E. Perry
Appropriate Technology International, Washington D.C., USA
Irrigation in sub-Saharan Africa
Improved manual irrigation technologies
Mechanized technologies for small-scale irrigation
Conclusion
References
The major bottleneck to increased irrigated food production in sub-Saharan Africa is the lack of low-cost productive technologies. This paper describes low-cost, manual and mechanized irrigation technologies capable of providing considerable production increases to small farmers. The relatively inexpensive and productive nature of these technologies has the potential for increasing the number and the degree to which farmers will participate in the development of the irrigation subsector. While the manual irrigation technologies described herein address the needs of farmers with holdings of 0.5 hectares or less, the mechanized technologies will satisfy the needs of farmers irrigating more than 0.5 ha. The proposed improved technologies will be of interest to farmers already irrigating surface areas in these size ranges by reducing costs as well as those who wish to graduate from smaller farms to larger irrigated areas.
There are 42 082 000 ha of irrigable land in sub-Saharan Africa of which only about 13 percent, or 5 564 000 ha, is actually under irrigation (FAO, 1995). Development of the irrigation subsector in sub-Saharan Africa has been constrained by the high cost of irrigation schemes constructed until now as well as their management complexity. The investment cost of a full-control irrigation scheme in Niger is US$ 10 000 - 25 000/ha. However, the practice of traditional irrigated agriculture going back several centuries in some arid regions south of the Sahara, the availability of significant water, land, and labour resources in many areas, good and growing domestic and regional export markets for irrigated food crops, and appropriate low-cost manual and mechanized irrigation equipment promise a bright future for the subsector.
Improved irrigation allows for the increased production of many crops. However, sub-Saharan Africa's competitive edge appears to be in the production of high value vegetables and fruits, not such increasingly consumed crops as rice and wheat which can frequently be produced more cheaply elsewhere. As urban populations continue to increase and economic growth rates continue to expand throughout Africa, market prospects are bright for horticultural production. This paper focuses on low-cost technologies for irrigated horticulture as a means of improving food security and increasing small farmer incomes.
The majority of market gardeners in sub-Saharan Africa have farm holdings of less than 0.5 hectares. (The average irrigated surface area in Burkina Faso is 1063 m2 (Government of Burkina Faso, 1995), while the average in Cameroon is 565 m among manual irrigators (ATI, 1987)). These farmers will benefit most from improved manual irrigation technologies.
In addition, however, a significant portion of vegetable and fruit production is accounted for by larger farmers. These farmers will benefit from low-cost mechanized irrigation technologies. Although these larger farmers are fewer in number than the smaller producers, their contribution to total marketable production may be greater. Smaller farmers, who graduate to larger scale production, will also benefit from mechanized equipment.
A number of conditions must be met for successful small-scale irrigated horticultural development to occur: (1) availability of suitable land; (2) availability of water resource; (3) availability of labour; (4) availability of non-irrigation inputs to production; (5) access to markets; (6) capital resources; and (7) appropriate water lifting technology (Norman, 1992;
Alien and Perry, 1996). Box 1 provides a general description of the current status of the first six prerequisites for successful irrigated horticulture. However, sustainable development of this potential will require appropriate irrigation equipment, in particular equipment for water lifting. The key attributes of this equipment are:
· greater productivity reflected in higher flow rates relative to traditional water lifting devices; and,
· low capital and recurrent costs and low levels of maintenance.
Three water lifting options are assessed here in the context of Burkina Faso - the traditional rope and bucket method, the motorized pump and the treadle pump. (An assessment of other human powered pumps is not performed here because, as shown elsewhere, they are relatively expensive and poorly suited to use in irrigation due to low output and high human energy requirements (Hyman, 1995)).
Rope and bucket method
Traditional water lifting equipment is usually produced by local artisans using local materials. Examples in West Africa include the chadouf and the rope and bucket. The major advantage of these technologies is their low cost. The major disadvantage of traditional water lifting devices is their low flow rate capacity and resulting small size of irrigated plots which, in turn, limit production and incomes. This technique is very arduous and time consuming, allowing for a flow rate of only about 1 000 litres of water per hour when water is 4.5 metres from ground level. Not unlike most sub-Saharan African countries, approximately 80 percent of horticulturists in Burkina Paso use this type of water lifting system (Government of Burkina Faso, 1995).
Motorized pump
Burkina Faso has experienced a significant increase in the number of motorized pumps in the last 10 years. While there is some limited use of diesel-powered irrigation pumps, the vast majority of these pumps consist of gasoline engines of 2-5 horsepower coupled with a low lift centrifugal pump. The major advantages of motorized pumps are their considerable capacity relative to traditional water lifting means, making it possible to expand irrigated surface areas. Disadvantages include: high capital costs; high recurrent costs; and high maintenance levels.
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BOX 1 Six CONDITIONS FOR SUCCESSFUL SMALL-SCALE IRRIGATED PRODUCTION In addition to appropriate irrigation technology, a number of conditions must be met for successful small-scale irrigated horticultural development to occur availability of suitable land, water, and labour resources and non irrigation inputs to production, access to markets, and capital resources (Norman, 1992, Alien and Perry, 1996) Availability of Land Resources A horticultural development programme is justified if it has strong potential for achieving increased production and incomes Land is one of the most important factors of production linked to this achievement It must exist in adequate quantities and with the appropriate physical properties for an expansion of irrigated horticultural production to occur Experience in several sub-Saharan countries confirms that land availability is not a constraint to increased irrigated production and that resulting increases in irrigated surface area is one of the main contributing factors to successful horticultural development In Senegal and Mali, where farmers have benefited from improved manual water lifting technologies, gardens have increased in size by an average of 39 percent and 61 percent, respectively (Hyman, 1995, Niambélé and Togola, 1996) In Burkina Faso, farmers using motorized pumps irrigate an average of 2 74 hectares (Gay 1994) Horticulturists in north Cameroon irrigate an average of 3,178 m when motorized pumps are used, more than five time greater than the surface area irrigated using traditional manual water lifting means (ATI, 1987) Interviews with individual farmers and representatives of farmer's groups in other African countries have disclosed that while the average manually irrigated garden is usually very small (frequently between 250 m and 1 000 m2), additional land is available to most farmers for expanded production (Perry, 1996, Perry, 1997) For productive market gardening to occur suitable soils must exist Problems can arise if soils are either too sandy or too heavy Soils that are too sandy may lead to high seepage losses in distribution canals and in basins Their low moisture retention capacity reduces water available to the crop If soils are too heavy, the low infiltration rates will cause excessive time for water application (Norman, 1992) Water Resource Availability Irrigation of vegetables requires significant quantities of water of suitable quality To avoid over expenditure of labour and/or energy, water must be relatively close to the surface, preferably within 0 7 metres In the case of wells, these must penetrate the water table to sufficient depth and the aquifer must provide adequate recharge to assure necessary quantities of water. Water lifted from surface water sources (e g rivers or lakes) must not require a vertical lift greater than 7 metres Groundwater and surface water having a considerable salt content are not considered to be of suitable quality for irrigation purposes Information regarding well volume and recharge rates has been collected in some West African countries In many cases, low recharge rates require that wells be widened and deepened or their numbers multiplied, if improved, higher capacity water lifting technologies are to be fully utilized (Perry, 1996, Perry, 1997) Minor modifications to the lifting technology (e g smaller diameter cylinders in the case of the treadle pump) and ancillary equipment (e g wrapped filters), where appropriate, may also be helpful in increasing pumping ease and well flow capacity Some horticultural areas suffer from permanent or seasonal water shortages This shortage, of course, occurs to a greater or lesser extent in all sub-Saharan Africa countries Availability of Labour Traditional irrigated horticulture is a highly labour intensive activity In Senegal, it is estimated that as much as 80 percent of traditional market gardening labour time is devoted to irrigation related tasks (i.e water lifting and distribution) Senegalese horticulturists using manual water lifting and distribution means average more than 7 000 hours for the irrigation of one hectare (Hyman, 1995) In Niger, the labour requirements for manual water lifting (not including water distribution or other non-irrigation activities) from a well over a four-month crop cycle can exceed 6 000 hours per hectare for a single farmer (Norman, 1992) Using the chadouf, horticulturists in north Cameroon take approximately 5 800 hours to irrigate one hectare over the same four month period (ATI, 1987) In Benin, a small sample of market gardeners found average time spent to be in the order of the Niger and Cameroon findings (Perry, 1997). 1 The chadouf or counterpoise lift, is used for water lifting from shallow wells (2-6 meters in depth) It consists of a container, sometimes a 10 litre metal can attached to the end of a rope which hangs from a lever with a counterweight on the other end Using the concept of mechanical advantage, the weight may be sufficient to balance between one-half and the entire weight of the full can so that the operator need only lift up to one half of the combined can and water weight To return the receptacle to the water source, the operator uses at least some of his/her weight to tip the counterweight in order to pull the lever down The weight of the counterweight depends on the lift, terrain, and operator's liking Given the availability of land during the dry season for the expansion of irrigated farming, it is anticipated that the introduction of an improved water lifting technology will lead to larger irrigated surface areas. The labour saved by the using the new lifting device can be applied to increase the amount of hectarage under cultivation This increase in irrigated area has occurred in Senegal with the introduction of improved manual water lifting equipment (Hyman, 1995). In north Cameroon, farmers using motor-driven centrifugal pumps and irrigating approximately 3 200 m employ an average of 2 8 persons, while manual irritations employ 2.1 persons (ATI, 1987). On balance, it is not expected that the number of farm workers will significantly decrease or increase However, in some cases, these larger surface areas may require greater numbers of workers. Availability of Non-Irrigation Inputs While by no means optimal, the availability of non-irrigation inputs is not, in most cases, the major obstacle to the development of the small-scale irrigated horticulture. In general, although used in relatively limited amounts in most locations in sub-Saharan Africa, non-irrigation production inputs (e.g. seeds, fertilizer, and pesticide) are generally available locally and in sufficient quantities to allow for expanded horticulture production. Increased availability will be driven by increased producer demand for such inputs. Access to Markets Market outlets for vegetable and fruit production are imperative for successful small-scale irrigated horticulture to occur. Relative proximity and reliable physical linkages to a market must exist. Regardless of the other investments made in the subsector, horticulturists will require expanding markets to increase their incomes. Without a sufficient market for vegetables and fruits, increased market garden production will not have the desired effect of increasing producer household incomes Based on the growing numbers of newly active market gardeners in all of the West African countries, apparently attracted by the prospects of higher incomes, the subsectoral outlook has been good in recent years in that part of sub-Saharan Africa. The future potential for an expanded market for vegetables and fruits will depend on three factors increased local demand; increased substitution of locally produced fruits and vegetables for imported produce and increased exports. Given the highly competitive, quality sensitive nature of the European markets, the best promise in the near future (or short term) for expanded commercialization of West African vegetables and fruits resides in the domestic and, to a lesser degree, in the regional market The trend whereby urban dwellers in West Africa have in recent years increased their consumption of vegetables and fruits has been noted by informed observers. Even the local market potential has been strengthened in some countries as the same tendency has also been observed in the rural sector In recent years, as vegetable and fruit consuming urban populations in West Africa have grown in size and as consumer tastes, rural as well as urban, have changed to incorporate greater amounts of vegetables and fruits in the diet, local demand has expanded. As the phenomena of increasing urban populations and changing tastes persist, continued growth in domestic demand is anticipated In general, interventions that extend the agricultural calendar (e.g. improved low-cost water lifting and accessing technologies) and allow for the storage and/or the processing of fresh produce may help to further improve the market outlook for vegetable and fruit production. However, countries where consumers have only recently acquired a taste for some fresh fruits and vegetables, the widespread consumer acceptance of processed agricultural products is still to be market-proven and is likely to take another generation before it becomes established. Access to Capital Financial capital can be important to the expansion of horticultural production. However, this variable should not be over-emphasized in the case of small producers who require relatively small amounts of capital A sample of horticulturists (both traditional manual and mechanized irrigators) in Benin revealed average annual cash expenses, not including hired labour, of US$ 329 per hectare (Perry, 1997) This expenditure compares to Côte d'Ivoire, where non-labour inputs for the production of one hectare of onions costs US $256 (Government of Benin, 1995b) While not insignificant, these costs are bearable by active commercial horticulturists. Income earned from irrigated horticultural production is well above the earnings of the average West African farmer Four Beninese small-scale horticulturists surveyed reported an average annual net income of US$ 691 (Extrapolated to a uniform irrigated surface area, one hectare of irrigated vegetables yields an annual net income of US$1 870) (Perry, 1997). Unlike the situation of traditional farmers practising rainfed agriculture, where there is little or no cash income, this revenue makes new investments in the horticultural subsector much more feasible, and makes less necessary recourse to formal financial institutions. |
Since the great majority of users operate their motorized pumps at well below the recommended engine speed in an effort to save on fuel costs, their actual flow rates are far from the rated capacities. Gay (1994) found that the actual capacities averaged from 5.2 m3 per hour to 11.3-15.6 m3 per hour, depending on whether installation occurs at a well site or a surface water source. This is a significant finding, indicating that in some instances (e.g., water lifting from wells) high performance manual technologies can compete favourably with motorized pumps in the critical area of flow rate capacity.
Treadle pump
The treadle pump originated in Bangladesh in the early 1980s. In late 1990 and mid-1995, commercial dissemination began in Senegal and in Mali, respectively. By the end of December 1996, twenty-five manufacturers in Senegal had produced and sold more than 1 900 pumps, while ten such producers in Mali had sold approximately 600.
The treadle pump has a number of features which set it apart from other manual irrigation pumps. The standard version can lift 5 000 to 7 000 litres of water an hour from wells, boreholes or surface water sources for a suction head of up to 7 metres. Because the pump employs the user's body weight and leg muscles, it is much less tiring than other manual pumps that utilize the upper body and arm muscles. Fabricated from locally available materials, it can be manufactured by metal working shops equipped with welders and simple hand tools such as those frequently found in large numbers in sub-Saharan African capitals and many secondary towns.
TABLE 1 Comparisons of alternative water lifting technologies
|
Water lifting device |
Capacity at 4.5 m (l/sec) |
Initial cost (CFAF) |
Depth range (m) |
|
Rope and bucket |
0.3 |
5 000 |
0 - 7 |
|
Treadle pump |
1.7 |
63 000 |
0 - 7 |
|
Motorized pump |
2.1 |
361 000 |
0 - 7 |
At a lift of 4.5 metres, the treadle pump has a discharge of 1.7 1/sec. It can be made for approximately CFAF 63 0001 in Burkina Faso. Drawing water from a surface water source or from a well with sufficient capacity, this pump can irrigate an area of approximately one-half hectare. Table 1 summarizes the performance parameters and initial investment cost of the rope and bucket technology, the treadle pump, and a locally available motorized pump.
1 Five hundred CFAF are roughly equivalent to US$ 1.
A major constraint to increased irrigated crop production in Burkina Faso is low water lifting and distribution capacity. Any pump supplying significantly greater flow rates relative to the traditional rope and bucket system will increase irrigated surface areas and reduce irrigation labour time relative to the original irrigated surface area, resulting in increased production (Hyman, 1995 and Gay, 1994).
The question then becomes which improved method, the treadle pump or the motorized pump, is most cost-effective within the range of surface areas achievable by the treadle pump (i.e. 0.5 ha or less). Assuming that both the treadle pump and a motorized pump will result in similar production increases in that range of surface areas attainable by the treadle pump and that, except for water costs, the cost of inputs are the same for both improved methods, a determination has been made within the context of Burkina Faso as to whether the treadle pump or the motorized pump produces the least costly water supply, maximizing to the greatest degree the net income of the market gardening enterprise (see Box 2 for general and pump-specific assumptions).
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BOX 2 COMPARATIVE COSTS OF WATER PUMPED USING A TREADLE PUMP AND A GASOLINE-POWERED PUMP: THE CASE OF BURKINA FASO This comparison of pumping costs using the treadle pump and a small motorized pump available in Burkina Faso is based on the assumptions cited below for market gardens of 0.50 hectare. Key general assumptions on the performance of this comparative cost analysis are: · 80 m3 of water are required per hectare per day, or 40 m3 per 0.50 hectare; · 180 days of irrigation are required per year; · 14 400 m3 are required annually per hectare, or 7 200 m3 per 0 50 hectares. Treadle Pump Assumptions · The treadle pump is operated by two people and delivers 6 m3 per hour. While one person pumps, the other is directing the flow of the water to different sections of the field. Therefore, 6.6 hours of labour are needed for two persons at CFAF 63 per person-hour. The total labour cost is CFAF 840, or CFAF 21 per cubic metre. · The treadle pump and 27 metres of PVC pipe cost a total of CFAF 85 500 and have an expected lifetime of 6 years. Therefore, given an annual depreciation of CFAF 14 250 and 7 200 m3 of water pumped annually, the depreciation cost per cubic metre is CFAF 2. · It is estimated that spare parts and repairs will cost CFAF 3 500, or CFAF 0.5/m3, and lubricant CFAF 13 500 per year, or CFAF 1.9/m3. Therefore, spare parts, repairs and lubricant will cost CFAF 2.4/m3. Motorized Pump Assumptions · The Barbera pump with a capacity of 7.5 m3 per hour is operated by one person. Virtually all of the person's time is spent directing the water being pumped to different parts of the field being irrigated. Therefore, 5.3 hours of labour are needed for one person at CFAF 63 per person-hour. The total labour cost is CFAF 334, or CFAF 8.4 per cubic metre · The motorized pump, 7 meters of suction hose and 20 meters of delivery hose will cost a total of CFAF 361 000 and have an expected lifetime of 5 years. Therefore, given an annual depreciation of CFAF 72 200 and 7 200 m3 of water pumped annually, the depreciation cost per cubic meter is CFAF 10. · Spare parts and repairs cost CFAF 50 000 a year, or CFAF 6.9 per cubic metre. · The motorized pump will consume 0.4 litres of gasoline per hour at CFAF 390/litre for 5.3 hours a day. Therefore, CFAF 827 is spent daily, or CFAF 20.7 per cubic metre. · Lubricating oil is consumed at a rate of 1 litre per 20 hours of pump operation at CFAF 1 438/litre, that is, CFAF 381 per day, or CFAF 9.5 per cubic metre. |
The total cost for a cubic metre of water to irrigate 0.5 hectares is significantly greater with a motorized pump than with a treadle pump. Instead of a total expenditure of CFAF 55.5/m3, the cost of a cubic metre of water is CFAF 25.4 when the treadle pump is used. Therefore, use of the treadle pump will save CFAF 216 720 per year relative to the motorized pump, generating a significant increase in net income.
These same comparisons can be made for 0.33 hectares. At one-third of a hectare the cubic metre cost difference is even greater (see Table 2).
TABLE 2 Comparative cost of one cubic metre of water for the treadle pump and a motorized pump and for different surface areas
|
Costs |
TP (0.33 ha) |
TP (0.5 ha) |
MP (0.33 ha) |
MP W (0.5 ha) |
|
|
Labour |
21 |
21 |
8.4 |
8.4 |
|
|
Deprec. |
|
|
|
|
|
|
|
3 years |
|
|
|
|
|
4 years |
|
|
|
|
|
|
5 years |
|
|
|
10 |
|
|
6 years |
|
2 |
12.7 |
|
|
|
7 years |
|
2.6 |
|
|
|
|
Spare parts & repairs |
0.5 |
0.5 |
6.9 |
6.9 |
|
|
Lubric. |
1.9 |
1.9 |
9.5 |
9.5 |
|
|
Fuel |
0 |
0 |
20.7 |
20.7 |
|
|
TOTAL |
26.0 |
25.4 |
58.2 |
55.5 |
|
TP = Treadle Pump
MP = Motorized Pump
Manual groundwater development
The hand augured tube-well, a low-cost water source for small farmers, has been widely disseminated in Niger and to a lesser extent in some other West African countries (e.g. Benin, Nigeria, Senegal and Mali). This technology is inexpensive and quickly installed. In Benin the hand augured tubewell costs as little as US$ 30 for a ten-foot deep well. Working in teams of two workers, two such tubewells can be installed daily. Depending on the aquifer and soil conditions, hand augured tubewells can yield up to 14 cubic metres of water per hour.
Other manual methods, such as the sludge technique, which have gained widespread acceptance in Asia, have had less success in Africa due probably to the less favorable hydrological and soil conditions found where it has been tried. Nevertheless, these techniques deserve greater consideration in sub-Saharan Africa's efforts to develop the irrigation sub-sector.
Some sub-Saharan African countries (e.g. Niger, Nigeria, Zimbabwe, and Cameroon) possess large areas of land having shallow aquifers recharged by seasonal rainfall and flooding. While some areas exhibit low recharge rates only appropriate for traditional lifting of water or improved manual technologies, such as the treadle pump, in many locations hand-dug lined wells or tubewells inserted into these shallow aquifers will yield sufficient water for higher discharge mechanized pumps. These same high-capacity mechanized pumps are appropriate to surface water sources found in many African countries. There are two main areas where mechanized technologies can improve the efficiency of small-scale irrigation: water lifting and groundwater development. Improved water distribution technologies will also help to lower the cost of irrigation water.
Mechanized water lifting
Mechanized water lifting has been plagued by a number of technical problems in sub-Saharan Africa. These problems include high investment and operating costs, limited suction head, and seasonal, as opposed to year around, usage.
The author is grateful to Carl Bielenberg for his contribution to this section of the paper.
High Investment Cost. Low per caput income of sub-Saharan African farmers limits their ability to procure relatively expensive pumpsets of European and Japanese manufacture which comprise all of the motorized pumps in use in many countries (Gay, 1994). Low purchasing power has played an even greater role as regards the more expensive diesel pumpsets which have a longer life and lower operating costs per cubic metre of water pumped than the relatively inexpensive gasoline engine-powered pumps. Diesel engine-powered pumps sold in West Africa cost between US$ 3 200 and US$ 12 000, depending on pumping capacity. According to their power rating, gasoline engine-powered pumps marketed in West Africa tend to cost between US$ 700 and US$ 900.
TABLE 3 Relative cost of fuels useable in irrigation in Niger
|
|
Price per litre (in CFA francs) |
Percent of cost of gasoline |
|
Kerosene |
130 |
42 |
|
Diesel Fuel |
205 |
66 |
|
Gasoline |
310 (375 for super not used for irrigation) |
100 |
Imported diesel-powered centrifugal pumps from Chinese and Indian manufacturers as well as locally produced axial flow pumps provide low investment cost options for horticulturists and rice farmers who require large amounts of irrigation water.
High Operating Cost. High operating costs, in particular the cost of fuel, reduces the profitability of many mechanized pumps in use in West Africa. The cost of pumped irrigation water in Niger using a gasoline-powered pump is 30-50% of the total pump operating cost (Gay, 1994). Therefore, operating costs will be lower for motors that use less expensive fuels. In Niger, the most expensive engine fuel is gasoline, followed by diesel fuel, and kerosene. Kerosene and diesel fuel are 42 and 66%, respectively, of the cost of gasoline (Table 3). The price differentials are representative of many other West African countries.
Relatively low-cost fuels, including kerosene for spark ignition engines, diesel fuel for diesel engines and locally produced plant oil as a diesel fuel substitute in diesel engines have the potential for significantly reducing the costs of pump operation. Taking the case of Niger, Box 3 assesses the comparative cost of water using these alternative fuels.
Limited Suction Head. The vast majority of mechanized pumps used in sub-Saharan Africa are motorized centrifugal pumps. One of the drawbacks to this technology is that the suction lift is theoretically limited to 6-7 metres. In Niger a survey of motorized farmers around Maradi found that the net suction head is actually between 2 and 5 metres (Gay, 1994). At these relatively shallow depths the recharge rate will not be as high as it is at greater heads. Low recharge rates will limit the potential for irrigated agriculture and increase the pumping cost as pump users choose to run the engine at slower than optimal speed to better match the pump's discharge capacity with the well's recharge rate, thereby increasing fuel consumption per cubic metre of water pumped. Established farms cannot grow as much as they might, and some areas will never develop irrigated agriculture at all because the aquifer is too deep to be tapped by standard centrifugal pumps.
Low-cost jet pumps in conjunction with centrifugal pumps have the potential for lifting water from aquifers up to 30 metres in depth. The potential for immediate impact is considerable. Not only would new mechanized farmers be interested in such technology, but hundreds, perhaps thousands, of farmers who are already using centrifugal pumps would have the opportunity, at very low incremental cost (approximately US$ 50 per unit, if produced locally) to expand surface areas under irrigation by pumping deeper, more abundant groundwater.
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BOX 3 COMPARATIVE COSTS OF WATER PUMPED USING MECHANIZED MEANS-THE CASE OF NIGER Of primary importance in the selection of mechanized water lifting devices is the relative cost of the water pumped This appendix compares gasoline powered pumps with kerosene powered pumps for 1 and 2 hectares, and, gasoline-powered pumps with Chinese-made diesel-powered pumps for 3 and 4 hectares The data presented here are specific to Niger General Assumptions Key general assumptions in the performance of this comparative cost analysis are · 80 m3 of water are required per hectare per day; Gasoline-Powered Pump Assumptions · The gasoline powered pump with a capacity of 20 m3 per hour is operated by one person. Virtually all of the person s time is spent directing the water being pumped to different parts of the field being irrigated Therefore, 4 hours of labour are needed for one person at CFAF 63 per person hour The total labour cost is CFAF 252 or CFAF 3.2 per cubic metre. · The gasoline-powered pump and 7 metres of suction hose and 20 metres of delivery hose will cost a total of CFAF 450 000 and have an expected lifetime of 5 years Therefore, given an annual depreciation of CFAF 90 000 and 14 400 m3 of water pumped annually, the depreciation cost per cubic metre is CFAF 6.3. · Spare parts and repairs cost CFAF 50,000 a year, or CFAF 3.5 per cubic metre. · The gasoline-powered pump will consume 0 5 litres of gasoline per hour at CFAF 310/litre for 4 hours a day Therefore, CFAF 620 is spent daily, or CFAF 7.8 per cubic metre. · Lubricating oil is consumed at a rate of 1 litre per 50 hours of pump operation at CFAF 1 400/litre, that is, CFAF 11.2 per day, or CFAF 1.4 per cubic metre. Kerosene-Powered Pump Assumptions · The kerosene-powered pump is operated by one person and delivers 20 m3 per hour Therefore, as in the case of the gasoline engine, 4 hours of labour are needed for one person at CFAF 63 per person hour The total labour cost is CFAF 252 or CFAF 3.2 per cubic metre. · The kerosene-powered pump costs approximately CFAF 500 000 and has an expected lifetime of 4 5 years Therefore, given an annual depreciation of CFAF 100 000 and 14 400 m3 of water pumped annually, the depreciation cost per cubic meter is CFAF 6.9. · It is estimated that annual spare parts and repairs will cost CFAF 50 000, or CFAF 3.5/m3. · The kerosene-powered pump will consume 0 4 litres of kerosene per hour at CFAF 130/litre for 4 hours a day Therefore, CFAF 208 is spent daily, or CFAF 2.6 per cubic metre. · Lubricating oil is consumed at a rate of 1 litre per 50 hours of pump operation at CFAF 1 400/litre, that is, CFAF 112 per day, or CFAF 1.4 per cubic metre. The total cost for a cubic metre of water for the irrigation of one hectare is greater with a gasoline-powered pump than when a kerosene-powered pump is used Instead of a total expenditure of CFAF 22 2/m3, the cost of a cubic metre of water is CFAF 18 4/m3 when the kerosene powered pump is used Therefore, use of the kerosene pump will save more than CFAF 246 000 over the 4 5-year life of the pump Fuel savings will total almost CFAF 75 000 in Year 1 and CFAF 374 400 over the life of the pump Use of the kerosene powered pump to irrigate 2 ha will generate CFAF 397 400 over the 3-year life of the pump. Diesel-Powered Pump Assumptions · The diesel-powered pump is operated by one person and delivers 40 m3 per hour Therefore, to allow for the irrigation of 3 hectares, 6 hours of labour are needed for one person at CFAF 63 per person hour The total labour cost is CFAF 378 or CFAF 1.6 per cubic metre. · The diesel-powered pump costs approximately CFAF 1000000 and has an expected lifetime of 8 years Therefore, given an annual depreciation of CFAF 125 000 and 43 200 m of water pumped annually, the depreciation cost per cubic meter is CFAF 29. · It is estimated that annual spare parts and repairs will cost CFAF 62 500, or CFAF 1 4/m. · The diesel-powered pump will consume 1.2 litres of diesel fuel per hour at CFAF 205/litre for 6 hours a day Therefore, CFAF 1 476 is spent daily, or CFAF 6.2 per cubic metre. · Lubricating oil is consumed at a rate of 3 litres per 100 hours of pump operation at CFAF 1 400/litre, that is, CFAF 252 per day, or CFAF 1.1 per cubic metre. The cost of one cubic metre of water for the irrigation of 3 hectares is CFAF 25 8 when a gasoline-powered engine is used This compares with CFAF 13.2 when a diesel-powered pump is employed saving CFAF 12.6 relative to the gasoline engine Therefore, a total of CFAF 544 320 is saved by using a diesel powered engine to irrigate 3 hectares, CFAF 4 354 500 over the 8 year life of the pump Irrigation of 4 hectares using a diesel powered engine will save CFAF 725 700 during Year 1 of use, CFAF 5 080 000 during its 7-year life. |
TABLE 4 Cost of one cubic metre of water for different pumps and for different surface areas
|
Costa |
GP (1 ha) |
KP (1 ha) |
GP (2 ha) |
KP (2 ha) |
GP (3 ha) |
DP (3 ha) |
GP (4 ha) |
OP (4 ha) |
|
Labour |
3.2 |
3.2 |
3.2 |
3.2 |
3.2 |
1.6 |
3.2 |
1.6 |
|
Deprec. |
|
|
|
|
|
|
|
|
|
1 year |
|
|
|
|
10.4 |
|
10.4 |
|
|
2 years |
|
|
|
|
|
|
|
|
|
3 years |
|
|
5.2 |
5.8 |
|
|
|
|
|
4 years |
|
|
|
|
|
|
|
|
|
4.5 yrs |
|
7.7 |
|
|
|
|
|
|
|
5 years |
6.3 |
|
|
|
|
|
|
|
|
6 years |
|
|
|
|
|
|
|
|
|
7 years |
|
|
|
|
|
|
|
2.5 |
|
8 years |
|
|
|
|
|
2.9 |
|
|
|
Spare parts & repairs |
3.5 |
3.5 |
2.8 |
2.8 |
4.6 |
1.4 |
4.3 |
1.2 |
|
Lubric. |
1.4 |
1.4 |
1.4 |
1.4 |
1.4 |
1.1 |
1.4 |
1.1 |
|
Fuel |
7.8 |
2.6 |
7.8 |
2.6 |
6.2 |
6.2 |
7.8 |
6.2 |
|
TOTAL |
22.2 |
18.4 |
20.4 |
15.8 |
25.8 |
13.2 |
27.1 |
12.6 |
GP = Gasoline-Powered Pump; KP = Kerosene-Powered Pump; DP = Diesel-Powered Pump
Seasonal Usage. Mechanized irrigation pumps are rarely used at other times of the year than the annual dry season. Pump operating costs can be reduced by using pumpsets for applications other than irrigation. Both centrifugal and axial flow pumps can very easily and inexpensively be adapted for boat propulsion, using a design found widely in Asia that makes river travel possible, even when water depths in the river are only 1-2 metres. In Sudano-Sahelian West Africa this use is compatible with their use for irrigation as river navigation is most practicable from the end of the rainy season (August-September) until the end of the year, while irrigation is primarily practised from November/December through April. Boat-mounted pumpsets will greatly enhance transportation on the rivers, improving produce marketing in countries where transport infrastructure is underdeveloped, and will allow the pump/boat owner to contract with a number of farmers located along the banks of the river to supply them with irrigation water.
There is a wide range of mechanized water lifting technologies which have been developed around the world. These pumps have varying capacities, capabilities and costs. A number of these technologies have promise in sub-Saharan Africa for increasing the efficiency of irrigation water use. They include: kerosene-fueled centrifugal pumps; low-cost diesel-powered centrifugal pumps; water lifting using venturi ejectors with conventional centrifugal pumps; river-based low head and ultra low head irrigation pumps; and use of vegetable oils as a diesel fuel substitute in diesel powered centrifugal pumps (see Boxes 4 and 5).
Mechanized groundwater development
Another major obstacle to increased irrigation capacity is the cost of accessing adequate quantities of water for the purpose of irrigation. In Senegal and Botswana, a technology called the "wrapped filter" (also referred to as a "well-point") has been developed to improve the recharge rate of lined and unlined hand dug wells. This low-cost technology is essentially a short washbore injected into the floor of the well using a motorized pump and into which the intake hose from the pump is then inserted for water lifting purposes. The "wrapped filter" significantly increases the recharge rate of wide-diameter wells, doubling the availability of water for irrigation purposes. Based on a small sample of farmers using the wrapped filter in Senegal, this technology has made it possible to more than double the irrigated surface area.
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BOX 4: PROPOSED MECHANIZED WATER LIFTING DEVICES Kerosene-Powered Centrifugal Pumps Depending on pump capacity, irrigation practices and engine fuel consumption, it is estimated that 30-50 percent of the cost of irrigation water can be attributed to fuel cost (Gay, 1994) Kerosene-powered spark ignition engines would enable small farmers to avoid the high cost of gasoline, which is frequently heavily taxed, using less expensive kerosene instead. Kerosene in Niger for example is approximately 40 percent of the cost of gasoline Kerosene-powered engines are essentially the same as gasoline-powered, but are started on gasoline using one of two tanks and switched to the tank containing kerosene after warm up. The engines are slightly modified to provide the optimal compression ratio for burning kerosene Small, lightweight kerosene-fueled engines are made by FUJI Heavy Industries of Japan, but may also be available from India and China They cost only slightly more than gasoline-powered engines of the same horsepower Kerosene-fueled engines have been widely used in some African countries, including the Central African Republic, where they operate maize and cassava grinding mills In addition to its relatively low price, another major advantage of kerosene compared to gasoline is its convenient availability in many village settings There are two main disadvantages of kerosene use greater carbon deposits, necessitating more frequent engine cleaning and increased contamination of the crankcase lubricating oil, requiring more frequent crankcase oil changes to avoid shorter engine service life. The cost of water calculations account for these factors by assuming a shortened service life of 4 5 years Improvement in engine maintenance could be achieved through appropriate training of project technical staff, merchants and manufacturers. Low-Cost Diesel-Powered Centrifugal Pumps In combination with low-cost tubewells, locally manufactured diesel pumpsets have helped make India and China the countries with the most irrigated surface area in the world (In 1990, India's net irrigated area was 43 050 000 hectares, an increase of more than 20 million hectares since 1950.) Diesel-powered pumps are significantly heavier and more expensive than gasoline- or kerosene-powered units of the same capacity. However, diesel engines, if well made and properly serviced, are much longer lasting than spark ignition engines and use less fuel per cubic meter of pumped water. A project to promote diesel-powered pumps should pre-select small well made, affordable and adapted diesel engines and diesel powered pumps from India and China. In addition to the price, quality, and adaptability of their products, selected manufacturers from these Asian countries should also have experience exporting their products to Africa. Given the importance of maintenance to the longevity of diesel-powered pumps, added emphasis should also be given to this criterion during training of project staff, merchants, and manufacturers. River-Based Low Head and Ultra Low Head Irrigation Pumps River-based irrigation should focus on major rivers and their tributaries, and should utilize technologies which reduce pumping costs by reducing the initial cost of the pumping equipment, by encouraging multiple usage of irrigation pumps and contract irrigation, and by promoting low-cost fuels Low head pumps will be similar to the centrifugal pumpsets described above Such pumps will be of small (5-10 horsepower), single cylinder as well as medium (10-40 horsepower) multicylinder design Ultra low lead technologies will consist of locally made axial flow (propeller) pumps driven by similar or identical single and multicylinder engines. While centrifugal pumps are able to operate against lifts of 30 metres, propeller pumps work efficiently at up to 5 metres lift, but provide a much larger flow These pumps propel water by the reaction to lift forces produced by rotating its blades This action pushes the water past the impeller while imparting a spin to the water which passes through fixed guide vanes to straighten the flow and convert the spin component of velocity into extra pressure A portable, high capacity axial flow pump capable of delivering 100-200 m3 at heads in the range 1-5 metres is recommended The International Rice Research Institute (IRRI) has developed such a pump requiring a 5 hp engine capable of driving a 3 7 meter shaft at 3 000 rpm to discharge water through a 1 50 mm delivery tube The IRRI axial flow pump can be manufactured in small machine shops Such axial flow pumps can be so constructed to allow the owner to easily disconnect the engine and the propeller from the water pumping unit so that the engine/propeller unit can drive a boat transporting goods and passengers. Alternatively, axial flow pump owners could perform contract irrigation along water courses, stopping their boats along the banks of the river to use the boat propeller and shaft to irrigate rice paddies or vegetable fields. This system is used extensively in Southeast Asia to irrigate thousands of hectares of land and for river transport. Water Lifting from Aquifers of Medium Depth Using Venturi Ejectors with Conventional Centrifugal Pumps Centrifugal pumps have a maximum suction lift of 6 7 meters and are often difficult to prime at more than 5 metres suction lift. Conventional centrifugal pumps can be made to lift water from much greater depth by the addition of a low-cost venturi ejector. The combination of a centrifugal pump and a venturi ejector is commonly referred to as a jet pump. Electrically operated jet pumps supply water to many homes in the United States having wells up to 30 metres deep. It is recommended that low-cost gasoline, kerosene, and diesel powered jet pumps for small-scale irrigation from aquifers up to 30 metres deep be field tested. Jet pumps installed in tubewells of 100 mm diameter should be capable of lifting up to 15 m3 of water per hour at a depth of 30 meters, or up to 40 m per hour from 1 50 mm diameter wells. Open wells can accommodate larger venturi ejectors providing greater flows |
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BOX 5: ALTERNATIVE FUELS FOR DIESEL-POWERED PUMPS Vegetable Oils as a Diesel Engine Fuel ATI, in collaboration with the Better World Workshop in Vermont, is testing inexpensive diesel engines using Jatropha curcas oil as a fuel Jatropha curcas is a small tree that grows wild or is planted for live fencing by small farmers in much of sub-Saharan Africa. Jatropha curcas seeds are not edible, and therefore is not usually harvested by farmers. The seed contains about 35 percent inedible oil by weight, which can be easily extracted using simple manual presses or motorized expellers. Jatropha oil burns very well in diesel engines of the prechamber or swirl chamber type, producing nearly the same work output as when run on diesel fuel. |
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BOX 6: MECHANIZED DEVICES FOR IRRIGATION WATER DEVELOPMENT Well Jetting Well jetting is a low-cost technique for establishing small diameter wells (50-160 mm) using the forces of water to cut directly into the ground, liquefy the soil, and allow the insertion of riser pipe or well screens The applicability of well jetting and the modification of the technique that has to be used where it is applicable depend on the nature of the soil above the aquifer, the depth of the aquifer, and the grade of sand in the aquifer. In northern Nigeria, well jetting has been used with temporary casings to install over 5 000 new wells in just a few hours per well in places with 3-4 m of heavy soil overburden. By contrast, it can take three days to construct a well using manual techniques Highly favorable conditions over extensive areas in the southern part of the country, very similar to those that exist in northern Nigeria, could allow well jetting to flourish in Niger. In these areas, coarse sand is under pressure and former river beds have formed very permeable aquifers. Wrapped Screens The ability of some farmers to expand their irrigated area or provide crops with a larger amount of water is sometimes limited by insufficient water availability due to low well recharge rates. In Senegal it has been found that hand-dug, cement-lined wells typically have overnight recharge rates of 3-4 m3 of water and this amount can easily be pumped out in less than an hour Deepening cement-lined wells by adding cement rings is time consuming, expensive, and might allow more fine sand to enter the well - reducing the well's capacity and water quality In addition, as in the case of newly constructed hand-dug wells, deepening a well using traditional methods is dangerous. The wrapped filter reduces this risk The installation of a wrapped screen in a short borehole at the bottom of an existing cement lined well is a cost-effective alternative for farmers in areas with sandy soil and low well recharge rates. Although results might differ depending on local conditions, field tests conducted in Senegal in 1994 found that well recharge rate increased by 100 percent following installation of the wrapped filter. Most water enters artesian wells from the bottom and a wrapped screen increases the recharge rate significantly by expanding the surface area for collection of water. Without the wrapped screen, the only benefit market gardeners with limited water availability would gain from an improved manual water lifting device or mechanized pump over the traditional system would be the labour time savings in lifting water because they lack the additional water needed for expanding production Wrapped screens are made of PVC tubing with drilled perforations wrapped with a single outer layer of permeable fabric (usually locally purchased woven polyester) that is stitched around the entire circumference of the screen to prevent sand from entering the PVC cylinder and clogging it Once drilled and wrapped, the wrapped screen is driven into the bottom of a well by water pressure applied through a PVC pipe using a motorized pump. For installation, the wrapped screen is attached to the end pipe of the pump where water normally comes out. PVC pipe is also used to connect water in a cement basin to the pump's water intake pipe. Water is then pumped into the ground from the basin and the force of pumping drills the borehole. The cost to the farmer is approximately US$ 60. |
Another water accessing technique, a motorized washbore method of installing tubewells, is capable of releasing significant quantities of water at low cost. It has very good potential in countries where the hydrological and subsoil conditions are appropriate (i.e. coarse sand and good recharge rates). In Northern Nigeria these tubewells number in the thousands. Very good potential exists in parts of Niger, Cameroon, Benin and possibly Zimbabwe, Botswana and Ghana.
Both the wrapped filter and the washbore techniques allow for rapid installation and are low cost. The introduction of these water development technologies also complement the use of mechanized irrigation pumps that sometimes cause the collapse of the sides of traditional wells. The more resistant PVC wall of the wrapped filter and the washbore will prevent this potentially dangerous and costly situation from occurring (see Box 6 for a more detailed description of the wrapped filter and washbore technologies).
Water distribution technologies
The cost of irrigation water lifted using mechanized means is increased due to inefficient water distribution methods (frequently unlined canals that permit water losses through seepage) and/or the high cost of reinforced distribution hose. Improved, inexpensive water distribution technologies will lower the unit cost of irrigation water. Promising low-cost techniques include lined canals, light weight plasticized hose, drip irrigation (using PVC pipe instead of more expensive materials), PVC pipe, and thin-walled water holding tanks. These and other technologies will be considered for testing, bearing in mind the need to keep these products low in cost and affordable to small farmers and adapted to local conditions. PVC pipe and holding tanks have been tested and promoted by ATI in Senegal. Low-cost holding tanks have proven to be well adapted to the sandy soil conditions encountered in Senegal and other parts of West Africa. PVC pipe is used in both Senegal and Mali as a low-cost solution to water distribution.
There are hundreds of thousands of small farmers practising irrigated agriculture in sub-Saharan Africa. The technologies described herein are capable of assisting them to increase production, resulting in greater incomes and increased food security. The low cost of the proposed technologies relative to currently available equipment will facilitate acquisition. Reduced operating costs will make use more sustainable. Because some of the proposed equipment (i.e. treadle pump, axial flow pump, venturi ejector, and all of the various tubewells) can be produced locally, there will be strong linkages to the manufacturing sector that will create some employment and increase the income of manufacturers.
Appropriate Technology International. 1987. Treadle Pump Project Plan. Washington, D.C. Appropriate Technology International.
Alien, H. and Perry, E. 1996. Human Powered Irrigation for Smallholders: Approach to Implementation. Addis Ababa: CARE International and Appropriate Technology International.
FAO. 1995. Irrigation in Africa in Figures. FAO, Rome.
Gay, B. 1994. Irrigation Privée et Petites Motopompes au Burkina Faso et au Niger. Paris: Groupe de Recherches et d'Echanges Techniques.
Government of Benin, Ministry of Rural Development. 1995a. Filière piment. Cotonou: Government of Benin.
Government of Benin, Ministry of Rural Development. 1995b. Schémas de relance des filière de pomme de terre et d'oignon. Cotonou: Government of Benin.
Government of Burkina Faso, Ministry of Agriculture and Animal Resources. 1995. Enquête maraîchère campagne 1994/95 (résultats préliminaires). Ouagadougou: Government of Burkina Faso.
Hyman, E., Lawrence, E. and Singh, J. 1995. The ATI/USAID Market Gardeners Project in Senegal. Washington, D.C.: Appropriate Technology International.
Niambélé, Yacouba and Oumar Togola. 1996. Rapport d'évaluation de l'utilisation de la pompe Ciwara par les maraîchers. Bamako: ATI/Mali.
Norman, W. Ray. 1992. A Field Manual for Water Lifting and Management in Small-Scale Irrigation Systems in Niger. Niamey, Niger/Morrilton, Arkansas: Government of Niger and Winrock International.
Perry, E. 1996. Private Irrigation in Burkina Faso and the Potential for Improved Manual Technology. Washington, D.C.: Appropriate Technology International.
Perry, E. 1997. Strengthening the Enabling Environment for Small Enterprise Development through Improved Technology. Washington D.C.: Appropriate Technology International.
