Based on ongoing kilo by the salt-making practitioners, it has been observed that wave overtopping of the beach berm occurs during periods of large summer swell and high tides, and the magnitude of overtopping increases when the beach berm is deflated. This situation was exacerbated by vehicle activity on the beach, leading to sand compaction. This was indicated by lower permeability along the beach profile measured using the self-potential (SP) method. However, recent restriction of vehicle activity has resulted in passive restoration of the beach berm and in-turn reduced frequency of wave overtopping events. The primary focus of mitigation measures should be directed towards preserving the health of the beach, and restoring the sand dune and near shore reef systems. Additional berm rehabilitation and ongoing maintenance, as described in Sea Grantʻs dune restoration guide, could allow additional protection from wave runup in the near-term, mitigate additional flooding in the area, and contribute to enhancing the resilience of this important coastal ecosystem., Working closely with the salt-making practitioners and the local community to undertake sand dune restoration initiatives will enhance the resilience of this vital ecosystem, help to reduce erosion, and create a buffer against storm surges and sea-level rise. This may extend the time in which the salt making can be practiced in its current location.
As sea level continues to rise, erosion is projected to narrow the beach beyond what was experienced primarily due to vehicle-induced erosion. This is indicated by the Hawaiʻi Sea Level Rise Viewer. In order to prolong the viability of salt-making in its current location, it is crucial to maintain restrictions to vehicle access on the sand dunes. Nevertheless, the erosion caused by vehicles offers a glimpse into the imminent impact of sea-level-rise-related erosion on the salt ponds in the near future.
Flooding caused by rainfall, including runoff, predominantly takes place during the winter months when salt making activities are not underway. Nevertheless, with the ongoing rise in
global temperatures and resulting climate changes, rainfall patterns are undergoing shifts. To address this, it is advisable to install a weather station at the pond or a nearby secured location and employ traditional kilo methods to monitor the changing rainfall patterns along with other climatic changes in the area. On-going kilo by salt-making practitioners and collective analyzing of their kilo data as a community will continue to inform their practice and conversations that can provide valuable insights for adapting the salt-making season to the evolving conditions.
As inundation becomes a recurring issue in the upcoming decades, it is advisable to plan for a phased inland relocation when marine flooding has become intolerable to the practice. Historical evidence demonstrates that former salt making areas have been decommissioned in the past, making way for the possible restoration of these sites in accordance and with consent of the salt makers. By pursuing this approach, the practice of salt making on the peninsula can potentially be sustained for future decades. Additional study could be used to inform relocation. Various research analyses performed here illustrate the presence of the thick clay layer inland of the present salt-making site. This indicates that some of the unique geology elements needed for the salt-making process is not limited to its present harvesting location, and suggests that inland migration may be possible.
Based on observed water level fluctuations in the pond there is a slow/dampened but existing subsurface connection with the ocean, so pond water levels can be expected to rise with sea level and eventually become more consistently inundated. Chronic inundation from this source (sea level influenced coastal groundwater) may occur with as little as 0.5 ft of sea level rise as indicated by the passive flood layer of the Hawai‘i Sea Level Rise Viewer. Long-term monitoring by the salt-makers of puna salinity and rates of evaporation would help to better understand any changes in the salt-making environment. According to the Hawaiʻi Sea Level Rise Viewer, a sea level rise of 1.1 ft is projected to start affecting the salt-making site in its current location due to annual high wave over-wash. This level of local sea level rise is expected to occur by midcentury.
The presence of contamination from non-point source pollution in the salt-making area remains uncertain, as testing was not part of this study. Self-potential results indicate that the site allows for more groundwater flow in the study area, suggesting that the salt-making area is vulnerable to contamination from the road, and/or anthropogenic activities. In order to safeguard the health and resiliency of this sensitive, historical and cultural ecosystem, it is strongly recommended that neighboring properties and sites implement actions to mitigate any potential sources of contamination, ensuring that any adverse impacts on the groundwater and adjacent ecosystems are minimized or eliminated. This recommendation is important to protecting salt from Hanapēpē as a cultural and spiritual resource that exists because of the intrinsic relationship between the salt makers and their ancestral lands.