Estimating transient freshwater lens dynamics for atoll islands of the Maldives

A Modeling Approach for Assessing Groundwater Resources of a Large Coral Island under Future Climate and Population Conditions: Gan Island, Maldives

“…The main threats to coral island groundwater supply are as follows: (1) overwash events from storm surges [11][12][13], which can salinize fresh groundwater due to infiltrating seawater; (2) extended droughts [4,6,14,15], during which groundwater flow and discharge to the ocean is much greater than recharge to the water table, thereby decreasing storage of fresh groundwater through time and thinning the lens; (3) over-pumping, which thins the lens and can cause seawater upconing, particularly during times of drought [6,16]; (4) changes in long-term rainfall patterns; and (5) sea level rise, which causes a decrease in island surface area due to shoreline recession and a resulting thinning of the lens [17][18][19][20]. According to a recent study [21], the majority of atoll islands will be uninhabitable by the mid-21st century due to overwash flooding that is becoming more severe due to sea level rise.…”

“…Many modeling studies have been conducted in recent years to assess current and future groundwater volume of freshwater lenses on coral islands. Several studies [15,20,25] have used an empirically based algebraic model that relates freshwater lens thickness to the key factors governing lens thickness (island width, recharge rate, upper aquifer hydraulic conductivity). The model assumes a sharp interface between freshwater and seawater along the boundary of the freshwater lens [9].…”

Assessing groundwater availability of the Maldives under future climate conditions

“…More recently, freshwater lens thickness was estimated for the islands of the Maldives during the 1998-2011 time period (Bailey, Khalil, & Chatikavanij, 2014a) and during the coming decades under different scenarios of SLR (Bailey, Khalil, & Chatikavanij, 2014b), with model results tested against the data from Falkland (2000Falkland ( , 2001 and…”

“…States of Micronesia(Bailey et al, 2009) and the Maldives(Bailey et al, 2014a), interception depth is set to 1.0 mm, field capacity and wilting point are set to a soil water content of 0.15 and 0.05, respectively, and potential ET is set to a constant daily value of 3.5 mm/day.3.2.5 | Summary of GCM-based simulationsSimulations are run for each accepted GCM for both RCPs (RCP2.6, RCP8.5), for each of the four island width models and for each of the three geographic regions. The initial conditions (salinity concentration and pressure at each mesh node) for each 1998-2050 simulation are achieved by imposing a steady recharge rate until the freshwater lens reaches steady-state conditions, followed by a transient simulation from 1991 to 1998 using recharge calculated from historical daily rainfall rates.…”

“…Properties of the atoll island aquifer system, including general properties, and properties for the Holocene and Pleistocene aquifer units (afterBailey et al, 2014a) General circulation models (GCM) and their organizations…”