Coastal Hydrogeology - Groundwater Resources Tarawa Atoll - Kiribati
Project: Bonriki Inundation Vulnerability Assessment
Collaborating Organisations: The BIVA project is part of the Australian Government’s Pacific-Australia Climate Change Science and Adaptation Planning Program (PACCSAP), within the International Climate Change Adaptation Initiative. The project was developed by the Secretariat of the Pacific Community’s (SPC) Geoscience Division (GSD) in partnership with the Australian Government and the Government of Kiribati (GoK). The project was undertaken over 22 months, from May 2013 to February 2015.
The BIVA project focused on Kiribati’s National Water Reserve in Bonriki, South Tarawa, which is Bonriki’s source of raw, fresh water. Change Adaptation Initiative. The project comprised three interlinked components: stakeholder engagement, groundwater investigations and analysis, and coastal investigations and analysis. It aimed to improve our understanding of the vulnerability of the Bonriki Water Reserve to coastal hazards, and climate variability and change. Improving our knowledge of risks to this freshwater resource will enable better adaptation planning by the government.
Key Outcomes
The BIVA project has improved our understanding of the potential for wave overtopping at the Bonriki Water Reserve, and developed advanced numerical models to represent and investigate the impacts of saltwater intrusion on the freshwater resource. The project has helped us to understand how the freshwater lens recovers from a range of inundation, abstraction and climate scenarios.
The inundation and groundwater modelling has demonstrated that, although inundation of the Bonriki Water Reserve in an extreme event will significantly impact the lens, the probability of this extreme event occurring is relatively low (based on a 50-year intermediate–high climate change scenario and an extreme event with a 1% chance of occurring in any one year). The majority of modelled inundation events tend to be localised and confined to the coastal fringe, and the lens should recover after 2–5 years, depending on rainfall. The analysis has also shown that, although an extreme inundation event will impact the lens, threats from over-abstraction and low rainfall recharge are far more critical influences on its condition. However, the models did not consider morphological responses of the coast to climate change, climate variability and human activity over time, and the risk of inundation may increase in the future if coastal zone management plans are not implemented to ensure resilient shorelines.
The project has investigated the economic costs and benefits of potential management options in the event that the groundwater resource is too saline for distribution. The economic analysis considered using either desalination or large-scale rainwater harvesting to augment the Bonriki groundwater supply. In all scenarios modelled, desalination is the cheapest suitable option for backing up the Bonriki supply, while groundwater remains the cheapest source of water overall.
Project: Climate and Abstraction Impacts on Atoll environments
Collaborating Organisations: European Union, ACP Group of States, Secretariat of the Pacific Community, The University of the South Pacific, Flinders University
Researchers: Professor Adrian Werner, Professor Ian Cartwright and Graham Green
The CAIA project aims to improve the understanding of climate variations and human impacts on atoll groundwater resources and identify technical and practical management tools that can be used by Government and communities to strengthen water security.
Small Island Resources
Small island atoll states have limited and vulnerable groundwater resources. With the CAIA project, groundwater resources will be assessed in two different atoll environments, Bonriki in Kiribati and Vaitupu in Tuvalu, using hydrogeological investigations techniques and groundwater modelling.
Assessment
The assessment of these resources coupled with the development of a sustainable yield concept for a freshwater lens under predicted climate and abstraction pressures will improve the resilience of Pacific Islands Communities in the future.
Freshwater Lens
The groundwater on atolls is often described as a ‘lens’ of freshwater ‘floating’ on more dense brackish water. This very thin and fragile freshwater resource relies on being regularly recharged by rainfall. Concerns over the salinisation of these fragile water sources due to rises in sea level, changes in climate variability and extremes, and human activities are increasingly raised by atoll communities and governments.
Threats to Groundwater
Whilst rises in sea level pose a longer-term threat to freshwater lenses, the more immediate threats are from over-abstraction and inappropriate land use activities, including poor sanitation practices, intensive cropping or animal husbandry in unsuitable locations. It is expected that population pressure and climate impacts will place the limited groundwater resources of atoll countries under an ever-increasing threat.