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

• Published in: Journal of hydrology (Amsterdam) Vol. 535; pp. 235 - 255
• Main Authors: Ketabchi, Hamed, Mahmoodzadeh, Davood, Ataie-Ashtiani, Behzad, Simmons, Craig T.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-04-2016
• Subjects: Aquifers; Climate change; Coastal; Coastal aquifers; Groundwater; Hydraulics; Marine; Mathematical models; Recharging; Sea water; Sea-level rise; Seawater intrusion; Slopes; Climate change; Seawater intrusion; Groundwater; Coastal aquifers; Sea-level rise
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2016.01.083

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•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.
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.