Sustainable Aquifer Management in Small Island Developing States : A case study of Mauritius

Abstract: Small Island Developing States (SIDS) are amongst the most vulnerable states in the world. They are subject to a number of stresses including economical, climatic and spatial restraints. This thesis investigates the effects that certain critical ‘stresses’ will have on the groundwater reserves of SIDS. Mauritius was chosen as the case study for this project because of three main reasons, which were that 1) islands of the Indian Ocean are the least studied compared to the pacific and Caribbean islands, 2) there is no actual groundwater model for the aquifers of Mauritius and finally 3) information and background knowledge was more accessible to the author.  Two critical aquifers of Mauritius were chosen according to their respective vulnerability (extraction rates of groundwater, geological features, and rainfall patterns), Aquifers II and V. The aquifers were calibrated using data that was published by the Mauritian local authorities and through an extensive literature review. Aquifer II and Aquifer V were modelled using the software ModelMUSE and a steady state model (with a time series of 100 years) was used to calibrate the models using limited data that was obtained through the literature review. Aquifer V was successfully modelled while Aquifer II gave inconsistent results. A transient model using four scenarios inspired by the IPCC scenario analysis was used to investigate the salt water intrusion as well as the piezometric levels in both aquifers. The scenarios (run for a period of 100 years, i.e. until 2100) were of varying degrees of severity and included the main drivers of change that were believed to affect the groundwater consumption of Mauritius. The attributes that were targeted in this thesis were: economy, demography, technology and climate. These were then converted into quantifies inputs that were used in the model to assess the migration of the saltwater/freshwater interface in the aquifers. Scenario 4 which involved low recharge rate of the aquifer, high sea level rise, low GDP growth and increasing population subjected the aquifer to a reduced water table, and consequential sea water intrusion of the order 1.5 km across the cross section analysed. Scenario 3, which consisted of investment in green technology, increase in recharge of the aquifers on the other hand gave the more optimistic results with the salt water - fresh water interface moving seawards. Scenario 4 rendered unusable around 50 % of the wells in the aquifer while Scenario 3 on the other had the effects of increasing the freshwater lens of the Aquifer V. Measures such as sustainable urban drainage systems, managed aquifer recharge and Seepcat (a method which involves placing a series of pipes around coastal aquifers to prevent the intrusion of salt water) were recommended to decrease the salt water intrusion risk and eventually increase the fresh water lens of the island on various spatial and time scales. It is suggested that the coarse groundwater model developed for Aquifer V of Mauritius be refined and applied to different aquifers of the island. Moreover it is also recommended for future work that discontinuities in the geology be integrated in the groundwater model. A more detailed and nuanced water balance is also recommended to get more accurate initial conditions for the model. This thesis, by providing a coarse model to tackle the impending challenges that await Mauritius, can support a more sustainable water management of the country.