By 2015, 62% of buildings were built in headland regions, 27% in transition regions, and 11% in embayed regions. Development activity and beach stability are negatively correlated. The greatest number of buildings was built on the most erosive shoreline, a pattern no doubt aided by lack of data on historical shoreline changes. This unfortunate pattern may be the result of the coastal highway running closer to the ocean where the coast curves landward in an embayment, and being furthest from the ocean in headland regions thus giving more room for development, but simultaneously hemming it in.
Concurrent to the growth in development, coastal hardening increased by 63%, comprising 4.67 km of seawalls and revetments. None of the shoreline was armored in 1928. As development in the study area boomed throughout the 1940’s, so did the hardening of coastal lots. Prior to the adoption of the HCZMP in 1975, 45% was armored. From 1975 to 2015, hardening increased by 18%.
An extensive amount of hardening occurred first in headland regions. By 1975, 63% of headland regions were armored, while 42% of transition regions and 22% of embayed regions were armored. Headland regions were subject to coastal hardening before transition and embayed regions for two reasons: (1) the majority of coastal development was concentrated in headland areas, and (2) the geomorphology of headlands and embayments influences sediment transport and deposition. Waves refract at headlands such that their energy is focused on the shoreline. As a result, headlands experience accelerated erosion while embayments tend to be more stable and may even act as depositional locations for sand eroded from an adjacent headland (Romine et al. 2016).
After the 1980s, coastal hardening dramatically increased in transition regions. By 2015, 77% of headland regions and 78% of transition regions were hardened. The increase in the length of seawalls despite the reduced rate of new development after 1975 could be attributed to other variables including the process of “flanking,” sea level rise, and an increase in extreme swell events, which may accelerate coastal erosion rates.
A similar trend was observed along 3.14 km of shoreline directly adjacent to the coastal highway. Data show that 46% of the coastal highway was armored by 2015. Although 52% of the coastal highway travels through embayment coasts, areas where the highway ran closer to the ocean in headland regions were armored first.
By 1975, 31% of the coastal highway was fronted by hardening and more than half (53%) of the hardening occurred in headland coasts. However, after the 1980’s, coastal hardening to protect the highway had spread to transition regions. By 2015, 46% of the coastal highway was fronted by hardening and of that percentage, 20% occurred in headland and transitional coasts.
Erosion in the study area increased from 57% in 1967 to 74% in 2015. Prior to 1967, there had been no beach loss aside from localized seasonal loss on 10% of the coast. Seasonal beach loss, followed by recovery, typically occurs with changes in the seasonal wave climate and may be a signal that a beach is severely sand-depleted.
By 2015, 19% of the beach had been permanently lost to erosion (Fig. 7). Beach loss intensified in headland regions compared to embayed regions. Shoreline change rates in headland regions show a steady erosional trend both pre- (1928 to 1975) and post- (1975 to 2015) coastal zone policy. In transition and embayment regions, rates changed significantly from accretion to erosion (Table SI7). Beach loss violates CZM goals of 1) Protecting beaches for public use and recreation, 2) Protecting, preserving, and restoring coastal scenic and open space resources, 3) Protecting valuable coastal ecosystems, 4) Reducing exposure to coastal hazards, and most of the other objectives and policies set forth in Hawai‘i coastal law (HRS205-A).
Between 1928 and 1975, the number of buildings in the study area increased from 39 to 177, an annual growth rate of 3.20%. Between 1975 and 2015, the annual growth in new buildings fell to 0.16%. By 1975, for every empty lot, there were seven developed lots. Thus, the slowed rate of individual building construction after 1975 reflects a coastal zone that was largely built out prior to enactment of state and county coastal zone policies.
Since 1975, redevelopment of existing buildings into structures with larger footprints has increased overall density. Expansion of existing single-family homes is allowed under SMA policy (ROH § 25-1.3.2A) and this constitutes a de facto increase in coastal development that continues to present day. Rapid build-out prior to coastal policy, followed by subsequent expansion of these buildings under policy authority, sets the stage for widespread seawall construction against a background of sea level rise.
We calculated average building surface area from digitized coastal buildings shapefiles created in ArcGIS. The average building surface area in the 1970’s was 170 square meters whereas the average building surface area in 2015 was 203 square meters, an increase of 20%.
Photogrammetric analysis reveals that throughout the 1970’s many existing structures along the coastline were either demolished and replaced by larger structures, or they were expanded. The increase in building size combined with the location of the coastal highway directly behind these structures prevented the relocation of threatened buildings in the face of chronic erosion.
CZM policies appear to have done little to prevent a 29% increase in coastal hardening that occurred between 1975 and 2006. Data shows this spike in hardening followed the build-out of 78% of shoreline lots by 1975, and was concurrent with the expansion in average building area that occurred between the 1970’s and 2015.
The shift from a stable beach to an eroding beach may often be attributed to flanking (Romine and Fletcher 2012a) resulting from a long-term pattern of shoreline hardening (Fig. 8) that still continues today.Footnote 1
We tested this phenomenon by calculating shoreline change rates directly north and south of armored locations before and after installation. Data reveal that erosion rates on more than 27% of the study area significantly accelerated due to flanking. In many cases, rates shifted from an accreting trend to an erosional trend following hardening on the adjacent shore. To illustrate, directly adjacent to hardening installed in the 1960’s, shorelines became unstable, shifting from an average 0.3 ± 0.06 m per year (accreting) prior to the installation of hardening to − 0.4 ± 0.08 m per year (eroding) after the installation of hardening.
Coastal property owners adjacent to seawalls will often harden their own properties in response to flanking. Shoreline history confirms the existence of a “hardening domino effect” in which the first seawall triggers a succession of seawalls by adjacent property owners (Romine and Fletcher 2012a). The domino effect of coastal hardening has been documented in other regions, for example, Manno et al. (2016) traced the decadal evolution of hardening along a portion of the Mediterranean coast and demonstrated protection structures produce a deficiency in sediment while shifting downdrift erosion processes, which are then countered by additional structures.
In our study, by 2015, roughly 45% of the observed hardening was constructed in response to an adjacent seawall or revetment. Contributing to this pattern was the continued construction of beachfront buildings, initially on stable shorelines, but which became vulnerable to erosion due to flanking. Our data reveal that construction of first seawalls along a coastal reach destabilizes adjacent shorelines and promotes subsequent coastal hardening that can sentence an entire region of sandy beach to narrowing and eventual loss.
Failure to achieve CZM goals
Hawaii’s coastal land use management system is complex, but three main laws govern its uses: county zoning ordinances, shoreline setbacks enacted in 1970 that established a minimum 40′ setback from the shoreline,Footnote 2 and the Hawai‘i Coastal Zone Management Program. There are 10 objectives in the authorizing statute for the HCZMP (HRS §§ 205A), summarized here as protecting and improving natural resources and ecosystems, reducing exposure to hazards, providing for public participation, and affording economic activity in suitable locations. Objective 9 is simply “Beach Protection - Protect beaches for public use and recreation.” Each objective is further expanded with an accompanying policy. Policy 9—Beach Protection, has three elements: (1) locating new structures inland, (2) prohibiting private erosion-protection structures, and (3) minimizing public erosion protection structures.
The HCZMP mandates the establishment of an SMA extending inland “no less than 100 yards from the shoreline.” Responsibility for implementing the law rests with county government. Each county established procedures for identifying SMA boundaries and adopted their own permit guidelines (consistent with state law) for new buildings [or substantial renovations] within the SMA.
A challenge to implementing the SMA is county zoning. Land use zoning creates “entitlements” or expectations about how private land owners can use their land. Courts have generally deferred to landowner claims that denial of building permits consistent with underlying zoning would constitute an unconstitutional “taking” of private property. Hence, while the SMA permit provides counties the legal authority to deny permits for building inconsistent with SMA guidelines, few permits are denied for land units. In practice, the SMA permit has been used primarily to impose permit conditions, such as modifications in building site plans to ensure increased shoreline setbacks, requirements for additional public access, and changes in landscaping plans to reduce runoff and similar requirements.
The data-based history of shoreline change rates reported here shows that beaches in the study area experienced either a transition from accretion to erosion, or from light erosion to strong erosion. Shoreline change was observed when comparing rates from 1928–1975 (pre-HCZMP period) to 1975–2015 (enforced HCZMP period) for beaches in all geomorphic settings.
Over the period of our study, the influence of increased coastal development in the study area is evident; continued building and highway construction is eventually threatened by chronic erosion, triggering hardening, beach narrowing, and loss. In addition, widespread shoreline hardening activated the process of flanking, contributing to the shift from stable/accreting to erosional beaches.
This detailed history of shoreline change reveals human-induced factors that likely drove important aspects of the recent erosion trend, a trend that could be partially to blame for O‘ahu losing at least 24% of its sandy beaches to hardening, and possibly more (Fletcher et al. 1997). Other factors that could be driving the erosional trend besides coastal construction, expansion, and hardening include sediment transport processes and SLR. Romine et al. (2013) studied shoreline change across the Hawaiian Islands and found a wide variation in erosion rates across different segments of island shoreline despite a rather homogeneous SLR for the island. This suggests that human impacts and persistent physical transport mechanisms may have a larger influence on historical shoreline change than SLR.
In spite of substantial legal authority to address shoreline erosion, appointed and elected land use officials have frequently:
Approved hardship variances allowing seawall construction,
Permitted expansion of single family homes within the SMA,
Approved building on coastal lots without regard to shoreline stability, and
Allowed maintenance and expansion of non-conforming buildings.
These practices have been repeatedly approved over decades since the enactment and enforcement of HCZMP with consequences that fail to meet the goals of the program.
Consequently, our data reveals that despite strategies to mitigate the negative effects of shoreline development and hardening on the beach, the establishment of Hawaiʻi coastal zone management policies did not adequately protect beaches in the study area, public access along the shoreline, nor open space in a meaningful way.
Like other states, local governments in Hawaiʻi are the primary implementers of coastal policies through land use powers and infrastructure improvements (Nolon 2012). Several previous studies show that state mandates for coastal management do not guarantee effective policy implementation at the local level (Blizzard and Mangun 2008; Windrope et al. 2016). There are several reasons why local officials and land use managers might not be using the full weight of HCZM laws. Local governments avoid “taking” claims by either imposing permit conditions on applicants or by issuing variances all together for new development or building expansions.
In Florida, Ruppert (2008) suggests strengthening the state setback law by stipulating that variances only be granted on the condition that a deed restriction is recorded which disallows seawalls and requires the removal of structures at owner’s expense if they impact the beach. Local governments can also issue temporary emergency hardening permits. Oftentimes, these emergency provisions, which were meant as temporary, become permanent (Cheong 2011; Ruppert 2008).
Another potential explanation is that local political actors exert significant pressure on officials to obtain permits or to shape local policies all together (Feiock 2004). Coastal properties in Hawai’i hold tremendous value and their owners may translate that wealth into political clout that can be used to obtain a permit (Ruppert 2008). Another complication is disentangling the causal mechanisms of beach loss. Local regulators have had little data to base efforts to strengthen or enforce regulations for restricting structures (Dethier et al. 2017). More longitudinal and place-based studies such as this one are needed to help assess the success or failure of coastal policies and their implementation.