Geology Reference
In-Depth Information
This method is of primary interest to the exploitant of a water well, as it
enables a direct evaluation of the reserve in the part of the aquifer directly
connected to the pumping well. It can be complemented by appropriate
research (tracer tests and physical and chemical monitoring), enabling a
very good optimisation of our knowledge of karst aquifers, with the goal
of actually managing their groundwater resources over both time and
space. Two different examples of this method's applications are presented
in chapter C5 (Mangan, 2000).
8 MODELLING GROUNDWATER FLOW
Porous environments, in which the three-dimensional distribution of
properties is the most easily predicted, were the fi rst type of aquifer
examined through numerical modelling.
Depending on the quality and amount of quantitative data gathered
for an aquifer, several types of models can be created.
8.1 Deterministic models
These use the hydraulic equation describing a porous medium, and consider
the intergranular medium to be continuous. Their goal is to mimic the
functioning of the aquifer: knowing its geometric parameters, its porosity,
its transmissivity, its permeability, and its storativity, the model can simulate
the impact of recharge (precipitation, stream losses) on the piezometry of
the aquifer. The different phases of model construction are:
the vertical and spatial discretisation of parameters in space (geographic
gridding, Figure 89);
the referencing of piezometric data (correlation between observed
and calculated values)—this operation requires back-and-forthing
between the results obtained and the hypotheses made based on the
parameters;
the predictive simulation of natural or artifi cial scenarios (fl ooding,
drought, climate change, pumping, artifi cial recharge). They rely on
three basic principles: conservation of mass from one grid square to
another, fl ow according to Darcy's Law, and the elastic behavior of
water. Deterministic models solve the diffusivity equation:
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