Department of Civil Engineering

Auburn University

Understanding the mixing dynamics of dense water within freshwater aquifer systems is an important fundamental research problem.  Analysis of this problem requires the simulation of density coupled flow processes in the presence of both stable (e.g., saltwater intrusion) and unstable (e.g., tsunami/hurricane invasion, dense leachate discharges from landfills or salt ponds) interface conditions.  In this work, we will present multiple experimental datasets to illustrate the dynamics of density coupled flow in saturated groundwater systems under conditions involving stable and/or unstable (or conditionally stable) interfaces.   These datasets are useful for visualizing the fate and transport of the dense fluid discharged within a saturated porous media formation.  In addition, these datasets can also serve as benchmark problems for testing numerical formulations.

The first set of experiments focused on studying the transport patterns of a saltwater wedge within a freshwater aquifer using a laboratory-scale, porous media tank.  Three types of experiments were performed to develop: a) steady-state salt wedge data observed under different hydraulic gradient conditions; b) transient salt wedge data observed under intruding wedge conditions; and c) transient salt wedge data observed under receding wedge conditions.  A numerical model was used to simulate these datasets.  The model results along with the experimental data are presented as benchmark problems for testing density-coupled groundwater flow models.  A worthiness analysis was completed to test the sensitivity of the experimental problem to density coupling effects.  The results of the analysis show that proposed benchmark is a more robust alternative to the traditional Henry problem.  The new experimental datasets can be used to assess the performance of saltwater intrusion models under both steady-state and transient conditions.

The second set of experiments focused on investigating the fate and transport of saltwater deposited by a tsunami wave into a coastal unconfined aquifer.  The laboratory analysis included three types of contaminant sources: (i) a pond-type source, (ii) a beach infiltration source, and iii) a well source.  These sources were specifically used to model the contamination scenarios that could have occurred in the coastal regions of India and Sri Lanka during the December 2004 tsunami event.  The results show that three types of plumes, namely stable, unstable, and highly-unstable plumes, can evolve from the dense saltwater discharged on the top of an unconfined water table.  Among the three plumes the highly unstable plume, which is also a slow moving plume, appears to be the most hazardous since it has the potential to penetrate deep into an aquifer and contaminate a relatively larger aquifer volume.  This experimental dataset provides a preliminary conceptual model for saltwater transport after a tsunami- or hurricane event in a coastal aquifer.

Dr. Prabhakar Clement is a professor and also hold the distinguished Arthur H. Feagin Chair position at the Department of Civil Engineering, Auburn University, Alabama, USA.   Before joining Auburn University, Dr. Clement worked as a senior research engineer at the Battelle Pacific Northwest National Laboratory for over six years and later as a senior lecturer at the Department of Environmental Engineering, University of Western Australia for three years.  Dr. Clement is the lead author of the widely used reactive transport code RT3D; he is also a co-author of the EPA’s natural attenuation screening tool BIOCHLOR.  His current research interests include development of laboratory scale models to visualize groundwater transport processes, modeling of density-coupled flow problems, numerical modeling of metals transport involving surface complexation reactions, derivation of analytical solutions to reactive transport equations, and management of erosion in engineered hydrological systems.  He has authored over fifty peer-reviewed journal articles.  Web site: http://www.eng.auburn.edu/users/clemept/