Modeling Concepts - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 283

Environmental impact assessments. Here , a set of scenarios is examined using
some criterion in order to find the best solution to an environmental prob-
lem. Usually, time-dependent model solutions resulting from some forcing
factor (e.g., new positions of wastewater inlets or some dredging work in
the lagoon) are compared to a “basic state,” which corresponds to some
initial reference situation. These can be the situations of previous years,
the absence of wastewater inlets, or other situations. Both the scenario and
the basic solution usually represent the diurnal, synoptic, seasonal, annual,
or inter-annual variability of the variables under study. These variables have
to be identified in the formulation of the objectives.
Long-term forecast modeling. Here, the model solution is obtained from long-
term forecasts of the driving forces. The accuracy and confidence of a
forecast model will depend on both the accuracy of the driving forces
forecast and on the model sensitivity to these forces.
Operational modeling

This type of modeling is used to provide real-time or
short-term forecasts on the basis of real-time weather and boundary data
measurements. For example, operational modeling can provide real-time
information on daily currents and waves in a lagoon for safe navigation,
fishing, or recreational activities. Operational modeling is also needed for
contingency analysis (e.g., in the event of an oil spill), when the transport
model solution must be available immediately. In this case, the constraints
on the solution accuracy and the simulation time are very high because the
model results are needed quickly for emergency actions, which are usually
very expensive.
Diagnostic analysis or analysis with data assimilation . During this analysis
the spatial distributions of some variables are obtained by imposing existing
data on other variable distributions. One example is the study of the volume
flux structure resulting from an imposed (constant or variable) density
distribution to the model throughout the simulation.
Basic studies of the hydrodynamic and transport processes in a lagoon . In this
case, all physical factors affecting these processes are studied. The
researcher's task is to seek model solutions for some simple initial and
boundary conditions (e.g., annual average wind and river discharge, on simple
tidal mode) and to understand the lagoon response to the various factors. For
example, the model can be used to compare current patterns caused only by
river discharge, or by wind action, or by tidal inflow/outflow. Another example
is the study of the influence of the Coriolis force on currents and transport
in the lagoon.

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The above list indicates some of the main types of environmental analysis tasks
that can be solved by numerical modeling. Real practical applications, which are
more diverse, usually will fall into one of the above types of modeling activities.

6.3.5 R ECOMMENDATIONS FOR M ODEL S ELECTION

The information presented here should help the readers get their bearings in the choice
of model. In the authors' opinion, it is not possible to make rigid recommendations