Identifier

etd-03302007-173916

Degree

Master of Science in Civil Engineering (MSCE)

Department

Civil and Environmental Engineering

Document Type

Thesis

Abstract

This study develops a saltwater intrusion simulation model using a lattice Boltzmann method (LBM) in a two-dimensional coastal confined aquifer. The saltwater intrusion is described by density-dependent groundwater flow and mass transport equations, where a freshwater-saltwater mixing zone is considered. The problem is formulated in terms of hydraulic head instead of pressure, which is recommended in those cases where static pressures dominate to reduce computational cost. The aquifer heterogeneity is explicitly a function of the speed of sound, relaxation parameter and time steps in the LBM. This study explores the equivalent squared sound speed to deal with the spatial-temporal heterogeneity arising from the inhomogeneous hydraulic conductivity and fluid density to update the equilibrium distribution functions in each time step. The Henry problem and its variants are used to demonstrate the LBM applicability to solve the saltwater intrusion problem. The inverse relationship between the time step and diffusion coefficient results in a very small time step for the groundwater flow problem due to the high hydraulic diffusion coefficient. The study demonstrates the ease of implementing the LBM to different salt concentration boundary conditions at the seaside and shows that the isochlors distributions are significantly different. Due to doubts regarding the validity of the Henry problem to test variable-density flows, numerical simulation of freshwater injection into a sediment saturated with saltwater have been carried out, showing the capability of the LBM to represent strong buoyancy effects. Some examples with correlated and uncorrelated random hydraulic conductivity (K) distributions show reasonable flow fields and isochlors distributions. It was found in the Henry problem that completely random heterogeneity in K is insignificant in changing the scale of the saltwater intrusion from that predicted using the mean K value. However, the correlated K field may have significant impact on the saltwater intrusion, resulting different from that obtained by the mean K field.

Date

2007

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Frank T. C. Tsai

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