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View the documentPaper 11 Small-scale irrigation in sub-Saharan Africa: a balanced view
View the documentPaper 12 Environmental and health aspects of irrigation

Paper 12 Environmental and health aspects of irrigation

P. Bolton

Overseas Development Unit, HR Wallingford

Summary: The paper shows how awareness and understanding of the relationship between human activity and environmental change have developed over the last 20 years with regard to irrigation in developing countries. The terminology of 'impacts' and of 'sustainability' are examined in relation to irrigation projects and to the wider environment, resources and societies within which they are located. From this discussion various key issues are identified concerning the environmental impact and sustainability of irrigation systems. These have implications both for policy formulation and research. The paper ends by examining the difficulties of research in such interdisciplinary subject areas using projects undertaken by the Overseas Development Unit at HR Wallingford by way of example.

The rise in environmental consciousness and conflict in irrigation and water resources development

The Overseas Development Unit (ODU) of HR Wallingford (formerly the Hydraulics Research Station) was established in 1973 to provide specialist expertise and undertake research on behalf of the Engineering Division of the ODA in problems of water resources and irrigation in developing countries. The ODU endeavours to ensure that its research programme addresses the water resources and irrigation problems considered most acute, at a particular time, by practicing engineers in developing countries and specialists and aid officials from the UK. Surprisingly the term 'environment' does not feature in the title of any ODU research project prior to 1987 (An investigation of schistosomiasis control in irrigation schemes, begun in 1983, was later given an 'environmental' title). By contrast, the current (1992/93) programme groups approximately one third of the Unit's work under a theme 'Environmental Effects'.

The deduction from this, that the environment was not an important consideration until approximately five years ago in the perception of most Third World irrigation and water resources engineers and researchers would, however, be misleading: although key terminology and concepts were absent, the processes were under active study. For example, one of the projects on which the ODU started its research 19 years ago was a study of salinity (sea water) intrusion in tropical estuaries. This phenomenon, resulting from freshwater abstraction and the regulation of river flows particularly for irrigation, has major environmental implications. The types of numerical modelling technique developed in that early project remain invaluable as part of the tool-kit used by engineers in seeking to understand, predict and manage environmental change in tropical river basins. Undoubtedly this project would legitimately be included as part of the 'Environmental Effects' theme if it were part of the ODU's current research programme. Similarly, studies of catchment erosion and soil salinisation which have featured in the ODU's research for many years are now regarded as 'environmental' issues.

On the same basis, almost every other project on which the ODU has been engaged over the last 19 years could be considered as having an important bearing on 'the environment'. This is hardly surprising when one considers that irrigation is a process which involves interactions between almost every facet of the environment: atmospheric gases, water, soils and minerals, energy, biological species and communities and human activities and relationships.

Yet vocabulary and concepts relating to 'the environment' have, as noted above, assumed importance only relatively recently in irrigation and water resources development. Unfortunately this change has arisen for largely negative reasons as a result of the publicity given to particular water resources projects which have been built without adequate consideration for their overall and long-term effects. In response to this, the techniques of Environmental Impact Assessment were developed and, in many countries, enforced through legislation in order to prevent projects from proceeding if they were likely to cause adverse environmental impacts. This inevitably created a situation of conflict between engineers and planners on the one hand and environmental specialists and 'conservationists' on the other over the implementation of new projects; disputes which led to severe delays and, in some cases, to the cancellation of projects which may have taken many man-years of planning and design. Such conflicts came as a psychological shock to many engineers who had previously believed that their's was a profession which was entirely and self-evidently serving the needs of society.

The basis for future co-operation

Situations of conflict and inertia as described above are beginning to give way to a realisation that the traditional roles of engineers and other professional groups are changing and that closer co operation is needed to address the complex issues which we face in seeking to optimise decisions concerning the future development of water resources and their impact on the environment. However, considerable progress must first be made in clarifying concepts, in developing a broader understanding and new ways of working and in evolving new technical skills. The principal needs, as I see them, are discussed below.

To develop a dearer understanding of 'the environment'

One source of confusion in considering 'environmental effects' is the different shades of usage which are given to the term. Often when examined closely, the intended meaning is restricted to effects related to wildlife and natural ecology. The use of the term 'environmental effects' to refer primarily to ecological changes accords with the increasing concern about 'conservation' in 'industrialised' countries which have already undergone substantial social and land-use changes and where the most common and far-reaching effects of current water-related activity are changes to water quality affecting wildlife. By contrast, in most tropical developing regions physical changes to the environment and changes which affect society are equally, if not more, important than the biological changes. It is, therefore, necessary to ensure that in discussions concerning 'environmental' effects the physical, biological and social aspects are each considered in full (see Figure 1).

In the remainder of this paper the combined interactions of the human, biological and physical spheres will be intended whenever the terms 'environment' or 'environmental' are used. In this usage, they are synonymous with such words as 'comprehensive', 'global', 'holistic'. This meaning, which links with the development of EIA procedures, carries the connotation 'everything we can possibly think of which might be influenced by or influence the activity under examination'. This is the meaning envisaged by the Environmental Impacts Working Group of the International Commission on Irrigation and Drainage (ICID) when it drafted a Check-list of possible environmental impacts (see Figure 2).

A further step towards clarification of terminology is suggested by the phrase "might be influenced by or influence.. A distinction can be drawn between those effects which the environment has on the project and those which the project has on the environment. The merit of stressing this distinction is that it ensures that a project planner, designer or manager is assigned the full responsibility for all factors which affect the primary productivity of the project. Effects such as sedimentation, soil salinisation, social, financial or organisational problems and agricultural weeds and pests cannot be pushed to one side as 'environmental impacts' simply because the person responsible for the project does not know how to deal with them. Such effects must be considered to ensure that a project's primary productivity will not decline with time.

In this respect, the relatively recent introduction of the term 'sustainable' development is particularly helpful. Rather than talking in teens of the impact of the environment on a project, the question "is the project sustainable?" clearly places the responsibility for ensuring that such effects are considered on the person responsible for the project. For practical purposes, this question may be sub-divided into separate questions concerning the resources on which the project depends. The first part of Table 1 lists the separate resources and illustrates how concern over impacts (e.g. salinisation) translates into questions of sustainability (in that case, sustained soil fertility). Thus, with respect to the effects of the environment on the project the term 'sustainability' provides a better framework for guiding the project official than does the term 'impacts'.

Figure 1 Examples of disciplines relating to the major components of the environment associated with irrigation

Figure 2 ICID Check-list of possible environmental impacts of irrigation, drainage and flood-control projects

Table 1 Selected items to illustrate the links between impacts and sustainability

The extent to which the project official carries responsibility for wider environmental effects depends to some extent on the institutional framework which exists. Such effects might also be viewed in terms of 'sustainability', as shown in the right-hand columns of Table 1, but it would generally be the responsibility of a higher authority such as a river basin authority or environmental protection agency, rather than the project official, to ensure that individual projects do not compromise the sustainability of these regional, or even global, resources and systems. If competent authorities do exist at this higher level, the official responsible for an individual project can treat wider environmental effects as 'impacts' of his project whose nature he/ she must attempt to specify but whose implications the higher authority has the responsibility to assess. Thus the terms of 'impacts' and 'sustainability' may both have a role to play depending on the particular context.

Unfortunately in many situations in developing countries institutional responsibilities may not be dearly defined and a project official may not be in a position to pass to others the responsibility for considering how the sustainability of wider environmental systems is affected by the project. In such cases the above attempt to clarify the terminology may not be relevant and the project official may find he/she has responsibility for impacts which are more far reaching than he/she has resources to assess.

To understand the special circumstances relating to tropical developing regions

There are substantial differences between temperate (industrialised) and tropical (developing) countries with regard to the environmental effects associated with irrigation and water resources development. It has already been mentioned that the main environmental preoccupation in 'western' countries tends to be the effect of water quality changes on wildlife. In the Third World this is only one of several major environmental changes which are occurring alongside or as a result of irrigation and water resources development. The reasons for the wide range of factors to be considered include:

· a greater intensity, seasonality and variability of rainfall leading to high rates of erosion and geomorphological activity and the need for substantial reservoir storage capacity

· higher temperatures leading to higher rates of evaporation and hence higher crop water requirements and also to greater productivity and diversity of ecological systems which in turn cause increased problems of human disease and crop pests

· higher population growth rates leading to increasing demands for agricultural land and for irrigation, domestic and industrial water

· weaker economies and a poorer population leading to problems of poverty-related disease and environmental degradation as well as intense competition for capital which results in the desire for cost savings (for example, by the omission of drainage works) which have long-term environmental repercussions

· social, political and institutional systems which are less capable of coping with the conflicts which arise in resource allocation and environmental management, conflicts which the projects themselves may generate

· relative scarcity of the technical and managerial skills needed to predict and manage environmental change.

Considering the above differences in relation to the scope of environmental effects defined in Figure 1, it is clear that a vast amount of skill, knowledge and experience would be needed to 'manage' the environmental changes associated with irrigation if it were to be undertaken with the thoroughness and confidence that is implied by those who call for improved environmental management.

Throughout the remainder of the paper I shall try to highlight practicable ways in which progress can be and is being made, albeit slowly, in the areas of environmental management with which I am most familiar. My starting point is always to consider how to assist the existing professional staff, many of whom are engineers like myself, to broaden the scope of their activities and understanding, with respect to identifying and managing more effectively environmental change, given the severe constraints and conflicting demands which characterise their situation.

To address the key issues

The central issue with regard to future irrigation development, an issue which is of growing importance for the environment, is the impact of the consumption of water for irrigation on surface water and groundwater resources and hence on other human water users and on the physical and ecological characteristics of the terrestrial areas and water bodies depending on these resources. Irrigation is man's most significant consumptive use of water with typically a depth of between half and one metre of water being evaporated from every topical irrigated field during the growing period of a single crop. During the process the sediment and dissolved solids (salts and pollutants) previously carried by the water are left behind either through deposition (resulting in sedimentation or salinisation) or by causing increased concentrations in the water which remains. Apart from the evaporated water, some of the water diverted for irrigation will percolate into the ground where it may result in a progressive rise in water-table and eventual waterlogging. These processes are, therefore, the source of several major types of environmental impact and the cause for a lack of sustainability in many individual projects. Moreover, irrigation's high consumptive use of water is likely to feature as an increasingly important cause for water shortage and hence conflict in the overall management of water resources.

For the above reasons, water-use efficiency (the productivity of a unit volume of water in terms of the amount of crop it produces) is becoming a key parameter in irrigation planning and management. In the first analysis it can be assumed that if water-use efficiency can be improved, the overall environmental impact of irrigation will be reduced. There are a number of practical ways in which possible improvements in efficiency can be sought: from the purely physical (improved canal linings and seepage reduction, software to assist the scheduling of irrigation releases, micro irrigation and sprinkler techniques); to the biological (alternative crops or varieties); and human aspects (institutional, managerial and financial factors). Work on each of these is progressing in various institutions in the UK and around the world. They are important but by themselves they are not enough to ensure reduced environment impacts. This is why I used the phrase "in the first analysis" when referring to the importance of water-use efficiency in relation to environmental effects.

Unfortunately there are other interlinking factors which are environmentally significant and must also be considered. For example, to achieve the highest possible crop yields for a given volume of water is likely to entail the use of agrochemicals. These introduce both a direct financial cost as well as an environmental cost in terms of pollution. Likewise high water-use efficiencies may be environmentally harmful if low rates of water application lead to progressive accumulation of salts in the soils and consequent loss of soil fertility. As a further example, some crops which are highly productive in terms of water use may demand high levels of farm labour or mechanisation or require post-harvest processing which have possible social and pollution implications.

Two aspects of environmental change which relate less closely than most to the efficiency of irrigation water use are the ecological impacts and the social impacts (including health impacts). In many instances, the attempt to increase the 'efficiency' of exploiting natural resources inevitably leads to a loss of species diversity and 'poorer' ecosystems. This is true in an irrigation scheme where large tracts of land are converted to monocropping and the creation of 'managed' canals and reservoirs provides only limited support for aquatic life. Modified operation of existing schemes to achieve less 'wasteful' use of water may also lead to the drying out of wetland areas which had previously been rich in wildlife. (However, in relation to human health, the opposite is generally true: for example, high water-use efficiency is likely to produce fewer water bodies suitable for colonisation by the vectors or hosts of human parasitic diseases.) In other respects, social impacts often bear little relation to the efficiency of water use: resettlement, which in many countries is one of the most contentious issues, relates to the land area under development, not the water use.

Thus, whilst high water-use efficiency is a key parameter to consider it is not sufficient to rely solely on this as a means of ensuring that adverse social and environmental changes are minimised. For this reason there is need for some caution in applying the principle of water as an 'economic good' as an environmental management tool without also introducing safeguards to avoid certain damaging changes which are not directly related to water-use efficiency. The optimum solution to complex water allocation and management decisions is unlikely to be achieved through oversimplification of the problem.

To be aware of areas of special sensitivity

The key issues in relation to environmental change associated with irrigation and water resources development are likely to vary from locality to locality and project to project. It is necessary to be aware that certain regions or certain types of project are particularly sensitive. In relation to the physical environment the four factors which lead to particular environmental sensitivity in relation to irrigation are:

· areas of low or erratic rainfall

· areas where sediment loads in rivers are high whether due to high erodibility (e.g. the loess plateau of China) or to earthquake and volcano activity

· areas in which solute loads are high especially resulting from the re-use of drainage water

· areas with problematic soils.

In the biological and human spheres the factors leading to particular sensitivity are:

· areas which have hitherto been largely undeveloped

· areas of high population density

· projects which lead to rapid or large-scale social disruption or migration.

There are, moreover, different degrees to which environmental management may be expected to control or ameliorate adverse environmental effects. A desire to avoid certain changes would be virtually unreconcilable with the development of a region for irrigation: the preservation of the ecology of wild or undeveloped areas and the preservation of rural society with its particular socio/political and economic structures may both lie in this category.

Other changes, although having the potential for serious adverse effects, also have the potential, with appropriate resources and skill, to be managed in such a way that the net positive effects far outweigh the negative. Such changes include the control of pollution, the control of human disease, the control of weeds and pests, the achievement of economic and social well-being and the management of ecology within regions which have already been 'developed'.

Two types of environmental change have potential for some amelioration through careful and well-resourced management but may nevertheless have cumulative impacts which will, in the long term, have important water resource management implications: the sedimentation of reservoirs and the salinisation of soils. Both must be studied carefully in relation to the sustainability of irrigation in certain regions and further research and strategic thinking are required to clarify the potential for managing these changes.

The role of interdisciplinary research

Methods to identify key issues

In the above context of seeking to address complex environmental management decisions the ODU, through its collaboration with the ICID Working Group on Environmental Impacts, identified the need for a systematic procedure to assist engineers and others who are unfamiliar with many of the necessary environmental disciplines to highlight key issues in relation to the planning and management of irrigation, drainage and flood-cntrol projects. The result of this initiative was the ICID Check-list which provides a comprehensive summary of the areas of environmental concern which should be considered in relation to these types of project (in this instance issues of 'sustainability' and 'impacts' were combined into a single category of effects to simplify usage). In its summary form (Figure 2) the Check-list appears to provide little practical guidance to the non-specialist user but the Working Group amplified the procedure by providing detailed descriptions, a targeted bibliography, data sheets for recording relevant information and results sheets for recording whether the user judges particular impacts to be important or whether he/she has insufficient data or knowledge to make a judgement. The relationship of the various components to each other is shown in Figure 3 and the first draft of the procedure is presented in Mock and Bolton (1991). The procedure has undergone field trials in a number of countries (including Pakistan and Sri Lanka) where the main benefits reported have been in relation to educating and involving the engineering profession in the environmental implications of their planning, design and management decisions.

Figure 3 Procedure for assessing key issues based on the ICID Check-list

Education and involvement of the non-specialist are the primary objectives of this work rather than to replace the need for specialists in the various environmental disciplines. This is well illustrated by one of the ODU's current research projects, in northern Nigeria, in which a questionnaire developed under the framework of the ICID Check-list is being used to collect information about the environmental status of some existing small irrigation schemes (see Bolton et al., 1990 and 1991). In this, and many other similar situations, there are few resources available to undertake thorough environmental studies but the people with first-hand knowledge of a particular project (the project manager, the community leaders, the village health workers) are not pooling their knowledge, nor are they trained to assess the implications of their local knowledge in terms of environmental change. The questionnaire enables an initial assessment to be made of the most important health and environmental factors so that specialist help and advice can be targeted to best effect. In other words, non-specialists are able to use the procedure to undertake an initial scoping of the situation in order to optimise the use of scarce specialist skills. The preliminary work, in which a team of scientists collected field data to validate the results obtained from the questionnaire, suggests that this approach has merit both for identifying hitherto unrecognised problems and for creating awareness and understanding amongst the project officials.

Development and testing of methods for environmental management

With reference to Figure 1, I believe that the principal areas where new initiatives and research are required are in the areas in which there is an overlap between the three broad spheres of knowledge, physical science, biological science and human science. I have deliberately highlighted these three spheres because the disciplines within them have, to some extent, developed under different sets of principles concerning the way in which new knowledge is acquired, validated and presented. They also have different understandings about the ways in which systems behave and about the extent to which future change can be predicted. I have become particularly involved at the meeting-point of physical and biological sciences. It took me some time to understand that my fundamental belief in the deterministic nature of physical systems (excluding sub-atomic phenomena) and the over-riding desire to describe their behaviour with rules which enable quantitative generalisations and predictions to be made is not embedded so deeply within the fundamental tenets of biological scientists. Their outlook is more strongly descriptive and probabilistic: the desire to prove direct causality is less strongly present.

The different approaches are highlighted when joint research is attempted in the field of environmental management. Engineers and physical scientists are accused by biologists of being too ready to ascribe causality in situations where changes may simply be coincident and of being too ready to generalise without understanding that only slight changes from one situation to another may result in major differences in the response of biological communities. Biologists, on the other hand, are accused of being too tied to scientific procedures which are observational rather than experimental and, therefore, of being too cautious in designing studies which will demonstrate how changes in the management of a physical system may affect biological productivity.

The main focus of my own research in this area has been the developing and testing of measures for the control of water-related disease in irrigation systems In particular, the ODU has recently completed the first phase of a seven-year study in Zimbabwe to develop techniques which engineers can adopt to help reduce the transmission of schistosomiasis (see Chimbari et al., 1991 a and b) The study has attracted particular attention since few previous attempts have been made to pilot test methods for the environmental management of schistosomiasis within an operational irrigation project. Measures under investigation involve physical changes to the irrigation system to discourage the colonisation of water bodies by the aquatic snails, which are the intermediate hosts of the disease (canal lining, development of free-draining irrigation structures, careful scheduling of irrigation releases, attention to the design and operation of local storage ponds and adequate drainage provision), to discourage humans from contaminating water bodies (construction of household and in-field latrines) and to discourage humans from coming into contact with infected water (careful village location and provision of adequate, safe supplies of domestic water).

To a large degree, practices which are considered good engineering are also good for reducing schistosomiasis transmission. However, as the preliminary results indicate, see Figure 4, the effectiveness of these measures is variable and difficult to predict. In two of the irrigated areas, disease prevalence appears to have been held at a low level for three years whereas in a third, where similar measures had been introduced, the prevalence has risen to a level equivalent to that in an area without control measures. The research has increased our knowledge about the effectiveness of particular control measures but has also highlighted the difficulty of controlling this disease by environmental means: deviation from the recommended control strategy by only a small amount may result in transmission levels which are as high as if no measures were used.

Of more direct relevance to the subject of this paper are some of the lessons learned concerning the overall strategy for control and the methods by which research can be undertaken In terms of strategy, the work has clearly demonstrated that to focus on planning and design alone is mistaken. Irrigation systems mature with time and biological communities change and adapt. More focus must be given to the dynamic aspects of control and, in particular, to the involvement of the local community so that they can be enabled to monitor the situation and know how to respond to changes which might occur In this way research which was previously considered to be interdisciplinary only to the extent of involving the physical and biological sciences is now seen to include an important human element as well. With regard to research method, the work has demonstrated the importance of working within the constraints of a normal operational irrigation scheme rather than in a 'laboratory'. The Zimbabwe work has shown the importance of considering financial, social and administrative constraints in seeking to develop environmental management measures suitable for wider replication.

Figure 4 Prevalence of schistosomiasis (haematabium) in adults and pre-school children, Mushandike, Zimbabwe


The conclusions of this paper reflect the personal interests and experience of the author rather than presenting a comprehensive review of the subject. Particular emphasis has been laid on the need to clarify terminology. The suggestion made is that the 'environment' should include all physical, biological and human components (see Figure 1), that ideally 'sustainability' is the preferred term when discussing environmental changes which affect the project or region over which the interested person or institution has responsibility and that the term 'impacts' be used to refer to changes for which another individual or organisation has responsibility. This distinction clearly has little relevance unless responsibilities are first set and agreed. The special circumstances surrounding environmental change in developing countries are discussed and point to the conclusion that techniques of environmental management developed for temperate conditions are not adequate to address the situation in tropical developing countries: new techniques must be developed and field tested. Because of the diversity of factors that must be considered some attempt must be made to pinpoint key issues. The primary consideration in many cases is to improve water-use efficiency since not only does this reduce the likelihood of conflict in water-short situations but also water-use efficiency and 'wastage' relate directly to several important aspects of environmental change. The identification of key issues must be supported by an awareness of areas of particular environmental sensitivity.

Among the large number of possible research topics which relate to this subject, two have been discussed from the author's own experience: the development of procedures to enable engineers and other professional groups who do not have specialist environmental knowledge to recognise existing or potential environmental hazards in order that specialist assistance can be sought; and the development and field testing of environmental management techniques for the control of water-related parasitic diseases. In each case the work points to the need for a reassessment of the relationship between subject disciplines, for an awareness of the financial, social and administrative constraints within which environmental management techniques will be applied and for a pragmatic recognition that, faced with the complexity of environmental relationships and systems, a small step in the right direction, albeit taken cautiously, is better than no step at all.


BOLTON, P., IMEVBORE, A. M. A. and FRAVAL, P. (1990) A Rapid Assessment Procedure for Identifying Environmental and Health Hazards in Irrigation Schemes. Report OD 120, HR Wallingford.

BOLTON, P., IMEVBORE, A. M. A. and FRAVAL, P. (1991) Field evaluation in northern Nigeria of a rapid assessment procedure for identifying environmental and health hazards in irrigation schemes. In: Techniques for Environmentally Sound Water Resources Development, WOOLDRIDGE, R. (ed) Pentech Press, London.

CHIMBARI, M., NDHLOVO, P. D., CHANDIWANA, S. K., CHITSIKO, R. 1., BOLTON, P. and THOMSON, A. 1. (1991a) Schistosomiasis control measures for small irrigation schemes in Zimbabwe Results from three years of monitoring at Mushandike Irrigation Scheme. Report OD 123, HR Wallingford.

CHIMBARI, M., CHITSIKO, R. 1., BOLTON, P. and THOMSON, A. 1. (1991b). Design and operation of a small irrigation project in Zimbabwe to minimise schistosomiasis transmission. In: Techniques for Environmentally Sound Water Resources Development. WOOLDRIDGE, R. (ed) Pentech Press, London.

MOCK, J. F. and BOLTON, P. (1991) Environmental effects of irrigation, drainage and flood control projects: Checklist for environmental impact indication. Report OD/TN 50, HR Wallingford.


In discussion it was commented that the interacting role of the political economy should be highlighted further in Figure 1 and that an appropriate blend of politics economic-biosphere is necessary. A note of caution about the success of irrigation in raising agricultural production was expressed since pest and disease incidence often increases at the same time; the extended cropping season enables pests and diseases to overcome natural limitations imposed by the absence of food or host plants. The question was raised as to whether sufficient account of these factors was being taken in the planning and management of irrigation schemes.