ENVIRONMENTAL

IMPACT

ASSESSMENT (ARC

811)

GROUP 1

METHODS OF INVESTIGATING IMPACTS: MATRICES

Table of Contents

1.0 ENVIRONMENTAL IMPACT ASSESSMENT

2

2.0 MATRICES OR MATRIX METHOD 2

3.0 APPLICATIONS AND USES 3

4.0 TYPES OF MATRICES 4

4.1 Simple Matrices

5

4.2 Stepped Matrices

6

4.3 Weighted Matrices

7

4.4 Advanced Network Matrices

7

4.5 Leopold Matrix (LM) 8

4.6 Modified Graded Matrix (MGM)

11

4.7 Impact Summary Matrix (ISM)

11

4.8 Loran Methodology (Matrix)

13

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4.9 Peterson Matrix

13

4.10 Rapid Impact Assessment Matrix (RIAM)

13

5.0 ADVANTAGES 15

6.0 DISADVANTAGES 15

REFERENCES 16

1.0 ENVIRONMENTAL IMPACT ASSESSMENT

Environmental Impact Assessment (EIA) can broadly be defined as a study

of the effects of a proposed project, plan or program on the environment.

The legal, methodological and procedural foundations of EIA were

established in 1970 by the enactment of the National Environmental

Policy Act (NEPA) in the USA. (Ogola, P. 2007)

Environmental Impact Assessment is a method of analysis that attempts

to predict the likely repercussions of a proposed development on the

social and physical environment of the surrounding area and (if negative

impacts are predicted) to propose alternative methods of carrying out the

project that might help to prevent or mitigate the negative impacts.

One of the methods of identifying these negative impacts is by using

matrices amongst others.

2.0 MATRICES OR MATRIX METHODS

In 1971, Leopold, et al. promulgated a simple interaction matrix for usage

across the range of actions conducted by the U.S. Geological Survey

(Leopold, et al, 1971). The “Leopold matrix” displayed project actions or

activities along one axis (typically the x-axis), with appropriate

environmental factors listed along the other axis (y-axis) of the matrix.

When a given action or activity was expected to cause a change in an

environmental factor, this was noted at the intersection point in the

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matrix and further described in terms of separate or combined magnitude

and importance considerations. Many variations in the Leopold matrix

have occurred over the four decades of EIA practice. Arguably, matrices

have been the most widely used methodology in EIA practice. (Canter, L.

W. 2008)

Matrix methods identify interactions between various project actions and

environmental parameters and components. They 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). They should preferably cover both

the construction and the operation phases of the project, because

sometimes, the former causes greater impacts than the latter. However,

matrices also have their disadvantages: they do not explicitly represent

spatial or temporal considerations, and they do not adequately address

synergistic impacts. (Ogola, P. 2007)

Interaction matrices were one of the earliest types of methodologies

developed for usage in impact studies.

3.0 APPLICATIONS AND USES

The major use of matrices is to indicate cause and effect by listing

activities along the horizontal axis and environmental parameters along

the vertical axis. In this way the impacts of both individual components of

projects as well as major alternatives can be compared. The simplest

matrices use a single mark to show whether an impact is predicted or not.

However it is easy to increase the information level by changing the size

of the mark to indicate scale, or by using a variety of symbols to indicate

different attributes of the impact.

Matrices are a more complex form of checklist. They can be used

quantitatively and can evaluate impacts to some degree. They can be

extended to consider the cumulative impacts of multiple actions on a

resource. Matrices are similar to checklists in that they use a tabular

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format for presenting information. The matrix is however, more complex

and can best be described as a 2-dimensional checklist.

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 cannot be used in themselves to quantify the actual

significance of impacts; this can only be done using other methods. It is

however possible to weight matrices to reflect factors such as duration,

frequency and extent. They can also be used to score or rank impacts. If

weighting or scoring is used, the criteria must be clearly set out. This

approach relies on expert opinion to provide ranks/weights for each

project with respect to each environmental effect. 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.

In doing so, probable impact interactions can also be identified. Matrices

can be used during the Scoping stages of impact assessment. They are

also useful tools to summarise and present impacts within the

Environmental Statement.

Developing a matrix will be dependent upon a number of activities. The

steps that could be followed are:

Consider and list the activities associated with project;

Identify and list the sensitive resources;

Select an appropriate matrix depending on the nature of the

assessment. A simple matrix may be appropriate for the Scoping stage

or alternative site assessment. For a more detailed assessment the

sensitivity of the receptors and the nature of the activities associated

with the project will be important factors. A complex matrix is unlikely

to be appropriate for a simple project. Conversely a project in a

particularly sensitive area may benefit from the use of a more complex

matrix;

Identify where impacts arising from activities may occur on the matrix;

4

Identify cumulative impacts by identifying if a number of different

activities (including those from other developments) impact on a single

resource or receptors.

For more complex matrices, extend the matrix to give cause and effect

relationships or impact chains.

The most efficient way to use the matrix is to check each action (top

horizontal list) which is likely to be involved significantly in the proposed

project. Generally, only about a dozen actions will be important. Each of

the actions thus checked is evaluated in terms of magnitude of effect on

environmental characteristics on the vertical axis, and a slash is placed

diagonally from upper right to lower left across each block which

represents significant interaction.

Matrices can be applied to a range of projects and environmental

conditions by selecting a matrix which is appropriate; for example, a

simple matrix would be suitable for scoping or option assessment. A more

complex matrix would be better suited to a larger scale project or a

project in a particularly sensitive location. The choice of matrix must

therefore be appropriate to the nature of project and the receiving

environment. Matrices can be adapted and can be applied to consider

both physical and socio-economic impacts. (Walker & Johnston, 1999)

4.0 TYPES OF MATRICES

There are several types of matrices used in Impact Identification in EIA.

The simple matrix refers to a display of project actions or activities along

one axis, with appropriate environmental factors listed along the other

axis of the matrix. When a given action or activity is anticipated to cause

a change in an environmental factor, this is noted at the intersection point

in the matrix and can be further described in terms of magnitude and

important considerations. Many variations of the interaction matrix have

been utilized in EIA.

4.1 Simple Matrices

Simple matrices can be organised to cross reference the different phases

of a project (e.g. construction, operation and decommissioning) against

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elements of the environment or sensitive receptors. Cumulative impacts

may for example be considered in a separate column by including the

effects of past, present and future actions on resources, alongside the

range of effects caused by the action of immediate concern. The following

is an example of a simple matrix using symbols. Numerical scores could

be used equally well to show the approximate scale or magnitude of the

impact. (Walker & Johnston, 1999)

The figures below are illustrations of a simple matrix.

Source: SARI-ENERGY

Example of a Simple Matrix

Source: HYDER

4.2 Stepped Matrices

6

Stepped matrices are a more advanced type of matrix that considers how

the various activities of a project relate to the environmental resource or

parameter. It shows resources against functions of the environment. This

approach therefore shows how one action can impact on a resource,

which can then cause changes on another resource. (Walker & Johnston,

1999)

An Example of a Stepped Matrix Developed by Froelich and Sporbeck for a

Road Scheme

7

Source: HYDER

4.3 Weighted Matrices

By introducing weighting into a matrix it allows the ranking of impacts. It

also provides a tool for assessing complex effects. However, use of such

complex approaches may make interpretation of the results difficult for

others.

Weighting an impact will be subjective and it is therefore important that

the assessment explains assumptions made and the criteria used.

Weighted matrices allow the magnitude of impacts to be used

quantitatively. A weight is assigned to each environmental component,

indicating its importance. The impact of the project on each component is

then assessed and scored. Weighting or scoring can also be used to give

an overall total score for the project or alternative options. Extreme

caution should be practised if these weights are to be used additively

during the comparison of project options or to determine combined impact

values as the rankings do not work in a strict additive way. (Walker &

Johnston, 1999)

The following is an example of a weighted matrix developed to compare

alternative sites.

Example of a Weighted Matrix

Source: HYDER

4.4 Advanced Network Matrices

This is a complex method which can be considered as both a stepped

matrix and a network. It identifies the activities of the project and

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assesses the impact on the resource (the matrix part of the method).

However this is then considered in greater depth (the network part of the

method). It is therefore a tool which is flexible in its use. This tool provides

a way of linking the matrix and the cause and effect impact chains. It

integrates into one diagram a matrix and a network of consequent

impacts. The initial impact can be followed through successive stages of

cause and effect until it reaches what is considered the final impact.

Although this tool provides a more comprehensive approach to impacts

identification than many of the simpler methods, it is still not quantitative.

It does not identify the magnitude of the impacts or their

interrelationships, and neither does it assess the significance of the

impacts. In addition, compilation of such a matrix can be time consuming.

However, its main advantage is its ability to trace the indirect impacts of

proposed developments. (Walker & Johnston, 1999)

The figure below is an example of such a matrix.

9

An Advanced Stepped Matrix used for a Hypothetical Port Development.

(Adapted from Sorenson 1971)

Source: HYDER

Other types of matrices include:

4.5 Leopold Matrix (LM)

This matrix is used to identify potential impacts associated with a project

or alternatives. It assists performing a comprehensive review of the

variety of interactions between project elements and environmental

parameters to identify important environmental factors, data needs, and

less damaging alternatives. (ELAW, 1998)

It was developed by Leopold et al. (1971), and it has been used for the

identification of impacts. It involves the use of a matrix with 100 specified

actions and 88 environmental items. In constructing the matrix, each

action and its potentiality for creating an impact on each environmental

item must be considered. Where an impact is anticipated, the matrix is

marked with a diagonal line in the interaction box. The second step in

using the Leopold Matrix is to describe the interaction in terms of its

magnitude (M) in the upper section and importance (I) in the lower section

of each box.

The magnitude of an interaction or impact is represented by numerical

scale; it is described by the assignment of a numerical value from one to

ten. The value, ten represents the largest magnitude and the value, one

represents the lowest magnitude, whereas values near five represent

impacts of intermediate magnitude. Assignment of a numerical value for

the magnitude of an interaction is related to the extent of any change (for

example, if noise levels in a village were expected to increase by 20

dB(A), this is a large increase at night and may score 8 or even 9). The

scale of importance also ranges from one to ten. The higher the value, the

higher the importance; the lower the value, the lower the importance.

Assignment of a numerical value for importance is based on the subjective

judgement of the multi-disciplinary team working on the EIA. Plus (+) or

minus (-) can be used to show whether an impact is beneficial or adverse.

(SARI-ENERGY ?)

10

Example of a Leopold Matrix Showing Magnitude and Significance on a Scale of

1-10

Source: SARI-ENERGY

A Leopold Matrix

Source: Prof. S. Chieng

11

A Section of the Leopold Matrix

Source: Prof. S. Chieng

4.6 Modified Graded Matrix (MGM)

Lohani and Thanh (1980) used another grading system in which relative

weights are assigned to each development activity. If the relative priority

of development activity is determined, the total value of a particular

activity is the sum of the vertical column represented by that in the

matrix, multiplied by the priority value. Finally, the total value of all the

interactions is the sum of all horizontal values in the matrix. This method

is particularly helpful in identifying major activities and in defining areas

where attention is mostly needed in the process of analysis. (SARI-

ENERGY ?)

4.7 Impact Summary Matrix (ISM)

An impact summary matrix can clearly identify the potential impact areas,

predict the impact severity, specify the corresponding mitigation

measures, and help in identification of agencies responsible for

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implementing mitigation measures. This kind of matrix is simple, covers

all the aspects, and provides a complete overview of EIA in summary

form. Additionally, it provides an easy guide for decision-makers. (SARI-

ENERGY ?)

A Sample of an Impact Assessment Matrix

Source: Prof. S. Chieng

13

Part of an Environmental Impact Summary Matrix of Arun III Hydropower Project

Source: SARI-ENERGY

A Three-Dimensional Impact Matrix

Source: Prof. S. Chieng

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4.8 Loran Methodology (Matrix)

This method uses a matrix of 234 project activities and 27 environmental

features to critical environmental areas. Each element in the matrix is

scaled and results input to an algorithm that aggregates impact scores. It

is used to identify critical environmental areas. (ELAW, 1998)

4.9 Peterson Matrix

Peterson Matrix is a modified version of the Leopold matrix. This matrix

relies directly on the multiplication properties of matrices. An ordinal scale

is used to evaluate individual impacts, and separate matrix layers are

produced for physical and human impacts. The matrices are also

multiplied to find the effect of the casual elements on human environment

while the resulting product is weighed according to the significance of the

human impact. (Akintunde & Olajide, 2011)

4.10 Rapid Impact Assessment Matrix (RIAM)

The rapid impact assessment matrix (RIAM), which was developed in

Denmark, is a new tool for the execution of environmental impact

assessments. RIAM is quite flexible, transparent and leaves a permanent

record, which can be independently checked, validated or updated.

The Rapid Impact Assessment Matrix (RIAM) was originally developed for

carrying out Environmental Impact Assessment (EIA) (Pastakia, 1998).

RIAM has an advantage over the existing EIA methods. In particular, it

minimizes the element of subjectivity and introduces some degree of

transparency and objectivity. It also provides a transparent and

permanent record of the analysis process while at the same time

organizing the EIA procedure, which in tum considerably reduces the time

taken in executing EIAs (Pastakia, 1998). The simple, structured form of

RIAM allows reanalysis and in-depth analysis of selected components in a

rapid and accurate manner. This flexibility makes the method a powerful

tool for both executing and evaluating EIAs.

The scales in RIAM allow both quantitative and qualitative data to be

assessed. RIAM, which is used in several impact studies, was therefore the

preferred method and subsequently selected because of its flexibility and

the numerous advantages over the known EIA methods as outlined by

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Pastakia and Jensen (1998). In the RIAM process the impacts of project

activities are evaluated against the environmental components, and for

each component a score (using the defined criteria) is determined, which

provides a measure of the impact expected from the component. The

important assessment criteria fall into two groups: A. Criteria that are of

importance to the condition, that individually can change the score

obtained; and B. Criteria that are of value to the situation, but should not

individually be capable of changing the score obtained. For group A, the

overall quotation system consists in multiplying the marks attributed to

each criterion. The principle of multiplication insures that the weight of

each criterion intervenes directly. For group B, the overall quotation

system consists in adding the marks attributed to each criterion. This

insures that a mark taken in isolation cannot affect much the overall

result.

The process is thus expressed by the following set of equations (Jensen,

1998):

(al) X (a2) = aT (1)

(bl) + (b2) + (b3) = bT (2)

(aT) X (bT) = ES (3)

(al) and (a2) are individual criteria scores that are of importance to the

condition (group A), and which can individually change the score

obtained; (bl) to (b3) are the individual criteria scores that are of value to

the situation (group B), but individually should not be capable of changing

the score obtained;

aT is the result of multiplication of all (A) scores;

bT is the result of summation of all (B) scores; and

ES is the assessment score for the condition. (Kankam-Yeboah et al, 2004)

The first step in the RIAM is to set up a number of different options for the

assessment in question, and the RIAM program will individually process

these. These options should be saved in the program. Then, the

component screen records the results of the scoping of the assessment.

All four types of components in the RIAM system are catered, and each

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component is individually coded. The component list displays all the

elected components for each option. Under these components RIAM

allows automatic recording of the criteria values given by the user for

each component. The scales for each cell are displayed to allow rapid and

easy checking of attributed values. After completing the RIAM analysis,

the RIAM report shows the actual values attributed to each component, as

well as a summary of the scores. Moreover, from the RIAM report it is

possible to view the result of the analysis as a histogram for each option

and corresponding components. The ranges were not expressed as ±5,

but as ±A to E (with N representing the zero range). The histograms

provide comparative pictures of positive/ negative impacts between

options, to identify important negative components. (El-Naqa, A. 2004)

5.0 ADVANTAGES

A more detailed approach is given in matrices, where project activities

are cross-tabulated with environmental components.

Also matrices can be made quite simple or be developed into a stage

with a large amount of information.

The strength of the matrix approach is the usefulness in designing

further studies, the inexpensive nature (also true for checklists) and

their comprehensiveness.

Using a standard matrix format will help to ensure that potential

impacts are not overlooked. Matrices provide a good visual summary

of impacts. They can be adapted to report indirect and cumulative

impacts as well as impact interactions in a comprehensive format.

Matrices are a useful tool for presenting results, for example from

subjective assessments, or from numerical modelling. This is because

they are easy to interpret.

Matrices can be designed to include the potential for interactions and

can combine the impacts from various actions or from a number of

projects. They can also be used to compare alternative options.

Matrices can be adapted to identify and evaluate to some degree

indirect & cumulative impacts and impact interactions.

Matrices can be weighted/ impacts ranked to assist in evaluation.

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6.0 DISADVANTAGES

Matrices can however be complicated and cumbersome to use.

Limitations may be an inability to handle indirect impacts and

temporal aspects, a potential rigidity of categories, and a difficulty to

get an overview when many variables are included.

In many cases numbers of magnitude and severity of impact are

included on a very poor basis ("this feels larger than the other"). Thus

many matrices used give much less and lower quality information than

thought on first impression. (Anderson, K. 2000)

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