Starting up; early stages - Introduction to Environmental Impact Assessment - page 116

simple matrix . Three-dimensional matrices have also been developed in which the third
dimension refers to economic and social institutions: such an approach identifies the
institutions from which data are needed for the EIA process, and highlights areas in
which knowledge is lacking.
The time-dependent matrix (e.g. Parker & Howard 1977) includes a number sequence
to represent the tim escale of the impacts (e.g. one figure per year). Figure 4.10
P roject action

Environmental
component

Construction (3 years) Operation (25 years, evens out after 4

years)

Utilities Residential and

commercial
buildings

Residential
buildings

Commercial
buildings

Parks and
open
spaces

Soil and geology 211 321 0000 0000 0001

Flora 221 422 1223 1111 1123

Fauna 221 311 1100 1100 1122

Air quality 000 000 0123 0034 0011

Water quality 010 022 1223 0111 0000

Population density 011 112 2344 0222 0011

Employment 120 342 1111 1334 1111

Traffic 220 332 2333 2333 1111

Housing 010 121 2344 0000 0000

Community
structure

010 232 2344 1111 1233

Figure 4.10 Part of a time-dependent
matrix.

shows an example where magnitude is represented by numbers from 0 (none) to 4 (high),
over a course of 7 years.
Magnitude matrices go beyond the mere identification of impacts by describing them
according to their magnitude, importance and/or time frame (e.g. short-, medium- or
long-term). Figure 4.11 is an example of a magnitude matrix.
The best known type of quantified matrix is the Leopold matrix, which was developed
for the US Geological Survey by Leopold et al. (1971). It is based on a horizontal list of
100 project actions and a vertical list of 88 environmental components. Figure 4.12
shows a section of this matrix and lists all its elements. Of the 8,800 possible interactions
between project action and environmental component, Leopold et al. estimate that an
individual project is likely to result in 25-50. In each appropriate cell, two numbers are
recorded. The number in the top left-hand corner represents the impact's magnitude, from
+10 (very positive) to −10 (very negative). That in the bottom right-hand corner
represents the impact's significance, from 10 (very significant) to 1 (insignificant); there