Sea‐level rise impact on fresh groundwater lenses in two‐layer small islands

Abstract

The fresh groundwater lenses (FGLs) of small islands can be highly vulnerable to climate change impacts, including sea-level rise (SLR). Many real cases of atoll or sandy islands involve two-layer hydrogeological conceptualizations. In this paper, the influential factors that affect FGLs in two-layer small islands subject to SLR are investigated. An analytical solution describing FGLs in circular islands, composed of two geological layers, is developed for the simplified case of steady-state and sharp-interface conditions. An application of the developed model is demonstrated to estimate the FGL thickness of some real-world islands by comparison with existing FGL thickness data. Furthermore, numerical modelling is applied to extend the analysis to consider dispersion effects and to confirm comparable results for both cases. Sensitivity analyses are used to assess the importance of landsurface inundation caused by SLR, relative to other parameters (i.e. thickness of aquifer layers, hydraulic conductivity, recharge rate and land-surface slope) that influence the FGL. Dimensionless parameters are used to generalize the findings. The results demonstrate that land-surface inundation has a considerable impact on a FGL influenced by SLR, as expected, although the FGL volume is more sensitive to recharge, aquifer thickness and hydraulic conductivity than SLR impacts, considering typical parameter ranges. The methodology presented in this study provides water resource managers with a rapid-assessment tool for evaluating the likely impacts of SLR and accompanying LSI on FGLs.

Quantifying threats to groundwater resources in the Republic of Maldives Part I: Future rainfall patterns and sea‐level rise

“…The effect of SLR on atoll island groundwater resources is expected to be as severe as that of future rainfall (Ketabchi, Mahmoodzadeh, Ataie‐Ashtiani, Werner, & Simmons, ). As sea level rises, and depending on beach slope, which typically ranges from 0.5% to 2% (Tsyban et al, ), seawater will inundate beachfronts leading to beach shoreline recession, also termed “land‐surface inundation” in island studies (Mahmoodzadeh, Ketabchi, Ataie‐Ashtiani, & Simmons, ; Morgan & Werner, ), which can be significant even for a small rise of sea level.…”

“…Relatively few studies have been conducted for small coral islands. These studies (Bailey, Khalil, & Chatikavanij, ; Chui & Terry, ; Comte, Join, Banton, & Nicolini, ; Ketabchi et al, ; Morgan & Werner, ; Terry & Chui, ) are summarized in Table . Studies for other oceanic islands (Holding & Allen, ; Mahmoodzadeh et al, ; Sulzbacher et al, ) also are included to provide a broader range of methodologies.…”

“…Ketabchi et al (), Morgan and Werner (), and Bailey et al () employed analytical or empirical techniques to investigate the influence of SLR on atoll island lens thickness in a 2D vertical cross‐sectional domain. Morgan and Werner () applied results to three islands in the Pacific and Indian Oceans, and Bailey et al () applied the freshwater lens algebraic model (Bailey, Jenson, & Olsen, ) to 52 islands in the Maldives, with results indicating that lens thickness will decrease 10% by the year 2030.…”

Evolutionary algorithms for the optimal management of coastal groundwater: A comparative study toward future challenges

“…They showed that non-intrusive polynomial chaos expansions provided a reliable and yet computationally efficient surrogate of the original numerical model. Conceptualizing some global and significant concerns such as the effects of climate change (e.g., Ketabchi et al, 2014;Mahmoodzadeh et al, 2014) is one of areas which demand further examinations to identify how these impacts change the coastal groundwater management. As these issues (e.g., climate change-induced sea-level rise and variations in recharge rates) are essentially uncertain, stochastic conceptualization is compelled to properly distinguish between the various impacts and different SWI underlying factors (Werner et al, 2013).…”

“…Comprehensive reviews on SWI simulation approaches are given by Bear et al (1999) and Werner et al (2013). The SWI status depends on several factors including scale, aquifer properties, groundwater inflow and outflow, upconing due to well pumping, the tidal oscillation of the sea level, and climate change features such as sea-level rise and variations in recharge rate (e.g., Ataie-Ashtiani et al, 1999, 2013bKetabchi et al, 2014;Mahmoodzadeh et al, 2014) and there are unreliability or uncertainty in many of these factors, that cause the SWI analysis more complex .…”