5.1 Second generation water development schemes have emerged in all parts of the world. They usually incorporate some of the elements essential to success as discussed in the previous section. This section presents a brief review of successful approaches to water development.
LOW-VOLUME, HIGH-FREQUENCY IRRIGATION
5.2 In recent years, revolutionary developments have taken place in the science and art of irrigation. A more comprehensive understanding has evolved of the interactive relationships governing the soil-crop-water regime as affected by climate and irrigation methods. These scientific developments have been paralleled by a series of technical innovations in the methodology of water control that have made it possible to establish and maintain nearly optimal soil-moisture conditions almost continuously. Foremost among these innovations are techniques for high-frequency, low-volume applications of water (and nutrients) as a precise and timely response to changing crop needs. The advent of relatively inexpensive, permanently or seasonally installed (solid set) water application systems, and the development of self-controlling ancillary devices, have apparently removed some of the prior economic constraints to the widespread adoption of high-frequency irrigation (FAO, 1996a).
5.3 Properly applied, the new irrigation methods can raise yields while minimizing waste (by runoff, evaporation and excessive seepage), reducing drainage requirements and promoting the integration of irrigation with essential concurrent operations (e.g. fertilization, tillage and pest control). The use of brackish water has become more feasible, as has the irrigation of coarse-textured soils and of steep, sandy or stony lands previously considered unproductive. Such advances and their consequences could hardly have been foreseen in the irrigation literature of prior decades.
5.4 Despite all the advances, old and inefficient ways still persist throughout many irrigated areas. On a worldwide basis, the modern technologies have been applied to only about 3 percent of the land under irrigation. In too many places, inefficiency is perpetuated by institutionally imposed standards based on excessive and hence wasteful applications of water. However, institutional inertia and conservative attitudes are only part of the problem. Some of the new irrigation systems developed in the industrialized countries are too highly mechanized, complex, energy-intensive and large in scale to be directly applicable to the low-capital, low-technology circumstances of non-industrialized countries, where farming is often practised on a small scale and the relative costs of labour and capital are very different. Hence ready-made modern technology often fails when introduced arbitrarily in developing countries. Elaborate and expensive systems, imported in the hope of achieving instant modernization, can quickly become white elephants, monuments to hasty progress based on inappropriate technology. The best principles of modern irrigation should be disseminated, not necessarily the most elaborate machinery. Technology must not be simply transferred, but rather adapted or redesigned to suit differing conditions.
5.5 Overall, the best chance for improving the efficiency of water delivery is embodied in a system that conveys water in closed conduits and provides measured amounts of water on demand, at a rate calibrated to meet continuous crop needs while preventing waste, salinity and water-table rise. Likewise, the most promising strategy for improving the efficiency of water utilization appears to be a regime of low-volume, low-pressure, high-frequency, partial-area irrigation applied to suitable crops of high potential yield.
5.6 Water harvesting is an ancient technique based on a simple concept: to collect (harvest) runoff from a larger catchment area and to concentrate the collected water on a smaller runon area in order to augment the moisture content of the soil. Alternatively, runoff water can also be stored in tanks, ponds and cisterns, for domestic consumption, livestock watering or small-scale irrigation. Runoff can be collected from roofs and ground surfaces, as well as from intermittent or ephemeral water courses. In the context of water scarcity, water harvesting expands water supply because most of the water harvested would otherwise be evaporated on the surface or by natural vegetation, or run off in spates.
5.7 Yield and reliability of agricultural production in semi-arid areas can be significantly improved with water harvesting. Experiences in Burkina Faso, Kenya and the Sudan have shown three- to fourfold yield increases as compared with dryland farming. Stored water, if combined with efficient irrigation methods, e.g. drip irrigation or hand watering, allows the cultivation of high-value crops in areas where other water sources are not available.
5.8 The costs of water-harvesting schemes vary widely. While cash requirements are low, if labour-intensive construction methods are used, labour requirements are initially in the range of about 70 to 150 working days per hectare, depending on natural conditions and the harvesting technique applied. Labour needs for maintenance may vary between 20 and 40 working days per hectare per year. However, recent technological developments (e.g. special machinery for subsoiling and contour bunding) can accelerate implementation and at the same time reduce the labour requirements, which still constitute one of the major obstacles to the large-scale adoption of water harvesting. Furthermore, with the introduction of cheap, durable soil-treatment substances (e.g. sodium methyl silanolate) it will be possible to treat larger areas in order to increase surface runoff rates.
5.9 There is no reliable estimate of the overall potential of water-harvesting development. There is, however, sufficient evidence that both medium-sized and micro-catchment water-harvesting schemes could play a significant part in increasing food production in semi-arid areas. The widespread desertification process in these regions has created large denuded or crusted surfaces which are extremely difficult to revegetate. These surfaces yield high quantities of runoff water which could be utilized with medium or micro-catchment systems, especially with hillside conduit systems for irrigation of orchards.
5.10 Water-harvesting systems have been in operation for centuries in Near Eastern countries, thus proving their sustainability. However, present social and economic conditions of farmers in (semi)-arid countries are different. Many recently constructed water-harvesting schemes have been abandoned, despite their obvious advantages. The technology is not being taken up as expected. It is perhaps time to reassess water harvesting from the farming system perspective, taking into account potential yield at various input levels, the associated risks of crop failure, cash flow at the household level and labour requirements. The solutions for most of the technical problems associated with water harvesting are known. Advances in remote sensing, hydrology and soil science have helped to identify promising areas for water-harvesting schemes. Now research and development emphasis has to be placed on economic and institutional aspects as well as on supporting government policies. The promotion of water harvesting should be recognized by governments as an important measure for rural development and should become an integral part of any water and agricultural development policy in arid and semi-arid countries.
INLAND VALLEY SWAMP DEVELOPMENT
5.11 Inland valley swamps are defined as the upper sections of a river drainage system, comprising valley bottoms, their hydromorphic fringes and flood plains. Their soils are submerged or saturated during a substantial part of the year. Locally, they are known as bas-fonds, marais or marigots in French-speaking Africa; fadama in Nigeria; and vleis, dambos or mapani in southern Africa.
5.12 The heterogeneity among inland valley swamps is great, depending on climate, geology and geomorphology; and so are their hydrological functions. Traditionally, they are used mainly for hunting, fuelwood extraction, fishing, water supply and dry-season grazing. Only 10 to 25 percent of their area is currently cultivated in West Africa (mainly for rice) and yields are often low.
5.13 The estimates for total area of inland valley swamps vary widely due to the absence of a universally accepted classification method. Furthermore, the width of a typical riverine swamp (often less than 200 m) prevents detection on a small-scale map. It is estimated that in West Africa between 20 and 50 million hectares could be classified in this category, which thus offers a considerable potential for increasing food production, thanks to the abundance of its water resources. An important contribution to food security could be made if only a part of the existing inland valley swamps could be converted to agricultural use.
5.14 The large variability among swamp areas demands location-specific development solutions. For example, for the development of rice cultivation in the inland valley swamps in the Sudano-Sahelian zone (rainfall between 800 and 1 100 mm), supplementary irrigation could be used to overcome dry spells during the rainy season. An example can be found in Benin, where shallow wells have been constructed together with storage reservoirs for the irrigation of vegetables. In the wet equatorial zone, drainage lowers the water level in the cultivated plot and therefore permits the planting of improved varieties. In Zimbabwe, a broad ridge and furrow system has been developed for the rice/maize intercropping system in dambos. The system retains as much water and silt from the uplands as possible, while excess water cleared of silt is released into the stream. Subsurface water drains slowly and thereby maintains stream flow in the dry season for a longer period. The system is highly promising. In a wet year a maize yield of 7.6 t/ha was recorded, while in the extremely dry year of 1992, it was still possible to harvest 1 t/ha, compared with only 80 kg/ha in the contiguous uplands.
5.15 Compared with conventional irrigation development projects, the development of inland valley swamps is cost effective. For example, in Ghana the costs for simple water-control structures and earthen bunds in swampy lands were only US$450 per hectare. Participation of farmers in the construction of these systems could bring the costs down further.
5.16 Careful preparation and planning must be exercised in the development of swampy areas. For example, in a project in Burkina Faso, neglecting labour constraints and gender issues resulted in poor project performance. In feasibility studies, the functions and traditional uses of an area are often overlooked. The hydrological function of these wetlands, such as flood control and groundwater recharge, can be adversely affected by uncontrolled drainage. Furthermore, their reclamation may result in a loss of biological diversity. One lesson which has been learned in the process of carrying out sustainable intensification of inland valley-bottom farming is that cropping such an area must be integrated within farming systems that include cultivation of the slopes.
5.17 The advent of cheap, dependable motors and pumps and the increasing availability of fuel or electric power has revolutionized irrigation more than any other technological or managerial innovation. In many parts of the world, large areas of land could not be economically irrigated by gravity flow. A case in point is land located on the banks of large rivers where the construction of diversion structures is not feasible for technical and economic reasons. Pump irrigation can reach such land. Pump irrigation is suitable for those areas where water supplies require only a few metres of pumping from a canal or another water source.
5.18 Small pump schemes, individual or communal, have begun to play a very important role in augmenting food production. They are widely used as a means of supplementing irregular canal water supply, particularly in the river deltas of Asia but increasingly also in Africa. The traditional notion that pump irrigation is bound to fail because of operational costs and maintenance problems has definitely been proved wrong. Pump schemes are easy to install and simple to operate. Experience has shown that pump schemes with a small number of farmers having small landholdings are more productive in terms of yield per hectare and more efficient in terms of water use than are large gravity schemes.
5.19 Alternative sources of energy can be tapped for pump schemes taking advantage of the fact that energy can be stored in the same water pump, provided that a reservoir is available. Each of these pump-powering systems has advantages and disadvantages that need to be assessed in the context of the application site. Wind power has been used for centuries in regions where wind is steady and reliable and there is now a choice between traditional methods and perfected new technology. Solar power based on solid-state cells is used for pumping drinking-water, and as the price is consistently decreasing the technology may in future also be used for irrigation water. Draught power, hydropower and non-petroleum fuels are also used in water lifting (FAO, 1986).
5.20 Besides their direct economic benefits in terms of agricultural production, pump schemes often provide considerable indirect benefits. Water supply for domestic use can often be linked to irrigation water supply. Exposure to water-borne diseases such as schistosomiasis (also known as bilharzia) is reduced if water is distributed through pipes. As water becomes scarce and valuable, the use of pipes for water conveyance will increase to reduce losses, protect the resource from pollution and facilitate metering.
PERI-URBAN IRRIGATION, A SPONTANEOUS DEVELOPMENT
5.21 The global process of urbanization is projected to proceed with the number of urban dwellers likely to double to 5 billion by the year 2025. Natural demographic growth and population migration resulting from climatic change or ethnic conflict are at the source of this poorly organized urban growth, which entails economic, social and environmental problems. As an example, West Africa, which has for a long time been the least-urbanized region in the world, is now undergoing an urban explosion, with town dwellers increasing from 4 percent in 1930, to 14 percent in 1960, to 40 percent in 1990 and likely to exceed 60 percent by the year 2020. Future growth may change somewhat in relation to the macroeconomic environment but could be about 4 to 5 percent in this region.
5.22 Peri-urban agriculture is an important source of income and nutrition for urban populations. As the share of wages in income has fallen drastically under the effect of structural adjustment programmes (SAPs), increased engagement in farming in urban and peri-urban areas has been the most visible response to the crisis. Vegetable cash crops are often produced by experienced farmers and marketed directly or by short chains without much processing. In the case of leaf vegetables, harvesting and sale must take place daily. Short production cycles and rapid adjustment to market demand and climatic conditions result in a surprisingly high, regular income to peri-urban farmers as well as to market entrepreneurs.
5.23 The pervasive economic importance of peri-urban irrigation has created at all production levels an investment incentive for private economic operators. Under the pressure of political and economic forces and encouraged by international organizations, various actions have taken place in an attempt to help organize this new production sector. NGOs are becoming increasingly involved. This movement is supported by the credit institutions, which are now lending to both individuals and groups.
5.24 Despite its successes and growing importance, peri-urban irrigation is still subject to numerous constraints. Among them are insufficient access to clean water and the ensuing associated health problems; uncertainty about land tenure; the low level of expertise; the increasing pressure of pests; and marketing difficulties.
5.25 The term shallow aquifer refers to groundwater in which the water is accessible using indigenous methods of well construction and low-cost techniques such as washbores, hand-drilled wells and well points. Water for irrigation is abstracted through centrifugal pumps located at ground level or in a nearby pit.
5.26 The advantages of shallow aquifers for small-scale irrigation are numerous:
5.27 Shallow aquifer development can be associated with inland valley development, since flooding of the plain during and immediately after the rainy season facilitates storage of water underground, which can easily be used during the dry season.
5.28 Among the constraints to shallow aquifer development is insufficient information on the extent and yield of these aquifers. Exploitation of shallow aquifers in fractured rocks requires special techniques such as horizontal wells. A difficult problem is the management of shallow aquifers to avoid excessive extraction and ensure equal access. The development of the fadama in Nigeria is a striking example of the potential offered by shallow aquifer development.
Box 3 |
| In the early 1980s small inexpensive petrol pumps appeared on the market in Nigeria, and farmers spontaneously
replaced their traditional water-lifting devices. The success of the small pumps encouraged the government to
launch a National Fadama Development Project (NFDP) with the aim of accelerating fadama development through
small-scale irrigation and to install about 50 000 tube-wells irrigating about 100 000 ha. The programme is based
on the use of simple technology for shallow tube-wells, privatization of drilling activities and improved irrigation
management through water users’ associations. The washbore and tube-well technologies were introduced from India in the early 1980s. The washbore, with an average depth of 6 to 8 m, is simpler and cheaper, but the washbore programme has been discontinued in some states as water could not be found at shallow depth. The construction of tube-wells, with an average depth of 12 m, requires a drilling rig; however, the success rate is high, close to 90 percent. Sometimes the pump is lowered into a pit down to 2 m. The pumps are normally 3 to 5 h.p. with a capacity of 12 litres per second. A washbore or a tube-well can irrigate up to 2 ha but is generally limited to 1 ha. Pumps and spare parts are sold through different outlets without subsidy to the farmers. As the availability at government outlets is often limited, farmers rely on the open market where the price level is often more than double. The cost (in 1993) for a washbore is US$40, and for a tube-well US$170; the pumps cost about US$300 to $500 (US$350 to $700 per hectare). Irrigation of 1 ha requires eight to ten hours of pumping. The reliability is relatively good with about two breakdowns per season for a lifetime of the pump of four to ten years. Farmers are responsible for the maintenance of the pumps by local mechanics. Production focuses on cash crops with a high dependency on markets. For example, the net profit on a crop of garlic on 1 ha varied in recent years between US$10 and $8 500. Farmers have responded to the increasing costs and removal of subsidies on farm inputs by increasing their prices, but there are doubts that this development can continue. Diminishing returns have already discouraged some farmers, who only plant half of the irrigated land and even return to traditional water-lifting systems and a low level of input use. |
CONJUNCTIVE USE OF SURFACE AND GROUNDWATER
5.29 In most climates of the world, precipitation, and consequently peak runoff corresponding to a significant part of the total discharge of the rivers, occurs during a particular season of the year that usually coincides with the lowest water demand. The water development problem therefore consists of transferring water from the high-supply season to the high-demand season. The most obvious and most common solution to this problem is to store surface water behind dams, but storage of water underground may be a valuable alternative to surface storage systems.
5.30 Reservoirs are liable to evaporation and seepage, and to sedimentation which reduces storage capacity. They require loss of land and human habitation as well as costly canal distribution systems. However, in some circumstances they can provide hydroelectric power and a measure of flood relief. Resettlement, if sensitively handled, can be successful and reservoirs can provide fish resources. Groundwater may be an alternative to surface reservoirs, offering less evaporation and less sensitivity to recent rainfall, fewer harmful social and environmental impacts (unless the water is saline), cheaper capital costs than dams, and possibly storage closer to users. However, the recurrent costs of groundwater pumping must be taken into account.
5.31 Conjunctive use of surface and groundwater consists of combining the use of both sources of water in order to minimize undesirable physical, environmental and economic effects and to optimize the water demand/supply balance. Storing excess surface water in the ground for retrieval during dry periods is a very attractive solution. This possibility should be systematically explored when considering a river-basin management programme.
5.32 The major factors to be considered in assessing the feasibility of conjunctive use of surface and groundwater are:
REHABILITATION OF LARGE SCHEMES
5.33 One of the main issues in medium- and large-scale irrigation schemes in Africa is the transfer of management responsibility from government agencies to farmers’ associations. This transfer will require the following technical and organizational restructuring (GRID, 1994).
5.34 The rehabilitation design process should involve regular discussions and consensus with the water users at all stages. A wide range of technical options needs to be discussed to ensure that farmers’ priorities are taken into account, including the site, plot size, method of field irrigation, number of participants per canal group, boundaries of blocks and routing of canals. Experience has shown that this discussion process helps to avoid costly modifications and that the costs do not exceed those of conventional designs.(5)
6.1 In many developing countries, especially in Asia, domestic spending for irrigation has dominated agricultural budgets during these past decades, while a significant portion of international development assistance has also been used to implement irrigation projects. The World Bank alone lent US$31 billion for projects with irrigation components during the period from 1950 to 1993 (World Bank, 1994). The peak of investment in irrigation was reached during the mid-1970s, when some US$2.5 to $3 billion were committed annually by external funding agencies. Since the early 1980s, however, total investments have decreased. The World Bank is now investing less than US$1 billion per year in irrigation projects and total spending by all donors and financial institutions averages around US$2 billion annually.
6.2 During the 1950s and 1960s all funding for irrigation went to development of new irrigation schemes. However, from the 1970s onwards more and more funds have been committed for rehabilitation, modernization and expansion. At present, more than half of all irrigation investment is devoted to these purposes.
6.3 Asia has always been the main recipient of funds for irrigation. That is not surprising as some 75 percent of the developing world’s irrigated area is in Asia. For example, Asia has received 69 percent of total World Bank lending for irrigation, although lending and assistance to the Asian region by the end of the 1980s was less than 50 percent of lending during the peak period of the late 1970s (Yudelman, 1994). Africa, in contrast, has only received 12 percent of total World Bank lending, especially in the arid and semi-arid regions of North Africa, the Sahel and Madagascar. The average size of projects in Africa is small, hence Africa accounts for 30 percent of the number of World Bank-funded projects (World Bank, 1994). The International Fund for Agricultural Development (IFAD) has been supporting more projects in South and East Asia than anywhere else (IFAD, 1994).
6.4 There are objective reasons for the decrease in investment in irrigation, among them:
However, it is urgent that the trend be reversed. Considering the long gestation period of development schemes, basic investment in water development and irrigation must be made now if there are to be fully functioning schemes in the coming 15 years.
6.5 Construction costs for both new and rehabilitated water-control projects have risen steadily over the past decades. In many developing countries they have at least doubled or tripled. Rehabilitation and modernization costs vary normally between 25 and 40 percent of the costs for new developments in a region.(6)
6.6 Irrigation developments are generally less expensive in South and East Asia than in other regions of the developing world. This is partly due to the large areas being irrigated in flat plains and with reliable water sources (large perennial rivers), which permit relatively simple diversions and conveyance of water. As rice is the dominant crop, the distribution system need not be dense, a fact that also reduces costs. There is also a long tradition of irrigation, supported by experienced, effective institutions.
6.7 It is a fact that large- and medium-scale irrigation developments in Africa have so far been more expensive than in other regions. The possible reasons for the high costs in Africa are numerous and include the following.
6.8 Often infrastructure costs, such as supporting items (offices, workshops and staff houses), access roads, settlements and social services (schools, clinics, water supply, etc.) are lumped into the irrigation development cost. These costs, which could more than double the direct irrigation investments,(7) are generally much higher in sub-Saharan Africa than in other regions, as irrigation schemes in Africa are often in remote and undeveloped areas.(8)
POSSIBLE WAYS TO REDUCE WATER DEVELOPMENT COSTS
6.9 The planning of water-control schemes should be improved. Schemes are often planned and designed with insufficient and inaccurate geological, hydrological or topographical data. Therefore components of the schemes are based on incorrect designs, which may necessitate costly delays and changes during the construction phase.
6.10 Technical designs do not always need to be complex or constructed with the most expensive materials. For example, smaller structures could be constructed equally well, but more cheaply, with bricks or concrete blocks rather than with concrete.(9)
6.11 Water development schemes should not be planned and constructed in isolation. In spite of what has been said above, certain essential elements of infrastructure should be planned simultaneously and implemented so that they are available when needed. For example, access roads to schemes should be in place before construction starts, otherwise there may be costly delays in construction. Financing should be from other sources whenever possible.
6.12 The establishment of capable local construction companies should be encouraged. The economic climate should be such that contractors can purchase necessary equipment and materials in time. Where possible, larger contracts (e.g. to construct a number of small schemes within a district) should be given to guarantee a continuous programme, so as to reduce establishment and other costs. Tender documents should be properly prepared, with clear specifications based on detailed designs. For public schemes, governments should ensure that contractors are paid on time.
6.13 Imported materials and equipment should be substituted as much as possible, as importation and often high duty rates imposed on these items have a direct bearing on the cost of an irrigation system. However, some materials cannot be substituted, and it is not always feasible for a country to set up local industries to manufacture all irrigation equipment and materials. Care should be taken to find the low-cost source for a given quality taking into account terms and servicing. Regional groupings, such as the South African Development Community, should facilitate purchases from member countries with already established industries. Project costs could also be reduced by lowering tariffs on imported project inputs.
6.14 The development of private irrigation should be encouraged in order to reduce government investment costs. Governments have a responsibility to provide infrastructure that will not be built by the private sector, such as roads and sometimes electricity supplies. Governments could, where needed, develop the basic infrastructure such as water development, conveyances and main drains.(10) Thereafter private initiative may take over to develop the final distribution, including low-lift pumps. Along rivers and streams more emphasis should be placed on pumped irrigation. This would avoid investment costs for diversion structures, conveyance and distribution systems. Individuals developing private irrigation will only do so if they believe it is profitable and secure. They will apply different design criteria than public organizations, leading to a reduction in costs. Some form of government control, however, remains necessary to ensure public safety, environmental protection, water rights of others, and so forth.
6.15 Many positive developments have taken place during the last decade in a number of developing countries. Considerable progress has been made with infrastructure developments (electricity, roads, etc.) in rural areas. Institutions involved in irrigation planning and development have gained considerable experience in many countries. Salary restructuring aims at retaining and attracting qualified and experienced personnel. Macroeconomic reforms, including currency exchange adjustments and reduction of import duties, are taking place in many countries. All these positive developments mean that a new era is being entered into with good prospects for efficient water development.
Box 4 |
| Zimbabwe is implementing a programme of medium-scale dam development in rural areas. These dams have full supply capacities of 800 000 m3 to 10 million m3. Most of the dams are designed by consultants and constructed by private contractors. Because the dams are located in rural areas and there is no specific owner, they tend to be overdesigned. Spillways are very large and constructed in solid concrete or masonry, dam bodies are very big and both the upstream and downstream slopes are protected with a thick layer of riprap. No attempts are made during the planning stage to involve the users and prepare them for maintenance of the dams. Therefore no risks are taken and dams are designed for minimum maintenance, but this is done at a high initial cost. |
ECONOMICALLY JUSTIFIABLE INVESTMENT IN WATER CONTROL
6.16 The most comprehensive evaluation of irrigation development is the recently completed review of World Bank experience. The average economic rate of return was 15 percent. This was satisfactory, although it was 7 percent lower than appraisal estimates. If the project outcomes are weighted by their size, the evaluated rate of return is 25 percent (29 percent at appraisal), indicating higher returns from larger projects. On the other hand, an FAO review of investment performance showed somewhat higher success rates, with, for example, 50 percent of African irrigation projects achieving re-estimated rates of return higher than appraised rates. The gap between appraisal estimates and evaluation findings evidently caused disappointment with irrigation projects and contributed to the negative image of the technology. As many as one-third of the projects were rated as unsatisfactory, and the review noted that there is generally ample room for improvement. Nevertheless, it should be stressed that, in general, World Bank irrigation projects yielded positive rates of return equivalent to or greater than other agricultural projects.
6.17 The return-rate situation is different in various parts of the world. Overall, results indicate that large-scale water projects face significant constraints in Africa. The difficult physical environment places high demands on project design and implementation. However, successful investment in large-scale systems is feasible with good project design and implementation, provided other constraints are removed and a favourable policy environment is in place.
6.18 To make small- and medium-scale irrigation schemes successful, a distinction should be made between direct and indirect investment strategies. Under a direct investment strategy, the government, operating through technical agencies, acts directly using its own budget and staff to design, construct and operate irrigation facilities. In contrast, the indirect investment strategy is one in which government makes resources available to farmers and the private sector (grants, loans, technical expertise) to implement irrigation development on works owned and controlled by individual farmers or groups of farmers. Based on case-studies in South Asia, the indirect approach clearly seems superior.
6.19 It is also worth noting that many irrigation projects were completed when domestic terms of trade were weighted against agriculture with overvalued exchange rates and a variety of indirect taxes or subsidies to competing urban interests. In future these public (and private) irrigation investments and any new schemes may well provide higher returns for the reasons discussed below.
SOLVING OPERATIONAL AND MAINTENANCE PROBLEMS
6.20 Most public water systems are affected by poor maintenance and water deliveries are not responsive to farmers’ demands and needs. It is often argued that this situation results from the fact that many farmers do not pay water charges and therefore proper services cannot be provided. Farmers on their side argue that crop returns are too low, that services provided are inefficient, and that they cannot pay the charges.
6.21 Several studies have proved that public irrigation schemes have usually had lower productivity than those developed by individual farmers or farmers’ groups. Individual farmers using private pumps were able to apply water in a more timely fashion and obtained yields that were several times those of the farmers in public schemes. Furthermore, the former were able to schedule crop planting so that better prices were obtained at harvest. Although these farmers faced much higher operating costs, since they had to cover the costs of the pump sets plus those of operating them, higher returns through increased flexibility of water delivery compensated for the higher costs.
6.22 These experiences make two important points. First, farmers are willing to pay for water provided it is available in timely and adequate amounts, and second, it is obvious that water distribution in public systems leaves much to be desired from the farm perspective. Supervisory agencies are often involved in too many aspects (such as village concerns, land-use restrictions, inheritance rules, fuel supplies, eviction procedures, crop marketing, crop harvesting and many others) that render their water distribution services inefficient. On the other hand, it has been demonstrated in several innovative experiences that when irrigation agencies are made accountable and farmers pay for services actually received, irrigation performance improves considerably.
6.23 In summary, the recovery of operation and maintenance costs is not so much a financial as an economic question where the issue is the efficient provision of a service in terms of water delivery. It is unlikely that this objective will be reached without formal and effective participation by farmers in the management of the irrigation scheme. Pilot experiences in several places in Africa have shown that much can be achieved when management responsibilities are properly shared with, or transferred to, farmers. Now the political will is needed to transform these experiences into more general policies and practices.
6.24 An effective approach for assessing the potential benefits from new irrigation investment is to consider possible without-irrigation scenarios. To justify the massive investments necessary to make existing irrigation sustainable, scenarios with and without maintenance and rehabilitation should be compared. A wide range of technical obstacles must be overcome to ensure the sustainability of irrigation. These include flooding, waterlogging, salinity, silting of reservoirs and deterioration of infrastructure. All these problems are solvable in principle, provided the necessary economic resources are available.
6.25 Facing the problems of mastering water-control technology, it is well to recall that rain-fed agriculture alone cannot be expected to keep up with growing demands for food. New land suitable for rain-fed agriculture is scarce. Rain-fed agriculture in regions subject to irregular, unreliable rainfall and drought meets fundamental soil-moisture constraints to productivity. Strong productivity increases under rain-fed agriculture are seen as possible in the medium term in Eastern Europe in particular. However, existing rain-fed agriculture has in part already reached a high level of productivity and is meeting sustainability limits. Industrialized countries may adopt policies of not exporting precious water and topsoil in the form of low-value basic grains. However, irrigation is in fact neglected in many countries as a consequence of economic problems, competing priorities, poor performance and environmental constraints, with very serious implications for national welfare.
6.26 Any retrenchment in irrigation, or even a failure to expand it in line with the proven potential, will inevitably lead to further expansion of rain-fed agriculture. Much of this expansion would take place under risky rainfall regimes. Moreover, expansion of the area of rain-fed agriculture will inevitably result in deforestation and produce more cultivation on slopes and close to stream banks with a consequent increase in soil erosion and the accelerated sedimentation of river beds, estuaries and reservoirs.
6.27 Unless water development projects are undertaken, therefore, it seems clear that population expansion will force millions of impoverished people to undertake unsustainable farming systems in arid, drought-prone, low-productivity areas or otherwise ecologically fragile areas. Land of low productivity would not justify significant investments in remedial measures such as terracing or in purchased inputs such as fertilizer. Already many examples of soil mining and destruction of biological diversity are being witnessed in Africa and other regions. Intensification of agriculture, including animal production, is the only option for the majority of farmers who have now run out of unused land. Intensified production methods will be the preferred option for many who would otherwise cause considerable environmental harm if they extended their cultivation into rapidly diminishing uncultivated areas. Water control must be a key element in this intensification. A new effort at water-control projects should now be seen as an environment-friendly undertaking.
7.1 The engineering measures necessary to make water available where and when needed do have environmental consequences. It has already been said earlier that water control, as a key to intensive, high-value agriculture, can have many positive environmental effects, in particular when compared with the without-irrigation scenario. However, water abstraction from rivers, whether for irrigation or other purposes, also threatens the health of the aquatic environment. Surface storage of water radically changes land use and creates a new landscape. Negative effects of mismanaged irrigation, such as soil degradation due to salinity and waterlogging, and the possible spread of water-borne diseases, cannot be neglected and preventive as well as mitigating measures should be applied. Fortunately, understanding of the causes of the negative effects of irrigation has greatly increased and in almost all circumstances preventive and corrective measures are possible. As in any other development activity, water development calls for trade-offs with the environment. Costs and benefits of development must be fully understood. The effects of development on the environment cannot, as was often the case in the past, be ignored or externalized. By the same token, the displacement of populations to make room for water storage requires full understanding, consultation, fair treatment and adequate budgeting to minimize its impact.
7.2 Water is abstracted from rivers and stored in reservoirs to make it available when required. Reservoirs are not only for irrigation: many of them supply drinking-water and others are used for hydroelectric power generation. The overall trend is towards integrated and conjunctive management of reservoirs in order to obtain maximum benefits from the overall hydraulic system. Reservoirs usually provide a degree of flood control; floods, however, feed riverine wetlands important for fisheries and waterfowl, among other beneficiaries. Agriculture is the largest user of water overall, and water use by irrigation is largely consumptive, with virtually no returns when irrigation efficiency is high. Thus, the effect of irrigation is demonstrated by the fact that rivers like the Colorado and the Nile are nearly or totally exhausted before reaching the ocean. Usually, as rivers are depleted, the concentration of pollutants conveyed by the river increases with dire consequences for the aquatic ecosystem and biological diversity. At particular risk are estuarine systems which are very important for fisheries. The lack of fresh water flowing out to sea results in an advance of the front of saline water, causing disruption in the estuary. In river deltas, the lack of water and sediments result in progressive delta erosion.
7.3 How much water needs to be left in a river depends on a number of factors: the time of year; the habitat requirements of riverine life; the salt and sediment balance of the system; the significance of the river for local people; and other factors specific to each river basin. The complex ecological workings of rivers are far from being well understood and require scientific research. A preliminary minimum flow sets at least some degree of insurance for the health of the river system. In regions where rivers are already depleted beyond the level of environmental sustainability, meeting minimum requirements will involve shifting some water away from users (farms, cities) and back to the environment. Such actions are already taking place in, for example, the state of California. Reserving water for the environment may be more difficult in developing countries where the population increase entails rising demands for food and drinking-water. However, minimum water flows to protect fisheries, river delta economies and the health of local people are not less necessary in developing countries than in the developed world.
7.4 To factor instream flow requirements in water demand, the amount of 1 000 m3 per person per year is sometimes used if waste water is returned untreated, corresponding to a dilution factor of 30 litres per second per 1 000 people (Postel, Daily and Ehrlich, 1996). On the assumption that 50 percent of municipal and industrial waste receives at least secondary treatment before discharge, the instream flow requirement is halved to 500 m3 per person per year. However, such figures do not take into consideration the complex and poorly understood situations specific to each river basin.
THE CRUCIAL ROLE OF UPPER CATCHMENTS
7.5 Degradation, sometimes devastation, of the upper catchments in river basins is a phenomenon of global dimensions. The hydrological regime of rivers depends on the seasonality and characteristics of rainfall and on catchment properties such as slope, soil and vegetation. Owing to the orographic effect of mountain barriers, rainfall usually increases with altitude and in most rivers a significant part of the water carried stems from the upper catchment. Under intense rainfall, a rocky, impervious upper catchment will give rise to sudden, intense floods heavily loaded with sediments, while under similar meteorological conditions a forested catchment will yield a moderated flood and facilitate subsurface flows and groundwater recharge. Downstream riparians derive substantial benefits, including reduced water-storage requirements, less flooding, groundwater supply, better water quality and less river sediments, from the integrity and good condition of the upper catchments.
7.6 Human activities can degrade upper catchments and expose soils to erosion through deforestation, overgrazing and mismanagement of arable land, to which improper logging and road construction are added as specific sources of river sediments. It is estimated that over 200 million people live in the mountains, mostly under marginal conditions, contributing to activities that actually or potentially influence the characteristics of the water resource. Substantial efforts and large sums of money have been spent over the last 50 years in forest, soil and water conservation projects and programmes, often with disappointing results. Some projects have been successful, however, and much has been learned on the way.
Box 5 |
| The Aral Sea used to be the planet’s fourth largest lake. Because of river diversions to grow cotton in the desert,
it has now lost three-quarters of its volume and half of its surface. Prior to 1960, the two major tributary rivers
poured an average 55 km3 of water per year into the Aral Sea. During the 1980s, the combined contribution of
these rivers to the Aral Sea dropped to 7 km3, about 6 percent of their annual flow. In their lower reaches, these
rivers now run dry most of the time. The riverine forest has been decimated, together with the services and habitat
it provided, and wetlands have shrunk by 85 percent. The high level of chemical pollution stemming from
agriculture has greatly reduced biological diversity. The fish catch in the lake, which totalled 44 000 tonnes per
year in the 1950s and supported 60 000 jobs, has dropped to zero. The Aral Sea ecosystem would require a substantial allocation of water to halt the decline. This had been considered in the original project planning, but the envisaged projects, involving diversion of water from the Arctic Ocean catchment, were never carried out. To stabilize the sea at its present level would require some 35 km3 annually, five times the inflow of the 1980s. Shifting this much water back to the environment would require the removal from irrigation of marginal lands, a reduction in the area planted with cotton and rice and substantial improvements in irrigation efficiency. Indeed, a fundamental fact of the Aral Sea is that there is not enough water in the basin to meet all the demands upon it; this is the very background to a scarcity situation in which low-efficiency irrigation is a weak competitor. The presidents of the five newly independent Aral Sea basin countries met in 1994 and approved an action plan for improving the situation. The plan includes developing a regional water management strategy. A short-term goal is to improve health and environmental conditions in the disaster zone surrounding the lake. |
7.7 Generally it is now recognized that it is pointless to start rehabilitation on schemes that treat the symptoms of catchment mismanagement without treating the root causes. One of the reasons for failure has been that on-site benefits accruing to the local poverty-stricken population are neither sufficient nor equitable. Most of the benefits of the improved hydrological regime are reaped off-site through more stable river flows and groundwater recovery. Erosion control in the mountains is often beyond the means of mountain farmers, while the benefits of reforestation may be too distant in time for their concern. When water development in the river basin leaves winners downstream and losers upstream, it is bound to be unsustainable.
7.8 Improved and imaginative new approaches to the management of upper catchments are required, based on equitable sharing of the benefits and burdens among upstream and downstream interests. It is recognized that headwater conservation must be included in water resources development projects, but satisfactory methods for economic evaluation of the positive effects downstream of water and soil conservation measures taken upstream, and of the negative consequences of not taking such measures, are as yet lacking. The effects of forestry and water and soil conservation on dams, canals and engineering works are poorly understood and not well quantified. Achieving equity within the whole river basin is a necessary step towards sustainability and is likely to be reflected in higher costs of future water development projects.
7.9 Forestry policy and environmental regulations for forests as well as for marshlands affect water supply, floods, droughts, runoff timing and water quality. Such policies also relate to issues of water rights, water sharing and water conflicts but adequate tools for evaluation are not available. People living upstream and people poised to lose their homes and livelihoods in order to make room for water management infrastructure, must be involved in the process of taking decisions. The art and science of integrated river-basin management need to be revised in the light of the recommendations put forward by ICWE and UNCED. These require that true resource and environmental costs be incorporated into all decisions, and that the needs and wishes of the local and indigenous populations be considered. Moreover, they require that these people participate directly in decisions about activities and benefits from the revenues derived from those activities.
7.10 Water is a conducive medium for the spread of disease-carrying bacterial and viral pathogens. It also plays an important role in the transmission of parasites, either directly or by providing habitats for their vectors. Water-related vector-borne diseases are most likely to be found in areas where irrigation has been introduced.
7.11 Among water-related diseases, malaria is by far the most important, both in terms of the number of people annually infected, whose quality of life and working capacity are reduced, and in terms of deaths. Worldwide, some 2 billion people live in areas where they are at risk of contracting malaria. The total number of cases is estimated at 100 million per year. Ninety percent of cases and deaths occur in sub-Saharan Africa. Drug treatment has become difficult recently because the parasite has become resistant to certain drugs that have been used for a long time in many parts of the world. Interruption of disease transmission using chemicals for the control of the vector, the mosquito, has become less effective because some mosquito vector species have become resistant to previously effective insecticides, and some insecticides have been banned for environmental reasons. Sustainable and ecologically sound interventions should be included in irrigation schemes from the design stage onwards, based on health impact assessments.
7.12 Schistosomiasis (bilharzia) is almost as widespread as malaria, but it rarely causes immediate death. It is a chronic debilitating disease, caused by a nematode (blood fluke) parasite whose life cycle includes stages passing through an aquatic snail species. An estimated 200 million people are infected worldwide and transmission occurs in 74 countries. The infection is particularly common in children who play in water inhabited by the snail intermediate host. Severe infection in childhood leads to long-term damage to bladder, kidneys and liver, which may cause death many years after the original infection. Infection at any age makes people feel unwell and reduces working capacity.
Box 6 |
| The practice of an intensifying cycle of slash-and-burn agriculture for food production in countries such as Laos
and Madagascar has been the main reason for the process of irreversible deforestation. Declining yields force poor people to clear ever larger land areas, requiring progressively more physical efforts. To feed a village in Laos of 1 000 inhabitants, a forest area of 200 ha needs to be cleared every year with a two-year production phase and average yields of 600 kg of cereals per hectare. Allowing five years of fallow to restore soil fertility, a total forest area of 1 000 ha is required for the village. Any increase in population and any further decline in soil fertility or destruction by erosion would require additional land to be cleared. The development of an irrigation area for the same village of 100 ha of irrigated rice with a modest production of 2 400 kg/ha once a year would provide food self-sufficiency. Substantial time is saved by greatly reduced land clearing and weeding activities for rain-fed crops, time which can be devoted to other income-generating activities. Extension of food production under irrigation into a second growing season and introduction of fertilizers and high-yielding varieties can further increase agricultural production, while greatly reducing the environmental degradation resulting from shifting cultivation. |
7.13 The risk that one or more of these diseases is introduced or has an increased impact is most likely in irrigation schemes where:
7.14 Control of these diseases can be effected in a number of ways, some of which are mutually reinforcing. Three types of measures are recognized:
Of the above, environmental control measures are considered to be long-lasting and environmentally sound. A number of successful interventions of environmental management for vector control have been reported.
PREVENTING DEGRADATION OF IRRIGATED LANDS
7.15 Poor irrigation practices can cause the water-table to rise near the surface, clogging the soil and drowning plants, and can cause secondary salinization when this underground water brings dissolved salts from lower soil layers towards the surface. In arid zones, rising water movement and evaporation often exceed downward water percolation. When irrigation or underground water or the soil contains salts, these can become concentrated in the upper layers of the soil, and can become sufficiently toxic to cause reductions in agricultural production.
7.16 It is estimated that, on a global scale, there are about 20 to 30 million hectares of irrigated lands severely affected by salinity. An additional 60 to 80 million hectares are affected to some extent by waterlogging and salinity. Many of these areas will go out of production unless corrective measures are introduced.
7.17 Many factors influence the salinity or sodicity hazard, including the quality and depth of the water-table, physical characteristics of the soil, irrigation practices and the presence or absence of natural or artificial drainage in the zone. When there is excess water in a system in which the drainage capacity is reduced, there will be waterlogging of the soil and concentration of salts by evaporation.
7.18 It is possible to limit or control the risk of salinization and alkalization through improving irrigation practices, constructing field drainage, leaching of excess salts and other land-improvement measures.
7.19 Establishing field drainage is costly, as is the provision of main drainage. The maintenance of drains at the field level is taxing during farmers’ normal working hours. It is also costly at principal drain level for district authorities. However, the proper functioning of the drainage system is essential for the sustainability of irrigated agriculture. Drainage costs must be added to standard operation and maintenance costs for the irrigation network.
7.20 Disposal of drainage water sometimes represents a major problem. Usually the concentration of salt increases gradually from upstream to downstream in major rivers as a result of many drainage-water inflows. If the concentration of salt in the irrigation water reaches critical levels, alternative solutions must be found such as the conveyance of drainage water in special outfalls either to the sea or to evaporation ponds. It is the task of the public authorities to ensure that drainage effluents are disposed of safely. Especially in areas with active private-sector development, drainage is often neglected due to the short-term economic objectives of the developers. It is essential that in these areas the basic infrastructure for a main-drain system is created and maintained from the beginning.
8.1 Water and soil-moisture control enables realization of the production benefits to be derived from high-yielding varieties and from improved cultural practices resulting from agronomic research. Rain-fed agriculture cannot be expected to keep up with growing demands for food because of environmental constraints. The implications of neglecting irrigation for food security can be serious. Water is a limited resource and the list of water-scarce countries keeps growing as demand is getting closer to the limits of the hydrological cycle and the environment is winning recognition as a legitimate user of water. Trade allows food consumption to exceed production in those countries where food production is constrained because of a lack of water. Countries and regions that continue to be in a weak trading position, which include many of the poorest and most food-insecure of the world, will have to pursue policies of local production. Adequate, successful technologies for water control to supply soil moisture are available but need adaptation to local physical and social conditions. Investment in water infrastructure, continued reform of supporting institutions, and an enabling environment are necessary to improve food production. The priority areas for action are identified below.
ASSESSMENT OF RESOURCES AND USE
8.2 At a time when water planning and management must become more precise in order to cope with scarcity, in many water-scarce developing countries surprisingly little is known about water resources and water use, thus adding to uncertainty in planning and investment cost. Computers, satellites and communications allow for comprehensive, low-cost data collection. However, national and international data collection programmes are underfunded while the approximative nature, or outright guesswork, of existing data is used as a justification for deferring decisions on water development. Water development takes time from the moment a decision is taken until the scheme is fully productive. Governments can take steps to have small but functional services systematically assemble a strategic selection of data, while the international community and donors could develop a consistent policy regarding the required level of information and the resources allocated to this activity.
8.3 An urgent task for governments, food producers’ associations and international organizations is to ascertain, according to the specific conditions of each country, the potential of national land and water resources to increase food production in a lasting manner. In so doing, it will then be possible to determine where more intensive and more productive use could be made of resources, and where and why their use hitherto is likely to prove unsustainable. Special efforts are required to develop national capacities (databases, decision-support systems and tools) in the low-income food-deficit countries (LIFDCs).
8.4 Transition from an era of plenty to a situation of scarcity requires a review of existing policies for water development and allocation among users. Establishing an institutional structure for allocating water is a fundamental role of social policy for any nation. Different cultures make trade-offs based on the relative importance of their particular objectives. Water policy and strategy in general, and in relation to food security in particular, is a matter for decision at the national and sometimes the provincial level. FAO and donors can, however, support the review process and capacity building.
8.5 Water policy, institutions, law and regulations should promote sustainable, economically efficient and socially equitable use of water. Water is not only an economic good: a certain level of access to water use is a human right. Efficient water allocation needs to guard against possible abuses and monopolistic practices. As water becomes scarce, legal title to water needs to be established to facilitate private investment. The establishment of water titles, and an overview of reallocation and sometimes of trading, requires effective and capable institutions. Donors are well placed to advise countries that are in the process of developing the institutional and legal framework for an efficient and largely privatized water sector.
8.6 In recognition that all surface and subsurface water in a river basin is closely linked through upstream-downstream relations and water-quality interactions, a river-basin approach is a first option in all water development activities. River-basin authorities should have regulatory powers but refrain from acting themselves as developers of the water resource. Generally, sequential water use should be promoted according to the quality requirements of various users.
8.7 Global targets by the year 2010, within an appropriate framework of national and regional water policies and plans, are: to increase water-use efficiency by at least 20 percent of current levels; to increase irrigated area by an average of 1.1 percent per year, opening 40 million hectares of land to irrigation by the target date; and to reclaim 10 million hectares of waterlogged and salinized lands.
RESEARCH AND TECHNOLOGY TRANSFER, CAPACITY BUILDING AND EXTENSION
8.8 In taking advantage of new technology in computers, sensors and communications, water management and irrigation research have taken strides towards more efficient, low-cost, small-scale, distributed water and soil-moisture control technology. Technological changes will allow for the continued improvement of reliable and accurate water-control methods needed to obtain the utmost benefit from a limited resource. Technological research in the developed countries of the temperate belt should further reach out in partnerships to cater for the needs of developing countries in the tropical and arid regions. There is a need for integration of technological and social research: irrigation technology is for farmers to use, and the viewpoint of farmers in developing countries has too often been neglected or misunderstood. Developing countries can foster their public and private research institutions in water management in particular in those aspects dealing with the assimilation, in the local context, of technological development.
8.9 The complex relations between water development and water environment are poorly understood. Not all water in rivers and lakes can be abstracted, and a certain amount must be left to its natural course to preserve the integrity of aquatic systems and biological diversity. The cost of neglecting this aspect in the past has been high, and environmental restoration, even when successful, is never complete. There are many situations, which are specific to each region and river basin.There is a need for research leading to a better understanding of the aquatic system and better planning and management, resulting in rational projects and adequate environmental preservation.
8.10 Technology transfer is a two-way process of learning. The foundations of technology are constant but its use can take many different forms. The distance between the research station in a developed country and the farmer in a developing country needs to be bridged in its technological, environmental and social aspects. The conditions for progress in this area have never been as good as at this time, when electronic communications are becoming widely available in developing countries. The opening up of low-cost multilateral communications among government services, research institutions and community groups, and eventually also reaching the farmer, can give massive support to the technology-transfer process leading to improved water management. As importantly, communications open the way to increased South-South cooperation. Governments should make the most of this opportunity, and donors should support the related infrastructural development.
8.11 Without investment in water infrastructure supported by reformed institutions, the prospects for improving food production are remote. Water-control infrastructure should not be developed in isolation, but should be part of a wide-ranging area development programme. At the scheme level, public authorities should be responsible for construction and operation of dams, headworks and main irrigation and drainage canals, while users’ associations or the private sector should be responsible for managing, and where possible building, the on-farm distribution system. Innovative ways to finance irrigation have to be developed. Donors, governments and external support agencies are urged to reverse the trend of declining investment in irrigation.
8.12 The success of irrigated agriculture depends as much on economic factors and the presence of adequate services as on technology. Inadequacies in market systems, storage facilities, management of agricultural produce and credit sources have contributed to failures in the past. These constraints need to be overcome through sound government macroeconomic policies to permit increases in production and to ensure the economic viability of projects.
8.13 There is the potential and the need to reduce the cost of irrigation development. An important aspect of cost reduction can be the employment of national engineering and construction firms for the design and construction of projects. Promoting local manufacture of irrigation material is equally important. Government policy should encourage the development of a local irrigation industry, including a manufacturing home base and a strong servicing sector.
8.14 Sound government management of the macroeconomy so as to promote agricultural investment and profitability, and high-quality technical support within the agricultural sector in the public or private domain, are preconditions for improved production. A service-oriented approach to management, in the context of sound economics and adequate profitability, will go a long way towards ensuring the maintenance and efficiency of irrigation systems with the capacity both to serve the market and to adjust to change. Managing agents, divorced from the stranglehold of normal government procedures, are able to apply private-sector procedures in the provision of efficient, cost-effective and timely services to farmers. Governments, however, must be able to retain the necessary control of policy issues and to monitor the performance of agents in accordance with contractual obligations.
PRESERVATION OF NATURAL RESOURCES
8.15 Natural resources in food-producing areas as well as in adjacent forest lands and watersheds need to be rehabilitated, conserved and monitored. Policies, institutional systems and rules should be adapted to create economic and social incentives for farmers and others involved in the food sector to reduce degradation and adopt sustainable management practices. In addition to national investments, this entails increased international and regional technical cooperation.
8.16 To preserve the hydrological regime and reduce destructive floods and soil erosion, the deforestation rate in upper catchments needs to be reduced. The contributions of forests, trees and forestry to food security, as a source of food, medicines, animal feed and soil nutrients should be maintained and developed. Intensification of production through the irrigation of existing agricultural land can slow down the clearing of forests for expansion of rain-fed agriculture.
Andriesse, W., Fresco, L.O., van Duivenbooden, N. & Windmeijer, P.N. 1994. Multi-scale characterization of inland valley agro-ecosystems in West Africa. Neth. J. Agric. Sci., 42: 159-179.
Appelgren, B.G. & Klohn, W.E. 1996. Approaches, constraints and misconceptions in water resources management policy. CFWA Workshop. New York, NY, USA, Stockholm Environment Institute.
Ayibotele, N.B. 1992. The world’s water: assessing the resources. Keynote paper at the International Conference on Water and the Environment (ICWE), Dublin, Ireland.
Barthelemy, F. 1993. Water for a sustainable human nutrition: inputs and resources analysis in arid regions. Montpellier, France, Ecole nationale du génie rural, des eaux et forêts.
Brown, E.P. & Nooter, R. 1992. Successful small-scale irrigation in the Sahel. World Bank Technical Paper No. 171. Washington, DC, USA, World Bank.
Carruthers, I. & Morrison, J. 1994. 2020 vision – dramatic changes in the world agricultural and industrial production systems. IIMI Rev., 8(1): 14-20.
FAO. 1986. Water-lifting devices. FAO Irrigation and Drainage Paper No. 43. Rome.
FAO. 1992a. Water for sustainable food production and rural development – UNCED Agenda 21; targets and cost estimates. Rome.
FAO. 1992b. A note on estimation of investment requirements for WAT2010, by S. Marzin. Rome. (Internal document)
FAO. 1993. The state of food and agriculture 1993. Rome.
FAO. 1994. Gender issues in irrigated agriculture and irrigation extension. Discussion paper for the Technical Consultation on Irrigation Extension. Accra, Ghana, Regional Office for Africa (RAFR).
FAO. 1995a. Irrigation management transfer in Asia. Bangkok, Thailand, Regional Office for Asia and the Pacific (RAPA).
FAO. 1995b. Irrigation in Africa in figures. Water Reports No. 7. Rome.
FAO. 1995c. Water resources of African countries: a review. Rome.
FAO. 1995d. Reforming water resources policy: a guide to methods, processes and practices. FAO Irrigation and Drainage Paper No. 52. Rome.
FAO. 1996a. Small-scale irrigation for sub-Saharan Africa, by D. Hillel. Rome. (In press)
FAO. 1996b. Water and agriculture: a global view, by D. Hillel. Rome. (Internal document)
FAO. 1996c. Irrigation potential in Africa. A basin approach. Rome. (In press)
FAO/UNDP. 1995. Water sector policy review and strategy formulation – a general framework. FAO Land and Water Bulletin No. 3. Rome.
Frederiksen, H.D. 1996. Water crisis in developing world: misconceptions about solutions. J. Water Resour. Planning Manage., 122: 79-87.
Gleick, P.H., ed. 1993. Water in crisis. A guide to the world’s fresh water resources. New York, NY, USA, Oxford University Press.
Gleick, P.H. 1996. Minimum water requirements for human activities: meeting basic needs. Water Int. (In press)
Global Resources Information Database (GRID). 1994. Irrigation design in Africa. IPTRID Network Mag., 5: 5-6.
Harrison, P. 1987. The greening of Africa. London, UK, Paladin Grafton.
International Fund for Agricultural Development (IFAD). 1994. The IFAD experience with project design and implementation. Rome.
Magai, R.N. 1994. Wetland soils in Zambia. Proceedings of the World Soil Conference, Acapulco, Mexico.
Margat, J. 1996. L’alimentation en eau de l’humanité, situation et tendances présentes – prospectives. L’eau et la vie des hommes au XXIe siècle. Colloque Mouvement universel de la responsabilité scientifique, France.
McCalla, A.F. 1994. Agriculture and food needs to 2025: why we should be concerned. Sir John Crawford Memorial Lecture. Washington, DC, USA, Consultative Group on International Agricultural Research (CGIAR) and World Bank.
Mharapara, I.M. 1993. Technical research and management practices on dambos in Zimbabwe. In Sustainable use of dambos in southern Africa. Lusaka, Zambia, Adaptive Research Planning Team (ARPT).
Millier, C. 1995. Prospective mondiale de l’eau a l’horizon 2025. Bull. Cons. gén. GREF, 43: 109-126.
Moris, J.R.,Thom, D.J. & Humpal, D.S. 1987. African irrigation overview: main report. WMS Report No. 37. Logan, UT, USA, Water Management Synthesis II Project, Utah State University, and United States Agency for International Development (USAID).
Organisation for Economic Co-operation and Development (OECD). 1995. West Africa long-term perspectives: regional opportunities and policy issues. Paris, France, OECD Club du Sahel.
Pacific Institute for Studies in Development, Environment and Security. 1995. California water 2020: a sustainable vision. Oakland, CA, USA.
Plusquellec, H., Burt, C. & Wolter, H. 1994. Modern water control in irrigation. World Bank Technical Paper No. 246, Washington, DC, USA, World Bank.
Postel, S. 1992. Last oasis: facing water scarcity. World Watch Environmental Alert Series. New York, NY, USA, W.W. Norton & Co.
Postel, S.L., Daily, G.C. & Ehrlich, P.R. 1996. Human appropriation of renewable fresh water. Science, 271: 785-788.
Raskin, P.D., Hansen, E. & Margolis, R.M. 1996. Water and sustainability: global patterns and long-range problems. Nat. Resour. Forum, 20: 1-15.
Rockström, J. 1995. Biomass production in dry tropical zones: how to increase water productivity. In Land and water integration and river basin management. Proceedings of an FAO informal workshop. FAO Land and Water Bulletin No. 1, p. 31-47. Rome, FAO.
Rosegrant, M.W. & Perez, D. 1995. Water resources development in Africa: a review and synthesis of issues, potentials, and strategies for the future. Washington, DC, USA, International Food Policy Research Institute (IFPRI).
Schultz, B. 1993. Land and water development: finding a balance between implementation, management and sustainability. Delft, the Netherlands, International Institute for Infrastructural, Hydraulic and Environmental Engineering (IHE).
Seckler, D. 1996. The new era of water resources management: from “dry” to “wet” water savings. Washington, DC, USA, Consultative Group on International Agricultural Research (CGIAR).
Shiklomanov, I.A. 1996. Assessment of water resources and water availability in the world. St Petersburg, Russian Federation, State Hydrological Institute.
Shuval, H. 1996. Sustainable water resources versus concepts of food security, water security, water stress for arid countries. CFWA Workshop. New York, NY, USA, Stockholm Environment Institute.
Singh, I. 1990. The great ascent: the rural poor in South Asia. Baltimore, MD, USA, Johns Hopkins University Press, for the World Bank.
World Bank. 1993a. Water resources management strategy for sub-Saharan Africa. Initiating memorandum. Washington, DC, USA.
World Bank. 1993b. Water resources management: a World Bank policy paper. Washington, DC, USA.
World Bank. 1994. A review of World Bank experience in irrigation. Washington, DC, USA.
World Bank/UNDP. 1990. A proposal for an internationally supported programme to enhance research in irrigation and drainage technology in developing countries, Vol. II. Washington, DC, USA.
World Conservation Union (IUCN). 1991. Wetlands Conservation Conference for Southern Africa. Gaborone, Botswana.
World Meteorological Organization (WMO). 1992. The Dublin statement and report of the conference. International Conference on Water and the Environment (ICWE), Dublin, Ireland, 26-31 January 1992. Geneva.
World Resources Institute (WRI). 1994. World resources, a guide to the global environment. New York, NY, USA, Oxford University Press.
Yudelman, M. 1994. Demand and supply of foodstuffs up to 2050 with special reference to irrigation. IIMI Rev., 8(1): 4-14.
______
(5) L’Office du Niger covers 55 000 ha surface-irrigated primarily under rice and cultivated by family farms. The
project is a classic irrigation laboratory. Started in the 1930s, it went through all the possible ups and downs of the
history of irrigation. Although it was in a difficult situation in the early 1980s, it has reached today a level of
productivity equal to the best schemes in Asia, with highly performing installations, good management,
high-yielding rice varieties and innovative farmers. Back to text
(6) Broad, composite average new development costs and rehabilitation costs for the different regions of the
developing world have been quoted by a number of sources, based on recent cost data. The costs of new irrigation
development vary between US$1 400 per hectare for South Asia and US$18 300 per hectare for sub-Saharan
Africa. Similarly, rehabilitation costs range between US$520 and US$2 900. Most of the analysed projects were
medium- to large-scale gravity irrigation schemes, with full water control. Back to text
(7) For example, when non-productive infrastructure was included in the Chad polder project, the development
costs increased by 150 percent (Brown and Nooter, 1992). Back to text
(8) Recently designed or constructed medium- to large-scale projects (ranging in area from 1 500 to 150 000 ha) in
South and East Asia confirm more or less the cost data given by FAO. New irrigation costs average US$1 490
(range US$810 to $2 530) per hectare in Viet Nam and US$2 600 (range US$950 to $3 600) in India. Average
rehabilitation costs were US$450 (range US$160 to $3 200) per hectare in Viet Nam and China. Recent
development costs for large schemes, along rivers especially in West Africa, with flood protection, vary from
US$2 000 to $6 500 per hectare, depending on the control of water and the local conditions. Construction generally
includes dykes, canals, drains, structures and land levelling. These costs are much higher (double to triple) than
average costs for similar Asian projects. This is partly because major flood dykes, which are necessary for most
projects and which constitute a large part of the costs (up to 30 percent), were built a long time ago in Asia and are
rarely part of present irrigation development. Back to text
(9) The following is an example where different options for a weir design were prepared, including one where local materials were used to the maximum.
A small radial gate, supplying water to a 193-ha rice scheme, was bypassed by floods. The headworks were subsequently extended by 25 m with a concrete weir, but had to remain unfinished because of poor foundation conditions. Therefore an investigation of the foundation conditions was carried out (of course, this survey should have been carried out at a much earlier stage, before the concrete weir was designed; this is an example of insufficient data collection during the planning stage). From the survey it could be concluded that the bearing capacity of the foundation was good, but that the foundation materials would allow seepage and would therefore be liable to piping. On the basis of the foundation survey a design was prepared by foreign consultants to close off the river and to avoid piping. This design included the use of sheet piling for a cut-off wall, a masonry wingwall next to the existing concrete weir structure and an embankment with gabion and riprap protection. The construction costs were estimated at US$187 500. This was thought to be too high and alternative designs had to be prepared, also because there was no equipment or skill for sheet piling in the country.
The revised design for the completion of the headworks included the use of local materials and labour as much as
possible. This was done, however, without affecting the safety and function of the structure. It was decided to opt
for a gabion weir, which would close the river gap of 23 m. The actual construction cost of this structure was
US$107 500 (57 percent of the cost for the original design). The structure has been operational for more than ten
years without any problem and with few maintenance requirements. Back to text
(10) This could also be the way forward in many rehabilitation projects where the major works would be developed
centrally, but where in-field developments would be left to the farmers. Back to text
(11) Lessons from evaluations of irrigation should be included in new investments in any modernization or
rehabilitation. Important among these lessons is the need to complete projects (including drainage, properly
designed field channels and land levelling), to deal with the whole catchment area including the non-irrigated
upland areas, and to ensure that mechanisms are in place that will maintain the scheme over the life of the project.
Back to text
