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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 folder1. Agricultural technologies
close this folder1.1 Fresh water augmentation
View the document(introduction...)
View the document1.1.1 Planting pits (zai)
View the document1.1.2 Demi-lunes or semi-circular hoops.
View the document1.1.3 Katumani pitting technical description
View the document1.1.4 Permeable rock dams
View the document1.1.5 Contour stone bunding
View the document1.1.6 Tied contour ridges
View the document1.1.7 Fanya-juu terracing
View the document1.1.8 Flood harvesting using bunds
View the document1.1.9 Earthen bunds
View the document1.1.10 External catchments using contour ridging
View the document1.1.11 Sand abstraction technical description
View the document1.1.12 Lagoon-front hand-dug wells
View the document1.1.13 Sub-surface dams, small dams, and sand dams
View the document1.1.14 Cloud seeding
View the document1.1.15 Tidal irrigation

1.1.12 Lagoon-front hand-dug wells

Technical Description

The land adjacent to a lagoon is called the lagoon front. This land is commonly divided into family- or individually-owned plots. Farm development starts by making row beds of approximately 1.5 m in width and 6 m in length on which vegetables are grown. Hand-dug wells are then constructed in between the rows of beds (Figure 19). One metre diameter well rings are constructed by trained masons. The rings for the well are left for at least a week to dry.


Figure 19. Vegetable beds among a well field.

In order to sink a well a suitable place is chosen among the rows of bed and a hole of about one metre diameter is dug in soil with a shovel. The first ring for the well is lowered into the hole. The well digger goes into the well and digs the soil out from under the ring with a hoe. As the soil is removed the ring moves downwards until the top edge of the ring is flush with the ground surface. A new ring is added on top of the old one, and the well digger continues digging. New layers are added until the groundwater table is reached, at which time water flows into the bottom of the well. Usually the groundwater table on the lagoon-front is at a very shallow depth. Having struck water, digging continues for about one metre below the groundwater table. When the well reaches the desired depth, a 0.5 m ring is added at the surface so that the well stands above the ground level. A bucket with an attached rope is commonly used as the mechanism for lifting water from the hand-dug wells.

Operation and Maintenance

After the system has been installed, ongoing maintenance costs range from $10 to $40 annually. There is no need for power and spares.

Level of Involvement

This technology is traditional and farmer-managed. Construction is done by local masons and workers with simple hand tools (e.g., shovels, etc.). Because the scheme is entirely privately-owned and farmer-managed, there are fewer potential organizational problems.

Effectiveness of the Technology

The technology of lagoon-front hand-dug wells yields quality of water good enough quality for vegetable crop irrigation in an area filled with salty water. Without this technology, commercial farming would be impossible in the densely populated sand bar region of southeastern Ghana.

Costs

1995 cost of constructing a well is approximately $20. The operation and maintenance costs range from $4 to $10, annually.

Suitability

This type of irrigation scheme is suitable for irrigation of small rural farms, ranging in area from 0.1 ha. to 0.5 ha, in coastal areas.

Advantages

The materials for making the wells are obtained locally, and local skills are employed. These skills are traditionally passed on for generations. Once installed, the wells can be used for many years. Interviews with local farmers revealed that income from irrigated farming activities constitutes up to between 90% and 100% of family income. The viability of the farming activities helps to curb the drift of youths from the rural areas to the cities. It is labour-based and provides employment for the youths, thereby providing a vibrant economic activity in an otherwise poor rural area.

This technology requires no pumps or power-driven tools.

Disadvantages

The shallow depth of the well sometimes makes it dry up during the growing season. It also makes the well susceptible to contamination from the surface.

Cultural Acceptability

The rural life style of the coastal dwellers makes it easy for them to accept this technology.

Further Development of the Technology

Geophysical surveys to determine the freshwater - seawater interface will improve the technology. This will enable the depth of the well, the pumping rate, etc. to be determined. Such determinations will improve overall water management in the coastal zone.

Information Sources

Dr C.S Kpordze, UST, Kumasi, Ghana.