Cover Image
close this bookSourcebook of Alternative Technologies for Freshwater Augmentation in Africa (International Environmental Technology Centre - United Nations Environment Programme, 1998, 182 p.)
close this folderPart B - Technology profiles
close this folder2. Domestic water supply
close this folder2.1 Fresh water augmentation technologies
View the document2.1.1 Protected springs
View the document2.1.2 Rock and roof catchments
View the document2.1.3 Fog harvesting
View the document2.1.4 Groundwater abstraction in urban residential areas
View the document2.1.5 Groundwater abstraction using handpump-equipped wells
View the document2.1.6 Rope-washer pump
View the document2.1.7 Artificial groundwater recharge
View the document2.1.8 Well-tank borehole well
View the document2.1.9 Cisterns
View the document2.1.10 Palm petioles

2.1.1 Protected springs

Technical Description

There are three elements which comprise a spring catchment installation (Figure 27); namely, a) the “effective” catchment, consisting of a perforated pipe within a trench or dry walled channel (stone package), b) a supply pipe leading to an inspection chamber, and c) an inspection chamber, which consists of an entry basin for receiving the spring water and an operation chamber which helps to control water quantity and quality. Sometimes it can also serve as a sedimentation basin, and, in such cases, may be called silt trap.


Figure 27. Typical spring protection box (WHO, 1992).

Construction should be done during the peak of dry season in order to identify and use the most reliable springs. Nevertheless, spring protection structures have to be designed with overflow pipes so that they can function during peak flows during the rainy season. Usually, the excavation around the spring, necessary for construction of the catchment, is started from the point where the groundwater emerges. Once that excavation is completed, the construction of the other system components starts. There are two parts; preparation of a permeable construction into which the source waters enter, and a dam which prevents the water from bypassing the catchment or reservoir. The dam, or barrage, is constructed opposite to the point of entry of the water into the catchment. It has to direct the source waters into the supply pipe, which conveys the water to the inspection chamber. The barrage has to be built into the impermeable layer, as well as into both side walls, to prevent the water from bypassing the system. The foundation of the barrage is cast into the excavation directly against the ground in order to create a tight seal with the ground. The barrage is then constructed, of either concrete or stone masonry, on top of the foundation. The height of the dam should be positioned lower than the level of the top of the water bearing layer. Difficulties may arise when the source waters have to be bypassed during construction of the foundation. (The flow should never be obstructed!) Usually a temporary dam is constructed of clay behind the excavation, and water is diverted with a temporary pipe or syphoned by a tube.

The permeable construction consists usually of a drain in the dry-stone masonry or of perforated pipes. The cross-section of this catchment drain should be sufficient to ensure that the maximum yield of the spring can be drained off without obstructing the natural spring flow. The drain has to be sloped at 1% to 2%. In the case of a solid substrate, no flooring is normally provided, but, for sandy ground, a dry pavement is needed. The velocity of water should be limited by providing additional catchment drains, considering the maximum flows to be expected during rainy season. Around the drains, a sand and gravel filter should be built up with gravel. The purpose of this filter package is to support the water bearing layer and prevent the fine particles that often comprise this layer from being washed out into the protection structure, resulting in the subsequent collapse of the water-bearing layer. A watertight cover, in the form of a 5 to 10 cm concrete cap, should be placed on top of the drains and the gravel filter. This cover needs to extend 20 cm into the slopes on all sides of the structure. Surface water reaching this cover should be drained off to minimise the potential for groundwater contamination.

Extent of Use

This technology is extensively used for projects in Africa. In Malawi, huge, gravity-fed, piped water schemes have been built, tapping spring water. Likewise, in Lesotho, a number of villages are supplied this way.

Operation and Maintenance

The operation and maintenance of spring protection structures is simple. They require few skills to construct and manage, making them suitable for management by user communities. Where steep drops are encountered (such as in the Lesotho Highlands), good structural designs are required to cater to the increased pressures built up in the supply pipes.

Maintenance activities may include protection of the catchment area from potential contamination, periodic maintenance of the filter package, and cleaning the spring area of leaves and other terrestrial debris. Maintenance is carried out by controlling human and animal activities around the spring, repairing the perimeter fence, and repairing the surface water drainage system. It is also necessary to control of the growth of trees around the spring to prevent roots from causing piping to occur in the sand and gravel filter beds and/or breaching the impervious seals around the reservoir and dam. Periodic testing of the water for bacterial contamination is also recommended.

Level of Involvement

Local input of skills and materials from the beneficiary community is often needed to implement this technology. Technical support may be needed from government, NGOs, and other implementing agencies in the conduct of hydrogeological investigations, structure design, and construction. These activities require the inputs of technically-qualified staff, which depends on the size and nature of the scheme.

Costs

Spring protection is an inexpensive in comparison to the development of a conventional point source. The cost of the protection structure, itself, is largely a material cost (cement, pipes). However added costs may be incurred in the form of costs associated with the delivery mechanisms, which are dependant upon the length of piping, the number of storage reservoirs, and/or the number of pressure break tanks needed.

Effectiveness of the Technology

Springs have been used by local communities as a source of water supply for many years. Their relatively good quality water, and generally very low operation and maintenance costs, coupled with the ease of community management, make them quite effective for supplying rural communities with water for domestic purposes. Protecting these water sources from contamination is an natural way of ensuring the continuity of this supply.

Suitability

This technology is suitable in locations where springs occur and no unresolved pollution problems prevail. They may be managed as point sources for communities or distributed to individual households by connection to a distribution system.

Environmental Benefits

No environmental impacts have been reported.

Advantages

The advantages of this technology are several-fold: groundwater is a relatively safe water source for use without treatment, springs are the most inexpensive source of groundwater, and spring protection structures can be constructed using local skills and materials. Further, this technology incurs few or no operating costs, and requires very little maintenance, if the water is obtained at its source.

Disadvantages

Service level is dependent on groundwater yields, which seldom can be improved (unlike in conventional systems). Further, there is difficulty in ensuring the hygiene of the springs, especially during the rainy season when it is not always possible to protect the spring from surface water intrusion. The location of springs is not always near the point of consumption and, in many cases, access is difficult. Springs may also run dry during times of drought.

Cultural Acceptability

Spring water is associated with witchcraft amongst some East African communities. It is also the belief in some communities that women who have given birth to twins and/or whose husbands have died must not use springs before certain cleansing rituals are performed for fear that their “unclean” condition would cause the springs to dry up.

In Southern Africa, communities often associate the placement of cement on springs with the spring drying. Such communities would be reluctant to install concrete catchments around their springs.

Further Development of the Technology

The technology does not require any further technical development, but it may be necessary to carry out social research on the cultural beliefs of communities to determine their basis and the effect this has on spring protection.

Information Sources

Contacts

Ministry of Land Reclamation Regional and Water Development, Post Office Box 30521, Nairobi, Kenya, tel (254 2) 716103.

Blair Research Laboratory, Post Office Box CY 573, Causeway, Harare, Zimbabwe, Tel. 792747

Bibliography

SKAT 1987. Manual for Spring Catchments.

Kenya-Finland Western Water Supply Programme 1990. Water Supply Development Plan 1990 -2005. Ministry of Land Reclamation Regional and Water Development, Nairobi.

WHO (World Health Organization) 1992. Fact Sheets on Environmental Sanitation for Cholera, WHO Publication No. WHO/CWS/92.17, Geneva.

2.1.2 Rock and roof catchments

Technical Description

Rock catchments are simple systems for the collection of rainwater. Siting of these structures should take into account ease of access of the users and the geological structure of the site. The best sites are found on the lower reaches of bare rock inselbergs, where runoff losses to the soil, vegetation and structures is minimised. Storage may be provided in dams or open tanks.

Roof catchments are suitable for individual household use, and use in schools and other institutions where sufficient impermeable roof cover exists. To collect rainwater from roof catchments, gutters and ground storage tanks are required (Figure 28). “First flush” water from each shower should be prevented from entering the storage facility to reduce the degree of pollution of the stored water by dust, leaves and bird droppings washed from the rooftop into the reservoir. Underground tanks may also be used (Figures 29 and 30).


Figure 28. Lateral view of a rainwater catchment system.

When calculating the size of the storage for rock or roof catchments, the demand for water, and the length of the dry periods, must be considered. The required catchment area also depends on the amount and variability of rainfall. In most cases, however, the available area is often the limiting factor due to local conditions.


Figure 29. Rock catchment with underground storage tank.

Extent of Use

This technology is extensively used in arid and semi-arid areas of Africa, such as Mauritania, Benin, Burkina Faso, Uganda and Kenya.

Operation and Maintenance

Limited regular maintenance of gutters, and removal of leaves and other debris from the catchment surface, is required. Cleaning of the tanks is necessary before and after the first rains. All of these activities can be handled by the community. Water is drawn by bucket or taps fitted to the storage tank.

Level of Involvement

This technology is installed and operated primarily by local communities, sometimes using hired labour. Technical advice from government, NGOs, or private sector agencies may be required. Once the technical training of locals has been completed, the roof catchment system installation and management can be left in the hands of the householders.

Costs

In 1994, a typical roof catchment system in Benin, constructed of ferrocement, cost $346/7 m3 storage, $496/12 m3 storage, or $800/24 m3 storage. In Burkina Faso, Uganda and Kenya, costs ranged from $852/20 m3 storage, constructed of ferrocement, to $1016/30 m3 storage constructed of masonry.

Effectiveness of the Technology

Rain water catchment systems have been successfully utilized by people all over the world for many centuries. Presently, rain water is collected from many types of surfaces to provide water for domestic, livestock, agricultural and fish-farming use. Rain water is also used as a

The effectiveness of rain water collection systems depends on the type of roofing material used. For example, thatched grass gives lower yields than corrugated iron sheets.

Environmental Benefits

No environmental benefits have been reported.

Suitability

This technology has good potential in areas of rugged and steep terrain. It is more feasible in high rainfall areas, because rain can fill the storage reservoirs more frequently. On the other hand, it is quite suitable for arid and semi-arid areas where rain water is the most accessible water source. It also has good potential for community management.

Advantages

The advantages of using this technology are that water is provided at the point of consumption, and there is good potential for community-based management of the collection systems (with low operating and maintenance costs). Relatively good quality water can be obtained using this technology.


Figure 30. Artificial roof catchment with ground water storage tank.

Disadvantages

Disadvantages of this technology include difficulties in controlling the water quality, an high per capita cost of development, and a lack of reliability as a source of water. It cannot serve large users, although, it is usually adequate to provide a low level of service, suitable for family use.

Cultural Acceptability

No negative cultural factors have been observed.

Further Development of the Technology

There is very little that needs to be done to further develop this technology.

Information Sources

Contacts

Ministry of Land Reclamation Regional and Water Development, Post Office Box 30521, Nairobi, Kenya.

CREPA, Ouagadougou BP. 7112, Ouagadougou, Burkina Faso, tel 310359, fax: 310361.

The Institute of Agricultural Engineering, Post Office Box BW330, Borrowdale, Harare, Zimbabwe.

AGRITEX, Post Office Box CY 639, Causeway, Harare, Zimbabwe.

Ministry of Agriculture, Private Bag 003, Gaborone, Botswana.

Ministry of Agriculture, Post Office Box 92, Maseru 100, Lesotho.

Coordenacao Geral dos Projectos Integrados, Prorural, Ruo da Resistencia 1746, Maputo Mozambique.

Direction de l'hydrologie et d'hydraulique. Programme d'Hydraulique Pastorale, Mauritane, Tel. 251611, Fax 251602.

Bibliography

Hissen-Petersen, E. and M. Lie 1992. Harvesting Rain Water in Semi-arid Africa, Nairobi.

Kenya-Finland Western Water Supply Programmes 1990. Water Supply Development Plan 1990-2005. Ministry of Land Reclamation Regional and Water Development, Nairobi.

Direction de l'hydrologie et d'hydraulique 1978. Programme d'Hydraulique Pastorale: survie du betail en Mauritane, 356 p.

2.1.3 Fog harvesting

Technical Description

Fog droplets are much smaller than both raindrops and drizzle drops, with diameters varying from 1 to 40 microns, and fall at velocities ranging from less than 1 cm/s to about 5 cm/s. These low velocities result in fog droplets being influenced even by light winds that can cause the droplets to travel almost horizontally. An appropriate fog droplets-collector, therefore, is a vertical or near vertical surface. Such surfaces can be constructed as vertical mesh panels on which fog droplets are intercepted and condensed.

Extent of Use

Fog harvesting is a rarely used technique in Africa. In Namibia, for example, the technology is still in the experimental stage. However, the actual application of this technology on a limited basis did begin in late 1995, as a project of the Ministry of Agriculture, Water and Rural Development.

Operation and Maintenance

Operational requirements include the measurement of the volume collected and the recording of meteorological data, either manually or by automatic weather station, since changes in weather conditions may change the operational design of the harvesters. Problems encountered include dust, rodents, game, and irregular fog formation. However, virtually all of the input materials to construct, operate and maintain the system are available locally.

Costs

The input costs are not yet known. However, an automatic weather station costs about $50 000 to purchase and install.

Effectiveness of the Technology

A surface area of about 50 m2 can harvest a significant amount of fog and convert it into water. However, experimental data from the system in Namibia are still forthcoming.

Suitability

Fog harvesting is suitable in regions which have hills or mountains close to potential users, on a coastline with a cold current offshore. The quantity of derived water is a function of the scale of the project and the fog available. In Namibia, the resulting water is slightly salty as a result of the inclusion of some marine aerosols, and contains some dust.

Environmental Benefits

No direct environmental benefits have been reported or are foreseen.

Advantages

No extensive, permanent structures are necessary to implement this technology, and the derived water is normally potable. The technology can easily cater to the water needs of coastal, or desert, settlements or camps currently relying on a saline water source or some other expensive option such as tanker delivery. The water is available within the demand area and therefore requires little, if any, pumping. The water source is also sustainable over many years. Clouds normally bring a large amount of water and extend over a wide front. Therefore, the amount of water collected can be varied by varying the number of collectors installed. The collectors are simple and require no energy other than the wind.

Disadvantages

Deforestation can lead to reduced fog water inputs. Further, it may result in dust and other pollutants entering the harvested water.

Information Sources

Contacts

P. Heyns, Department of Water Affairs, Ministry of Agriculture, Water and Rural Development, Private Bag 13193, Windhoek, Namibia, Tel. 061-263141, Fax 061-263222.

D. Lucks, Department of Water Affairs, Ministry of Agriculture, Water and Rural Development, Private Bag 13193, Windhoek, Namibia.

Bibliography

Heyns, P. 1995. Desalination Development in Namibia, New World Water.

Schemenauer, R.S. and P. Cereced 1994. Fog Collection's Role in Water Planning for Developing Countries. Natural Resources Forum, 18 (2): 91-100.

2.1.4 Groundwater abstraction in urban residential areas

Technical Description

This is the abstraction of groundwater through boreholes, by private householders or water supply agencies.

Extent of Use

The technique is extensively used in a number of countries in Africa. In rural areas, it may be the only reliable source of water supply. In urban centres, it augments conventional municipal supplies.

Operation and Maintenance

The operation and maintenance requirements for groundwater abstraction systems usually relate to type of pumping system used. For poorly constructed boreholes, collapse may be experienced.

Level of Involvement

Both household and water supply agencies make use of this technology.

Costs

Borehole drilling and components costs have been estimated to be about $3000 for a typical installation. Energy costs depend on source of energy used, usually the cost of electricity.

Effectiveness of the Technology

Household use of groundwater reduces demand for treated urban water. It is also efficient for industrial use since each industry can treat the water to meet its own requirements.

Suitability

This technology is suitable in all areas with groundwater reserves, in particular, during droughts.

Environmental Benefits

There could be environmental damage from over pumping as the water table recedes. In years of water shortage, this over-pumping may negatively affect the groundwater discharge into rivers, lakes and reservoirs.

Advantages

The advantages of this technology include its site-specificity; no significant delivery (reticulation) systems are necessary. The technology may be used where urban services are poor or unreliable.

Disadvantages

Over pumping may lead to ground subsidence. Subsidence is of great concern in crowded urban areas. Further, groundwater is susceptible to contamination from wastes.

Cultural Acceptability

Generally, there are no cultural problems with the use of groundwater supplies.

Further Development of the Technology

Techniques for the rapid assessment of safe yield to avoid over pumping are required.

Information Sources

Simpson, G.C. 1990. Research into Groundwater Abstraction in Residential Areas. Vol 1. Water Research Commission Report No. 211/1/90, Division of Building Technology, CSIR, Pretoria.

2.1.5 Groundwater abstraction using handpump-equipped wells

Technical Description

Handpumps tap groundwater from shallow or medium depth aquifers and from deep aquifers if the at rest water level is high enough. Handpumps are water conveyance systems used to bring groundwater to the surface. There are a number of such pumps in operation in Africa and numerous textbooks provide specific descriptions of these devices (Figure 31).

Figure 31. Some commonly used handpumps.


Model “B” bushpump


Volantia pump


Afridev pump

In normal circumstances, handpumps are installed in wide diameter wells, which can be constructed by hand to depths of up to about 15 m, or drilled by rigs to much greater depths. The type of well most widely used is the hand-dug well, which is one of the cheapest means for providing a small supply of water in rural areas. A depth of about 10 to 20 m is usually considered the limit of practical manual sinking. The diameter of the well should not be less than 1.2 m, allowing two persons to work together in the well. A lining, that serves several purposes, should be used as the well is sunk. The lining is a protection during construction against caving and collapse, and retains the well wall after completion. There are many materials suitable for linings; e.g., masonry, brickwork, and plain or reinforced concrete. On the bottom of the well, it is usual to place a filter of graded layers of gravel to prevent the ground material from being drawn upwards into the well with the water. At the surface, the lining of the well should be raised at least 0.6 m above ground level and provided with a protection platform to channel drainage away form the well,

Small diameter wells may also be constructed by means of an auger. The auger, which is usually about 100 mm across, may be rotated by hand. Mechanised augers, or power augers, are also available. Once the water-bearing layer has been penetrated, the necessary length of piping, tipped with a screened wellpoint, or strainer, is lowered into the hole; a pump attached to its upper end, and the well “cleared” by pumping.

Tube wells consist of a perforated or screened pipe which is jetted or driven into the groundwater-bearing aquifer. Tube wells can yield large quantities of water, but the depth to which they can be driven is limited and the ground formation must be appropriate for their use. Their most common application is in the extraction of groundwater from water-bearing sands, especially those forming the beds of ephemeral streams. Tube wells can also be installed in perennial rivers, making use of the natural filtering properties of sandy beds of the rivers by drawing water through the river beds instead of from the rivers themselves. The pipes are usually 25 to 100 mm in diameter. The wells constitute a good means of obtaining water from areas with relatively coarse sand.

Extent of Use

Wells using handpumps are extensively used throughout Africa.

Operation and Maintenance

The operation and maintenance of handpumps varies depending on the type and complexity of the pump. Attempts at designing a reliable pump which can be maintained at the village level continue. Experimentation with these village level operation and maintenance (VLOM) schemes are shifting gradually to focus on institutional-level operation and maintenance. Preventative maintenance operations carried out by villages and institutions include greasing moving parts (taking care not to contaminate the water supply with oils and greases), tightening bolts, replacing seals (for some pumps), and cleaning the surroundings.

Level of Involvement

Local inputs to implementation of this technology are generally in terms of skilled labour and materials. Technical advice may be necessary in the conduct of hydrogeological investigations and well drilling.

Costs

While hand dug wells are quite inexpensive, boreholes drilled by rigs are fairly expensive in terms of initial capital costs. Dug shallow wells and augured tube wells have a per capita construction cost of $6 to $20, with an operation and maintenance cost of $0.02 to $0.14 per capita per year. Machine-drilled boreholes, equipped with a hand pump and serving a population of about 200 to 300 people, will have an estimated per capita construction cost of $19 to $23, and an operation and maintenance cost of $0.26 to $0.52 per capita per year.

Effectiveness of the Technology

The delivery rate of most handpumps is around 20 l/min, and their ease of operation makes them ideal for rural operations.

Suitability

Dug wells are an appropriate option in areas where groundwater is less than 20 in below ground level. Augured tube wells, dug using motorised and/or manual rigs and augers of limited penetration, are appropriate in areas in which groundwater occurs at depths between 20 and 35 in. Motorised, conventional drilling rigs are an ideal means of developing water supply sources in areas where groundwater occurs at depths greater than 35 m below ground level, or in hard rock between 20 and 25 m depth, where the weathered material is thin.

Environmental Benefits

The existence of a well may lead to increased erosion in its immediate vicinity. However, wells are focal points for other development such as the planting etc.

Advantages

Well water is relatively safe without treatment. Hand dug wells are inexpensive and can be constructed using local skills and materials; community participation is easy to organize. Further, the operation of handpumps requires no external power and few skills, and the pumps may be maintained by local technicians. The use of spare parts is small.

Disadvantages

The capacity of a well is limited, and service supply levels are lower than in piped schemes supplied from conventional sources. Hand dug wells are reliable only in areas where good quality groundwater is available at shallow depth. The hygienic quality of the wells, especially shallow wells, is not always satisfactory as a result of surface water intrusions leaking through the slab and superstructure, and around the pump casing.

Cultural Acceptability

There are no cultural problems in utilizing groundwater for domestic purposes. However, communities do not like wells to be developed too close to sacred places such as shrines.

Further Development of the Technology

There is need to improve on the methods of digging the shallow wells. Also, the handpump needs further developmental work to make it more suitable for village level operation and maintenance. Maintenance systems require further development to ensure sustainability.

Information Sources

Further information can readily be obtained from the Departments of Water in the various countries, and also from organisations such as UNICEF, World Vision, CARE, and Save the Children, among others.

2.1.6 Rope-washer pump

Technical Description

The rope-washer pump consists of a rope with knots or rubber washers, whose diameters are slightly less than the diameter of the pipe, placed at intervals along it (Figure 32). This assembly is drawn up inside a rising pipe, and is capable of drawing relatively large volumes of water to the height of the pump. During operation, the pipe is inserted into water and the rope drawn upwards through the pipe by means of a winding drum with a crank. Water is also drawn up and discharged at the top. The rope and washers pass round the winding wheel and return to the bottom of the pipe thus completing the circuit. This design can be modified to avoid slippage of the rope on the pulley by using old tyre casings to make the pulley wheel. To prevent the washers getting caught, and to support the bottom of the pipe above the bottom of the well or river bed, a suitable pipe stand and rope guide is necessary. Friction should be kept low by allowing leakage between the washers and the pipe stem.


Figure 32. The rope and washer pump (Lambert, 1990).

Extent of Use

The rope-washer pump is receiving moderate use in Kenya, Zimbabwe and Burkina Faso.

Operation and Maintenance

Rope-washer pumps rely are manufactured locally, and, therefore, are amenable to local repair and maintenance using simple, locally-available materials.

Level of Involvement

The components of this technology are community-manufactured and operated. Government and NGOs are often involved in the promotion of this technology and development of refinements.

Costs

Rope-washer pumps cost between $30 to $50 to construct. The construction cost increases in proportion with the lift required.

Effectiveness of the Technology

This technology is appropriate for all domestic uses and micro-irrigation or garden irrigation uses. This pump can pump high volumes with a low lift.

Suitability

The technology is suitable for abstraction from shallow wells of up to 10 m depth or from rivers and streams. It is easily adaptable to changing volumes by adapting the diameter of the pipe and washers.

Environmental Benefits

The introduction of a simple device such as the rope washer pump, lends itself to micro-scale gardening and the accompanying positive environmental management practices.

Advantages

The pump has no valves and does not require complicated bearings. It is easy to manufacture, with local resources, and is ideal for flood irrigation of small gardens.

Disadvantages

The pump has limited lift and poor pumping efficiency, as water is allowed to leak through the valves.

Cultural Acceptability

There are no known cultural inhibitions.

Further Development of the Technology

The rope-washer pump technology needs to be further disseminated to gain additional field experience of its operation. The efficiency of the pump needs to be improved.

Information Sources

Chleq, J.L. and H. Dupriez 1988. Vanishing Land and Water. Soil and Water Conservation in Drylands. Macmillan, 117 p.

Lambert, R.A. 1990. How to Make a Rope Washer Pump. Intermediate Technology Publications, London.

2.1.7 Artificial groundwater recharge

Technical Description

Artificial recharge is the use of infiltration basins (Figure 33) or injection wells (Figure 34) to recharge groundwater resources. Infiltration basins can take many forms. For example, a storage dam can function as an infiltration basin under certain conditions. With infiltration basins, it is essential to construct the pond on an infiltration zone lying above an impermeable layer.


Figure 33. Recharge by infiltration basin.


Figure 34. Recharge by injection well.

Extent of Use

Infiltration basins and injection wells have been implemented in Botswana, Egypt, Tunisia, and Algeria. In Zimbabwe, small infiltration dams are being developed.

Operation and Maintenance

There is need for a source of the water to be recharged. Groundwater recharge using infiltration basins in areas with high evaporation rates is not likely to be effective. Likewise, the presence of clay lenses covering parts of an aquifer can be a problem as they can prevent the infiltrated water from reaching the aquifer. Both problems can be overcome through the use of injection wells, which allow the recharge water to be inserted into an aquifer under pressure.

Level of Involvement

Construction of recharge basins can be undertaken by local personnel with experience in well digging. Government assistance may be required to identify appropriate recharge sites.

Costs

The costs are moderate, depending on the scale of operations.

Effectiveness of the Technology

Recharged water may take on the qualities of normal groundwater, as impurities are removed within the soil profile. However, there is also the possibility of introducing contaminants into the groundwater system through the use of this technology, depending on the source of the recharged water. Groundwater recharge as a stormwater management technology creates the least cause for concern, and ensures the reliability of water supplied from nearby wells.

Suitability

This technology is appropriate for arid regions lacking alternative water sources. Water reclaimed in this fashion may be used as an alternate source of drinking water. Recharge may be appropriate in areas where behaviour of naturally-occurring groundwater is uncertain.

Environmental Benefits

The construction of infiltration basins may help to control soil erosion. The basins are usually appropriate habitat for a number of birds and wild animals.

Advantages

Groundwater recharge, especially using injection wells, conserves water through reduced evaporation. Clean drinking water may be recovered from wells in the vicinity of the recharge field without using complicated treatment systems.

Disadvantages

The water from a recharged aquifer cannot be used without a system of abstraction. There is also a possibility of polluting the aquifer with the recharged water.

Cultural Acceptability

The technique is culturally acceptable.

Further Development of the Technology

There is limited scope for further development of technology, especially in terms of ensuring the quality of the recharged water and the prevention of groundwater contamination.

Information Sources

Gustafsson, P. and J. Johansson s.d. A Study of Water Resources in Botswana. Department of Geology, Chalmers University of Technology and University of Goteborg, Goteborg, Sweden.

2.1.8 Well-tank borehole well

Technical Description

This is a type of borehole in combination with a well. The latter serves as storage. This technology is used in cases where hydrogeological conditions are such that neither structure alone can meet the operational needs of the beneficiaries.

The borehole is drilled to groundwater level, and the well-tank, which is 0.5 m to 1 m away from the borehole, is drilled to a depth such that the static level of the borehole is at least 6 m higher. This difference in elevation provides a sufficient water level in the well to permit easy abstraction of the stored water. This water depth in the well-tank is maintained by the construction of a junction between the well-tank and the borehole at the bottom of the well-tank at the static water level (Figure 35).


Figure 35. Well tank - borehole well.

Extent of Use

This technology has been used in projects in Mauritania. Similar systems, with slightly different arrangements of the components, exist in Egypt, Libya and Sudan.

Operation and Maintenance

Since the well-tank is below the static water level in the borehole, water enters the well-tank by gravity through the perforated junction between the well and the borehole. The depth of water in the well-tank becomes that of the borehole. Abstracting of water is carried out in the traditional way from the well-tank. Maintenance is carried out periodically by cleaning the well-tank as and when necessary. The well-tank should be protected against contamination as described elsewhere in this volume.

Level of Involvement

The capital investment in the borehole may be prohibitive for individuals, but the technique can be established jointly by individuals within communities. The technology can be implemented with limited technical support from extension agencies.

Costs

The costs include the drilling costs of the borehole and well-tank, on the one hand, and the cost of providing the superstructure of the well, on the other. The cost per linear metre of establishing the borehole, which can be up to between 100 m and 400 m deep, is over $300.

The cost of establishing and protecting the well is between $260 and $408/linear metre.

Effectiveness of the Technology

The borehole well is as efficient as the simple well, and, generally, is more reliable. The well-tank system experiences fewer seasonal fluctuations in water level compared to other wells in the regions in which the technology has been applied, and, as a result, rarely dries up.

Suitability

Well-tanks are adaptable for use in all terrains. However, in areas with discontinuous aquifers, where groundwater is captured in very hard, fractured geologic structures, and/or where wells cannot readily penetrate the substrate, storage can be provided by surface cisterns. Similarly, in sedimentary basins, shallow wells may be more appropriate storage structures.

Environmental Benefits

Use of this technology makes groundwater readily available at the surface. If used within conservation areas, this technology can provide water for environmental rehabilitation programmes, especially in areas where this would otherwise be impossible. However, care should be taken to avoid over-abstraction of groundwater, and prevent contamination of groundwater from surface sources.

Advantages

Use of this technology allows the use of simple abstraction methods, and can provide a reliable source of water.

Disadvantages

The technology has an high capital investment cost, and is dependent upon a reliable groundwater source.

Cultural Acceptability

There are no known cultural inhibitions relating to the use of this technology.

Information Sources

CIEH, 01 BP 369 Ouagadagou 01, Burkina Faso, Tel. 307112, Fax: 362446.

2.1.9 Cisterns

Technical Description

Cisterns are an ancient method of water harvesting, dating back to the early Roman empire. There are artificial reservoirs constructed by excavating bedrock, such as limestone, to depths of between 3 and 7 metres to provide water storage throughout the Roman world. While serving a similar purpose, modern cisterns are usually built with cement blocks or fired bricks.

Cisterns collect water in the form of runoff from a rock-lined catchment or other suitable, nonporous surface. There is commonly a settling basin at the cistern entrance which serves to settle sediments borne by the runoff. A screen is also provided to remove larger particulates.

Extent of Use

This technology is used in a number of north African countries, where it is known by a variety of different names. These names are indicated in brackets. The technology is used in Libya (where it is known as Fusqia or Majen), Algeria (Sahrij), Egypt (Roman reservoir), Tunisia (Fuskia pool), Morocco (Al Majel), and Sudan (ground reservoir).

Operations and Maintenance

Routine maintenance is necessary to reduce losses to leakage by repairing cracked walls. There is also a need for the periodic removal of sediments which might choke the entrance.

Level of Involvement

This technology can be constructed, operated and maintained by villagers.

Costs

The cost of implementing this technology is reasonably low, as most of the construction of the cisterns can be done by communities. However, mechanization is increasingly used for the digging of the cistern, which increases the cost.

Effectiveness of the Technology

The volume of water harvested depends on the amount of rainfall and the size of cistern. Major losses of water generally occur in the catchment area, through infiltration and evaporation, rather than from the cistern itself, provided the cistern is maintained.

Suitability

The technology is suitable for use in all regions of Africa and is similar to rock catchment systems. In areas of high evaporation, the cistern should be covered to minimize evaporative losses.

Environmental Benefits

The use of cisterns to capture runoff has no known negative environmental effects, and can provide water for a variety of environmental purposes in dry areas.

Advantages

This technology has the advantage of being a simple, low cost technology which can increase the yield of water from rock catchment systems.

Disadvantages

Use of this technology may require provision of an abstraction system to draw the water from the cistern. Because of the likelihood of contamination from surface sources, this technology is not ideal for use as a potable water source.

Cultural Acceptability

This technology is culturally acceptable by the communities in which it has been used.

Information Sources

UNESCO Regional Office for Science and Technology for the Arab States, Arab Centre for Studies of Arid Zones and Dry Lands (ACSAD) 1986. Regional Project on Rational Utilization and Conservation of Water Resources in the Rural Areas of the Arab States with Emphasis on the Traditional Water Systems, UNESCO Project ROSTAS/HYD/1/86.

2.1.10 Palm petioles

A suitable tree is planted in the homestead grounds. Suitable trees usually have broad leaves which collect rainwater which is channelled to a collecting pot (Figure 36).

Figure 36. Various methods of collecting rainwater using:


trees

leaves

plant materials.

Extent of Use

This technology is used in Nigeria.

Operation and Maintenance

The technology has very limited maintenance requirements.

Level of Involvement

The technology is usually used by individual households.

Costs

Costs are negligible, and, depending on the type of tree used, may result in a net profit to the householder.

Effectiveness of the Technology

The effectiveness of this technology depends on the effectiveness of the collecting channel. There are often significant losses resulting from spillage and other leaks within the system.

Suitability

The technology is suitable for collecting small volumes of water at the household level.

Environmental Benefits

Use of this technology promotes the growing and maintenance of trees. It may encourage the propagation of indigenous vegetation.

Advantages

It is a low cost technology that does not require extensive knowledge to construct or complex equipment to operate.

Disadvantages

Large volumes of water cannot be collected using this technology. Also, the water may be contaminated with dust, insects and bird droppings as well as plant material.

Cultural Acceptability

The technology is culturally accepted in those areas where it is practised.

Information Sources

United Nations University, Institute for Natural Resources in Africa, ISSER Building Complex, Nasia Road, University of Ghana, Accra, Ghana.