Methods for Impact Identification

A logical and systematic approach needs to be taken to impact identification. The aim is to take account of all of the important environmental/project impacts and interactions, making sure that indirect and cumulative effects, which may be potentially significant, are not inadvertently omitted.  


This process begins during screening and continues through scoping, which identifies the key issues and classifies them into impact categories for further study. In the next phase, the likely impacts are analyzed in greater detail in accordance with terms of reference specifically established for this purpose. Over time, a number of EIA methodologies and tools have been developed for use in impact identification.  


The most common formal methods used for impact identification are: 

• Checklists; 
• matrices; 
• networks; 
• Overlays and geographic information systems (GIS); 

A) Checklists 

Checklists annotate the environmental features or factors that need to be addressed when identifying the impacts of projects and activities. They can vary in complexity and purpose, from a simple checklist to a structured methodology or system that also assigns significance by scaling and weighting the impacts (such as the Battelle Environmental Evaluation System). Both simple and descriptive checklists can be improved and adapted to suit local conditions as experience with their use is gained. 
Checklists provide a systematized means of identifying impacts. They also have been developed for application to particular types of projects and categories of impacts (such as dams or road building). Sectoral checklists often are useful when proponents specialize in one particular area of development. 

B) Matrices 

A matrix is a grid-like table that is used to identify the interaction between project activities, which are displayed along one axis, and environmental characteristics, which are displayed along the other axis. Using the table, environment-activity interactions can be noted in the appropriate cells or intersecting points in the grid. ‘Entries’ are made in the cells to highlight impact severity or other features related to the nature of the impact, for instance: 

• Ticks or symbols can identify impact type (such as direct, indirect, cumulative) pictorially; • Numbers or a range of dot sizes can indicate scale; or 

• Descriptive comments can be made. 

C) Networks 

Networks illustrate the cause-effect relationship of project activities and environmental characteristics. They are, therefore, particularly useful in identifying and depicting secondary impacts (indirect, cumulative, etc). 

Simplified networks, used in conjunction with other methods, help to ensure that important second-order impacts are not omitted from the investigation. 

More detailed networks are visually complicated, time-consuming and difficult to produce unless a computer programme is used for the task. 

However, they can be a useful aid for establishing ‘impact hypotheses’ and other structured science-based approaches to EIA. 

D) Overlays and geographic information systems 

Overlays can be used to map impacts spatially and display them pictorially. The original overlay technique, popularized by McHarg, is an environmental suitability analysis in which data on topographic features, ecological values and resource constraints are mapped onto individual transparencies and then aggregated into a composite representation of potential impacts. This approach is useful for comparing site and planning alternatives, for routing linear developments to avoid environmentally sensitive areas and for landscape and habitat zoning at the regional level. Disadvantages: lack of precision in differentiating the likelihood and magnitude of impacts and relating them to project actions.  A modern version of the overlay method is the computerbased geographical information system (GIS). In simple terms, a GIS stores, retrieves, manipulates and displays environmental data in a spatial format. A set of maps or overlays of a given area provide different types of information and scales of resolution. The use of GIS for EIA purposes is not as widespread as commonly imagined. The main drawbacks are the lack of appropriate data and the expense of creating a usable system. However, the potential application of GIS to EIA is widely acknowledged and its use is expected to increase in the future, particularly to address cumulative effects. 

Methods for Impact Identification Comparison
Methods for Impact Identification Comparison

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