EIA Methodology

  EIA Methodology : Basics


EIA methodology is an approach developed to identify, predict and value changes of an action. Changes are reflected in the sequence of activities, steps, as well on the range of environmental issues considered (physical, chemical, biological, socioeconomic, cultural, landscape values and processes). Uses methods and techniques to quantify or to qualify those changes. All aspects and variables can be measured, problem is to value them.

Depends on…

Objectives of Methodologies

Focus of Methodology

  • Generating a list of potential impacts on selected environmental components
  • Should be dynamic, integrated group of natural and social systems
  • Type of impacts over time and space. Some impacts are immediate while others are delayed. Some impacts occur as a direct result of an activity; others occur as secondary or higher order impacts resulting from changes in other environmental components

Choosing a Method

EIA methods range from simple to complex, requiring different kinds of data, different data formats, and varying levels of expertise and technological sophistication for their interpretation. The analyses they produce have differing levels of precision and certainty. All of these factors should be considered when selecting a method.

Methodology Requirements

The EIA practitioner is faced with a vast quantity of raw and usually unorganized information that must be collected and analyzed in preparation of an EIA report. The best methods are able to:

  • organize a large mass of heterogenous data;
  • allow summarization of data;
  • aggregate the data into smaller sets with least loss of information; and
  • display the raw data and the derived information in a direct and relevant fashion
  • target audience should also be considered (example if target audience are not educated then, use of colour code, size, cross etc should be used rather that figures and tables)

General Criteria

Criteria for selecting methods at several stages of the assessment process changes. The objective is to select an array of methods that collectively will meet assessment needs. No single method can meet all the necessary criteria

Criteria for Selecting an EIA method

The methodology criteria are decided based on requirement, 5 major requirement can apply at one time or specifically. Cost and time effectiveness criteria, impact identication, measurement and assessment and communication. Impact identication, measurement and assessment are generally the requirement of Expert appraisal committee, however time & cost and communication criteria are important for Proponant.


  Major Methodologies for EIA

  Ad Hoc Method

Ad Hoc method indicates the broad areas of possible impacts by listing composite environmental parameters
Example Flora and Fauna

It involves the assembly of specialists to identify impacts in their area of expertise. Each environmental area, soil, air, water etc are taken separately and nature of impacts is predicted

  • Short term or Long term impacts
  • Reversible or Irreversible impacts

It is a rough assessment of broad parameters. Example of an adhoc method is a team of experts assembled for a short time to conduct an EIA based on a unique combination of experience, training and intuition. In other instances, when more scientific methods are available, it is not sufficient to rely on adhoc methods.

Broad qualitative information about factors useful in the comparative evaluation of alternative development actions is presented. The information is stated in simple terms that can be readily understood by the layman.

Example: The example presents the impact of reservoir with three alternative. Negative impacts are inundation of archeological sites, malaria cases,area, reduced open space etc, however the positives are new irrigation area, employment, enhances fisheries. Based on the expertise of specialist the positives and negatives are ranked and site is selected among A,B and C. It clearly shows the positive and negative impacts of project and that is the work of EIA.


However, in the present example; no information about the cause-effect relationship between project actions and environmental components is provided. Example; which parameter of water will be affected and how?. The actual impacts on specific environmental components likely to be affected by the project or those that may require further investigation are not identified.



  Checklist Method

Checklists are standard lists of the types of impacts associated with a particular type of project. All checklists have boxes or cells that must be filled with information about the nature of the impact.

Checklists range from listing of environmental factors to highly structured approach involving importance and weighting of factors and application of scaling techniques for the impacts of each alternative on each factor

Checklists are very strong in impact identification and capable of bringing to the attention and awareness of their audience.Checklists methods are primarily for organizing information or ensuring that no potential impact is overlooked.They are a more formalized version of ad hoc approaches in that specific areas of impact are listed and instructions are supplied for impact identification and evaluation

The simplest methods merely determine the possibility or potential existence of an impact, while others, like weighting-scaling checklists, make judgements about the magnitude and importance of the impact.

Types of Checklist


  Descriptive Checklist

Descriptive checklist includes an identification of environmental parameters and guidelines on how to measure data on particular parameters

They are strong in impact identification and also incorporate impact measurements, interpretation and evaluation of impacts which help in decision making process. This provides more information on the nature and magnitude of the impacts rather than just identifying whether they would occur or not.The information contained within each box can be quantitative or qualitative. The identification of the incidence of cumulative impacts is again essentially reliant upon expert opinion.

Example: This checklist provide the information about impacts and measurement methodology. Water quality will change depending on the present water quality and expected effluents.

The checklist can also discuss the cumulative impacts due to past activities, project and other nearby sources.

As the name says these checklists are very descriptive and focus on details about methodology, however not easy to understand. Generally used by decision makers during project appraisal.


  Simple Checklist

Simple Checklist consist a list of environmental parameters with no guidelines on how they are to be measured and interpreted. No information on methods of measurement, impact prediction and assessment

In its simplest form, a checklist can identify which resource/environmental component would be affected by a particular activity. For example, a tick to confirm that there will be an impact. Where there is no impact this is shown by leaving the box blank.

Example: The impacts are divided generally in construction and operation phase. During construction, there will be negative impact on open area, commercial and industrial area however in operation phase the impact will be on pollutant levels, odour etc. Positive impacts will be in services during operation phases. This does not tell anything about the magnitude of impact and what type of impact will be there.

Example: this shows more impacts as we have included more of parameters and environment affected. Therfore, if we list more and more environment parameters and activities, even a simple checklist can become very informative. Tick shows that impact is there, no tick means no impact.Very good for layman and uneducated stakeholders, and very easy visual explainations.


Many examples are given with the text which make it easy to understand and good for practice.

Simple Checklist can also give idea about type of impact (short term, long term, reversible, irreversible etc) by listing it thus can become more specific.



  Questionnaire Checklist

Checklist prepared based on the questions asked.This is used mainly for Public Consultation; it tells about the stakeholders awareness and responses towards the proposed project.

The questionnaire is then further evaluated in spread sheets to find the scale of impacts and weight of parameters based on public opinion.

  Advantages and Drawbacks of Checklist Method




  Matrix/Matrices Method

Matrix methods identify interactions between various project actions and environmental parameters and components. Matrices are similar to checklists in that they use a tabular format for presenting information. However, it is more complex and can best be described as a 2-dimensional checklist. The checklist and matrix can be differenciated, as the matrix has a strike in box to show the impact.

Incorporate a list of project activities with a checklist of environmental components that might be affected by these activities. A matrix of potential interactions is produced by combining these two lists (placing one on the vertical axis and the other on the horizontal axis).

Matrices can be used to evaluate to some degree the impacts of a project’s activities on resources, and can also be extended to consider the cumulative and indirect impacts, as well as impact interactions on a resource

Matrices can be two types

  • Scaling Matrix
  • Weighted Matrix to quantify the impacts of proposed activities

By looking for patterns in the finished matrix, for example columns or rows with numerous impact strikes, it is possible to develop a clear picture of how impacts combine in a cumulative way on a particular environmental receptor. Matrices can be used during the Scoping stages of impact assessment

One of the earliest matrix methods was developed by Leopold et al. (1971). Most matrices were built for specific applications, although the Leopold Matrix itself is quite general. Matrices can be tailor-made to suit the needs of any project that is to be evaluated. They should preferably cover both the construction and the operation phases of the project, because sometimes, the former causes greater impacts than the latter.


Leopold Matrix

In a Leopold matrix and its variants, the columns of the matrix correspond to project actions (for example, flow alteration) while the rows represent environmental conditions (for example, water temperature)

The impact associated with the action columns and the environmental condition row is described in terms of its magnitude (M) and significance (I)

The magnitude of the interaction (extensiveness or scale) is described by assigning a value ranging from 1 (for small magnitudes) to 10 (for large magnitudes). The assignment of numerical values is based on an evaluation of available facts and data. Similarly, the scale of importance also ranges from 1 (very low interaction) to 10 (very important interaction)

Assignment of numerical values for importance is based on the subjective judgement of the interdisciplinary team working on the EIA study. The matrix approach is reasonably flexible. The total number of specified actions and environmental items may increase or decrease depending on the nature and scope of the study and the specific TOR for which the environmental impact study is undertaken. This is one of the attractive features of the Leopold Matrix.  Technically, the Leopold Matrix approach is a gross screening technique to identify impacts. It is a valuable tool for explaining impacts by presenting a visual display of the impacted items and their causes.

Summing the rows and columns that are designated as having interactions can provide deeper insight and aid further interpretation of the impacts. The matrix can also be employed to identify impacts during the various parts of the entire project cycle— construction, operation, and even dismantling phases.

3D Matrix

Type of Matrix

  • Simple Interaction Matrices
  • Significance or importance-rated matrices

Simple matrix methods simply identify the potential for interaction

Significance or importance-rated methods require either more extensive data bases or more experience to prepare. Values assigned to each cell in the matrix are based on scores or assigned ratings, not on measurement and experimentation. For example, the significance or importance of impact may be categorized (no impact, insignificant impact, significant impact, or uncertain). Alternatively, it may be assigned a numerical score (for example, 0 is no impact, 10 is maximum impact).




  Network Method

Prepared formats such as adhoc, checklists, matrices etc are most useful during the initial stages of EIA. Once the initial assessment is completed, more systematic and scientific approaches should be used to conduct the detailed EIA.

The Networks or Systematic Sequential Approach (SSA) of assessment is required, a “scientific thinking through” of the potential impacts on the environment with and without the project

SSA aims to understand how environmental, social, and economic systems are interrelated, and how they will react to human disturbances. SSA views EIA as a continuing source of information throughout the project cycle. During the planning stages, broad economic goals and objectives are seen to give rise to planned projects.

Systematic Sequential Approach

Cause and Effect Relationship

Network as SSA

Network diagrams displays primary, secondary, tertiary, and higher order impacts. The network helps in exploring and understanding the underlying relationships  between environmental components that produce higher order changes that are often overlooked by simpler approaches. Networks or systems diagrams overcome the limitations of matrices by accommodating higher order impacts.

Identifying the interaction between a number of activities, components, and a single target resource. Qualitative predictions of the cumulative impact of a number of activities on a single target resource. Communicated well and are easy to develop using expert judgement, scientific documentation of complex systems.

Impact network for air environment

Primary Impact are the immediate impact of release of pollutants, secondary impacts deal with the changes or impacts caused by primary changes in environment quality and tertiary impacts are always the impact on economy and society because of primary and secondary environmental changes.









  Overlay Method

Overlays may be used to identify geographic areas where the environmental load or the sensibility of the environment to a load is high

Maps of different properties and environmental loads are superimposed. It involves the use of different transparencies to identify, predict and assign relative significance to, and communicate impacts in a larger geographical frame (Example highway corridors). Maps are shaded with three different shades to show the degree of impact,  resources likely are to be impacted and intensity of impacts can be presented through colour shading.

Easily adapted for use with a computer programmed, to predict impacts in a particular geographical area

Composite Overlays

The resulting composite maps characterize the area’s physical, social, ecological, land use and other relevant characteristics, relative to the location of the proposed development. To investigate the degree of associated impacts, any number of project alternatives can be located on the final map. The validity of the analysis is related to the type and number of parameters chosen. For a readable composite map, the number of parameters in a transparency overlay is limited to about ten.

Use of Overlays

The overlay method divides the study area into convenient geographical units based on uniformly spaced grid points, topographic features, or differing land uses. Field surveys, topographical land inventory maps, aerial photography, etc., are used to assemble information related to environmental and human factors within the geographical units. The scale of the maps can vary from large-scale (for regional planning purposes) to small-scale identification of site specific features

Overlays also are used in route selection for linear projects such as roads and transmission lines

Advantages & Limitations



“GIS is an integrated system of computer hardware, software, and  trained personnel linking topographic, demographic, utility, facility, image and other resource data  that is geographically referenced”

-National Aeronautics and Space Administration (NASA)

A GIS or Geographic Information System is a system designed for storing, analyzing, and displaying spatial data. Today, GIS manipulations are primarily accomplished through the use of computers, software and computer users

Themes of GIS

Each of our towns has many features such as roads, schools, shopping centers, rivers, lakes, forests, farms etc. A GIS stores these features as  separate data layers which is called Theme.

Themes (data layers) are stored in the computer as 3 different types:

  • Point theme: cities, wells, schools, airports
  • Line theme: roads, streams
  • Polygon theme: vegetation, land ownership

Data Format

Spatial elements can be represented in two models: Vector and Raster/Grid

In the vector model, the spatial locations of features are defined on the basis of coordinate pairs. These can be discrete, taking the form of points; linked together to form discrete sections of line; linked together to form closed boundaries encompassing an area

In raster model, one or group of cell/grid/pixel depending upon the grid resolution represents spatial elements

GIS Overlaying

Each of the themes in a GIS can be “overlayed” upon one another. Think of an overhead transparency projection system where each transparency shows a different data type. One shows roads, another streams, and yet another land use types. You can put all of these together, or look at just two data types

Gives very useful information for planners and developers

A GIS such as Arcview GIS works in a similar way as described above only operations and analysis are all done through the use of a computer and digital data



  Modeling Method


Modelling is an analytical tool which enables the quantification of impacts which can affect the environment by simulating environmental conditions. Often models use computer technology to predict the chemical or physical effects of a particular action within the environment

A mathematical model lends itself to the spatial and temporal analysis of aspects of the environment such as air and water quality, water volume and flows, noise levels and airborne deposition on soils and vegetation

Other types of model include socio-economic models, species habitat models and expert systems which allow the impact of a project to be determined through a programme of decisions.

Prediction of impacts - Models

Physical models – representation of the reality in a reduced scale, simulating processes

Visual models – elaboration of images that represent the environment before and after the development of a project and its alternatives. It can also address the timing dimension (e.g., seasonal changes, vegetation growth).

Mathematic models- maths or statistic simulations applied to the deterministic or probabilistic calculation, based on quantitative values

Cartographic models- representation of reality that will be affected by the project through maps or charts. Cartographic overlaps enable impact predictions

Models commonly used for Environmental Studies

Modeling- Pros and Cons



  EIA Methodologies Pros and Cons