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close this bookConducting Environmental Impact Assessment in Developing Countries (UNU, 1999, 375 pages)
close this folder5. EIA tools
close this folder5.1 Impact prediction
View the document(introduction...)
View the document5.1.1 Application of methods to different levels of prediction
Open this folder and view contents5.1.2 Informal modelling
View the document5.1.3 Physical models
View the document5.1.4 Mathematical models
View the document5.1.5 Modelling procedure
View the document5.1.6 Sensitivity analysis
View the document5.1.7 Probabilistic modelling
View the document5.1.8 Points to be considered when selecting a prediction model
View the document5.1.9 Difficulties in prediction
Open this folder and view contents5.1.10 Auditing of EIAs
View the document5.1.11 Precision in prediction and decision resolution

5.1.3 Physical models

In physical models the environment is simulated at a reduced scale. Physical models can be either two or three dimensional. Illustrative models simply present a visual image of the environment before and/or after implementation of the activity by sketches, photographs, cinefilms, or 3D models. They can be used to illustrate the effect of activities on the visual environment.

In working physical models the processes which occur in the environment are simulated at a reduced scale. When the proposed activity is simulated in the model (e.g., the release of a substance or a change in morphology) the resulting changes can be observed and measured in the model. Working physical models are used to predict air, water, and noise effects, either by direct simulation or by analogy. Direct simulation modelling is carried out in wind tunnels, wave chambers, and similar facilities. In analogy models, the environmental medium or the source is simulated using another medium (e.g., water to simulate water flows).

For a model to correctly represent all the phenomena and physical processes occurring in the environment, different conditions must be met with regard to scale. Usually it is not possible to satisfy all these conditions at the same time. As a result, most models are a compromise in which mistakes arising from scaling are minimized. In some circumstances it may be necessary to construct more than one model to overcome different scaling problems.

Most modelling exercises are carried out in ready-built facilities which are adapted to suit the particular requirements of a prediction. Such facilities are available at both public and private research organizations. However, in some circumstances special facilities must be constructed.