http://www.vliz.be/imisdocs/publications/242609.pdf

Seawater intrusion processes, investigation and management: Recent advances and future challenges

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1856&context=usdaarsfacpub

Beneath the surface of global change: Impacts of climate change on groundwater

A solution is presented for the change in water level in a well of finite diameter after a known volume of water is suddenly injected or withdrawn. A set of type curves computed from this solution permits a determination of the transmissibility of the aquifer.

Response of a finite-diameter well to an instantaneous charge of water. Paper No. H-21

Community-level molecular techniques are widely used in comparative microbial ecology to assess the diversity of microbial communities and their response to changing environments. These include among others denaturing and temperature gradient gel electrophoresis (DGGE/TGGE), single-strand conformation polymorphism (SSCP), length heterogeneity-PCR (LH-PCR), terminal-restriction fragment length polymorphism (tRFLP) and 16S rRNA gene clone libraries. The amount of data derived from these techniques available in literature is continuously increasing and the lack of a universal way to interpret the raw fingerprint itself makes it difficult to compare between different results. Taking the DGGE technique as an example, we propose a setting-independent theoretical interpretation of the DGGE pattern, based on a straightforward processing on three levels of analysis: (i) the range-weighted richness (Rr) reflecting the carrying capacity of the system, (ii) the dynamics (Dy) reflecting the specific rate of species coming to significance, and (iii) functional organization (Fo), defined through a relation between the structure of a microbial community and its functionality. These Rr, Dy and Fo values, each representing a score to describe a microbial community, can be plotted in a 3D graph. The latter represents a visual ecological interpretation of the initial raw fingerprinting pattern.

How to get more out of molecular fingerprints: practical tools for microbial ecology.

Variable density flow and solute transport simulation of aquifer systems containing narrow transition zones between freshwater and saltwater requires particular attention to certain aspects of the numerical method and its application to be successful. Typically, only cases involving wide transition zones have been simulated with variable density transport models, possibly because of inaccuracies in the modeling approaches used. The major components of a successful approach are threefold. First, functionally consistent approximation of terms involved in fluid velocity calculations is necessary. In the case of Galerkin finite element methodology, a significant modification is required to the standard approach in order to achieve consistency. Second, the simulator must be verified in a particular series of tests. The usual tests using Henry's problem for verification of density-dependent transport simulators are inadequate to check for consistency of the velocity approximations and for the accuracy of simulating flow driven by bouyancy forces. Third, adequately fine spatial discretization is required when applying the simulator for spatial stability of the numerical transport solution and to allow accurate representation of narrow transition zones and the effects of low transverse dispersivity. The effectiveness of this approach is demonstrated through simulation of the flow of fresh and saline groundwater in the layered basalt aquifer of southern Oahu, Hawaii. The transition zone in this regional flow system is narrow except near the discharge area where it is broadly dispersed. Simulation of this common situation with an inconsistent approximation gives grossly incorrect results, while simulation with a consistent model provides a robust tool for analysis of system hydrology.

Variable density flow and solute transport simulation of regional aquifers containing a narrow freshwater‐saltwater transition zone

A salt water lens is found above fresh water under the shore between Dunkerque (France) and Nieuwpoort (Belgium). This inverse density distribution is in a dynamic equilibrium. It develops due to the infiltration of salt water on the back shore during high tide. Under this salt water lens, water infiltrated in the adjacent dune area flows towards the sea and discharges at the seabed. This water quality distribution differs from the classic salt water wedge under fresh water described in the literature. Here, the evolution to this water quality distribution is simulated with a density dependent numerical model. A large tidal range, shore morphology and a permeable groundwater reservoir are the main conditions for the observed water quality distribution. By altering these conditions, intermediate water quality distributions between the classic salt water wedge and the one discussed here develop. Based on these simulations, it is expected that similar kinds of inverse density distribution could be present in a number of coastal areas, which have tides, a gently sloping shore and a permeable substratum.

Occurrence of salt water above fresh water in dynamic equilibrium in a coastal groundwater flow system near De Panne, Belgium

Imaging artificial salt water infiltration using electrical resistivity tomography constrained by geostatistical data

Both heat and solute transport in porous media are described by partial differential equations of similar form. Nevertheless, observing these phenomena in the field on the scale of well tests clearly indicates dissimilar behaviour. This article studies the aforementioned transport processes by interpreting two push-pull tests of different duration. In both tests, chloride is applied as a conservative tracer and lower temperature water is injected in higher temperature pristine water at different flow rates. Simulation and interpretation of the tests are performed by means of ReacTrans, a two-dimensional, axially symmetric, finite-difference, solute and heat transport model. Since conflicting views exist in literature on the relation between solute and thermal dispersivity, analysis of field observations focuses on parameters which describe aquifer characteristics affecting these processes. Parameter estimation is conducted through sensitivity analysis and collinear diagnosis in order to identify derivable parameters. It is concluded that longitudinal solute dispersivity and thermal diffusivity could be inferred accurately from chloride and temperature data sampled from the injection/extraction well respectively. Involving supplementary data sampled from an observation well enables derivation of effective porosity from chloride data and thermal retardation from temperature data. Moreover, it is inferred that longitudinal solute dispersivity is scale dependent. Thermal diffusivity, however, seems not to be. This points to dissimilar development of transition zones during solute and heat transport. It is concluded that conductive transport of heat is much more important than effects of velocity variations through the pore space.

Conservative Solute Versus Heat Transport in Porous Media During Push-pull Tests

Parameter identification in fresh-saltwater flow based on borehole resistivities and freshwater head data

Water extractions in coastal areas have to deal with salt water intrusion and lowering of hydraulic heads in valuable ecosystems. Therefore, sustainable management of fresh water resources in these areas is crucial. This is illustrated here with two water extractions in the western Belgian coastal plain which extract groundwater from a phreatic dune aquifer. One water extraction faced problems with salt water intrusion, while lowering of hydraulic heads was an issue for both. To remedy the salt water intrusion, it was found that decreasing the extraction rate was the only solution. To offset this and to increase hydraulic heads around both extractions, it was decided to artificially recharge the aquifer of the second extraction with tertiary treated wastewater. By taking these interventions, the combined production capacity of the water extractions was increased with 56% whereas 27% less water was extracted from the dune aquifer itself. Extraction history and the effects of interventions are illustrated for both water extractions with water quality data and fresh water head observations. A more detailed insight in groundwater flow and fresh-salt water distribution in the aquifer is provided by simulating the evolution of the water extractions with a 3D density dependent groundwater flow model.

Luc Lebbe

Papers

Occurrence of salt water above fresh water in dynamic equilibrium in a coastal groundwater flow system near De Panne, Belgium

Imaging artificial salt water infiltration using electrical resistivity tomography constrained by geostatistical data

Conservative Solute Versus Heat Transport in Porous Media During Push-pull Tests

Parameter identification in fresh-saltwater flow based on borehole resistivities and freshwater head data

Sustainable groundwater extraction in coastal areas: a Belgian example