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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)
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4.7 Impact Summary Matrix (ISM)
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4.8 Loran Methodology (Matrix)
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4.9 Peterson Matrix
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4.10 Rapid Impact Assessment Matrix (RIAM)
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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;
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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
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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
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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.
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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 ?)
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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
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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
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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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