Monitoring Program Design - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 322

Precise parameterization of diffusion will not improve the model solution accu-
racy for prediction of distribution of chemical substances over the lagoon if the
chemical loading from coastal sources (boundary conditions) is only roughly esti-
mated. Internal model parameters preferably have to be free for model tuning, and
field experiments on measurements have to determine only the range of its variations.
The final list regarding what internal parameters are to be used for calibration should
be defined by sensitivity analysis and/or for some specific practical reasons ( see
Chapter 6 for details).
How does one choose calibrated variables? In general, the model has to be
calibrated against all the variables simulated, but this calibration should be closely
connected with the objectives and spatio-temporal scale of expected model solutions.
If the objective of the modeling is the prediction of the hot water plume mixing in
the vicinity of a power plant inlet/outlet, it is senseless to expend great effort to
achieve the same accuracy for model solution in the entire lagoon. In this case the
calibration series for temperature (not for currents) has to be measured mostly in
the focus area, but during a rather long period, for example, 1 year.
We now try to emphasize the essential minimum for calibrated variables that
can ensure correct model tuning.

• Water level is an important variable both for water exchange and for

currents and transport problems. Water level variations (Table 7.1) should
be measured at a frequency according to tidal variations or once an hour
for random wind surge, but in any case not fewer than four times a day.
The tide gauges have to be sited at the lagoon entrance and at several
points around the lagoon coast to reveal the local inter-lagoon level incli-
nation and internal level variations. In the case of significant river inflow,
level measurements at the river mouth are very important. The measure-
ment technique is standard and well described in a number of national
manuals (e.g., National Engineering Handbook 11 ).

• Direct uninterrupted current measurements aimed at calibration are usu-

ally held during periods ranging from several tidal periods up to 2-3
months at several points in the lagoon simultaneously. The interval of
measurements depends on equipment used and its positioning, but often
it is 5-60 s if short-period pulsations are taken into consideration or 5-15
min if the general flow is rather stable. Generally speaking, the measure-
ment interval should be selected according to the scale of time averaging
used in the task considered. For example, Kundu 12 showed that the influ-
ence of the Coriolis force becomes significant after t > 0.25 f −1 (where f
is a Coriolis parameter). In this case, current adjustment time is in the
range of 2 3 / 4 h-30 min for lagoons at latitudes in the range of 10-75 ,

respectively, and at least 5 to 10 measuring casts are required to resolve
the characteristic time of current adjustment to wind variations (see
Chapter 6).

°

Due to high variability of currents in the lagoon area it is very important to find
the optimal positioning for current meters: on the one hand, their sites should