This document discusses methods for identifying, predicting, and evaluating environmental impacts. It defines key terms related to impact assessment and categorizes impacts by type, nature, magnitude, extent, timing, duration, and significance. Direct impacts result from direct interactions between a project and the environment, while indirect impacts are a result of subsequent interactions. Impacts can also be cumulative, site-specific, local, regional, national or transboundary. The duration of impacts may be short-term, medium-term, long-term, temporary or permanent. The magnitude of impacts is described as high, medium, or low, and the likelihood of unplanned events is unlikely, possible or likely.

1. Part II: EA: Principle and Process
Batu Uprety
16 November 2021, Tuesday
2.6 Identification, prediction and evaluation of environmental
impacts – methods, techniques and processes
Definition of Key Words

2. Concepts of Impact
Why Impact Assessment – to know the impacts in advance
 Once impacts known helps to categorise them and develop
environmental protection measures
Categorisation of impacts:
 Type – physical, chemical, biological, social, economic and
cultural impacts
 Nature – direct, indirect or cumulative
 Magnitude or severity – high, moderate, low
 Extent – site-specific, local, regional, national or
transboundary
 Timing – immediate, short-term, medium-term or long-term
 Duration – temporary or permanent
 Reversibility – reversible or irreversible
 Significance – unimportant or important

3. Types of Impact
Environmental impacts
 Physical and chemical aspects – land and landscape,
geology, climate etc
 Biological – flora and fauna etc
Social impacts
 Social aspects – demographic impact (displacement and
relocation of population), social services – health, education,
drinking water, recreation, electricity etc
 Economic aspects – change in income level, employment
opportunities, change in price of local goods and services
 Cultural aspects – change in traditional pattern of life and
work, religious and archaeological features
 Gender impact – implications of development projects on
women, and their access to income and resources etc.

4. Nature and Extent of Impacts
 Direct – impacts that result from a direct interaction between the
project and resource/receptor.
 Indirect – impacts that follow on from direct interactions between
the project and its environment as a result of subsequent
interactions.
 Induced – impacts that result from other activities that happen as a
consequence of the project
 Cumulative – impacts from different projects that result to additive
or synergistic effects of higher magnitude, wide spatial extent and
long-term duration.
 Site-specific – impacts that are limited to project location.
 Local – impacts that are limited to the surrounding areas of the
project location (surrounding area to be defined).
 Regional – impacts that are experienced beyond the local areas to
the wider region.
 National or Transboundary – impacts that are experienced at the
national or transboundary scale, that is, affecting another country

5. Duration and Frequency of Impacts
Duration of impacts
 Short-term - predicted to last only for the duration of the
construction activities (that is, up to approximately one year).
 Medium-term - predicted to last from one year to the end of the
project life (that is, say 5 years).
 Long-term - predicted to continue beyond the project life but will
cease in time.
 Temporary – predicted to last less than the project duration.
 Permanent – impacts that cause a permanent change in the
affected receptor or resource that endures substantially beyond
the project lifetime.
Frequency of impacts
 Continuous – impacts that occur continuously or frequently.
 Intermittent – impacts that are occasional or occur only under
specific circumstances

6. Magnitude and Likelihood
Magnitude of impacts
 High – If the adverse impact can not be mitigated and the use
value of resource would be reduced substantially. Example,
forest clearance, land subsidence or site-specific impacts that
are difficult to avoid
 Medium – resources could be used with inconvenience and
impacts can be mitigated in reasonable effort.
 Low – resources could be depleted but can be used with little
inconvenience, and impacts can be mitigated.
Likelihood of impacts for unplanned events only
 Unlikely – event is unlikely but may occur during the project.
 Possible – event is likely to occur at some point during the
project.
 Likely – the event will occur during the project (that is, say it is
inevitable).

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Project Initiated
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Environmental
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8. Impacts might be
Project Activities Site clearance/Land
acquisition/Forest clearance
Primary Impact Loss of agriculture land
Secondary Secondary Decline in production
Tertiary Tertiary
Tertiary Quality of life
Loss of forest area
Soil erosion, downstream
Sedimentation, less fish production
Present focus on primary impacts only

9. Different Categories of Impacts
Resources Land and Soil Forests Air and Water
Direct
impacts
Loss of arable
land
Loss of forests/
habitats
Emission/effluents
discharge
Indirect
impacts
Decline in crop
production
Soil erosion &
sedimentation
Change in
microclimate,
decline in
production
Flooding, river
course change
Cumulative
impact
Migration
Change in ecosystem
productivity
Change in
quality of life
Hydropower Project (Run-of-the River)