Physical Processes - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 42

3.4.4 Initial and Boundary Conditions
3.4.4.1 Initial Conditions
3.4.4.2 Conditions on Material Boundaries
3.4.4.3 Conditions on Open Boundaries
3.4.4.4 Conditions on the Sea Surface and the Sea Bottom
3.5 Boundary Processes
3.5.1 Bottom Processes
3.5.1.1 Bottom Shear Stress
3.5.1.2 Other Bottom Processes
3.5.2 Solid Boundary Processes
3.5.3 Free Surface Processes
3.5.3.1 Mass Exchange
3.5.3.2 Momentum Exchange
3.5.3.3 Energy Exchange
3.5.4 Cohesive and Noncohesive Sediment Processes
Bibliography

3.1 INTRODUCTION TO TRANSPORT PHENOMENA

Chapter 2 concluded that the calculation of spatio-temporal distribution of major
components of a lagoon's hydrogeomorphological unit and biocoenose is important
for the description of the structure and function dynamics (productivity and carrying
capacity) of the lagoon system and, consequently, for sustainable management. This
concept is required to understand the transport phenomena that describe the evolution
of properties due to fluid motion (advection) and/or molecular and turbulent dynam-
ics (diffusion). In the case of turbulent flows the small-scale motion of the fluid
particles is actually random, and this nonresolved advection is also treated as diffu-
sion (eddy diffusion).
A mathematical description of the transport phenomena (transport equations) is
based on the concept of conservation principle, which is valid in any application.
Conservation principle can be stated as

{The rate of accumulation of a property inside a control volume}

= {what flows in minus what flows out} + {production minus consumption}

Using this conservation principle, transport equations for any property inside a
control volume can be derived if production and consumption mechanisms are known
and if the control volume and transport processes are quantified. The control volume
is presented as the largest volume for which one can consider the interior properties
as uniformly distributed as well as fluxes across the surface.
In previous coastal lagoon studies the control volume was often implicitly
defined as the whole lagoon. Concepts of residence and flushing time were derived
from this global approach ( see Chapter 5 for details). In that case, only fluxes at
the boundaries were required. This type of integral approach cannot describe
gradients and is consequently not sufficient to support process-oriented research