Technologies

Dams with water-spreading weirs [Mali]

Creation: 09/24/2014 5:01 p.m.
Update: 05/28/2019 10:59 a.m.
Compiler: Dieter Nill
Editor: –
Reviewers: Deborah Niggli, Alexandra Gavilano

Barrages avec seuils d’épandage déversant (French)

technologies_1633 - Mali

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Completeness: 78%

1. General information

1.2 Contact details of resource persons and institutions involved in the assessment and documentation of the Technology

Key resource person(s)

SLM specialist:

Dieter Nill

SLM specialist:

Dembele Celestin

HELVETAS Swiss Intercooperation

Mali

SLM specialist:

Doumbia Moussa

ADEPE MALI

Mali

Name of project which facilitated the documentation/ evaluation of the Technology (if relevant)

Manual of Good Practices in Small Scale Irrigation in the Sahel (GIZ )

Name of the institution(s) which facilitated the documentation/ evaluation of the Technology (if relevant)

Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) - Germany

1.3 Conditions regarding the use of data documented through WOCAT

The compiler and key resource person(s) accept the conditions regarding the use of data documented through WOCAT:

Yes

1.4 Declaration on sustainability of the described Technology

Is the Technology described here problematic with regard to land degradation, so that it cannot be declared a sustainable land management technology?

2. Description of the SLM Technology

2.1 Short description of the Technology

Definition of the Technology:

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).

2.2 Detailed description of the Technology

Description:

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.

2.3 Photos of the Technology

Media Gallery

2.5 Country/ region/ locations where the Technology has been applied and which are covered by this assessment

Country:

Mali

Region/ State/ Province:

Mali

Further specification of location:

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

Specify the spread of the Technology:

evenly spread over an area

If precise area is not known, indicate approximate area covered:

10-100 km2

Comments:

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.

2.6 Date of implementation

If precise year is not known, indicate approximate date:

10-50 years ago

2.7 Introduction of the Technology

Specify how the Technology was introduced:

through projects/ external interventions

Comments (type of project, etc.):

Since 1998, through Helvetas Swiss Intercooperation

3. Classification of the SLM Technology

3.1 Main purpose(s) of the Technology

improve production

3.2 Current land use type(s) where the Technology is applied

Land use mixed within the same land unit:

Yes

Specify mixed land use (crops/ grazing/ trees):

Agro-pastoralism (incl. integrated crop-livestock)

Cropland

Annual cropping

Number of growing seasons per year:

Specify:

Longest growing period in days: 120, Longest growing period from month to month: August-November

Grazing land

Waterways, waterbodies, wetlands

Ponds, dams

Comments:

Major land use problems (compiler’s opinion): water loss, aridification, low water table
Livestock density: 1-10 LU /km2

3.4 Water supply

Water supply for the land on which the Technology is applied:

mixed rainfed-irrigated

3.5 SLM group to which the Technology belongs

irrigation management (incl. water supply, drainage)
water diversion and drainage
surface water management (spring, river, lakes, sea)

3.6 SLM measures comprising the Technology

structural measures

S5: Dams, pans, ponds

3.7 Main types of land degradation addressed by the Technology

water degradation

Ha: aridification
Hs: change in quantity of surface water
Hg: change in groundwater/aquifer level

Comments:

Main causes of degradation: over abstraction / excessive withdrawal of water (for irrigation, industry, etc.)

3.8 Prevention, reduction, or restoration of land degradation

Specify the goal of the Technology with regard to land degradation:

prevent land degradation
reduce land degradation

4. Technical specifications, implementation activities, inputs, and costs

4.1 Technical drawing of the Technology

Technical specifications (related to technical drawing):

Technical knowledge required for field staff / advisors: high
Technical knowledge required for land users: low
Main technical functions: increase of infiltration, increase / maintain water stored in soil, increase of groundwater level / recharge of groundwater, water harvesting / increase water supply, water spreading

Dam/ pan/ pond
Height of bunds/banks/others (m): 1

4.2 General information regarding the calculation of inputs and costs

other/ national currency (specify):

CFA Franc

If relevant, indicate exchange rate from USD to local currency (e.g. 1 USD = 79.9 Brazilian Real): 1 USD =:

517.0

4.3 Establishment activities

	Activity	Timing (season)
1.	It is in community-led planning initiatives that the request for a lowland development scheme takes shape.
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.
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
4.	the findings of the technical diagnostic exercise are developed as a 3D model
5.	The consultant then moves on to performing economic and financial analyses, which will con- firm the cost effectiveness of the scheme
6.	A funding agreement is signed by the commune, farmers and project team

4.4 Costs and inputs needed for establishment

	Specify input	Quantity	Costs per Unit	Total costs per input
Other	total construction	1.0	48703.0	48703.0
Total costs for establishment of the Technology				48703.0
Total costs for establishment of the Technology in USD				94.2

4.5 Maintenance/ recurrent activities

	Activity	Timing/ frequency
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
2.	public administration undertakes sporadic inspections to ensure relevant laws are respected

4.7 Most important factors affecting the costs

Describe the most determinate 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).

5. Natural and human environment

5.1 Climate

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

semi-arid

Thermal climate class: tropics

5.2 Topography

Slopes on average:

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

Altitudinal zone:

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.

5.3 Soils

Soil depth on average:

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):

medium (loamy, silty)
fine/ heavy (clay)

Topsoil organic matter:

medium (1-3%)
low (<1%)

5.4 Water availability and quality

Ground water table:

5-50 m

Availability of surface water:

medium

Water quality (untreated):

for agricultural use only (irrigation)

5.5 Biodiversity

Species diversity:

medium

5.6 Characteristics of land users applying the Technology

Market orientation of production system:

mixed (subsistence/ commercial)

Off-farm income:

10-50% of all income

Relative level of wealth:

poor
average

Level of mechanization:

manual work

Gender:

Indicate other relevant characteristics of the land users:

Population density: < 10 persons/km2
Annual population growth: 2% - 3%
10% of the land users are rich.
50% of the land users are average wealthy.
30% of the land users are poor.
10% of the land users are very poor.

5.7 Average area of land used by land users applying the Technology

< 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

Is this considered small-, medium- or large-scale (referring to local context)?

small-scale

5.8 Land ownership, land use rights, and water use rights

Comments:

The irrigated land is allocated by the chief

5.9 Access to services and infrastructure

health:

poor
moderate
good

education:

poor
moderate
good

technical assistance:

poor
moderate
good

employment (e.g. off-farm):

poor
moderate
good

markets:

poor
moderate
good

energy:

poor
moderate
good

roads and transport:

poor
moderate
good

drinking water and sanitation:

poor
moderate
good

financial services:

poor
moderate
good

6. Impacts and concluding statements

6.1 On-site impacts the Technology has shown

Socio-economic impacts

Production

crop production

decreased

increased

risk of production failure

increased

decreased

production area

decreased

increased

Income and costs

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

Comments/ specify:

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 cycle/ runoff

water quantity

decreased

increased

harvesting/ collection of water

reduced

improved

groundwater table/ aquifer

lowered

recharge

Soil

soil moisture

decreased

increased

6.2 Off-site impacts the Technology has shown

wind transported sediments

increased

reduced

6.3 Exposure and sensitivity of the Technology to gradual climate change and climate-related extremes/ disasters (as perceived by land users)

Gradual climate change

	Season	increase or decrease	How does the Technology cope with it?
annual temperature		increase	well

Climate-related extremes (disasters)

Meteorological disasters

	How does the Technology cope with it?
local rainstorm	well
local windstorm	well

Climatological disasters

	How does the Technology cope with it?
drought	well

Hydrological disasters

	How does the Technology cope with it?
general (river) flood	well

Other climate-related consequences

	How does the Technology cope with it?
reduced growing period	well

6.4 Cost-benefit analysis

How do the benefits compare with the establishment costs (from land users’ perspective)?

Short-term returns:

positive

Long-term returns:

very positive

How do the benefits compare with the maintenance/ recurrent costs (from land users' perspective)?

Short-term returns:

very positive

Long-term returns:

very positive

6.7 Strengths/ advantages/ opportunities of the Technology

Strengths/ advantages/ opportunities in the 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.

6.8 Weaknesses/ disadvantages/ risks of the Technology and ways of overcoming them

Weaknesses/ disadvantages/ risks in the compiler’s or other key resource person’s view	How can they be 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.

7. References and links

Links and modules

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