Modeling Concepts - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 245

to be uniform in its interior” is violated. This does not happen when half of the cell
has matter and the other half does not. If the plume were contained inside many
cells the problem would still exist but only in the plume limits and hence would not
deteriorate the solution.

6.3 PRE-MODELING ANALYSIS AND MODEL SELECTION

6.3.1 H YDROGRAPHIC C LASSIFICATION

Characteristics of lagoons around the world are very different. Geomorphological
characteristics depend on the type of shore, while hydrological characteristics
are determined by marine influence and hydrological balance for the lagoon
drainage basin. Lagoons with similar morphometry may exhibit completely dif-
ferent behavior in different ambient conditions. A careful classification of the
lagoon type according to its geomorphology, hydrology, and mixing processes is
a desirable first step toward the choice of the most appropriate physics to be
included in the numerical model. The proper identification of a lagoon type allows
the user to find a similar lagoon in another part of the world and benefit from
the previous knowledge available for that lagoon. At the same time, the hydro-
graphic classification database will be supplemented with new information that
can be used for future studies in similar lagoons. It is very tempting to classify
a lagoon according to its hydrographic features, i.e., utilizing only basic infor-
mation on its morphometry and hydrology, which is usually available without
additional field studies.
A proper lagoon, such as an atoll lagoon or a coastal lagoon (enclosed and much
more shallow than the adjacent marine area coastal water body and separated from
the marine area by an accumulative barrier), is a pure type of coastal water body.
The majority of coastal waters are a mixture of such pure types, open bay, proper
lagoon, and fjord (all of them without river outfall), and rivers ( Figure 6.7) , and
exhibit the features of estuaries, the most widely investigated and most popular
coastal water bodies. The hydromorphometric tetrahedron (Figure 6.7) provides the
conventional coordinate system where any coastal water body may be described as
a combination of the above pure forms and its position is expressed through specific
quantitative characteristics.

6.3.1.1 Morphometric Parameters

Lagoons around the world have various shapes and bottom relief configurations
that can change in the short run with time under the influence of tides, floods,
erosion/deposition, wind surges, and seasonal run-off. As a start, it is convenient
to consider a lagoon in terms of the classification proposed by Kjerfve, 2 which may
highlight some of its hydrographic features. According to this classification, lagoons
are divided into three types: choked lagoons, restricted lagoons, and leaky lagoons.
The type of lagoon is determined by the water exchanges with the adjacent coastal
sea, in the presence of tides and wind-driven circulation. 3 Related geomorphic