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Tidal boundary conditions in SEAWAT
Ann E Mulligan1, Christian Langevin, Vincent E A Post
1Marine Policy Center, MS-41, Woods Hole Oceanographic Institution, Wood Hole, MA 02543, USA. amulligan@whoi.edu
Ground Water
|February 1, 2011
Summary
This study compares seven methods for modeling tidal effects on coastal aquifers using SEAWAT. The General Head Boundary (GHB) method is recommended for simulating tidal flats, especially on gentle slopes.
Area of Science:
- Hydrogeology
- Coastal processes
- Numerical modeling
Background:
- Coastal aquifers are influenced by tidal motion, impacting groundwater flow and salinity.
- SEAWAT is a common tool for modeling these effects, but optimal tidal boundary simulation methods are unclear.
Purpose of the Study:
- To compare the effectiveness of seven different methods for simulating tidal boundaries in coastal aquifers using SEAWAT.
- To provide guidelines for selecting the most appropriate tidal boundary condition based on coastal geomorphology.
Main Methods:
- SEAWAT code was used to simulate groundwater flow and solute transport.
- Seven distinct methods were tested to represent the ocean-aquifer interface, including high-hydraulic conductivity zones, General Head Boundary (GHB), and Periodic Boundary Condition (PBC) packages.
- Simulations were conducted for both sloping beach and tidal flat scenarios.
Main Results:
- All tested methods showed similar water fluxes on steep beach slopes.
- Simulating a seepage face increased intertidal fluxes and affected nearshore salinity.
- For tidal flats, the General Head Boundary (GHB) method demonstrated less delay in tidal signal propagation and inundation compared to high-K and PBC methods, particularly on gentle slopes.
Conclusions:
- The choice of tidal boundary condition significantly impacts coastal aquifer simulations, especially on tidal flats.
- The General Head Boundary (GHB) approach is preferable for simulating tidal flats with decreasing ocean-aquifer interface slopes.
- High-K and PBC methods may yield less accurate results in low-slope environments due to SEAWAT's inability to simulate unsaturated flow.
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