Oceanic Island Water Resources

Groundwater supply of small oceanic islands under varying climate conditions for the Federated States of Micronesia.
Using the USGS SUTRA numerical model, which simulates density-dependent groundwater flow and solute transport, the dynamics of the freshwater lens of atoll islands is simulated during average climatic conditions and drought conditions. Using modeling results, a simple algebraic model was developed, which relates the freshwater lens thickness to island width, annual rainfall rate, and geologic characteristics (reef flat plate presence, hydraulic conductivity, etc…). Results demonstrate the fragile existence of the lens, with drought conditions causing complete depletion of fresh groundwater for most of the islands of the Federated States of Micronesia. Current work deals with estimating future groundwater resources as influenced by sea level rise and variable rainfall pattern

Recovery of atoll island aquifers after marine storm-surge overwash events
Another threat for atoll island fresh groundwater is marine storm-surge overwash events, in which the island is inundated with seawater. Seawater infiltrates the ground surface and mixes with and salinizes the fresh groundwater, thereby destroying an important water source for island residents. Simulation results for a 400-m wide island show that months to years are required for complete recovery of the aquifer and build-up of the freshwater lens after an overwash event. The following figure shows the salinization and recovery of the freshwater lens during and after an overwash event. Current work is aimed at performing an overwash-recovery analysis for different sized islands in different climatic regions. 3D modeling of overwash event salinization and recovery has been performed for the Republic of Maldives.

Current and future groundwater resources assessment for the Republic of Maldives
A project with the World Bank in 2012-2013 used the SUTRA model and the algebraic model to estimate freshwater lens thickness and freshwater lens volume under recent climatic conditions as well as future climatic conditions (using output from the General Circulation Models participating in CMIP5) for the atoll islands of the Republic of Maldives. The lens thickness for a variety of island sizes and geographic regions were simulated for the years 1998-2011, and then through the year 2050 using estimated monthly rainfall rates. Further work using 3D model simulations have been published here.

Island Rainwater Storage Assesment
Stored rainfall constitutes an important water source for atoll island communities. Recent work used a water balance model and historical rainfall rates to determine the operation of rainwater catchment systems in the Federated States of Micronesia (FSM) under average rainfall and drought conditions. The model was able to reproduce the depletion of stored rainwater during the intense 1998 drought in the eastern FSM, and was used to determine the required roof catchment area and storage tank size to be able to maintain a sufficient quantity of water during a major drought.