Environmental Engineering Reference
In-Depth Information
Ordinal
B
A
C
D
Ranking according to ascending value of L
10
dB
A
Binary
0
0
1
1
0=less than 70L
10
dB
A
1=70L
10
dB
A
or more
Based on Lee (1987).
Table 5.9
Weighting, scoring and
trade-offs
Impact
Weight (w)
Scheme A
Scheme B
Score (a)
(aw)
Score (b)
(bw)
Noise
2
5
10
1
2
Loss of flora
5
1
5
4
20
Air pollution
3
2
6
2
6
Total
21
28
positions. This internalization of the weighting exercise does not destroy the use of
weights, but it does emphasize the need for clarification of scoring and weighting systems
and, in particular, for the identification of the origin of the weightings used in an EIA.
Wherever possible, scoring and weighting should be used to reveal the trade-offs in
impacts involved in particular projects or in alternatives. For example, Table 5.9 shows
that the main issue is the trade-off between the impact on flora of one scheme and the
impact on noise of the other scheme.
Several approaches to the scoring and weighting of impacts have already been
introduced in the outline of impact identification methods in Chapter 4. The Leopold
matrix includes measures of the significance of impacts (on a scale of 1-10) as well as of
their magnitude. The matrix approach can also be usefully modified to identify the
distribution of impacts among geographical areas and/or among various affected parties
(Figure 5.7). The quantitative EES and Water Resources Assessment Methods (WRAM)
generate weights for different environmental parameters, drawn up by panels of experts.
Weightings can also be built into overlay maps to identify areas with the most
development potential according to vari
o
us combinations of
Project
A
ction
Group environmental component
Construction stage
acti
o
ns
Operational stage
acti
o
ns
A
B
C
D
a
b
c
d
Group 1
(e.g. indigenous population ≥45 years old)
various
• Social
• Physical
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