Elsevier

Journal of Hydrology

Volume 535, April 2016, Pages 235-255
Journal of Hydrology

Sea-level rise impacts on seawater intrusion in coastal aquifers: Review and integration

https://doi.org/10.1016/j.jhydrol.2016.01.083Get rights and content

Highlights

  • A comprehensive review of sea-level rise impacts on coastal aquifers is presented.

  • The main remaining challenges for future research opportunities are presented.

  • The need for an integrated assessment of controlling factors is identified.

  • Both analytical and numerical models are employed to investigate influential factors in an integrated framework.

  • Sensitivity assessment based on dimensionless parameters is implemented to scrutinize influential factors.

Summary

Sea-level rise (SLR) influences groundwater hydraulics and in particular seawater intrusion (SWI) in many coastal aquifers. The quantification of the combined and relative impacts of influential factors on SWI has not previously been considered in coastal aquifers. In the present study, a systematic review of the available literature on this topic is first provided. Then, the potential remaining challenges are scrutinized. Open questions on the effects of more realistic complexities such as gradual SLR, parameter uncertainties, and the associated influences in decision-making models are issues requiring further investigation.

We assess and quantify the seawater toe location under the impacts of SLR in combination with recharge rate variations, land-surface inundation (LSI) due to SLR, aquifer bed slope variation, and changing landward boundary conditions (LWBCs). This is the first study to include all of these factors in a single analysis framework. Both analytical and numerical models are used for these sensitivity assessments. It is demonstrated that (1) LSI caused by SLR has a significant incremental impact on the seawater toe location, especially in the flatter coasts and the flux-controlled (FC) LWBCs, however this impact is less than the reported orders of magnitude differences which were estimated using only analytical solutions; (2) LWBCs significantly influence the SLR impacts under almost all conditions considered in this study; (3) The main controlling factors of seawater toe location are the magnitudes of fresh groundwater discharge to sea and recharge rate. Regional freshwater flux entering from the landward boundary and the groundwater hydraulic gradient are the major contributors of fresh groundwater discharge to sea for both FC and head-controlled (HC) systems, respectively; (4) A larger response of the aquifer and larger seawater toe location changes are demonstrable for a larger ratio of the aquifer thickness to the aquifer length particularly in the HC systems; (5) The lowest sensitivity of seawater toe location is found for the density difference ratio of the seawater and freshwater, and also for the aquifer bed slope; (6) The early-time observations show seawater fingers below the inundated lands due to SLR which are diminished and ultimately extinguished; and (7) A less than 2% reversal effect on the seawater toe location after overshoot mechanism is observed in the transient simulations which suggests that this mechanism is an insignificant and impractical factor compared to other more significant factors.

Introduction

Groundwater is generally the most important freshwater resource in many coastal regions which are threatened by seawater intrusion (SWI) (Ataie-Ashtiani and Ketabchi, 2011, Ketabchi and Ataie-Ashtiani, 2015b). Climate change impacts such as sea-level rise (SLR) and precipitation variations that change recharge rates are the influential climatic factors that affect SWI (Werner et al., 2013, Ataie-Ashtiani et al., 2013a). The Intergovernmental Panel on Climate Change (IPCC, 2013) predicts that the global mean SLR may rise between 0.26 m and 0.82 m by the year 2100. A SLR in the range of 0.18–0.59 m was predicted by IPCC (2007) for a similar period. This shows a significant upward revision for SLR prediction between IPCC (2007) and IPCC (2013) and highlights the potential importance of SLR impacts on SWI.

Based on the assessments of IPCC (2013), annual mean precipitation can vary up to ±50% in the world. This range includes the estimate of projected uncertainties. The high latitudes and the equatorial Pacific Ocean are likely to experience an increase in annual mean precipitation by the end of this century. In many mid-latitude and subtropical arid regions, mean precipitation will likely decrease, while in many mid-latitude wet regions, mean precipitation will likely increase by the year 2100 (IPCC, 2013, Horton et al., 2014, Bring et al., 2015). Larger uncertainties surround the projections of surface runoff and recharge rate to groundwater resources, which are affected by many climatic factors, include changes in mean precipitation and temperature regimes. Further assessments have been provided by e.g. Holman, 2006, IPCC, 2013, and Bring et al. (2015).

Ketabchi and Ataie-Ashtiani, 2015b, Ketabchi and Ataie-Ashtiani, 2015c developed the efficient and robust decision models which have the superior abilities in terms of both solution quality and computational time criteria. Using such decision models, they highlighted a need for an integrated study to address how the conceptualization of climate change impacts e.g. SLR, land-surface inundation (LSI), and recharge rate variations can be handled on prospective coastal groundwater management strategies. Gorelick and Zheng (2015) emphasized that global changes such as climatic effects led to multiple stresses that should be considered in groundwater management plans. Ojha et al. (2015) assessed the long-term potential influences of climate change, e.g. SLR impacts in aquifers and efficient management of these resources in many regions of the world. They concluded that such studies are yet open challenges concerning uncertainties in modeling and in defining climate change scenarios, heterogeneities, estimation of recharge rate to groundwater systems, data challenges, and addressing the increasing threats from competing demands and mounting hydrologic stresses on groundwater systems, which all indicated a pressing need to develop effective management strategies.

The main objective of this study is to provide a systematic review of numerous previous studies and to then undertake an analysis of the relative importance of the purported influential factors controlling SWI. We present the literature review in tabulated and diagrammatic formats so as to be easily comprehensible and to easily identify what factors previous studies have and have not included. This is the first study that highlights the impacts of all of known SLR-induced influential factors and thus directs us to evaluate the relative importance of these impacts on SWI using both analytical and numerical methods. The SLR impacts on the SWI interface and in particular seawater toe location are the focus of this study. Such an integrated assessment does not exist because each previous study has only assessed a (different) subset of the purported controlling factors.

Section snippets

A review of previous studies

In recent years, there has been a growing body of research relating to climatic and hydrogeologic controls on SWI. It is not easy to rapidly discern the similarities and differences in these studies. Furthermore, it is also not immediately clear where current knowledge gaps might exist. Even more importantly, it is not indeed evident that any previous studies have conducted an integrated assessment to analyze the relative importance of the purported range of influential factors.

Recently,

Future research challenges

Based on the review, a list of future challenges is identified in this section. All previous studies have investigated a subset of controlling processes without considering many other ones that may be expected to exert a significant control on SWI processes. Integration of all the purported controlling factors studies in previous literature into a single, unifying, framework is required to conduct the fully-integrated analyses. Simultaneously examining many of the controlling factors, within

Integrated assessments using analytical modeling

The main objective in this section is to propose a simple tool for seawater toe location sensitivity assessments that are based on fundamental SWI mathematics as applied to a variety of idealized settings. Here, sensitivity refers to the relative propensity for SWI to occur. The basis of the methodology is that the rates of change in seawater toe location assessments in response to stress changes, described as partial derivatives of equations, offer insight into the propensity for SWI (Werner

Integrated assessments using numerical modeling

In this section, the saturated-unsaturated density-dependent flow and transport USGS code SUTRA (Voss and Provost, 2010) is employed. SUTRA (Voss and Provost, 2010) has been previously used by e.g. Michael et al., 2013, Ketabchi et al., 2014, Mahmoodzadeh et al., 2014, and Ketabchi and Ataie-Ashtiani (2015c) for investigating the SLR-induced SWI in coastal aquifers.

Schematized unconfined aquifer cross-sections (based on the presented data in Table 2) used for modeling with finite-element mesh

Conclusions

In order to better understand the previous research, current knowledge gaps, and opportunities for advancing the understanding of SLR impacts on SWI in more general terms, we first conducted a literature review with a greater focus on SLR-induced phenomena and the associated impacts. Therefore, the first review of previous literature is provided in a diagrammatic and tabular form on SWI in coastal aquifers. This review demonstrates that all studies to date have only investigated a subset of

Acknowledgments

The author Craig T. Simmons acknowledges funding support of the National Centre for Groundwater Research and Training, a collaborative initiative of the Australian Research Council and the National Water Commission, Australia. The authors appreciate the constructive comments of the reviewer, Dr. Antonis D. Koussis, three anonymous reviewers, and Editor-in-Chief Dr. Geoff Syme, which helped to improve the final version of this paper.

References (70)

  • C. Lu et al.

    Timescales of seawater intrusion and retreat

    Adv. Water Resour.

    (2013)
  • C. Lu et al.

    Seawater intrusion in response to sea-level rise in a coastal aquifer with a general-head inland boundary

    J. Hydrol.

    (2015)
  • D. Mahmoodzadeh et al.

    Conceptualization of a fresh groundwater lens influenced by climate change: a modeling study of an arid-region island in the Persian Gulf, Iran

    J. Hydrol.

    (2014)
  • A. Melloul et al.

    Hydrogeological changes in coastal aquifers due to sea level rise

    Ocean Coast. Manage.

    (2006)
  • L.K. Morgan et al.

    Seawater intrusion vulnerability indicators for freshwater lenses in strip islands

    J. Hydrol.

    (2014)
  • M.M. Rajabi et al.

    Sampling efficiency in Monte Carlo based uncertainty propagation strategies: application in seawater intrusion simulations

    Adv. Water Resour.

    (2014)
  • M.M. Rajabi et al.

    Polynomial chaos expansions for uncertainty propagation and moment independent sensitivity analysis of seawater intrusion simulations

    J. Hydrol.

    (2015)
  • M.M. Rajabi et al.

    Efficiency enhancement of optimized Latin hypercube sampling strategies: application to Monte Carlo uncertainty analysis and meta-modeling

    Adv. Water Resour.

    (2015)
  • P. Van der Veer

    Analytical solution for steady interface flow in a coastal aquifer involving a phreatic surface with precipitation

    J. Hydrol.

    (1977)
  • A.D. Werner et al.

    Seawater intrusion processes, investigation and management: recent advances and future challenges

    Adv. Water Resour.

    (2013)
  • B. Ataie-Ashtiani

    Comment on “Effects of tidal fluctuations on mixing and spreading in coastal aquifers: Homogeneous case” by María Pool et al.

    Water Resour. Res.

    (2015)
  • B. Ataie-Ashtiani et al.

    Elitist continuous ant colony optimization algorithm for optimal management of coastal aquifers

    Water Resour. Manage.

    (2011)
  • B. Ataie-Ashtiani et al.

    Optimal management of freshwater lens in a small island using surrogate models and evolutionary algorithms

    J. Hydrol. Eng.

    (2014)
  • B. Ataie-Ashtiani et al.

    How important is the impact of land-surface inundation on seawater intrusion caused by sea-level rise?

    Hydrogeol. J.

    (2013)
  • B. Ataie-Ashtiani et al.

    Inverse modeling for freshwater lens in small islands: Kish Island, Persian Gulf

    Hydrol. Process.

    (2013)
  • B. Ataie-Ashtiani et al.

    Tidal effects on groundwater dynamics in unconfined aquifers

    Hydrol. Process.

    (2001)
  • A. Bring et al.

    Implications of freshwater flux data from the CMIP5 multi-model output across a set of Northern Hemisphere drainage basins

    Earth’s Future

    (2015)
  • J.F. Carneiro et al.

    Evaluation of climate change effects in a coastal aquifer in Morocco using a density-dependent numerical model

    Environ. Earth Sci.

    (2010)
  • S.W. Chang et al.

    Experimental and numerical investigation of saltwater intrusion dynamics in flux-controlled groundwater systems

    Water Resour. Res.

    (2012)
  • R. Chesnaux

    Closed-form analytical solutions for assessing the consequences of sea-level rise on groundwater resources in sloping coastal aquifers

    Hydrogeol. J.

    (2015)
  • G. Ferguson et al.

    Vulnerability of coastal aquifers to groundwater use and climate change

    Nat. Clim. Change

    (2012)
  • T. Feseker

    Numerical studies on saltwater intrusion in a coastal aquifer in northwestern Germany

    Hydrogeol. J.

    (2007)
  • N.R. Green et al.

    An evaluation of the relative importance of the effects of climate change and groundwater extraction on seawater intrusion in coastal aquifers in Atlantic Canada

    Hydrogeol. J.

    (2014)
  • S.M. Gorelick et al.

    Global change and the groundwater management challenge

    Water Resour. Res.

    (2015)
  • I.P. Holman

    Climate change impacts on groundwater recharge-uncertainty, shortcomings, and the way forward?

    Hydrogeol. J.

    (2006)
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