Impact Assessment Methods

https://www.iisd.org/learning/eia/wp-content/uploads/2016/05/Impact-Assessment-Methods.pdf

By The International Institute for Sustainable Development

This document outlines several common impact assessment methods, including:

• Expert judgment
• Quantitative physical and mathematical models
• Cumulative impact assessment
• Matrices and interaction diagrams
• Rapid Impact Assessment Matrix (RIAM)
• Battelle Environmental Evaluation System

Expert judgment is based on the professional option of experts that have considerable experience in

the areas of assessed impacts such as on water, soil, biodiversity and communities. Expert

judgments can be used when limited data and information are available that did not allow for

predictive modelling to explore the impacts. Expert judgments can be used in conjunction with

quantitative modelling and to complement modelling. They can also help interpret results and their

consequences on other sectors and communities, for example.

For issues where data are available, quantitative physical and mathematical models linking different

aspects of the hydrological cycle, watershed-level impacts, impacts of changes in water and other

land and ecosystems available for biodiversity and resources accessible for the surrounding

communities. The choice and use of quantitative models for impact prediction should be suited to

the particular cause-effect relationship being studied; for example, transport and fate of oil spills,

sediment loadings and fish growth and pesticide pollution of groundwater aquifers; examples of the

use of quantitative models include (UNU, UNEP, RMIT, 2007):

• Air dispersion models to predict emissions and pollution concentrations at various locations

resulting from the operation of a coal-fired power plant.

• Hydrological models to predict changes in the flow regime of rivers resulting from the

construction of a reservoir.

• Ecological models to predict changes in aquatic biota (e.g., benthos, fish) resulting from

discharge of toxic substances.

Recently, there is a stronger focus within EIAs to assess social impacts and consequences of the

planned project and alternatives. The focus on the social issues is now formulated in a standardized

procedure called a social impact assessment.

Cumulative impact assessment: A key part of the impact assessment is the assessment of cumulative

impacts of the already listed impacts. Multiple and successive environmental and social impacts

from existing developments can reinforce each other, leading to more serious consequences on

environment and people than each of the developments separately. This may result in significant

cumulative impacts; such cumulative impacts could include (USAID, 2011):

• Increases in pollutant concentrations in a water body or in the soil or sediments, or their

bioaccumulation.

• Reduction of water flow in a watershed due to multiple withdrawals.
• Increases in sediment loads on a watershed or increased erosion.
• Interference with migratory routes or wildlife movement.
• Increased pressure on the carrying capacity or the survival of indicator species in an

ecosystem.

• Wildlife population reduction caused by increased hunting, road kills, and forestry

operations.

• Depletion of a forest as a result of multiple logging concessions.
• Secondary or induced social impacts, such as in-migration, or more traffic congestion

and accidents along community roadways owing to increases in transport activity in a

project’s area of influence.

According to the International Finance Corporation (IFC) (2013, p.26), “[b]ecause it is usually beyond

the capability of any one party to implement all of the measures needed to reduce or eliminate

cumulative impacts, collaborative efforts will likely be needed. Governments can play a significant

role in ensuring environmental and social sustainability by providing and implementing enabling

regulatory frameworks that guide and support the appropriate identification and management of

cumulative impacts and risks.”

Matrices and interaction diagrams: These are the most commonly used approaches in the EIA.

Matrices take the form of a grid or table that allows the assessment of linkages or impacts between

the issues listed in the rows and columns. This includes, for example, the impacts at all stages of the

project—development, operation and closure—for each of the elements of the environment and

society. The matrices can display quantitative information by, for example, listing the amount of

waste produced, water extracted or qualitative information such as high, medium, low impacts.

Information entered into the matrices can be based on all of the already discussed methods. The

advantages of using matrices is that they provide an easy-to-understand visual representation

across all the impacts. There are several types of matrices have been used in EIA. Most commonly

used matrix is the so-called Leopold Matrix applied in the paper industry in 1971. This matrix was

designed for the assessment of impacts associated with most types of construction projects, listing

100 different project actions along one axis and 88 environmental characteristics and conditions

along the other, including aspects of both the biophysical and socioeconomic environments (FAO,

1996).

Rapid Impact Assessment Matrix (RIAM)

RIAM is a systematic approach using qualitative data that can be expressed in a semi-quantitative

way. The RIAM method uses a multidisciplinary team to organize the analysis process into an

interactive and coherent form that encourages participation throughout the process (Inter-American

Development Bank, 2010).The system makes it possible to create an impact profile which allows the

practitioner to make a rapid comparison to the development options. There are four aspects of the

environment that are analyzed; physical-chemical, biological, human and economic. The process

that RIAM follows is to identify significant changes (positive and negative) caused by the project,

establish a baseline for the monitoring plan, identify mitigation strategies and design a monitoring

and evaluation system to determine the effectiveness of the mitigation strategies (FAO, 1996).

Using the RIAM method, public participation is carried out at the data collection and mitigation

stages of the process. Both of these stages are directly followed by quality control measures during

the analysis and program monitoring stages. The multidisciplinary team allows data from different

sectors to be analyzed at the same time in one common matrix. A rapid and clear evaluation of the

most important impacts the project may have is thus made possible. Such a matrix also allows the

team to compare different development options according to how the four aspects of the

environment may react to an action.

Battelle Environmental Evaluation System

In this method, environmental impacts are split into main categories; ecology, pollution, aesthetics

and human interest. This method is helpful to determine alternatives to the proposed project plan.

Indicators are then chosen to measure specific parameters within each category. For example:

Ecology includes species and populations, habitats and communities and ecosystems. Indicators

used to identify the current state of the environment. Once indicators are chosen for each category,

three steps are carried out (FAO, 1996):

1. Indicators are used to describe the current state of the environment, which is then rated

between 0 to 1, 0 being poor quality and 1 being good quality, so that environmental

deterioration or improvement can be quantified.

2. 1,000 total points (Parameter Importance Units) are shared among all the indicators to

reflect the importance of each parameter.

3. A comparison is then done on the quality of the state of the environment with and without

the project using the following equation:

(Vi)₁ environmental quality for indicator “i” project conditions

(Vi)₂ environmental quality for indicator “I” without the project

wᵢ relative weight of the indicator “i” (EIU)

m total number of indicators.