A team of specalists in coastal erosion, sea level rise, and urban planning quantified land use on a section of Oʻahu, Hawaiʻi coast over the period 1928–2015, a time of slowly rising sea level. They concluded that coastal zone management practices in the state, and nationally, will require new policies, or more effective ways for implementing existing policies, in a future characterized by accelerating sea level rise.
U.S. coastal zone management (CZM) relies on an integrated chain of federal to local programs that emphasize beach conservation, public shoreline access, and preservation of open space, as well as other goals. In testing the efficacy of these policies over a century of slow sea level rise, the team found a shift from accreting shorelines and wide beaches in the early data, to expanding erosion and beach loss concurrent with increasing backshore development and seawall construction throughout the period of study—trends at odds with policy objectives.
“The purpose of our study is not to point fingers at Hawaiʻi’s coastal zone managers. We donʻt want to be hard on the people. We want to be hard on the problem. The state’s political leaders, CZM managers, and stakeholders should use the information in this study to update policies so that beach conservation is achieved, and to develop sea level rise adaptation strategies,” said Chip Fletcher, associate dean and professor of earth sciences at the UH Mānoa School of Ocean and Earth Science and Technology (SOEST) and senior author on the study.
The Hawaiʻi Coastal Zone Management Program (HCZMP), a typical federal-local partnership, was established in 1977 to “provide for the effective management, beneficial use, protection, and development of the coastal zone.” The HCZMP regulates the coastal zone through state and local agencies.
As a state, Hawaiʻi relies heavily on beaches for economic, environmental, and cultural purposes. Rare and endangered species such as the Hawaiian Green Sea Turtle, the Hawaiian Monk Seal, and myriad shorebirds rely on beaches as critical habitat.
“With tourism being Hawaiʻi’s main industry, and beaches providing life-long memories for nearly every child and family, it is perplexing that authority figures have not implemented more effective policies and regulations to ensure beach conservation,” said Alisha Summers, lead author of the study who was an undergraduate student at SOEST while conducting this work.
Using a sequence of aerial photomosaics dating from 1928 to 2015, the team created geographic information system datasets to document a detailed history of shoreline change and coastal development over the past century. A number of features were analyzed including beach erosion and accretion, shoreline hardening, coastal development, flanking, and wave and weather events.
As development of beachfront lots increased, so too did the construction of seawalls
“Shoreline hardening increased from a complete absence of seawalls in 1928 to nearly 5 km of hardened shoreline today,” said Brad Romine, coastal management specialist with Hawaiʻi Sea Grant and co-author of the study.
“This century-long pattern of shoreline hardening and beach degradation seemed to escape notice until the research caught up in the last couple decades. Tracking cumulative impacts, as is required with the current environmental review process, must be a key part of the management doctrine in this case.”
The detailed history clearly shows several other trends and relationships over the 87 years of the study period.
Net shoreline change shifted from accreting to erosional on 74 percent of the coast, with more than 45 percent of this shift due to flanking, that is, erosion triggered by nearby hardening.
Data confirm the existence of a “hardening domino effect” in which the first seawall triggers a succession of seawalls by adjacent property owners as the hardened shoreline initiates and accelerates erosion on adjacent, once stable beaches.
Ultimately, nearly 20 percent of beach length has been lost, and 55 percent of beaches have narrowed
“Despite the adoption of a policy to preserve coastal ecosystems and environments, Hawaiʻi’s beaches continue to narrow and disappear while seawalls and revetments continue to be built,” said Daniele Spirandelli, assistant professor in the UH Mānoa Department of Urban and Regional Planning and extension faculty in Hawaiʻi Sea Grant.
“The data published in our new study are representative of state-wide and nationwide patterns of permitted coastal environmental destruction by shoreline hardening,” said Fletcher. “Rather than proving effective at achieving the stated goals of conserving the natural coastal system, ‘hardship variances’ embedded in these same policies allow shorefront owners threatened by erosion to build seawalls and other forms of shoreline hardening to protect upland development. This development includes private homes and property, public roads and parks, and federal lands such as military installations. Hardship variances undercut the very purpose of CZM conservation policies.”
“Why have we allowed the destruction of our beaches? I think there are multiple factors including legal loopholes such as the hardship variance. Other factors include a lack of strict enforcement, a misplaced emphasis on ‘balanced management,’ a legal bias toward private property rights and the simple fact that denying a homeowner a seawall permit may mean the destruction of their house,” said Fletcher. “Whatever the reason, it is time to develop an exit strategy, because living on a beach in a time of sea level rise acceleration puts lives, property and communities at risk.”
“If authorities intend to protect existing beaches for future generations, they must implement policies that allow beaches to migrate landward with rising seas,” said Fletcher.
The logic is simple: in an era of sea level rise, shorelines must migrate landward if they are to function as healthy ecosystems. Sea level rose more than 400 feet since the last ice age and beaches persist.
“Coastal systems are not intrinsically threatened by sea level rise provided they can freely migrate landward. However, seawalls prevent beach migration and will lead to their extinction unless we change how we manage our shoreline. Clearly, if we want beaches for our children and their children, we must get out of the way of migrating shorelines.”