The project is based in the Republic of Kiribati and the Kingdom of Tonga and involves collaboration between the governments of those countries, the Australian National University, the French agency CIRAD and the South Pacific Applied Geoscience Commission. The project is being run in two phases, techniques are being developed for atolls in the Republic of Kiribati and will be trialed in small islands in the Kingdom of Tonga. The work is divided into 4 subprojects.
Subproject 1. Agriculture and groundwater in atolls and small islands
This subproject is designed to answer the question: 'What are the impacts of cropping on groundwater and of groundwater management on cropping and groundwater resources?'
Water for human use in Tarawa Atoll, Kiribati, is sourced from domestic groundwater wells, from raintanks and from a pumped groundwater reticulation system in south Tarawa supplied from large, shallow, freshwater lenses in reserves on the islands of Buota and Bonriki. Because soils in coral atolls are mainly coarse coral sands, any surface contamination is carried down rapidly by rainfall or irrigation into groundwater. We have found elevated levels of dissolved nitrogen (up to 19 mg/L) in some groundwaters sourced from areas with some agriculture. Groundwater is also subject to saline intrusion from the surrounding sea.
The principal agricultural enterprises in Tarawa atoll are the cultivation of coconut trees for domestic use and export copra production, the growing of breadfruit and pandanus, the cultivation of vegetables for domestic use and pig and chicken production. The researchers have shown that, once mature, tree crops are able to tap into groundwater and coconut trees can transpire up to 150 L/day. Vegetables are mainly irrigated by hand from domestic wells and pig manure is often used for fertiliser. Because of this areas where water is extracted for reticulation have been declared water reserves and this has caused conflict with land owners.
Population growth in south Tarawa has increased pressure on freshwater supplies and has caused the search for additional sources of fresh water for reticulation. The researchers surveyed and assessed groundwater resources on two islands, Abatao and Tabiteuea, immediately north of Bonriki and Buota and installed 11 monitoring boreholes (5 on Abatao and 6 on Tabiteuea) to measure the thickness of the freshwater lenses and their response to climate extremes. Parts of the freshwater lenses on these islands are sufficiently thick to be sustainable during severe droughts. The maximum thickness of fresh groundwater found on both islands was about 15 m. The thickness varies with island width and other factors including the density of coconut trees. The thickest parts of the freshwater lenses are found on the wider southern ends of both islands. The average thickness over the entire lens was 3.1 m for Abatao and 2.9 m for Tabiteuea. Detailed measurements of the dynamics of groundwater levels at several locations indicate that the hydrogeology of the two islands is similar to Bonriki. The estimated potential sustainable yields of the freshwater lenses are 240 m3/day and 230 m3/day for Abatao and Tabiteuea, respectively.
Southern Abatao has extensive vegetable crops with ready access to markets. These provide cash income for villages. There is considerable concern that the development of a groundwater extraction scheme on Abatao could impact severely on the availability of water for vegetable production.
Subproject 2. Managing atoll and small island groundwater in times of drought
This subproject seeks to answer the question: 'What are the best options for managing groundwater equitably in times of drought?'
A simple nonparametric scheme has been developed to assess the severity of drought for different water sources (wells, raintanks, freshwater lenses). This works on monthly rainfall data accumulated over different time periods. The method has been tested for the large freshwater lens at Bonriki. Comparison with measurements of the thickness and salinity distribution in the lens showed that assessment over a running 12 month period provided an adequate representation of the impacts of the drought. Comparison with historic data suggests that a reasonable drought warning system can be developed from the technique with better than 50% accuracy. Measurements of the salinity distribution in the lens following the 1998 to 2000 drought have revealed that major saline intrusion in severe drought occurs at particular locations in the freshwater reserves. Strategies for reduced pumping at these locations as drought evolves have been developed
Subproject 3. Integration of hydrogeological, agronomic, social, economic and cultural information to assist in setting broadly accepted, long-term goals for groundwater management and allocation and in reducing conflict
This subproject is directed at discovering whether hydrogeological, agronomic, social, economic and cultural information can be integrated to assist in setting broadly accepted, long-term goals for groundwater management and allocation and in reducing conflicts.
In order to facilitate negotiations between sectors of the community with conflicting viewpoints and interest, it was decided to investigate an integrated model that encapsulates social and biophysical interactions. Multi-Agent Based Simulations (MABS) are able to: represent spatially the hyrogeology of atolls; to encompass the daily soil water balance and longer-term groundwater balance and incorporate the behaviour in time and space of water users and water regulators.
A MABS system, Atollscape, has been developed for South Tarawa. This system represents the islands of South Tarawa as 2157 hexagonal land cells. Each cell is isotropic and approximate shape of islands, the connections between them and their lagoon/ocean orientations are broadly represented. The time step corresponds to a 10-day period and the simulations are limited to 10 years.
AtollScape uses a three reservoir (plant interception, soil and groundwater) water balance model, WATBAL, to estimate groundwater recharge. Runoff is ignored because of the large permeability of the coral sand soils. WATBAL uses rainfall and potential evapotranspiration as input data. Recharge of the lens may occur only after plants satisfied their water requirements. Tree crops (mainly coconut trees) extract water directly from the lens. AtollScape takes into account the spatial heterogeneity of the processes and their time dependence. Each freshwater lens collects different recharge values coming from each of the different constituting cells and values are aggregated and averaged over a time step.
The shape and depth of the freshwater lens are estimated using a quasi-steady state, Dupuit-Forcheimer approximation, mass balance from WATBAL and from the estimated abstraction from the lens. The calculations are updated at each time step and adjusted after 12 months. This model is able to simulate the change of the thickness of the freshwater lens with changes in climate and abstraction.
Two classes of social actors have been identified. These are households that use water for domestic purposes and for irrigation and the government water supply agency. The main attributes of each household are: the number of people, the drinking and domestic water requirements, water-consuming equipment and a consumption satisfaction index. New households can be created every time step to simulate the population growth. The government supply agency entity is characterised by the volume of water pumped from the freshwater reserves.
A negotiation support system has been developed based on recently completed surveys of local and expert knowledge of water management issues
Subproject 4. Dissemination of research results
This subproject addresses the question: 'What are the best strategies for communicating research findings to stakeholders?'
The survey of local knowledge has revealed particular knowledge deficiencies at the village level. In particular there appears to be a general lack of understanding of the impact of surface activities on groundwater quality. The negotiation support system being developed will assist in the communication of this and other important aspects of groundwater management.

(actual reporting period: April 2004 to April 2005)
In low coral atolls, groundwater exists as freshwater lenses floating over saline transition zones, grading into seawater. To lessen the risk of seawater intrusion, groundwater is pumped from long, horizontal, infiltration galleries. Population growth, limited land, human activities including agriculture and frequent droughts place groundwater under stress. This project has four objectives: to understand the impact of agriculture on groundwater resources and the impact of groundwater extraction on agriculture; to explore management options for mitigating droughts; and to combine this information with information on hydrology and on the economics and social aspects of island communities to produce a system to lessen conflicts over water allocation and use. Work is being carried out in the Pacific, firstly in Tarawa Atoll in the Republic of Kiribati and then in the Kingdom of Tonga.
Tarawa atoll has two regions, heavily populated, urbanised South Tarawa and sparsely populated rural North Tarawa. In the low islands studied in Tarawa, Bonriki and Buota in South Tarawa, currently used for groundwater extraction, and the undeveloped Abatao and Tabiteua in North Tarawa, the spatial extents of their groundwater lenses have now been measured. These measurements permitted waterbalance estimates, using the highly variable climate record, of their sustainable pumping yields of fresh groundwater water and identified potential sites for additional galleries.
A critical concern in small island communities with land overlying fresh groundwater stores is the impact of groundwater pumping for reticulated water supplies on traditional crops such as swamp taro and coconuts. On Bonriki, the community attributes a general decline in productivity of coconuts to groundwater pumping. An extensive study of shallow groundwater drawdown and salinity by pumping from all infiltration galleries on Bonriki and Buota found the mean drawn down due to pumping was close to the theoretically predicted drawdown. This was an order of magnitude less than diurnal tidal fluctuations of groundwater that coconut tree roots are exposed to. Pumping also had a negligible influence on groundwater salinity. A theoretical study of the width of the saline transition zone beneath the freshwater lens estimated pumping increased its width by 37% but the frequent El Nio droughts increase the transition zone width by 90%. Examination of the sparse coconut trees at Bonriki and a review of their physiology indicate declines in productivity are due to senescence and lack of crop management.
Because of the scarcity of land on small islands, agricultural activities, such as market gardens and swamp taro production, often encroach over shallow groundwater reserves. The use of animal manures and inorganic fertilisers, construction of open wells for watering and increased cropping density of coconut trees have raised concern over impacts on groundwater. Extensive sampling of groundwater on Bonriki revealed E. Coli and elevated nitrate and dissolved organic carbon levels in areas with market gardens and abandoned swamp taro pits. Large concentrations of hydrogen sulfide were also found due to reduction of sulfate in groundwater. Chlorination and air sparging removes these materials.
A water balance model was used to examine impacts of coconut tree density on groundwater recharge. Tree density had little influence during major wet periods. During droughts, however, it has a major impact causing significant periods of net groundwater loss. Predictions are consistent with measured groundwater salinity records. Analyses of the drought impact on the thickness and salinity of the of the freshwater lens predicted watertable falls of up to 400 mm during prolonged droughts, close to the measured decrease of 440 mm. Predicted increases in salinity of the freshwater lens are consistent with observed increases and measured saltwater intrusion. The nonparametric method of identifying droughts can provide a lead time of about three months warning of droughts.
Local and expert knowledge on groundwater and water supply has been collected and this has been incorporated with the hydrology and salinity dynamics into a Multi-Agent System for groundwater use and management, AtollScape. The system includes all the principal actors in water extraction and use, down to households. A role playing game, AtollGame to explore different scenarios through use of AtollScape and reduce conflicts has been developed. A two-day trial of the game with relevant representatives from the islands of Abatao and Tabiteua and key government stakeholders produced a flow chart of financial, technical and social solutions and a proposal for a sequential refining of the process to arrive at equitable management options.

See final report