Environmental Impact Assessment

Matrices in Environmental Impact Assessment

There are many methods by which we can assess the impact of a developmental project on our site and it’s various components. The simplest of these methods are checklists, which I’ve written about before.

Checklists were too primitive to be used for large-scale projects. A step higher from the checklists is the matrices form of impact assessment in EIA.

How is this superior to checklists?

Checklists tend to be long. It also requires a lot of work in describing an impact or writing it out in words. In matrices, this ambiguity and extra work is removed by introducing a quantitative aspect in the assessment of an impact.

Checklist tends to get confusing when you assess multiple levels of impacts descriptively. This is resolved in matrices, to an extent, with the help of customized matrices. I’ll explain one such matrix below. Matrices are also versatile, as they can be used for small and large-scale projects alike.

Explaining the matrix-

Simple matrix

This is simply a list of environmental aspects listed along the vertical axis, against which we determine whether an activity would have an adverse effect, no effect or beneficial effect. A simple “x” or “tick” is given under the appropriate column.


Sometimes, the activities are listed along the horizontal axis with the environmental aspects in the vertical axis, and the same “x” is given to those pairs that have an interaction between themselves.


Simple matrix

Leopold matrix

There are two major forms of matrices used in EIAs, the first being the Leopold Interaction matrix. This matrix consists of a list of 100 project activities on the horizontal axis, and about 88 environmental/social aspects on the vertical axis. The environmental aspects listed on the vertical axis are those that are likely to be affected by any of the project activities. This was designed by Leopold in 1971.


The cells of the matrix are divided by a diagonal line. The top division is used to describe the magnitude of the impact that activity will have on the environmental aspect, and the bottom division is used to describe the significance of that impact. Both, the magnitude and the significance, are rated on a scale of 1 to 10. This is subjective to the surveyor and is based on the baseline data collected. If a cell has no division, it means that the activity has no impact on the environmental aspect.


Leopold matrix

Disadvantages of Leopold matrix

The one big disadvantage of the Leopold matrix is that it does not explicitly describe spatial and temporal effects of the environmental activity. It merely gives us the magnitude and significance of the interaction.

Second, it tends to be too simplified when you require a comprehensive analysis of the impacts on the project area. A numerical value of the magnitude and impact is not sufficient for a contractor to understand the impact their activities are having and why they should overcome it.

Third, they cannot explain linkages between two environmental aspects. In other words, it does not describe secondary and tertiary impacts. It is extremely likely that more than one activity will have multiple levels of impacts on the environmental aspects of the project area. How will you glean this information?

The Component Interaction Matrix

The inability to detect indirect impacts systematically and understand them easily was a big drawback of the Leopold matrix. To overcome this, Environment Canada proposed a different form of matrix in 1974. This was called the component interaction matrix. Here, instead of taking activities on the horizontal axis and environmental components on the vertical axis, both axes listed environmental components. So, if two components were seen to be linked by secondary or tertiary interactions, they would be marked by 1, 2, etc. And if they are not impacted by multiple levels of interactions, they would be marked zero. An example is given below-


Component Interaction matrix- 0-no linkage; 1-primary linkage; 2-secondary linkage.

Others forms of matrices

Once the elegance of matrices were recognized around the world, EIAs began to use them increasingly in their impact assessments. Consequently, modifications were made and more and more forms of matrices were developed. Some of them are-

  1. Modified Graded matrix
  2. Environmental Compatibility matrix
  3. Impact Summary matrix

I have described look each of these forms of matrices in this post.

Application of matrices

Matrices can be applied in medium to large scale projects where the number of developmental activities are many (up to 100). This will obviously result in effects on many environmental aspects. All of these cannot be covered easily in checklists.

It is perfectly acceptable to customize the matrix according to the project at hand. You are not required by law to have 100 activities and 88 impacts on each of the axes, if the project does not encompass so many components. Matrices are flexible, which is why they have been accepted and used the world over.

References and sources-

  1. http://www.ku.edu.np/aec/envs402/eia%20chapter%206.3%20%20methods%20of%20impacts%20identification.pdf
  2. http://www.doe.ir/portal/theme/talab/0DB/2-BS/WMRA/SO/bs-wmra-so-1997.pdf

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