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Hawaiʻi Beach Loss Caused by Shoreline Hardening

By: Monterey Rayman 

The impacts of global warming on our environment are becoming increasingly apparent. Sea level rise is imminent, and adaptation plans are still underway. Changes in our biosphere impact people globally, especially as natural disasters become more frequent and intense. According to UNICEF, residents on the Pacific Islands are particularly vulnerable, dealing with severe cyclones, earthquakes, tsunamis, and volcanic eruptions with limited preparedness (2023). As weather becomes more frequent and sea level continues to rise, communities in Hawaii are finding new ways to conserve their beaches.

Hawaiian monk seal basking in sun on hawaiian island.
Hawaiian monk seal resting on the beach at French Frigate Shoals (Lalo) in the Northwestern Hawaiian Islands. Image by: NOAA.

For those residing in Hawaiʻi, the beach is a focal point enjoyed by many. It serves as a crucial habitat for sea turtles during nesting season, and a place for hawaiian monk seals and their pups to rest. Unfortunately, this habitat is at risk not solely from sea level rise and coastal erosion, but from shoreline hardening tactics that can cause more harm than good. According to Tavares et al., a 40% loss of beach on the island of Oʻahu will occur by mid-century, due to outdated coastal management known as shoreline hardening (2020). 

Shoreline hardening is when hard structures are installed along a shoreline to prevent erosion. Using spatial data, Tavares et al. determined which properties may apply for an emergency permit with the predicted levels of sea level increase. Any property within 20 feet of evident erosion can apply for emergency protection. She found that approximately 51.5% of all sandy shorelines on Oʻahu will be hardened or are at risk of hardening. This is due to shoreline erosion and backshore land use. Today 28.6% of shorelines are hardened, with 3.5% at risk for hardening (2020).

sandbags placed along shoreline on north shore oahu to prevent erosion.
Emergency sandbags and "burritos" at Sunset beach, O'ahu. Image by: Cindy Ellen Russell.

Shoreline hardening causes harm and disruption to the natural accretion and erosion process of sand. The hardening blocks access to sand reservoirs and will reflect wave energy instead of absorbing it like a natural shoreline would. The reflection of wave energy increases the turbulence of offshore waves, which increases erosion nearby. Shorelines downdrift will erode faster without access to the sand reservoirs to replace them. The results of shoreline hardening on coastal habitats show distress within the coastal ecosystem (Shoreline Stabilization - NYDEC, n.d.).

shoreline hardening to protects coastal roads on the island of Oahu.
Shoreline hardening on windward side O'ahu that has led to beach loss. Image by: K Tavares

Gittman et al. conducted research looking at the effects of shoreline hardening. Data showed that seawalls decreased biodiversity by 23%, with 45% less organisms when compared to a natural shoreline. In contrast, data displayed that riprap and breakwater shorelines had no significant difference in the diversity of organisms or abundance. More research is needed to evaluate the effects of riprap and breakwater shorelines for accuracy (2016). Coastal inhabitants such as birds and marine life rely on natural shorelines for shelter and nourishment. At the same time, the natural shoreline helps prevent erosion and acts as a wave buffer (Hardened vs. Soft Shorelines, 2017).

Naupaka on a sand dune in Hawaii is creating a natural shoreline that prevents erosion and sand dispersal.
Natural shoreline with naupaka on a sand dune in Hawaii. Image by: Josh Silberg

Managing entities within Hawaiʻi often fail to address the shoreline as a whole but as parcels of land. Tavares et al. calls for interagency collaboration and public-private partnerships to come up with new ways to protect what sandy shores are left (2020). What is gone, can’t be replaced. Now is the time for change. New management of coastlines focused on natural landscaping can be a step in the right direction, for the betterment of the entire community and future generations to come.


Works Cited

Disaster risk reduction and emergencies | UNICEF Pacific Islands. (n.d.). Retrieved December 16, 2023, from

Gittman, R. K., Scyphers, S. B., Smith, C. S., Neylan, I. P., & Grabowski, J. H. (2016). Ecological Consequences of Shoreline Hardening: A Meta-Analysis. BioScience, 66(9), 763–773.

Hardened vs. Soft Shorelines. (2017, April 21). Florida Living Shorelines.

Prosser, D. J., Nagel, J. L., Howlin, S., Marbán, P. R., Day, D. D., & Michael Erwin, R. (2018). Effects of Local Shoreline and Subestuary Watershed Condition on Waterbird Community Integrity: Influences of Geospatial Scale and Season in the Chesapeake Bay. Estuaries and Coasts, 41(S1), 207–222.

Shoreline Stabilization—NYDEC. (n.d.). Department of Environmental Conservation. Retrieved December 31, 2023, from

Tavares, K. T., Fletcher, C. H., & Tiffany R. Anderson. (2020). Risk of shoreline hardening and associated beach loss peaks before mid-century: O’ahu, Hawai’i. Scientific Reports, 10(13633 (2020)).


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