The mayor of Zantiébougou (centre) takes part in the works on Mamissa dam (HELVETAS SwissIntercooperation)
Small dams are installed on minor river beds and are connected up to the riverbanks. Their above-ground dimensions are small, but trench depths can be quite substantial in the case of a subterranean dam two to three metres deep. Plastic sheeting is placed in the trench to stop the water flowing underground.
Weirs are low-level structures built in flat valleys as extensions of small dams. Dam walls are low in height, standing from 0.1 m to 1 m above ground level.
The underground section of the dam retains upstream waters. As a result, the ground absorbs water and moisture throughout the entire area affected by the dam. The above-ground section (a watertight wall equipped with outflow gates) discharges the upstream water. It has a weir running along the marigot. Downstream, a stilling basin is installed to prevent erosion caused by the falling water. Using the weir and outflow gates, the water level can be adjusted to the requirements of each rice growing stage. The water retained by a dam equipped with a weir cannot be conserved for long periods. The structure’s main role is to provide water to meet the needs of the rainy-season crops. Even though the trenches are deep and the plastic sheeting prevents underground water dissipation, weirs can help to ensure ground waters are well recharged. This is why farmers should wait before digging wells to extract water for vegetable growing.
Local people formulate the requirement and negotiate with the commune on the investment programme, identify the rules of access and set up the farming cooperatives and management bodies, provide materials and unskilled labour during construction, and undertake small-scale maintenance work. The commune plans investments and assumes overall control of the construction work, delegates management to users, validates the farming rules and oversees their correct application, and undertakes major repairs. Consultancies carry out the socio-economic, environmental and technical studies (scheme design, plans, models), draw up the invitation to tender document and support the tender selection process, and monitor and inspect works. Technical services oversee the application of technical and environmental standards, and participate in ensuring sound financial practices (collection, financial control, public service concessions). Contractors carry out the construction work. The project team provides training (planning, social engineering, studies involving farmers, etc.) and advisory support (organisation of users, formulation and validation of rules, area development plan, plan to develop and exploit value chains).
The scheme can remain functional for up to 20 years provided it is rigorously maintained. The users are divided up into management and maintenance teams and their respective responsibilities are clearly defined.
More than 120 schemes with an average area of 20 hectares were built between 1998 and 2012. These schemes cover an area of more than 2,400 hectares and directly benefit over 15,000 families. The low cost combined with quick returns makes this type of intervention suitable for poor communities and local authorities. These structures can also be installed in dry areas. In these areas, it is essential from the outset that anti-erosion measures are put in place to manage the risk of sand encroachment.
Location: Sikasso region (Yorosso, Koutiala, Sikasso, Kadiolo, Kolondiéba, Bougouni, Yanfolila), Ségou region, Mali, Mali
No. of Technology sites analysed:
Spread of the Technology: evenly spread over an area (approx. 10-100 km2)
In a permanently protected area?:
Date of implementation: 10-50 years ago
Type of introduction
| Specify input | Unit | Quantity | Costs per Unit (CFA Franc) | Total costs per input (CFA Franc) | % of costs borne by land users |
| Other | |||||
| total construction | 1.0 | 48703.0 | 48703.0 | ||
| Total costs for establishment of the Technology | 48'703.0 | ||||
| Total costs for establishment of the Technology in USD | 94.2 | ||||
At the community level, larger revenues have been generated. Farming yields have doubled, or even tripled, due to the availability of water supplies and the technical support delivered post-build. Watering livestock is now easier and the lowland pastures are more abundant
