Methods of EIA
- Adhoc method
- Checklist method
- Matrix method
- Network method
- Overlay method
- Environmental index using factor analysis
- Cost/Benefit analysis
- Predictive or Simulation methods
These methods might vary from:
Simple to Complex
Static piece-meal approach to Dynamic nature of the environment
The change in EIA is moving away from a simple listing of potential impacts to complex modes involving identification of feedback paths leading to higher order impacts as compared to the easily visible first order impacts involving uncertainities. This approach can be considered as an overall management technique requiring different
kinds of data in different formats along with varying levels of expertise and technological inputs to accurately forecast the results of any planned development.
- Ad hoc methods
Ad hoc methods indicate broad areas of possible impacts by listing composite environmental parameters (Ex: flora and fauna) likely to be affected by the proposed activity.
These methods involve assembling a team of specialists who identify impacts in their area of expertise. Here, each parameter is considered separately and the nature of impacts (long term or short term, reversible or irreversible) are considered.
These methods give a rough assessment of total impact while giving the broad areas and the general nature of possible impacts. In this method, the assessor relies on an intuitive approach and makes a broad-based qualitative assessment. This method serves as a preliminary assessment and helps in identification of important areas like:
- Endangered species
- Natural vegetation
- Exotic vegetation
- Social characteristics
- Natural drainage
- Air quality
- Visual description and services
- Open space
- Health and safety
- Economic values and
- Public facilities
Types of Ad hoc method are:
- Opinion poll
- Expert opinion and
- Delphi methods
This method is very simple and can be performed without any training. It does not involve any relative weighting or any cause-effect relationship.
It provides minimal guidance for impact analysis while suggesting broad areas for possible impacts. Moreover, it does not even state the actual impacts on specific parameters that will be affected.
The drawbacks of this method are listed below:
- It gives no assurance that a comprehensive set of all relevant impacts have been studied
- Analysis using this method lacks consistency as it different criteria are selectively evaluated by different groups
- It is blatantly inefficient as it requires a considerable effort to identify and assemble a panel for each assessment.
In this method, environmental factors are listed in a structured format by giving importance weightings for factors and application of scaling techniques for impacts of each alternative.
Checklists are strong indicators of impact identification. They effectively garner the attention and awareness of their audience. Impact identification is a fundamental function of an EIA. Checklists may be:
- Scaling or
- weighting type
Descriptive checklists include list of environmental factors along with information on measurement, impact prediction and assessment.
Scaling and weighting checklists facilitate decision making. Such checklists are strong in impact identification. While including the function of impact identification, they include a certain degree of interpretation and evaluation. The aforementined factors make these methods attractive to decision-making analysis.
However, the scaling and weighting methods are subjective and hence pose the danger of imparting equal importance to every impact. Another defect observed by critics is that numerical values assigned to impacts can be derived on the basis of expert knowledge and judgement alone.
Scaling and weighting checklist techniques quantify impacts reasonably well although they use subjective extimates. However, they make no provision for assessing dynamic probabilistic trends or mitigation, enhancement and monitoring programmes. These methods cannot identify higher order effects, impacts and interactions.
Simple and descriptive checklists simply identify the possible potential impacts without any rating regarding their relative magnitudes.
Scaling and weighting checklists remove decision making from the hands of decision makers while they impart a single number to various inherently different impacts and this aspect prevents the decision maker to consider the possibility of trade-offs.
In checklist method, the impacts are tabulated in the form of cells with information either in the descriptive form that gives information regarding possibility or potential existence of an impact whereas in the scaling or weighing methods the magnitude or importance of impact is given. Sample checklists or weighing methods used in EIA are shown below:
- It is simple to understand and use
- It is good for site selection and priority setting
Disadvantages of this method are:
- It does not distinguish between direct and indirect impacts
- It does not link action and impact
- It is cumbersome at times
3. Matrix Method
This methodology provides a framework of interaction of different activities of a project with potential environmental impacts caused by them. A simple interaction matrix is formed when project actions are listed on one axis (usually vertical) and environmental impacts are listed along the other axis. This technique was pioneered by Leopold et al in 1971. It lists about 100 project actions and about 88 environmental charateristics and conditions. An example of this matrix is shown below:
- The advantage of the matrix method is that it links action to impact
- This is a very good method for displaying EIA results
The disadvantages of this method are listed below:
- It is difficult to distinguish between direct and indirect impacts using this method
- There is potential for double-counting of impacts
- It is qualitative in nature and does not refer to quantity of impact
4. Network method:
- This method uses the matrix approach and extends it to include both the primary as well as the secondary impacts
- It is shown in the form of a tree called impact tree. This diagram is also called as reference or sequence diagram
- Identification of direct, indirect along with short, long term impact is a crucial and basic step of making an impact tree
- The impact tree is used to identify cause-effect linkages
- The impact tree is a visual description of linkages
- The diagram below shows the example of a network analysis:
The advantages of the network method are:
- It links action to impact
- It is useful to check second order impacts in a simplified form
- It handles direct and indirect impacts
The disadvantages of this method are:
- It becomes overly complex if used beyond simplified version
- It is completely qualitative in nature
- This method depends on a set of maps of a project area's environmental characteristics covering physical, social, ecological and aesthetic aspects
- It enables separate mapping of critical environmental features at the same scale as project's site plan (Ex: wetlands, steep slopes, soils, floodplains, bedrock outcrops, wildlife habitats, vegetative communities, cultural resources, etc)
- In the old technique, environmental features were mappped on transparent plastic in different colours
- Modern technique of the same activity is done using computer software, hardware, data and skilled people. It is called GIS (Geographic Information Systems)
The advantages of this method are:
- It is easy to understand and use
- It has a good display and
- It is good for setting site selection
- It addresses only direct impacts
- It does not address impact duration or probability