Evaluating seawater intrusion at the regional scale in intensely exploited coastal aquifers

Katerina Mazi, Georgia Destouni and Antonis Koussis

Stockholm University National Observatory of Athens

NGL ANNUAL SCIENCE MEETING Oskarshamn, 7-8th of November 2013

Causes of seawater intrusion in coastal aquifers

➪ Heavy exploitation of coastal aquifers, especially in semi-arid regions, due to Population concentration in coastal zones Groundwater-based water supply Intense economic activities, in particular agriculture.

➪ Concerns due to climate change Sea level rise Decline of recharge.

NGL ANNUAL SCIENCE MEETING, Oskarshamn, 2013

Modelling characteristics

➪ Regional-scale analysis

➪ 1st order vulnerability assessments

➪ Sharp-interface analytical solution

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Comparison of analytical sharp-interface solution to SUTRA results: Example application to the Akrotiri Aquifer, Cyprus

NGL ANNUAL SCIENCE MEETING, Oskarshamn, 2013

Zone of fresh water

flowZone of interface flow

l

sea

recharge

toe

inclined aquifer base - impervious

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inland boundary

outflow

intrudingseawater

fresh groundwateroutflow

sea

recharge

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water flowZone of interface flow

intrudingseawater

fresh groundwater

groundwater extraction

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water flow

Zone of interface flow

intrudingseawater

fresh groundwateroutflow

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Full seawater intrusion

groundwater extraction

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intrudingseawater

NGL ANNUAL SCIENCE MEETING, Oskarshamn, 2013

Thresholds beyond which seawater intrusion shifts abruptly from a stable state of moderate seawater intrusion and mild change responses to stresses, to a new stable state of complete seawater intrusion into the coastal aquifer.

Tipping points

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Mazi et al., 2013

Generalized analytical 1-D sharp-interface model

Koussis et al., 2012

K

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l

sea

recharge

zone of fresh water

flowzone of interface flow

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aquifer boundary

Limiting condition: lT/lw = 1

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gw dividewell

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Well intrusionNGL ANNUAL SCIENCE MEETING, Oskarshamn, 2013

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zone of fresh water

flowzone of interface flow

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aquifer boundary

Limiting condition: lT/lDIV = 1

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gw divide well

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Complete aquifer intrusionNGL ANNUAL SCIENCE MEETING, Oskarshamn, 2013

For analysing the resilience/vulnerability of different coastal aquifers to seawater intrusion, we developed performance curves, that show how the toe of the interface changes depending on the discharge conditions in the aquifer.

Performance curves and limiting conditions

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Intensely exploited regional Mediterranean aquifers

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Nile Delta Aquifer

(1)

(2)

Middle Nile Deltaslope of impervious aquifer base sinφ = 0.003 head at the inland boundary = 14 mK = 100 m/daquifer length = 175 kmaquifer depth at the coastline = 740 mnet recharge rate = 10 mm/yr

East Nile Deltaslope of impervious aquifer base sinφ = 0.004head at the inland boundary = 14 mK = 120 m/daquifer length = 180 kmaquifer depth at the coastline = 910 mnet recharge rate = 10 mm/yr

NGL ANNUAL SCIENCE MEETING, Oskarshamn, 2013

Nile Delta Aquifer – Performance curves

Current pumping: 2.4 billion m3/yr

pumping in the 50’s: 0

pumping in the 90’s: 1.92 billion m3/yr

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The site-specific vulnerability assessments show that the advance of seawater currently seriously threatens the Nile Delta Aquifer.

The inland boundary head must here be sustained at any cost, as even a 10% decline will cause sea intrusion advancement by around 5-8 km and a 20% decline may bring the NDA to its tipping point of complete aquifer intrusion.

Nile Delta Aquifer - Results

NGL ANNUAL SCIENCE MEETING, Oskarshamn, 2013

Israel Coastal Aquifer

Concept of Aquifer Modelinclined impervious aquifer base sinφ = 0.01 no-flow inland boundaryK = 30 m/daquifer length = 20 kmaquifer depth at the coastline = 200 mgroundwater recharge rate = 240 mm/yr

NGL ANNUAL SCIENCE MEETING, Oskarshamn, 2013

Israel Coastal Aquifer – Performance curves

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brackish water

The current pumping location allows for a marginal increase of groundwater abstractions.

The maximum pumping could here be increased by about 20% if the pumping location were moved more inland, at least at lw = 5 km from the coast, thereby allowing a groundwater divide to form down-gradient. However, complete aquifer intrusion could occur if that maximum pumping rate were exceeded.

Israel Coastal Aquifer - Results

NGL ANNUAL SCIENCE MEETING, Oskarshamn, 2013

3.39E-21 5.00E-06 1.00E-05 1.50E-05 2.00E-050

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Normalised pumping from the aquifer

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eA virtual Coastal Aquifer at the Baltic Sea – Performance curves

NGL ANNUAL SCIENCE MEETING, Oskarshamn, 2013

max pumping: 3200 m3/m/yr

max pumping: 4200 m3/m/yr

Pumping at 3 km

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Normalised remaining groundwater flow from the pumping location

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eComparison of performance curves for the Mediterranean and Baltic Sea aquifers

lw/L

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0.4brackish water

well intrusion

complete intrusion

Mediterranean aquifer

Baltic Sea aquifer

NGL ANNUAL SCIENCE MEETING, Oskarshamn, 2013

The generalized analytical sharp-interface model, with its simple yet realistic conceptualization of coastal aquifers, is suitable for first-order assessments of vulnerability to seawater intrusion.

Thus, aquifer management options in the Baltic, e.g. in the Oskarshamn region, could be explored and the exploitation limits and corresponding vulnerability to seawater intrusion could be assessed.

Furthermore, the detailed and reliable data that a research facility like NGL can provide could be used to field-test these model solutions in a controlled local setting. The combined local-regional test experience and the knowledge derived from it could be then transferred to coastal aquifers around the world.

Concluding remarks

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