analysis published in 2018.

In the decades between the first seawall being erected in 1890 near Kapi‘olani Park and the construction of the Ala Wai Canal in the 1920s, which drained the area’s wetlands and duck ponds, dozens of projects were completed – groins, more seawalls, coral dredging and sand fills. The shore became a fortified, engineered construction.

Since 1949, about 25% of O‘ahu’s beaches have narrowed or been lost to artificial hardening, and at least 60% are now in a state of chronic erosion, according to the O‘ahu Resilience Strategy, a set of action items released by the city in 2019. Yet coastal experts agree that beaches are more effective at keeping water at bay than hardening tactics, and far less prone to failure.

“Beaches are not just for recreational purposes and for tourists. They’re also important as a buffer between the properties and the ocean,” says Rick Egged, president of the Waikīkī Beach Special Improvement District Association. Among other projects, the nonprofit association collects fees from commercial properties to help pay for the area’s shoreline projects.

“The bottom line is that to protect a lot of these urban areas, you’ve got to armor them in some way. And the first step is to build a beach because that’s better than just a wall,” says Egged.

The process of coaxing sand to accumulate continues in earnest. In May, the final leg of a major beach project was completed, with 20,000 cubic yards of marine sand spread in front of the Moana Surfrider and Royal Hawaiian resorts. In June, the state Department of Land and Natural Resources released a draft environmental impact assessment for a fresh batch of projects, including a proposal to build a beach to front the Sheraton Waikiki and Halekulani resorts.

Unlike most projects that focus on maintenance, this is “a big, visionary, ambitious plan for (a group of ) T-head groins and beach fill – we’re building a beach where there never was one, as historically the beaches were very small in that area,” says Dolan Eversole, an extension agent with the UH Sea Grant College Program who works with the Waikīkī association. Eversole sees his role as translating the science of climate change into practical suggestions.

He says stakeholders he works with have started listening in earnest. “Among local government, state government and private developers, there was a very noticeable shift in perception and acceptance of the science, starting about five years ago,” says Eversole. Before that, “people were like, ‘Yeah, yeah, yeah, we’re going to wait and see.’ ”

Eversole has been collaborating with Chip Fletcher, Wendy Meguro of the UH School of Architecture and others to host what they term design charettes, small-group discussions geared at getting people to think about adaptation strategies. In June, I joined a group of civil engineers as they tossed around ideas that ranged from the straightforward, such as moving critical infrastructure and flood-proofing lower levels, to more dramatic steps such as elevating streets and moving commercial activity off the ground floor.

Others went big and suggested digging out Waikīkī’s streets and replacing them with canals – a Venice on the Pacific. Advocates say it’s the kind of radical idea that might actually help the area cope with chronic or permanent flooding.

Creating a Beach in Waikīkī Where None Exists

A draft environmental assessment for the state Department of Land and Natural Resources envisions installing T-groins to create a beach in front of the Sheraton Waikiki and Halekulani hotels. Currently, seawalls are the main barrier between the water and the properties.

Source: “Draft Programmatic Environmental Impact Statement, Waikīkī Beach Improvement and Maintenance Program”; prepared for the Hawai‘i Department of Land and Natural Resources and partnered with the Waikīkī Special Improvement District Association; released June 2021. | Illustration: Amy Ngo.            ■ Seawall and Walkway   ■ Existing Groins will be rebuilt   ■ New Groins

Living Shorelines, Adaptations and Retreat, at 6 feet of Sea Level Rise

With 6 feet of rise, the city will need visionary ideas to cope. UH Mānoa professor Judith Stilgenbauer’s map of Honolulu shows ferries linking the southern coast, with “living shorelines” such as wetlands and tidal marshes serving as a buffer between the ocean and the built environment.

Areas needing adaptations or strategic retreat are marked in blue and yellow. Adaptations could be building up the land, elevating structures or designing buildings to withstand flooding.

Source: “South Shore Promenade and Coastal Open Space Network Study: Resilience and Connectivity”; Hawai‘i Office of Planning and UH Community Design Center; Professor Judith Stilgenbauer, principal investigator; released November 2020. | Illustration: courtesy of University of Hawaiʻi Community Design Center

Living with Water

Some of the more intriguing ideas for dealing with rising oceans come from the UH Community Design Center on the Mānoa campus. Judith Stilgenbauer, a professor of landscape architecture and urban design, led a research and design team that looked at returning public lands to natural wetlands and opening up the largely industrial shoreline to recreation.

The result was a report called the “South Shore Promenade and Coastal Open Space Network Study,” released late last year with the help of state funding. The renderings reimagine some of Honolulu’s scrappier areas – such as Ke‘ehi Lagoon and a portion of the Kalihi Kai waterfront – as well as the Ala Wai Canal and the stretch from the ‘Aiea Bay Recreational Area to the Pearl Harbor Visitor Center.

Long-term, the plan envisions the entire southern shore linked by wetland buffers and coastal parks, all walkable and bikeable, with ferries and water taxis that stop along the shoreline and travel up the canal. This may seem fanciful, but if Honolulu sees the higher end of predictions for sea level rise, learning to live with lots of water will be a necessity.

“If we think strategically about moving things back from the shoreline or negotiating easements for the spaces we need to prevent sea level rise from affecting the built environment, why not then also create better connectivity along the shore and more recreational opportunities?” asks Stilgenbauer. “In many cases, we’re turning our backs on this beautiful waterfront.”

Among the three specific sites explored in the report, the one that gets the most attention is the Ala Wai Canal and the city golf course along its mauka edge. By creating wetlands spanned by wooden walkways, the plan tackles three water problems: rising oceans flooding the canal; rainwater flowing down the watershed; and groundwater inundation, which is already happening.

This kind of green infrastructure “allows the water in, absorbing it, but also increasing the distance between development and water, in many instances by creating physical barriers in the form of wide, landscaped berms,” explains Stilgenbauer.

She calls them soft, nature-based solutions that stand in contrast to hard, engineered solutions.

“An engineer is mainly concerned with keeping the water out,” says Stilgenbauer. “But urban designers or architects tend to be generalists, and we worry about things like beauty and ecological performance and social aspects. A big component of sea level rise has to do with social and environmental justice,” she says, as underserved communities can’t afford to move away or adapt.

Matthew Gonser, who is the chief resilience officer and executive director of Honolulu’s Office of Climate Change, Sustainability and Resilience, finds the designs inspiring.

“I think those visions really help us think about what’s possible. … The challenge now is that we haven’t had to consider this kind of integrated and coordinated infrastructure in a very long time – probably not since the city was first being built,” he says. “And in that case, a lot of it was either being done independently, whether it’s the state building the harbor or the airport, or private industry working on properties downtown all the way through Waikīkī.”

First Signs of Sea Level Rise

UH’s Fletcher warns that before ocean water begins encroaching on land, sea level rise in Hawai‘i will appear most often as “nuisance flooding.” Odd gurgles of water rising from storm drains on sunny days, standing water in grassy sections along the Ala Wai Canal, moderate rains that turn low-lying streets into ponds.

With a team of graduate students, he tracked rising oceans to rises in the water table, and first recognized the problem of groundwater inundation – a leading indicator of sea level rise.

“This is not your average thorny problem. Sea level rise is an unsolvable problem that needs to be managed.”

– Chip Fletcher, Associate Dean for Academic Affairs, UH’s School of Ocean and Earth Science and Technology

“Water tables rise and fall in synchrony with the tides in the oceans,” says Fletcher. “You can build all the seawalls in the world and keep the ocean out,” he says, “but the groundwater is still going to get you.”

During high tides, even without rain, the groundwater gets pushed up through storm drains, flooding streets. “It is already happening now,” he says, “but it’s going to seriously accelerate 10 years from now.”

Eversole from the UH Sea Grant College concurs.

“There are well-developed methods for controlling erosion and wave run-up along the coast. We’re going to try to build a beach and maintain a beach in Waikīkī, and we’ll keep doing that until we can’t afford to do it anymore. But with the groundwater table, there is no way to really prevent that from happening,” he says.

“If you think of the geology of Honolulu, it’s like a sponge, and you can put concrete over the sponge, but the water finds a way in.”

– Dolan Eversole, Extension Agent, UH Sea Grant College Program

Beyond the damage caused by flooding, the water is also filthy. Sewage leaking from corroded underground pipes and cesspools mixes with the brackish water.

Some shoreline areas such as Kaka‘ako Waterfront Park are built on landfill, which is just piles of accumulated rubbish, “so we don’t know what all is buried there and what could leach into the water table,” says Stilgenbauer.

Another landfill site, Māpunapuna, is built on old fishponds and is literally sinking. At times, heavy rains and king tides make the streets impassable.

Driving through water that hits the top of your tires could become common elsewhere too. A 2020 study from Shellie Habel, a coastal geologist and extension agent with the UH Sea Grant College, predicts that by the 2030s, even four-wheel-drive vehicles could run into trouble as groundwater inundation and storm drain backflow overwhelm city streets and trigger widespread drainage failures.

Architects and Planners are Reimagining the Southern Shoreline

Creating wetlands at the Ala Wai Canal at 3 feet of sea level rise – UH Mānoa professor Judith Stilgenbauer envisions turning the Ala Wai Golf Course into wetlands. The spot is already impacted by groundwater inundation and will be one of the first urban areas to experience chronic flooding with just 2 feet of SLR.

In the near term, nine holes of the current 18-hole course would remain intact and wetlands introduced to absorb water. An elevated boardwalk lets water flow underneath and pedestrians and bikers travel along the canal’s mauka bank. In the long term, the wetlands would naturalize and expand, taking over the golf course, absorbing more water and supporting more biodiversity. Ala Wai Boulevard would be elevated, and elevated landforms added along Date Street and the Ala Wai Community Park.

The cross-section shows the wetlands at 3 feet of sea level rise. | Source: “South Shore Promenade and Coastal Open Space Network Study: Resilience and Connectivity”; Hawai‘i Office of Planning and UH Community Design Center; Professor Judith Stilgenbauer, principal investigator; released November 2020. | Illustration: courtesy of University of Hawaiʻi Community Design Center; Amy Ngo

Small Steps Forward

Like climate change more generally, sea level rise is an immense problem with no easy answers – and no central decision-making authority to select, fund and implement the kind of wide scale adaptations needed to withstand huge influxes of water.

Jessica Podoski, a hydraulic engineer and climate change expert with the Honolulu district of the U.S. Army Corps of Engineers, says the state has to decide which areas to protect, which ones can adapt to rising seas, and which should be abandoned altogether.

“There will always be stakeholders with opposing interests, and Hawai‘i’s leaders need to have a vision for what the future of our state will look like,” she writes in an email. “The hard decisions and investments must be made now in order to head off more difficult and costly choices in the future.”

Some of those battles played out in the Corps of Engineers’ plan for the Ala Wai watershed, which was designed to prevent the kind of devastating flooding a 100-year storm would inflict on the city. (The Corps’ focus is storm-driven flooding and not sea level rise specifically, notes Podoski.) The plan featured a huge pumping station, as well as floodwalls and detention basins extending into the upper reaches of Mānoa, Pālolo and Makiki valleys. Community opposition contributed to the plan’s escalating price tag, which reached $651 million.

Though the project was killed, Honolulu Mayor Rick Blangiardi announced in July that the city had signed an agreement with the Corps of Engineers to revisit it.

Gonser from the city climate office says the Blangiardi administration understands the gravity of the situation facing Honolulu.

“We know that change is coming to our shoreline, whether we’re prepared or not. And we know that we will need to take action,” he says. “So the administration is super committed to engaging with the community and coordinating with the state, and trying to maximize our funding opportunities.”

Some funding ideas on the table are collecting stormwater fees, leveraging bonds and tapping federal funds, including “earmarks” in the federal budget. The infrastructure deal that passed through the U.S. Senate in August (but still faces a House vote as of this writing) includes at least $2.8 billion for the state to rebuild roads and bridges with climate change in mind, invest in clean energy, improve water and wastewater facilities, implement flood control projects and restore coastal habitats.

In July, Gov. David Ige signed into law two bills that specifically address sea level rise. One requires home sellers to disclose whether their properties are vulnerable to sea level rise. The other requires the Hawai‘i Office of Planning to identify state facilities that could be impacted by sea level rise and flooding. Some expect that city and state guidance to build for 3 feet of rise will become law soon and that shoreline setbacks are coming.

In the private sector, newer constructions such as the Whole Foods Market on Kamakee Street and the South Shore Market in Ward Village are slightly elevated, with entries above street level. Owners of the Princess Kaiulani hotel, tentatively slated to be torn down in 2022, plan to rebuild significantly above grade.

Architects and developers are going beyond the building code and considering sea level rise in both design and siting, says Nathan Saint Clare, a principal at the architecture firm AHL. For many large projects, they’re looking to build in areas away from the shore; Saint Clare’s team also employs features such as terraced walls and landscaping that can handle floodwaters.

Saint Clare sees Waikīkī’s hospitality sector as a creative source for new designs and adaptations. “We’ve got some great ones here – leading brands that have projects all over the world – and they’re going to bring some of their best ideas” to tackle the problem.

“A Lack of Anxiety”

Add them up, and there’s real momentum. But is it enough? Most people I spoke with don’t think so.

“What we run into is a lack of anxiety,” says Fletcher. “Developers, government officials, legislators, individuals all have different levels of anxiety about climate change. If you have high anxiety, you’re more motivated to implement potentially radical-looking policies or potentially expensive policies.” Most people fall in the medium range, he says.

There’s not nearly enough infrastructure work being done, says Matt Heahlke, a civil engineer and regional manager with Goodfellow Bros., which has worked on coastal projects around the Islands. “What really needs to happen is the community leaders and government need to realize that this is a priority and put emphasis on how we’re going to rebuild our infrastructure – to make it a daily conversation about how to be ready for sea level changes.”

Egged, the Waikīkī Beach Special Improvement District Association president, started a neighborhood advisory committee that includes lifeguards, beach boys and “everyone we could think of” to talk about problems and come up with solutions. Like others, he thinks this kind of community approach is the best way to build awareness and get buy-in.

“What are the issues we need to be worrying about right now? And what do we need to be planning to do in the 5- to 10-year level? And then the 10- to 20-year level, and so on,” says Egged. “I think that’s the kind of plan we need to work on together as a community because, otherwise, the whole issue starts to sneak up on you and become emergency situations. And that’s never the best way to do it.”

But that’s often how things work, with a dramatic event catalyzing change.

“Maybe it takes a major hurricane surge … to some of those high-value coastal areas for us to really become more serious about them, either rebuilding in a way that’s more resilient, or at least planning for future scenarios like sea level rise,” says Stilgenbauer. “Maybe that’s human nature.”