Recent High Wave Flooding a Reminder of Climate Crisis

By Ruby Pap

Ho‘one Road in Po‘ipū after being flooded and damaged by high waves. Photos by Ruby Pap

In July, a southwest swell of historic proportions produced by distant storms near New Zealand created waves upwards of 20 feet on the south and west shores of the Hawsaiian Islands.

Dubbed “Code Red Swell Part II” by surfline.com, due to “code red” conditions shutting down harbors and marinas in Tahiti (second time since August 2011), the swell came from a storm producing a large area of 50-knot wind and small pockets pushing hurricane force winds, impacting large swaths of the Pacific including Hawai‘i and California.

According to wave buoys at Barber’s Point on O‘ahu, ocean wave heights reached approximately 8 feet with periods of 20 to 30 seconds resulting in 20 foot waves on shore — historic levels for the South Shore — where large swells typically trend in the 10-foot range.

Here on Kaua‘i, we are used to large northwest swells but less so on the South Shore, which has many large hotels built by the water’s edge, shoreline roadways, and waterfront homes. All felt the brunt of July’s south swell, which combined with high tides resulted in significant coastal flooding which damaging infrastructure and closed roads. The result of July’s historic south swell in this area was dramatic, but relatively speaking could have been worse, and perhaps will be so with the continued rise of sea levels due to climate change.

Predicted annual high wave flooding on Ho‘one Road with 3.2 feet of sea level rise. Image by hawaiisealevelriseviewer.org

Wave runup flooded Ho‘one Road by Brenneke’s Beach, plus Ho‘onani and Lāwa‘i roads. It also swamped spectators at a popular shoreline restaurant (despite warnings to stay away from shoreline areas due to the dangerous surf). Valuable beach sand washed up onto the roads, perhaps reclaiming a pre-development area would have been a natural place for the beach to migrate to. While, luckily, there was little damage to the seawalls and roads, there was some undermining of the pavement in a few areas. This provides a good look of what is to come with continued sea level rise.

The Westside also experienced issues with the swell, including flooding of Kaumuali‘i Highway in Kekaha and flooding of the lo‘i pa‘akai of ‘Ukula at Hanapēpē (Hanapēpē Salt Pond). Thanks to the restored beach berm at Salt Pond Beach Park, makai of the salt-making area, the flooding of this important Hawaiian salt-making area was much less than in prior years, when the beach was deflated due to vehicle use that has now been curtailed. This speaks to the importance of maintaining and restoring healthy beaches and dunes as protective mechanisms against large swells and high tides.

Salt Pond on Kaua‘i’s Westside is seen here in this photo, after being flooded by high waves. Ideally, the pond stays dry in the summer to allow for salt making. In this case, the salt making area was spared but the area around it flooded. Impacts were minimized by the restored beach berm. Photo by Ruby Pap

Not surprisingly, areas that flooded due to the large waves are also predicted to be affected by sea level rise, now and into the future. The increased warming of our oceans due to climate change is predicted to raise sea levels on Kaua‘i one foot by 2050 and 3.7 feet by 2100 (intermediate scenario) according to a recent National Oceanographic and Atmospheric Administration report.

The Hawai‘i Sea Level Rise Viewer (hawaiisealevelrise.com) allows you to visualize SLR up to 3.2 feet on all of our coastlines, and it has a specific data layer showing predicted annual high wave runup. A quick tour of Hawai‘i’s sea level rise maps shows Ho‘one Road increasingly exposed to annual high wave runup under conditions of one to three feet of sea level rise with the first block of homes affected behind Brenneke’s.

Problems from exposure to annual high wave runup, coastal erosion, and passive flooding from sea level rise will increasingly be a problem islandwide. Each side of our island already shows examples of this, especially during large storms and king tides, which show us important glimpses into what is to come. As you can see by viewing the wave runup map for Ho‘one Road in Po‘ipū, the impacted areas are similarly showing us that this swell provides an important look at what is likely to become more common in the coming decades.

Coastal flooding events like this are expected to increase over time, and responses should be taken at all levels of our community, not just government. We can all do our part to reduce our carbon footprint to reduce and slow the impacts of climate change and to avoid the worst predicted impacts that will be inherited by future generations. We can also learn from our neighboring islands, like Maui, where highway flooding even without large storms has become such a nuisance that investments have been made in wave runup forecasts to assist with planning and response. See http://www.pacioos.hawaii.edu/shoreline-category/runup-westmaui/.

Ho‘one Road in Po‘ipū after being flooded and damaged by high waves. Photos by Ruby Pap

We also need to get more creative and proactive in our short-term response and longer-term adaptation strategies for our beaches, cultural treasures, infrastructure and homes. First, when sand washes up on land after a storm do not haul it away – put it back on the beach or the dune where waves can access it and gradually incorporate it back into the active beach. Beach sand is a valuable and severely limited resource and any loss of sand results in more erosion down the line. If you live on a shoreline subject to coastal flooding, pay attention to surf forecasts and move debris and other objects inside. It is also time to think seriously about relocating structures out of harm’s way. Get educated on Federal Emergency Management Agency programs that may be able to assist with flood mitigation and repetitive loss. A good resource for you would also be your county’s Floodplain Manager and the Coastal Zone Management program.

At the community level, there are many opportunities to get involved with climate adaptation planning islandwide. The Kaua‘i Climate Adaptation Plan (kauaiadaptation.com), which is in the process of being created, needs the public to be involved. It is the most important place to start for anyone who lives or works on the island as it will address all climate hazards – flooding, extreme heat, wildfire and drought. Sign up for the mailing list, get educated on the project documents and provide your input.

At the state level, there are many helpful resources to learn more about climate change in Hawai‘i. For sea level rise maps, see hawaiisealevelrise.com. According to State law (Act 179), sellers of residential property are required to disclose whether a property is within the sea level rise exposure area. Also, check out the Hawai‘i Climate Portal for a comprehensive, easy to navigate website on all things climate change: https://climate.hawaii.gov/. Hawai‘i Sea Grant has a whole host of opportunities to learn and participate in climate science as well. Community members who frequent the shoreline and like to take pictures can contribute to the King Tides Project every summer: pacificislandskingtides.org. Your photos will contribute to a growing database that will help to identify problematic flooding areas as sea levels continue to increase.

Dune restoration is an important tool for improving overall beach health and buffering the impacts of waves and erosion on the land. Hawai‘i Sea Grant recently published a how-to manual to get started:  https://seagrant.soest.hawaii.edu/wp-content/uploads/2022/03/Hawaii-Dune-Restoration-Manual-Final.pdf. This manual is intended for use by community groups, nonprofits, county and state agencies and departments, coastal resorts and condominiums, coastal landowners and managers, and anyone interested in conducting proactive dune restoration projects in partnership with Hawai‘i Sea Grant community extension agents.

I would be remiss if I didn’t acknowledge the work and involvement of the countless Kaua‘i community organizations working on community resilience to hazards on Kaua‘i. While the list is too numerous to state here, if you are new to the island, talk to your neighbors, stay tuned to local media for opportunities to volunteer, and learn more about mālama ‘āina, Native Hawaiian practices of caring for the land and properly managing the resources and gifts it provides.

Lastly, as your friendly island Sea Grant Extension Agent, I am available to talk story with any of you about your specific questions or issues about climate change and coastal hazards (rpap@hawaii.edu). Kaua‘i has an amazing history of coming together in crisis, whether it was after hurricanes Iniki and Iwa or the COVID-19 Pandemic. I look forward to continuing to work with this amazing community to do our small part to address the global climate crisis and to serve as a model for how to respond to its island impacts.

• Ruby Pap is a Coastal Land Use Extension Specialist with the University of Hawai‘i Sea Grant College Program. She is based on Kaua‘i.