Groundwater hydrology and management in small islands and their applicability to small islands in Maldives and Sri Lanka

Abstract

Small islands all over the world face drinking water scarcity issues due to low rainfall, high evaporation rates and salinity in groundwater. Their unique geo-hydrological setup which consists of a buoyant lens-shaped freshwater body underneath the landmass and surrounded by saline water have attracted much research interest recently as a result of aggravating impacts on Small Island Developing States (SIDS) and other similar islands due to increasing population and climate change. Relatively high soil hydraulic conductivities and limited land area of these islands lead to generate only minute surface runoff with no surface water bodies. Supplying water to these islands is extremely difficult due to their isolation from nearby land areas, and therefore, this fresh groundwater lens can be identified as the key source to fulfil the water requirements of the living beings in the islands. The scenic view of small islands has caused a boom in tourism industry in these areas leading to excessive extraction of water that causes an imbalance between draw off and recharge ratios. Algebraic and analytical methodologies as well as conceptual and empirical approaches have been developed to identify the existing groundwater profile and estimate the steady-state freshwater lens thickness by considering parameters such as the width of the island, precipitation, land use, hydraulic conductivity, recharge rate, tidal variations, climatic change and reef plate characteristics. Safe yield and artificial recharge have also been identified for a few small islands to achieve sustainable groundwater management. This paper provides a comprehensive insight into methodologies and models developed under past studies and study the applicability of selected methods to small islands of Maduvvari and Henbadhoo in Maldives in an attempt to proactively monitor and assess the freshwater lens thickness of small islands. The model applicability to small islands along the northwestern and northern coastal stretch of Sri Lanka is also considered.