3. 2
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 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)
4. 3
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 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;
5. 4
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;
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
6. 5
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 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
7. 6
Example of a Simple Matrix
Source: HYDER
4.2 Stepped Matrices
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)
8. 7
An Example of a Stepped Matrix Developed by Froelich and Sporbeck for a Road Scheme
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
9. 8
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 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
10. 9
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.
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
11. 10
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 ?)
Example of a Leopold Matrix Showing Magnitude and Significance on a Scale of 1-10
Source: SARI-ENERGY
13. 12
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 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 ?)
14. 13
A Sample of an Impact Assessment Matrix
Source: Prof. S. Chieng
Part of an Environmental Impact Summary Matrix of Arun III Hydropower Project
Source: SARI-ENERGY
15. 14
A Three-Dimensional Impact Matrix
Source: Prof. S. Chieng
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,
16. 15
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 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
17. 16
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 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.
18. 17
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.
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)
19. 18
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