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Network diagrams

A network diagram is a technique for illustrating how impacts are related and what the consequences of impacts are. For example, it may be possible to fairly accurately predict the impact of increased diversions or higher irrigation efficiencies on the low flow regime of a river. However, there may be many and far reaching secondary or tertiary consequences of a change in low flow. These consequences can be illustrated using network diagrams. For example, reduced low flows are likely to reduce the production of fish which may or may not be of importance depending on the value (either ecological or economic) of the fish. If fish are an important component of diet or income, the reduction may lead to a local reduction in the health status, impoverishment and possibly migration. Also, reduced low flow coupled with increased pollution, perhaps as a result of increased agricultural industry, may further damage the fish population as well as reduce access to safe water.

Table 4 shows an example of a network diagram for a proposed plan to increase the use of groundwater for irrigation by providing subsidies for sinking deep tube wells. This shows the primary through to quaternary impacts, as anticipated at the scoping stage. The main crop in the area is rice. Detailed prediction work following scoping would estimate the level to which the groundwater would fall and quantify the impacts which, together with economic analysis, would clarify which impacts were most important and most likely and also determine the most suitable mitigation measures.

FIGURE 2 Graphical comparison of alternatives. The final choice of either option B or option C will depend on the 'weighting' chosen (Source: Ahmad and Sammy, 1985)


Overlays provide a technique for illustrating the geographical extent of different environmental impacts. Each overlay is a map of a single impact. For example, saline effected areas, deforested areas, limit of a groundwater pollution plume etc can be analysed and clearly demonstrated to non experts. The original technique used transparencies which is somewhat cumbersome. However, the development of Geographic Information Systems (GIS) can make this technique particularly suitable for comparing options, pinpointing sensitive zones and proposing different areas or methods of land management.

Mathematical modelling

Mathematical modelling is one of the most useful tools for prediction work. It is the natural tool to assess both flow quantities and qualities (eg salt/water balances, pollution transport, changing flood patterns). However, it is essential to use methods with an accuracy which reflects the quality of the input data, which may be quite coarse. It should also be appreciated that model output is not necessarily an end in itself but may be an input for assessing the impact of changes in economic, social and ecological terms. Mathematical modelling was used very effectively to study the Hadejia-Jama' are region in Nigeria. In this case the modelling demonstrated the most effective method of operating upstream reservoirs in order to conserve economically and socially valuable, and ecologically important downstream wetlands. Optimal operation was found to be considerably different from the traditional method originally proposed. Under the revised regime the economic returns were also found to be higher.

TABLE 4 Example of network analysis showing the impact of a policy to utilize groundwater by subsidizing tubewells

Primary impacts

Secondary impacts

Tertiary impacts

Quaternary impacts


Lowering of groundwater in dry season

Loss of income & water from domestic hand pumps

Use of poorer quality water

Increased health risks

1. Ensure that the new DTW either hold domestic water locally or feed into distributary system
Note Effected group are poorer people

Income diverted to buy water

Decreased income & time

Travel to distant source

Reduced quality of life

Loss of income & water from shallow tubewells for irrigation

Income diverted to buy water

Decreased income & time leading to possible food shortage

1. Deepen STW

Crop failure

Reduced quality of life

2. Ensure new DTWs supply STWs in dry season

Abandonment of land & migration

3. Provide compensation from DTW taxation

Drawdown of surface water bodies

Decreased fish capture/fish mortality

Loss of protein intake

1. Artificially stock water bodies

Loss of income for fishermen

2. Recharge water bodies from DTW
Note: Fishermen are already poorer than farmers in general

Loss of wetland

Loss of wetland flora/fauna migratory birds, fish spawning areas

Loss of wetland products

1. Restrict DTW development in vulnerable areas Note Landless & Rural poor are greatest users of wetlands

Reduced navigation possibilities

Increased transport costs

1. Increase navigation depth by dredging

Agricultural intensification

Increased fertilizer

Groundwater contamination by nitrate

Polluted drinking water by nitrate causes various illness, particularly in babies

1. Control fertilizer use
2. Educate users of groundwater as well as fertilizer users babies

Eutrophication of surface water due to runoff

Increased weeds in channels & surface water bodies, algal blooms

1. Remove and control weeds

2. Educate about dangers of algal blooms

Increased pesticide use

Groundwater contamination

More expensive alternative for drinking water must be found

1. Regulate pesticide use

Poisoning of fish & shrimp

Reduction in fish catches & protein availability

2. Encourage rainwater storage

Reduced income for fishermen

3 Encourage integrated pest management

Bioaccumulation of pesticide in man

4 Subsidize non-persistent pesticides

5. Tax undesirable pesticides

6. Educate pesticide users & fish eaters

Increased level of pest & diseases vectors due to loss of fallow period

Increased pesticide use

Bioaccumulation of pesticide in man

1. Vaccinate to prevent epidemics

Increase in animal & human disease due to vector

Loss of quality of life

2. Encourage alternative cropping patterns

3. Educate about disease vectors

Reduced fallow land & grassland for grazing

Fewer livestock or poor quality livestock

Reduced protein intake & income for landless groups

1. Develop alternative grazing

Reduced scrubland for fuel wood

Alternative sources sought for fuel

Income & time spent collecting fuel

1. Develop fuelwood supplies

Destruction of trees

2. Introduce more efficient cookers

STW = shallow tubewells
DTW = deep tubewells

Expert advice

Expert advice should be sought for predictions which are inherently non-numeric and is particularly suitable for estimating social and cultural impacts. It should preferably take the form of a consensus of expert opinion. Local experience will provide invaluable insight. Expert opinions are also likely to be needed to assess the implications of any modelling predictions. For example, a model could be developed to calculate the area of wetlands no longer annually flooded due to upstream abstractions. However, the impact on wetland species or the reduction in wetland productivity resulting from the reduced flooding may not be so precisely quantifiable but require a prediction based on expert opinion.

Economic techniques

Economic techniques have been developed to try to value the environment and research work is continuing in environmental economics. This is a specialist subject and only a brief introduction is included here. For more detailed information the reader is advised to read Winpenny (1991) and other standard texts. It is important to stress that environmentally sound development brings long term economic benefits. Unfortunately, short term gains are often given priority.

The most commonly used methods of project appraisal are cost-benefit and cost-effectiveness analysis. It has not been found easy to incorporate environmental impacts into traditional cost-benefit analysis, principally because of the difficulty in quantifying and valuing environmental effects. An EIA can provide information on the expected effects and quantify, to some extent, their importance. This information can be used by economists in the preparation of cost-benefit calculations. Cost effectiveness analysis can also be used to determine what is the most efficient, least-cost method of meeting a given environmental objective; with costs including forgone environmental benefits. However, defining the objective may not be straightforward.

Valuing the environment raises complex and controversial issues. The environment is of value to the actual users (such as fishermen), to potential users (future generations or migrants), and to those who do not use it but consider its existence to have an intrinsic value (perhaps to their "quality of life"). Clearly it is difficult to quantify such values. Nevertheless, attempts have been made and the two most useful methods for irrigation projects in developing countries are "Effect on Production" (EOP) and "Preventive Expenditure and Replacement Costs" (PE/RC). The EOP method attempts to represent the value of change in output that results from the environmental impact of the development. This method is relatively easy to carry out and easily understood. An example would be the assessment of the reduced value of fish catches due to water pollution or hydrological changes. The PE/RC method makes an assessment of the value that people place on preserving their environment by estimating what they are prepared to pay to prevent its degradation (preventive expenditure) or to restore its original state after it has been damaged (replacement cost). Both methods have weaknesses and must be used judiciously.

Environmental health effects present similar problems, cost-effectiveness analysis is a useful tool in the selection of mitigating or control measures, but for ex-ante project appraisal the incompatibility of human health and monetary values has forced economists to develop other techniques and indicators. A recent publication by Phillips et al. (1993) deals with the principles and methods of cost-effectiveness analysis and its application to decisions about the control of vector-borne diseases, particularly the control of disease vectors. In its World Development Report of 1993 (Investing in Health) the World Bank proposes the cost-utility analysis which expresses health status in DALYs (Disability Adjusted Life Years).

Final report - Environmental impact statement

The final report of an EIA is often referred to as an Environmental Impact Statement (EIS). In addition to summarizing the impacts of the alternatives under study this report must include a section on follow up action required to enable implementation of proposals and to monitor long-term impacts. The purpose of an EIA is not to reach a decision but to present the consequences of different choices of actions and to make recommendations to a decision maker. Recommendations are a crucial part of the Environmental Impact Statement. The format of the report should preferably follow a standard as recommended by the appropriate institution or required by legislation. The executive summary of the EIS should only be 2 to 5 pages long and the main report, excluding appendices should be preferably about 50 pages long and no more than 100. An exceptionally complex study might require 150 pages.

Experts preparing an EIA must appreciate that the final report will be read by a wide range of people and the subject matter may be technically complex. Senior administrators and planners may not understand the importance of technical arguments unless they are presented carefully and clearly. The quality of the executive summary is particularly important as some decision-makers may only read this part of the report. The executive summary must include the most important impacts (particularly those that are unavoidable and irreversible), the key mitigating measures, proposed monitoring and supervision requirements, and the recommendations of the report.

The main text should maximize the use of visual aids such as maps, drawings, photographs, tables and diagrams. Matrices, network diagrams, overlays and graphical comparisons should all be included. The main text should cover the following points (adapted from EBRD (1992) and World Bank (1991)):

• A description of the programme, plan or project including the physical, social and ecological context as well as the time-scale of the proposals under study. Any major revisions made as a result of the scoping process should be identified here.

• A summary of the EIA methodology, including the limits of the study and the reasons for them.

• The policy, legal and administrative framework within which the project is situated.

• A summary of the baseline data providing an overall picture of present conditions and physical, biological and ecological trends. The consequences of the "no-action" option should be described together with a brief description of other developments taking place and their relationship to the study proposal.

• A description of the governmental and non-governmental participation during the EIA.

• Environmental impacts. The most significant beneficial and adverse environmental impacts associated with the options studied need to be clearly stated. Impacts need to be quantified wherever possible and uncertainties in the results need to highlighted, whether due to a lack of knowledge, lack of data or to critical but indeterminate assumptions such as future policy. The results of economic analyses need to be presented in the same section. Mitigation and enhancement measures that are proposed may either be presented together with information on the environmental impacts or as a separate section. Impacts with no effective mitigation need to be clearly identified as such.

• The Environmental Action Plan needs to be presented in two sections. The first part covers the implementation of proposed mitigation measures, including both costs and training, and institutional enhancements required to implement them. The second part should cover monitoring requirements to measure predicted impacts and to determine the success of mitigation measures. Again, costs and institutional requirements need to be included for each major proposal. A clear programme of implementation should be given.

• Recommendations and guidance to the decision maker.

• A statement of provision for auditing, who should carry it out and when.

The appendixes should include:

• a glossary of technical terms and units
• a list of the team who prepared the EIA
• records of public meetings and consultations
• a catalogue of information, both data and written material, and their source
• technical information too detailed for the main text.

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