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New Concepts for Groundwater Modelingin the Floridan Aquifer

Todd R. Kincaid, Ph.D.Timothy J. Hazlett, Ph.D.

Hazlett-Kincaid, Inc.www.hazlett-kincaid.com

Global Underwater Explorerswww.gue.com

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Problem Overview

• Degrading groundwater quality & increased demand

• Awareness

• Incorporating caves into predictive models & management strategies

- Photo by Wes Skiles

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Facts from the Field

• 27 (>1/3) of the 78 largestsprings in North America discharge from the Floridan Aquifer

• Average dischargefrom those springs> 6.5 billion gpd

• All of those springs discharge from mapped underwater cave systems

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Permeability (K) Issues

Porous Media Assumptions• Flow through single media• Standard approach• Isotropy (Kx=Ky=Kz)• Radial flow to wells & spring

Fractured Rock & Karst• Flow through 2 or 3 media• Anisotropic (Kx=Ky=Kz)• Flow trough fractures or conduits

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Permeability in the Floridan Aquifer

Modified Double Porosity Model • High matrix permeability• Large and extensive dissolved conduits• Fractures of lesser importance

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Cave Types in the Floridan AquiferFlow-dominated

Storage-dominated

• discharge to springs• fast through-flow• e.g. - Wakulla, Ichetucknee, Manatee, Blue Springs, etc.

• no surface discharge• slow through-flow• e.g. - Dipolder, Blue Grotto Gunpowder, 40 Fathom Grotto, etc.

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Woodville Karst Plain

• dual porosity system (matrix & conduit)• rapid recharge through sinkholes• discharge at springs

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Hydraulic Cave Development Model

(Huntoon, 1984)

• cave orientation function of flow system not geology• caves aligned w/ gradient• caves will be smaller and more branched up-gradient• feedback loop between gradient & conduits

• Caves can be included in groundwater flow models provided the model can handle permeability contrast

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Potentials for Groundwater Modeling

Improved Predictions• groundwater flow patterns & velocities• spring catchment areas• contaminant transport times

Probable Cave Locations• iterative modeling

Understanding Cave Development

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Preliminary Modeling

Wakulla Spring Sub-basinAdvanced Technology• finite-element grid• embraces anisotropy• high permeability contrasts• calibrate to spring discharge

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Preliminary Modeling – Hydraulic Head

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Preliminary Modeling - Velocity

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Preliminary Simulation – Particle Tracks

Wakulla Spring

Standard Methods / Modeling Our Modeling Including Cave

Wakulla Spring

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Work in Progress

- Photo by Wes Skiles

Applied • groundwater model of the Wakulla Spring sub-basin• adaptation to other spring basins

Theoretical • collaboration with FSU• developing new modeling code

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Concluding RemarksCritical Issue

• Aquifer Protection

– Contamination

– Over use

Critical Areas

• Suwannee River Basin

– Degrading water quality

• North Florida

– Aquifer management

Need

• Improved predictive capabilities - modeling that includes conduit flow

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