6. Types of
environmental
impact
HOW TO USE THIS CHAPTER IN THE CONTEXT OF EA AND ROAD PLANNING
EA activity
(I9
Stage in road planning
(A)
Involvement in addition to EA team
w
Evaluation
Reporting
Shaded area = (A) Stages of EA covered in this chapter; (8) focus of this chapter; and (C) primary target readers.
KEY QUESTIONS
m
E
M
E
ADDRESSED:
How are environmental impacts classified?
What are the basic criteria for defining the severity of environmental
impacts?
What is an indirect impact?
What is a cumulative effect?
ROADS AND THE ENVIRONMENT:
6.1
A HANDBOOK
IMPACT TYPES
Environmental impacts arising from road development projects fall into three categories:
i) direct impacts;
ii) indirect impacts; and
iii) cumulative impacts.
These three groups can be further broken down
according to their nature, into
positive and negative impacts;
0 random and predictable impacts;
l local and widespread
impacts;
* temporary and permanent impacts; and
l short- and long-term
impacts.
l
6.1.1
Direct impacts
Direct impacts are caused by the road itselfthat is to say, by road building processes such
as land consumption, removal of vegetation,
and severance of farmland. For example, the
removal of gravel material from a borrow pit,
for use in surfacing the road, is an obvious direct impact of road construction. In this case,
the land area in which the pit site is located has
been directly affected by activities associated
with the road project.
Direct impacts are generally easier to inventory, assess, and control than indirect im-
pacts, since the
usually obvious.
6.1.2
cause-effect
is
Indirect impacts
Indirect impacts (also known as secondary, tertiary, and chain impacts) are usually linked
closely with the project, and may have more
profound consequences
on the environment
than direct impacts. Indirect impacts are more
difficult to measure, but can ultimately be more
important. Over time they can affect larger
geographical areas of the environment
than
anticipated. Examples include degradation of
surface water quality by the erosion of land
cleared as a result of a new road (Figure 6.1),
and urban growth near a new road. Another
common indirect impact associated with new
roads is increased deforestation of an area,
stemming from easier (more profitable) transportation of logs to market, or the influx of settlers. In areas where wild game is plentiful,
such as Africa, new roads often lead to the
rapid depletion of animals due to poaching.
Environmental impacts should be considered not only as they pertain to road rights-ofway, but also to sites associated with the road
project, which include deposit and borrow
sites, materials treatment areas, quarries, access
roads, and facilities provided for project work-
FIGURE 6.1
Impairment of
downstream
quality of water
for the fauna
or for human
usage
60
relationship
TYPES OF ENVIRONMENTAL
ers. These “off-ROW” areas are often where in-
direct impacts appear (see Box 6.1).
IMPACT
EA practitioners should predict and evaluate
the significance of possible indirect effects by
BOX 6.1
EXAMPLE OF POTENTIAL DIRECT AND INDIRECT ENVIRONMENTAL
IMPACTS
Environmental impact study for the Guinea-Conakry Road Project (96 km road construction in a mangrove
swamp and rice-growing area). NOTE: Direct Impact (D); Indirect Impact (I).
Soils
’
Compaction of alluvial soils by earth moving equipment (D)
Erosion and modification of surface relief of borrow zones (275,000 square meters) (D)
Loss of topsoil (165 hectares) in the borrow areas (D)
Over-exploitation of agricultural soils due to future development in a zone sensitive to erosion (I)
Irreversible salinization and acidification of mangrove swamp soils (I)
Water
Modification of flowing surface water in borrow areas, causing erosion and siltation (I)
Modification of water flows during construction (stream diversion, modification of water table recharging) (D)
Sedimentation near crossings of presently cultivated flood plain (D)
Modification of surface and subterranean water flows and resulting drying or flooding (I)
Pollution of water tables by equipment lubricants, fuels, and detergents (D)
Displacement of salinity threshold into the mangrove swamp zone: effects on fauna and flora, impregnation of
soils with tannin, erosion of coastline (I)
Flora
260 hectares of deforestation and undergrowth clearance (D)
Destruction of plantings (2,800 oil palms, 1,600 various trees) (D)
Reduction of cornice forests around swamps, from modified water flow and increased agricultural use (I)
Disappearance of reproduction and food zones for species of fish, aquatic and migratory birds (I)
Reduction of mangrove plant population (habitat for fauna, purifying microfauna, firewood) (D)
Erosion of the coastline (I)
Increase in farming activity, reduction of fallow times, impoverishment of the soils (I)
Fauna
Reduction in mangrove fauna (crabs, shrimps, egrets, herons, kingfishers, spoonbills, ibises, terns, and other
species) (I)
Increase in poaching during the works period, and subsequent hunting and fishing (I)
Increase in tourism (Tristao Island, the center for many migratory birds) (I)
People
Loss of farms and homes (1,300 square meters) (D)
Reduction in agricultural production per surface unit (over-exploitation, impregnation of soils with tannin) (I)
Increase in consumption of wood, particularly from the mangrove swamps: erosion (I)
Reduction in fishing potential (I)
Increase in land tenure contlicts, and conflicts between farmers and nomad cattle breeders (I)
Increase in speed of propagation of endemic disease (I)
Positive Impacts
Providing all weather road link for coastal population with major urban markets, institutions and goods
Sale of dried fish products (90 percent of national production) increased through quicker transport and access
More effective sale of rice from industrial growers (3,500 hectares) and small-scale growers
Creation of jobs
Improved access to medical help
Source: SETRA
61
ROADS AND THE ENVIRONMENT:
A HANDBOOK
taking a holistic approach to impact assessment. It is especially important that any synergetic relationships between impacts be closely
examined, since indirect effects frequently lead
to synergetic impacts.
It is with indirect effects that impact linkages between the natural and social environment often take place. For example, the
appropriation of land to build a road may displace farmers, and may interfere with their
cropping pattern and force them to use another
water supply. This change could result in a depletion of a groundwater aquifer, intensification of new land clearing, erosion, water runoff
contamination with added fertilizers and pesticides, etc.
Good documentation of the assumptions
used in the determination of impacts is critical.
Margins of error and the quality of basic information must be indicated when assessing any
impacts that are difficult to quantify.
tacular views, and in the absence of designated
rest areas, motorists stop indiscriminately.
Roadside vegetation is damaged by vehicle and
foot traffic, and the soil is left unprotected. Subsequent rainfall causes erosion and siltation of
nearby watercourses. The vegetation never has
enough time to recover (because of high traffic
volume on the road), and the problem is exacerbated over time.
As this example illustrates, cumulative effects assessment (CEA) is a complex process
which requires extensive knowledge of ecological principles and ecosystem response mechanisms.
The success of a CEA relies heavily on the
framework that is set up before the assessment
is undertaken. The evaluation can begin once
6.1.3
l
Cumulative
impacts
The process of cumulative
environmental
change can arise from any of the four following
types of events:
single large events, i.e. a large project;
multiple interrelated events, i.e. road projects within a region;
iii) catastrophic sudden events, i.e. a major
landslide into a river system; and
widespread,
slow change,
iv) incremental,
such as a poorly designed culvert or drainage system along a long road extending
through a watershed.
9
ii)
These can generate additive, multiplicative or
synergetic effects, which can then result in
damage to the function of one or several ecosystems (such as the impairment of the water
regulation and filtering capacity of a wetland
system by construction of a road across it), or
the structure of an ecosystem (such as placement of a new road through a forest, leading to
m-migration or land clearing which results in
severe structural loss to the forest) (see Figure
6.2).
A cumulative impact, in the context of road
development, might be the de-vegetation and
eventual erosion of a roadside pullout. The scenario might unfold as follows: a road cutting
through a mountain range offers some spec-
62
.
.
temporal and spatial boundaries for the assessment have been defined;
measurable variables have been chosen;
and
the relationships between the chosen variables have been established.
The cumulative effects of the proposed road
project on the local environment can then be
evaluated by
.
l
.
compiling a list of activities that are part of
the proposed project;
estimating the changes that will occur in
the measurable variables as a result of these
activities; and
estimating the effects that the changes in
each of the measurable variables will have
within the area defined by the spatial and
temporal boundaries.
CEA is an effective impact assessment tool, but
it must be carried out properly in order to produce reliable results. 1
6.1.4
Ecosystem function impacts
Technically a subset or variant of cumulative
impacts, ecosystem function impacts, which
disable or destabilize whole ecosystems, are the
most dangerous and often the least likely to
manifest themselves over a short period of
time. Many road-related examples deal with
roads which need to traverse watersheds in
1 Those planning to undertake CEA as part of an EA are
urged to read Preston and Bedford (1988) as well as Spaling and Smit (1994) and (1993).
TYPES
OF ENVIRONMENTAL
IMPACT
FIGURE 6.2
CUMULATIVE IMPACTS: THE EXAMPLE OF A STREAM
Elementary
actions
WF
II
Road operation
Works
I
II
‘---7--Direct effects
Synergy effect
Increase in
water speed
* Reduction of
diversity
l Discontinuity
due to water
works
l
l
l
Opening up
to light
Rise In
temperature
0 Riskof chronic,
seasonal,
accidental
pollution
l
l
High rate of
suspended
matter
Riskof
Significant impairment of biological quality of the stream
Each elementary action produces a certain effect or a risk that can be limited, but the combination of such
actions and therefore their consequences may be the source of significant effects. In this example, steps
can be envisaged with reference to each elementary action, in order to avoid the synergy effect.
which surface and subsurface water movement
is complex. One striking example is the highway constructed across a mangrove forest
(100 ha in size) along the Caribbean coast. It
was not fully understood at the planning stage
to what extent the fresh and sea water needed
to mix in order for the healthy forest to survive
on both sides of the road. As a result, most of
the forest has died off;2 on one side the waters
were not saline enough, and on the other there
was not enough mixing with fresh water. The
2 Once weakened, the mangrove trees, some over 20 m
high, were destroyed by disease, etc.
effect on the ecosystem was devastating and
the impact on the local population which used
the mangrove forest area was severe. Almost
certainly, no sign of this impact appeared until
two to three years after the road was built. A
second example could develop in situations
where roads bisect wildlife migration routes,
which can inflict stress on the migratory population for many generations, or even permanently,
and
cause
instability,
increased
mortality, and possibly catastrophic decline.
Finally, there is the linkage with the social
environment.
Having had their traditional
grazing areas cut off by new or reconstructed
63
ROADS AND THE ENVIRONMENT: A HANDBOOK
roads with raised-horizontal alignments, cattle
farmers may be forced to move their herds onto
forest or park lands, which results in a rapid
depletion of the understory (grasses, etc.). This
destroys the forest edge ecotone and the basic
forest ecosystem, as well as threatening the inhabitants with possible invasion from species
better adapted to the newly created “grazingforest” ecosystem. The invaded forest ecosystem is stressed further, users of the ecosystem
are affected, and a chain reaction progresses
throughout the system, feeding back to the social environment in the form of community
disturbances and hardships.
6.1.5
Positive and negative impacts
The emphasis of this handbook is primarily on
avoiding and mitigating negative impacts,
which should be a high priority in all road
projects. Environmental
impacts sometimes
have both positive and negative effects; some
impacts can positively affect some people and
negatively affect others in the same environment. For example, rechannelling streams as
part of road construction might improve drainage for a roadside farmer, but wreak havoc on
the livelihood of others who depend on the
aquatic species disturbed by the rechannelling.
Positive outcomes that occur as a result of
project completion typically include improved
access, reduced travel time and cost, and perhaps reductions in accidents or noise. Other
positive outcomes can be designed into a project, for example, improving water retention for
local use, flood control, or providing better facilities for pedestrians and bicycles (see Box
6.2). In some cases, positive impacts can ap
pear without having been initially foreseen by
the road agency, such as the use of borrow sites
to water livestock in dry areas.
6.1.6
Random and predictable impacts
In the preliminary analysis (Chapter 3) of an
environmental impact assessment, it is useful to
distinguish between assured or highly probable
impacts, and more random or unpredictable
ones which have a low probability of occurring
but which nevertheless may have serious consequences for the environment. For example, in
a country with a large, densely settled population, it is reasonable to predict that the construction of a road through unsettled areas will
result in population migration, whereas incidents such as accidental pollution, fire, or spillproducts
are, by nature,
age of toxic
unpredictable. Well understood and predictable impacts can usually be mitigated with remedial measures, and therefore call for minor
EA requirements such as an IEE and environmental summary report, as opposed to a full
EA.
6.1.7
Local and widespread
impacts
Local impacts include effects in the immediate
BOX 6.2
ENHANCING WATER MANAGEMENT THROUGH INNOVATIVE ROAD DESIGN
In dry climates, millions of liters of rainwater are lost through conventional road drainage designs, which treat
runoff as a nuisance, not as a resource to be captured. In a survey conducted by the World Bank, it was established that simple small-scale water retention structures along large and small rural roads could make a significant difference to water supplies during the dry periods. The study identified three basic types of structures along
roads that, with minor modifications, could become retention areas, with water useable for agricultural purposes.
These were:
standard stormwater catchbasins - deepened and with controlled drainage added;
i)
ii) various forms of check-dams or fords, to slow drainage, creating pending; and
iii) various other damming devices, such as sluice gates, raised box culverts and dams.
A study resulted in the preparation of a general design manual to assist engineers in planning for the inclusion of
such structural modifications during the design of the roadway.
An important cautionary note: such retention structures should be avoided in high use corridors, since the runoff
water may be contaminated with heavy metals and oil. Such waters are not potable by people or animals, can
contaminate leafy vegetables, and, if stored in deep basins, can contaminate groundwater aquifers.
Source: La&an,
64
1995.
TYPES OF ENVIRONMENTAL
IMPACT
x
such as destruction of a
building, or restricted access to a farm. Widespread impacts can occur many kilometers
from the project. These impacts are often linked
to indirect effects that arise over the mediumor long-term existence of the project and include the influx of settlers, deforestation, and
the development of new industries. While the
focus of most road EAs has been on relatively
narrow
corridors
measuring
lOO-500m in
width, impacts can extend much further, particularly in new road projects which traverse
isolated areas. Major habitat conversion can
take place up to 10 km on either side of the
cleared ROW. Road planners and EA practitioners should be aware of this possibility and address it explicitly in the project scoping activity
(see Section 3.2 and Chapter 10).
vicinity
6.1.8
of a road,
Temporary and permanent impacts
Temporary impacts are those whose occurrence
is not lasting, and which will eventually reverse
themselves, the affected system having returned to its previous state. An example of this
type of impact might be the trampling of roadside vegetation during resurfacing; it recovers
6.3
REFERENCES
after a few weeks, to the point where no change
from the original state is observable. Permanent
impacts are those which are irreversible-the
affected system will not return to its previous
state on a human timescale. It is important to
note that llpermanentN from the viewpoint of
EA, is defined as “within one’s lifetime”. Therefore the destruction of a mangrove forest would
be permanent.
6.1.9
Short- and long-term impacts
Short-term impacts are those which appear
during or shortly after construction; long-term
impacts may arise during construction, but
many of their consequences appear during the
operational phase, and may last for decades.
6.2
IMPACT SEVERITY
To qualify environmental impacts by the type
of effect they have on the environment is not
sufficient. Impacts must also be categorized according to their seriousness. The most damaging and longest lasting impacts will obviously
be the first to be avoided or mitigated (see Section 4.3.2 for further details).
AND BIBLIOGRAPHY
Gilpin, A. 1986. Environmental
Planning: A Condensed Encyclopedia. Park Ridge, NJ: Noyes Publications.
Lane, P.A., R.R. Wallace, R.J. Johnson and D. Bernard. 1988. A Reference Guide to CumuZative Ef/ects Assessment in
Canada, Volume 2. Hull, Canada: Canadian Environmental Assessment Research Council.
Lantran, Jean Marie. 1995. Water Management and Road Design in the Sahel Region. World Bank Transportation,
Water and Urban Development Department; Infrastructure Note RD-20. Washington, DC: World Bank.
Preston, E.M. and B.L. Bedford. 1988. “Evaluating Cumulative Effects on Wetland Functions: A Conceptual
Overview and Generic Framework”. Environmental Management. 12:5:565-583.
Spaling, H. and B. Smit. 1994. “Classification and Evaluation of Methods for Cumulative Effects Assessment”.
Paper presented at the Conference on Cumulative Effects in Canada: From Concept to Practice. April 13-14,
Calgary, Canada: Canadian Societies of Professional Biologists.
Spaling, H. and B. Smit. 1993. “Cumulative Environmental Change: Conceptual Frameworks,
proaches, and Institutional Perspectives.” Environmental Management, 17:5:587-600.
Evaluation Ap-
World Bank. 1991. EA Sourcebook, Volume II. “Rural Roads” (pg. 113), and “Roads and Highways” (pg. 168).
Washington, DC: World Bank, Environment Department.
65
i