INTEGRATING TOOLS FOR SURFACE WATER QUALITY MANAGEMENT - Integrating GIS, Remote Sensing, and Mathematical Modelling for Surface Water Quality Management - page 53

Table (3-1): Indicators for selection of water quality models.
(source: world bank, 1998)
The level of detail required from modelling can vary tremendously across different management
applications. At one extreme, there might be an interest in the long-term impact of a small industrial
plant on dissolved oxygen in a small, well-mixed lake. This type of problem can be addressed with a
simple spreadsheet and solved by a single analyst in a month or less. At the other extreme, as an
example, if there is a need to know the rate of change in heavy metal concentrations in the
Mediterranean Sea that can be expected from industrial and agricultural practices in the Nile Delta, the
task will probably require many person-years of effort with extremely complex models and may cost a
lot of money.
For indicators of aerobic status, such as biochemical oxygen demand (BOD), dissolved oxygen, and
temperature, simple, well-established models can be used to predict long-term average changes in
rivers, streams, and moderate-size lakes. The behaviour of these models is well understood and has
been studied more intensively than have other parameters. Basic nutrient indicators such as ammonia,
nitrate, and phosphate concentrations can also be predicted reasonably accurately, at least for simpler
water bodies such as rivers and moderate-size lakes. Predicting algae concentrations accurately is
somewhat more difficult but is commonly done in the United States and Europe, where eutrophication
has become a concern in the past two decades. Toxic organic compounds and heavy metals are much
more problematic. Although some of the models reviewed below do include these materials, their
behaviour in the environment is still an area of active research. Models can cover only a limited
number of pollutants. In selecting parameters for the model, care should be taken to choose pollutants
that are of concern and are also representative of the broader set of substances which cannot all be
modelled in detail.