#SeawallsFAIL: TURNING THE TIDE ON MAUI’S COASTAL EROSION

Honoapiilani Highway is one of the most important roads on Maui. In addition to its incredibly scenic views, it is also the island’s primary transit corridor connecting West Maui. It is infamous for its traffic jams, road work and accidents. Delays can stretch for miles and last for hours. The nearest hospital is over half an hour away – and that’s when the road is clear.

To make matters worse, parts of Honoapiilani Highway are falling into the sea. Large summer wave events and high tides have proven particularly problematic. Waves crash over the highway and ocean surges undermine it, requiring expensive and environmentally damaging “emergency” repairs. There is serious concern that chronic coastal erosion will eventually do away with the highway entirely.

HOLDING BACK THE SEA

“Shoreline armoring” is the most common solution to protecting populated shorelines from erosion. This method typically involves building large structures that act as barriers between the ocean and coastal property like hotels, homes and roads. Without some sort of protection, this coastal property would eventually fall into the sea.

Seawalls are one of the most widely used examples of shoreline armoring. These massive concrete barriers parallel the shoreline, preventing the surf from eroding the land, while also stopping the sea from moving inland. Although seawalls are an attempt to halt coastal erosion, they can be extremely detrimental to neighboring beaches, nearshore ecosystems and water quality¹.

SEAWALL IMPACTS

In a nutshell, seawalls eliminate the ability of beaches to naturally fluctuate with changing waves and tide. With nowhere to go, sandy beaches are squished between an unyielding seawall and rising water levels¹. Without proper sand transport, beaches are eventually lost, public shoreline access is hindered, coastal habitats suffer and local economies are impacted². Worse, seawall projects typically cost in the millions of dollars, putting a serious drain on financial resources that could otherwise be spent to make the road better.

On Maui, the negative impacts of seawall are easily seen – especially along Honoapi`ilani Highway. In 2012, the State of Hawaii took emergency action to armor a 4,000 foot stretch of highway near Ukumehame Beach Park. A large seawall was constructed on the ocean side of the highway, and portions of the beach were paved over to expand the road. Almost immediately, a large plume of brown water developed just offshore – the result of extensive digging and excavation. The plume lasted for months, smothering the coral reefs hundreds of feet from the shoreline with sediment. In addition, the sandy beach directly in front of the seawall now disappears during high tide. Overall, the project cost taxpayers $7 million, not to mention the unmeasured cost of damaging the shoreline and reef.

 

On Maui, shoreline hardening projects have resulted in the loss of approximately 5 miles of the island’s beaches since 1949.

(Fletcher et al., 2007)

 

 

Today, waves continue to crash over the reinforced seawall, endangering travelers and damaging the roadway and barriers. It is likely that within the next decade, the seawall will require another round of multi-million dollar repairs. Over the past 20 years, numerous studies have highlighted the many problems associated with seawalls. It is time to learn from these failures and come up with less expensive, more durable and less damaging solutions.

FINDING A SUSTAINABLE SOLUTION

Coastlines are highly dynamic, unstable areas. Because of their inherent risk, roads and other structures need to be far enough inland that the ocean and shoreline can work together to maintain the beaches that have always been there. Where structures have already been built, the best option is to move/rebuild them further inland (“managed retreat”).

 

It is time to move Honoapi`ilani Highway further from the ocean. The current highway could be converted into coastal parks and public areas that would not need shoreline armoring. One project that has gained much public support over the years is the Pali to Puamana Parkway. This project advocates for the creation of a public, coastal corridor that stretches 8 miles from Papalaua Beach Park in the south to Puamana Beach Park in the north. In the short term, endangered parts of the road could be rerouted onto the existing cane haul road.

NEXT STEPS FOR MAUI

The Pali to Puamana Parkway (P2P) plan is an incredible opportunity for Maui to preserve coastal access and protect sensitive coastal habitats. The P2P plan has the backing of numerous community groups and government officials, including Mayor Alan Arakawa.

Unfortunately, additional seawalls and shoreline armoring projects are already underway. Construction has just been completed at Mile Marker 13.  At Olowalu, shoreline bouldering projects are slated to begin as early as August.

 

Seawalls are not the answer. They are a short-term reaction to a long-term issue. Instead, coastal erosion requires a holistic approach – one that carefully considers environmental, social, and economic aspects. One of most viable, long-term solution is to realign Honoapiilani Highway further from the ocean. Managers should also consider “soft engineering”¹ solutions such as stabilizing the coastline with vegetative walls using native hau.

Community support is a vital part of advocating for highway realignment. Currently, we need your help to accomplish 2 major goals:

1.Block shoreline armoring plans North and South of Olowalu – The State Department of Transportation (DOT) plans to harden shoreline areas of Olowalu with large boulder revetments. The construction of the bouldering project is a short-sighted solution that has the potential to affect the quality of the Olowalu surf break. Another seawall is planned south of Olowalu between Mile Markers 13 – 15.

2. Get the “Honoapiilani Highway Problem” back on SDOT’s Planning Horizons – The most immediate goal is to encourage SDOT to reinstate a volunteer task force that will evaluate alternatives to coastal hardening solutions with regards to the “Honoapiilani Highway Problem”. The formation of a task force would also ensure that the SDOT is taking steps to address the issue.

To learn more about the Realign Honoapiilani Highway project, check out the Save West Maui’s Coastlines website and Facebook page.

REFERENCES

1. Esteves, L.S., 2014. Managed realignment: A viable long-term coastal management strategy? SpringerBriefs in Environmental Science. New York: Springer. https://www.springer.com/earth+sciences+and+geography/earth+system+sciences/book/978-94-017-9028-4/
2. O’Connell, J.F., Shoreline Armoring Impacts and Management Along the Shores of Massachusetts and Kauai, Hawaii,in Shipman, H., Dethier, M.N., Gelfenbaum, G., Fresh, K.L., and Dinicola, R.S., eds., 2010, Puget Sound Shorelines and the Impacts of Armoring – Proceedings of a State of the Science Workshop, May 2009: U.S. Geological Survey Scientific Investigations Report 2010-5254, p. 65-76. https://www.realignhonoapiilani.com/uploads/8/0/4/8/80483190/oconnel_2010.pdf
3. Fletcher, C., Rooney, J., Barbee, M., Lim, Siang-Chyn, and Richmond, B., 2007. Mapping shoreline change using digital orthophotography on Maui, Hawaii: Journal of Coastal Research Special Issue 38, Fall 2003, p. 106–124.