A study prepared for the Ministry of Environment in the Netherlands involved the examination of 140 case studies of EIAs and related studies (Environmental Resources Limited 1982). The objectives were to identify predictive techniques used in the practice of EIAs, prepare descriptions of the techniques, and classify the techniques in terms of the effect predicted and the method used. A total of 280 predictive techniques were identified and broadly classified for use in determining effects on the atmospheric environment, effects on the surface aquatic environment, effects on the subsurface environment (groundwater and soils), effects on the acoustic environment, direct effects on plants and animals, direct effects on landscape, and accidental effects. Table 2.4.1 contains a summary of the different types of methods used in predictive techniques for each of the seven main effect groups (Environmental Resources Limited 1982). The identified methods can be divided into experimental methods, mathematical models, and survey techniques. Table 2.4.2 displays a systematic grouping of prediction techniques (Environmental Resources Limited 1982).
Experimental methods used for prediction include physical models, field experiments, and laboratory experiments. Physical models include scaled-down representations, in two or three dimensions, of the study area after an activity has been implemented. Field experiments refer to in situ tracer experiments where tracers are used to predict the behavior of releases to surface waters (usually marine) or to groundwater. Laboratory experiments refer to bioassay methods to determine the effect of pollution on a particular species. Standard toxicological methods are used to determine the effect of a pollutant (or mix of pollutants) in water on a species, usually fish. Laboratory experiments are useful where no data exist on the effect of a pollutant on plants or animals. An advantage is that these experiments can be set up to represent the environment in which the effect may occur by using, for example, water from the river to which a pollutant is discharged.
Mathematical models refer to predictive techniques which use mathematical relationships between system variables to describe the way an environmental system reacts to an external influence. Mathematical models can be divided into those models which are empirical or "blackbox" models, where the relationships between inputs and outputs are established from analysis of observations in the environment; and those models which are internally descriptive, that is, where the mathematical relationships within the model are based on some understanding of the mechanisms of the processes occurring in the environment.
Survey techniques are based on the identification and quantification of existing or future aspects of the environment that might be affected, in terms of their sensitivity to change or of the importance of their loss or disturbance. The three main groups of survey techniques include inventory techniques, evaluation techniques, and visibility techniques.
Inventory techniques involve determining the distribution of things which may be affected by an activity (receptors) usually because of their proximity to an activity. Evaluation techniques refer to surveys to determine the
TABLE 2.4.1 METHODS USED IN PREDICTIVE TECHNIQUES FOR DIFFERENT EFFECTS (ENVIRONMENTAL RESOURCES LIMITED 1982)
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