A Case Study of Finite-Element A Case Study of Finite-Element Numerical Modeling on Salt Numerical Modeling on Salt Water Intrusion for the Ping-Water Intrusion for the Ping-

Tung PlainTung Plain

Jing-Yea Yang, Ph.D., P.E.Stanley Consultants Inc.

Major Streams Showing Gaining, Losing, and Neutral Boundary Types

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Conceptual Cross Section through Proposed Dam/Reservoir at Mei Nanu

Conceptual Cross Section through Proposed Dam/Reservoir at Ma Chia

PROJECT OVERVIEWPROJECT OVERVIEW

GOALGOAL

Development of Numerical Model as a tool for Strategic Long-Term

Management of both Groundwater and Surface Water Resources.

PHASED SCOPESPHASED SCOPES

PHASE I: CONCEPTUAL MODELING

PHASE II: DEVELOPMENT OF NUMERICAL MODEL

PHASE III: SIMULATION OF RESERVOIR/WEIR CONSTRUCTION EFFECTS

PHASE IV: SIMULATION OF SALTWATER INTRUSION

Aquifer Hydraulic Conductivities in the Upper Aquifer, Including Both Unconfined and Confined

Fence Diagram

Finite-Element Numerical Model

• FEMWATER• 9070 triangular elements• 5291 nodes• Mesh extended offshore to

include shelf area• Visualized in 3D Using GMS

developed by US DOD

Soil Types

Numerical Model Mesh and Boundary Conditions

Boundary Conditions

Constant Heads Constant Concentrations

Rainfall Pumping

Model Water Levels

Chloride Extent in Groundwater

Calibrated Chloride Concentrations

Simulation Results

CONCLUSIONCONCLUSION

• The advancing chloride front will move North.

•Deeper aquifers in the areas near the mouths of the Kaoping and Tung Kang Creeks will experience increases in Cl¯.

•Shallow Aquifers already have significant damage.

•The rate of increase in Cl¯ is lower in SE part.

•Cl¯ will increase with well depth.

•The fisheries industry is the major cause of seawater intrusion.

Questions…. ?