Identifying and Evaluating Impacts - Mining and the Environment: From Ore to Metal - page 416

Impact magnitudes are estimated by assigning a weight 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 provide a total score for the proposed project or for
project alternatives. The most frequently used presentation of a comparison of alternatives
is a matrix, in which

, 0, and - are used to indicate how each alternative affects dif-
ferent environmental components. This method provides a quick overview of differences
between project alternatives. The presentation can be designed to illustrate the impacts of
each alternative against a reference scenario (usually the existing situation); or to compare
impacts of each project alternative with the preferred alternative. Using multiple signs
such as or - - allows further differentiation.

Weighting or scoring relies heavily on professional judgement in providing ranks/
weights to each project activity with respect to its environmental effects. It is important,
therefore, to state assumptions made and criteria used. While illustrative, caution should
be exercised in interpreting weighted matrices, because although they may provide useful
indications of relative impacts, environmental impacts are often too complex to be accu-
rately ranked by a simple numbering system.
Symbolized matrices - The symbolized matrix differs from the weighted matrix by
using symbols to capture signii cance attributes of impacts. Environmental impacts may
be described with words such as 'important' or 'signii cant', and further classii ed as 'posi-
tive' or 'negative' impacts by the use of plus or minus signs (for example,

While illustrative, caution should
be exercised in interpreting
weighted matrices, because
although they may provide useful
indications of relative impacts,
environmental impacts are often
too complex to be accurately
ranked by a simple numbering
system.

S, a positive
and signii cant impact). Other abbreviations include 'ST' for short term and 'LT' for long
term, or '10' to denote a very high impact and '1' to indicate an almost negligible one. A
symbolized matrix can often be a combination of descriptive and numerical scales. Note
that because these subjective, qualitative words and symbols are based on the professional
judgement of the evaluator, their interpretation may differ depending on his or her cul-
tural values, education level, or specii c circumstances. Simple rating schemes are often
used during early scoping exercises, before a more detailed assessment coni rms or dis-
misses the validity of conclusions reached in the matrix.
As one would expect, a wide range of more advanced types of matrices have emerged
over the years (Walker and Johnson 1999). While useful for some applications, advanced
matrix types are not routinely used in environmental assessment. Whether simple or
advanced, matrices do not quantify impact signii cance; this is only achieved by quanti-
tative methods such as mathematical or numerical modelling; however, matrices are easy
to interpret and provide a good visual summary of impacts. Matrices are especially useful
when comparing project alternatives.

Network and Flowchart Analysis

Network analysis and impact l owcharts are used in most environmental assessment stud-
ies. They are based on links and interaction pathways between causes and effects, and
between individual environmental components. If one component is affected, subsequent
impacts will occur on those components which interact with it. Network and l owchart
analyses identify pathways of an impact using a series of chains (networks) or l owcharts
between a proposed activity and the receptor of the impact.
Analyzing the response of a receptor to a particular stressor and identifying where
knock-on effects on other receptors or environmental components exist, enables indirect
impacts and interactions between both project activities and project impacts themselves to
be considered. If different activities or developments affect the same environmental receptor,