By Ruby Pap
In my humble opinion, Kaua‘i has the most amazing beaches in the world. Besides their stunning natural beauty, beaches provide important natural and cultural resources. Forty seven percent of the island’s perimeter is made up of sand, more than any other Hawaiian island. These beaches provide essential habitat for wildlife and act as a buffer between land and sea. They are also the foundation of our recreational and cultural activities and are the major draw of our tourism economy.
Kaua‘i’s carbonate beach sand is derived from nearshore reefs. While it has never been dated here, based on radiocarbon dating on O‘ahu, it’s assumed our sand to be older than 1,500 years. The implication of this aged resource is that it is limited in quantity and should be carefully managed. Beach erosion is a growing concern.
Historical beach erosion trends are documented in the Kaua‘i Shoreline Study Erosion Maps developed for the County of Kaua‘i by Dr. Chip Fletcher with the University of Hawai‘i Coastal Geology Group at www.soest.hawaii.edu. Researchers analyzed historical aerial photographs dating back to 1926, mapped the shorelines using geographic information systems and calculated erosion rates for all the sandy beaches.
This important work contributed to the U.S. Geologic Service’s National Assessment of Shoreline Change for the Hawaiian Islands, which concluded 71 percent of Kaua‘i’s beaches are chronically eroding, with 6 kilometers completely lost since the early 20th century. Based on the 2012 studies by Fletcher and Brad Romine, nearly all beaches lost are due to the presence of human-engineered shoreline protection (seawalls, revetments, etc.).
With this winter’s predicted large swells on the North Shore, we can expect to see increased erosion. A key question is whether it is seasonal or chronic (i.e. long-term). Many beaches experience dramatic erosion in one season, e.g. Lumahai in the winter and Kekaha in the summer, only to see the beach return the following season. In these cases, the beach will have a long-term erosion trend that doesn’t necessarily reflect the short-term fluctuations. More monitoring of seasonal erosion trends is needed to better understand this phenomenon.
What about future sea-level rise impacts on erosion? This is more complicated because computer modeling must be used to predict the future under different global warming scenarios. UH PhD student Tiffany Anderson is working to forecast future coastal change in Hawai‘i from sea-level rise under business-as-usual greenhouse gas emissions scenarios. A 2015 paper recently published in the journal Natural Hazards sadly predicts doubling of coastal erosion rates by mid-century due to sea-level rise.
So, what are our options for protecting and managing our amazing beaches? Proper siting and planning of structures away from the shoreline to avoid the need for future protection is a fundamental step. The Kaua‘i County shoreline setback ordinance uses the UH long term erosion rates to determine the setback and then adds additional distance to account for uncertainties with seasonal erosion trends, episodic events, and sea level rise.
In areas where our communities are already built too close to the shoreline, decisions will need to be made about whether to hold the line and put up seawalls to protect ourselves; or retreat — to allow nature to take its course. Other short-term successes have occurred with beach nourishment — importing sand to the beach. Expect to see these and other sand management measures to be continually discussed and enacted over the coming years.
In recognition of the hard facts, it might be time to start designating certain legacy beaches across the state to concentrate resources and planning toward their protection.
I’d love to hear from you. What is your favorite beach and why? How would propose to protect it?
- Ruby Pap is a Coastal Land Use Extension Agent at University of Hawai‘i Sea Grant College Program. She can be reached at firstname.lastname@example.org.