The mayor of Zantiébougou (centre) takes part in the works on Mamissa dam (HELVETAS SwissIntercooperation)

Dams with water-spreading weirs (Mali)

Barrages avec seuils d’épandage déversant (French)

Description

The role of small dams with weirs is to raise the water table, expand rice growing areas and extend the availability of water in lowland areas to complete the agricultural cycle of lowland areas (rice and vegetable growing).

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

Location: Sikasso region (Yorosso, Koutiala, Sikasso, Kadiolo, Kolondiéba, Bougouni, Yanfolila), Ségou region, Mali, Mali

No. of Technology sites analysed:

Geo-reference of selected sites
  • n.a.

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
Small dam in Bafaga village, Kebila Commune (HELVETAS SwissIntercooperation)

Classification of the Technology

Main purpose
  • improve production
  • reduce, prevent, restore land degradation
  • conserve ecosystem
  • protect a watershed/ downstream areas – in combination with other Technologies
  • preserve/ improve biodiversity
  • reduce risk of disasters
  • adapt to climate change/ extremes and its impacts
  • mitigate climate change and its impacts
  • create beneficial economic impact
  • create beneficial social impact
Land use
Land use mixed within the same land unit: Ja - Agro-pastoralism (incl. integrated crop-livestock)

  • Cropland
    • Annual cropping
    Number of growing seasons per year: 1
  • Grazing land
  • Waterways, waterbodies, wetlands - Ponds, dams

Water supply
  • rainfed
  • mixed rainfed-irrigated
  • full irrigation

Purpose related to land degradation
  • prevent land degradation
  • reduce land degradation
  • restore/ rehabilitate severely degraded land
  • adapt to land degradation
  • not applicable
Degradation addressed
  • water degradation - Ha: aridification, Hs: change in quantity of surface water, Hg: change in groundwater/aquifer level
SLM group
  • irrigation management (incl. water supply, drainage)
  • water diversion and drainage
  • surface water management (spring, river, lakes, sea)
SLM measures
  • structural measures - S5: Dams, pans, ponds

Technical drawing

Technical specifications

Establishment and maintenance: activities, inputs and costs

Calculation of inputs and costs
  • Costs are calculated:
  • Currency used for cost calculation: CFA Franc
  • Exchange rate (to USD): 1 USD = 517.0 CFA Franc
  • Average wage cost of hired labour per day: n.a
Most important factors affecting the costs
The cost of installing these schemes ranges from 5 to 25 million CFA francs (9740-48703 Dollar). With this sum, it is possible to irrigate between 2 and 50 hectares. The cost per hectare stands at around 0.5 to 2 million CFA francs (947-3897 Dollar).
Establishment activities
  1. It is in community-led planning initiatives that the request for a lowland development scheme takes shape. (Timing/ frequency: None)
  2. The request is analysed (in consultation with the client community) to ascertain the socio-economic gains for the beneficiaries, the strengths and development potential of the area, and the motivation levels of the actors involved. (Timing/ frequency: None)
  3. The results are summarised in a report on the ideal development scenarios put forward by local people. Results are fed back to the community at a public meeting (Timing/ frequency: None)
  4. the findings of the technical diagnostic exercise are developed as a 3D model (Timing/ frequency: None)
  5. The consultant then moves on to performing economic and financial analyses, which will con- firm the cost effectiveness of the scheme (Timing/ frequency: None)
  6. A funding agreement is signed by the commune, farmers and project team (Timing/ frequency: None)
Establishment inputs and costs
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
Maintenance activities
  1. The design consultancy conducts ongoing supervision of the works to ensure that the standards laid down in the technical dossier are adhered to. It is contractually bound to the commune through a monitoring and supervision contract (Timing/ frequency: None)
  2. public administration undertakes sporadic inspections to ensure relevant laws are respected (Timing/ frequency: None)

Natural environment

Average annual rainfall
  • < 250 mm
  • 251-500 mm
  • 501-750 mm
  • 751-1,000 mm
  • 1,001-1,500 mm
  • 1,501-2,000 mm
  • 2,001-3,000 mm
  • 3,001-4,000 mm
  • > 4,000 mm
Agro-climatic zone
  • humid
  • sub-humid
  • semi-arid
  • arid
Specifications on climate
Thermal climate class: tropics
Slope
  • flat (0-2%)
  • gentle (3-5%)
  • moderate (6-10%)
  • rolling (11-15%)
  • hilly (16-30%)
  • steep (31-60%)
  • very steep (>60%)
Landforms
  • plateau/plains
  • ridges
  • mountain slopes
  • hill slopes
  • footslopes
  • valley floors
Altitude
  • 0-100 m a.s.l.
  • 101-500 m a.s.l.
  • 501-1,000 m a.s.l.
  • 1,001-1,500 m a.s.l.
  • 1,501-2,000 m a.s.l.
  • 2,001-2,500 m a.s.l.
  • 2,501-3,000 m a.s.l.
  • 3,001-4,000 m a.s.l.
  • > 4,000 m a.s.l.
Technology is applied in
  • convex situations
  • concave situations
  • not relevant
Soil depth
  • very shallow (0-20 cm)
  • shallow (21-50 cm)
  • moderately deep (51-80 cm)
  • deep (81-120 cm)
  • very deep (> 120 cm)
Soil texture (topsoil)
  • coarse/ light (sandy)
  • medium (loamy, silty)
  • fine/ heavy (clay)
Soil texture (> 20 cm below surface)
  • coarse/ light (sandy)
  • medium (loamy, silty)
  • fine/ heavy (clay)
Topsoil organic matter content
  • high (>3%)
  • medium (1-3%)
  • low (<1%)
Groundwater table
  • on surface
  • < 5 m
  • 5-50 m
  • > 50 m
Availability of surface water
  • excess
  • good
  • medium
  • poor/ none
Water quality (untreated)
  • good drinking water
  • poor drinking water (treatment required)
  • for agricultural use only (irrigation)
  • unusable
Water quality refers to:
Is salinity a problem?
  • Ja
  • Nee

Occurrence of flooding
  • Ja
  • Nee
Species diversity
  • high
  • medium
  • low
Habitat diversity
  • high
  • medium
  • low

Characteristics of land users applying the Technology

Market orientation
  • subsistence (self-supply)
  • mixed (subsistence/ commercial)
  • commercial/ market
Off-farm income
  • less than 10% of all income
  • 10-50% of all income
  • > 50% of all income
Relative level of wealth
  • very poor
  • poor
  • average
  • rich
  • very rich
Level of mechanization
  • manual work
  • animal traction
  • mechanized/ motorized
Sedentary or nomadic
  • Sedentary
  • Semi-nomadic
  • Nomadic
Individuals or groups
  • individual/ household
  • groups/ community
  • cooperative
  • employee (company, government)
Gender
  • women
  • men
Age
  • children
  • youth
  • middle-aged
  • elderly
Area used per household
  • < 0.5 ha
  • 0.5-1 ha
  • 1-2 ha
  • 2-5 ha
  • 5-15 ha
  • 15-50 ha
  • 50-100 ha
  • 100-500 ha
  • 500-1,000 ha
  • 1,000-10,000 ha
  • > 10,000 ha
Scale
  • small-scale
  • medium-scale
  • large-scale
Land ownership
  • state
  • company
  • communal/ village
  • group
  • individual, not titled
  • individual, titled
Land use rights
  • open access (unorganized)
  • communal (organized)
  • leased
  • individual
Water use rights
  • open access (unorganized)
  • communal (organized)
  • leased
  • individual
Access to services and infrastructure
health

poor
good
education

poor
good
technical assistance

poor
good
employment (e.g. off-farm)

poor
good
markets

poor
good
energy

poor
good
roads and transport

poor
good
drinking water and sanitation

poor
good
financial services

poor
good

Impacts

Socio-economic impacts
Crop production
decreased
increased

risk of production failure
increased
decreased

production area (new land under cultivation/ use)
decreased
increased

farm income
decreased
increased

Socio-cultural impacts
food security/ self-sufficiency
reduced
improved

community institutions
weakened
strengthened

conflict mitigation
worsened
improved

reduction of outmigration
reduced
improved

contribution to human well-being
decreased
increased


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

Ecological impacts
water quantity
decreased
increased

harvesting/ collection of water (runoff, dew, snow, etc)
reduced
improved

groundwater table/ aquifer
lowered
recharge

soil moisture
decreased
increased

Off-site impacts
wind transported sediments
increased
reduced

Cost-benefit analysis

Benefits compared with establishment costs
Short-term returns
very negative
very positive

Long-term returns
very negative
very positive

Benefits compared with maintenance costs
Short-term returns
very negative
very positive

Long-term returns
very negative
very positive

Climate change

Gradual climate change
annual temperature increase

not well at all
very well
Climate-related extremes (disasters)
local rainstorm

not well at all
very well
local windstorm

not well at all
very well
drought

not well at all
very well
general (river) flood

not well at all
very well
Other climate-related consequences
reduced growing period

not well at all
very well

Adoption and adaptation

Percentage of land users in the area who have adopted the Technology
  • single cases/ experimental
  • 1-10%
  • 11-50%
  • > 50%
Of all those who have adopted the Technology, how many have done so without receiving material incentives?
  • 0-10%
  • 11-50%
  • 51-90%
  • 91-100%
Has the Technology been modified recently to adapt to changing conditions?
  • Ja
  • Nee
To which changing conditions?
  • climatic change/ extremes
  • changing markets
  • labour availability (e.g. due to migration)

Conclusions and lessons learnt

Strengths: land user's view
Strengths: compiler’s or other key resource person’s view
  • The scheme has enabled previously irrigable areas to be rehabilitated and extended. Farming yields have doubled, or even tripled, due to the availability of water supplies and the technical support delivered post-build. The water table has risen (wells no longer dry up).
  • The effect on rice-growing areas is immediate: the retained water allows the agricultural crop cycle to be completed more easily.
  • Several operational scenarios are being implemented (a second and, in some cases, a third growing cycle has been made possible). Sizeable vegetable crops have been produced. Watering livestock is now easier and the lowland pastures are more abundant.
  • At the community level, larger revenues have been generated. The local population is busier throughout the year, which reduces outmigration, particularly among young people.
  • These schemes are simple and low cost. Most local contractors are fully competent in the installation techniques and high-tech equipment is not required.
Weaknesses/ disadvantages/ risks: land user's viewhow to overcome
Weaknesses/ disadvantages/ risks: compiler’s or other key resource person’s viewhow to overcome
  • It is important to make it clear to farmers that the water held in these small dam schemes cannot be stored throughout the dry season. To avoid misunderstandings, users should be heavily involved in the design of the scheme.

References

Compiler
  • Dieter Nill
Editors
Reviewer
  • Deborah Niggli
  • Alexandra Gavilano
Date of documentation: Sept. 24, 2014
Last update: Mei 28, 2019
Resource persons
Full description in the WOCAT database
Linked SLM data
Documentation was faciliated by
Institution Project
Key references
  • Intercooperation (2008): Les aménagements de bas-fonds dans le bassin cotonnier de Sikasso. Expérience du programme Jékasy. [Developing lowland areas in the Sikasso cotton-growing basin. The Jékasy programme’s experience]:
  • Manual of Good Practices in Small Scale Irrigation in the Sahel. Experiences from Mali. Published by GIZ in 2014.: http://star-www.giz.de/starweb/giz/pub/servlet.starweb
  • Rapport collecte de données sur la valorisation des ouvrages réalisés dans le Pôle de Bougouni sur le financement APEL [Data collection report on developing the value of APEL-funded schemes carried out in the Bougouni Hub] – Bougouni, April 2013:
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