Masonry dam (PIPRO-DB)

Small-scale dams (Mali)

Micro-barrages (French)

Description

Small-scale dams are moderately-sized barriers built across valley bottoms to retain water from permanent watercourses or seasonal flows.

They can range in length from 100 to 200 m, and the dam wall is usually between 2 and 4 m high. Small-scale dams impound permanent or seasonal water behind them, covering areas from 5 to 15 hectares. They are built with buttresses and a stilling basin. Depending on local conditions, the dam wall can be made of quarry stone joined with mortar or concrete. The dikes are made of earth and can be reinforced with stones. Some such structures are built as bridge dams, providing a means of crossing the valley. The effect on the water table depends on the depth at which the dam is anchored. The deeper the foundation, the more groundwater is retained. Sometimes, they are fitted with geomembranes which extend down deeper to retain more groundwater.

In the rainy season, water gradually accumulates behind the dike, increasing the availability of surface water during the rainy season and groundwater in the dry season. The land is farmed upstream and downstream both in the rainy season and the dry season. During the rainy season, rice is grown, and the areas around the body of water are used for other crops (flood-recession cropping). Dams increase the area of farmable land, yields and production. The water is also used for livestock, for fish farming and sometimes for household needs. The recharged water table feeds market garden wells, enabling farmers to grow vegetables in the dry season and permitting two or three crop harvests a year which increases the availability of food, providing income for farmers and guaranteeing work all year round. This improves the stability of local communities, increases their income and raises their standard of living.

Sustainable operation and management depend directly on the participatory approach. At the planning stage, the condition of the valley upstream and downstream and all user groups must be taken into account. The question of land tenure, in particular, must be settled before construction begins. It must be determined who the owner of the bottomlands is, who will be entitled to use them once the dam has been constructed, what uses will be permitted and under what conditions. The question of project ownership and upkeep must also be clarified. Today, the role of project owner is normally assigned to the commune authorities, although management of the dam is often delegated to a management committee. In order to avoid conflicts, it is essential to take into account all the user groups, livestock keepers in particular. Watering corridors must be established to prevent animals from damaging the crops. In order to maximise the value of the investment, well-organised management committees must be set up to ensure efficient crop production and oversee maintenance work. A management committee controls the opening and closing of the gates. It organises the maintenance of the structure and the implementation of any additional measures necessary to protect the gabion structures and stone bunds. It also collects and manages funds for the maintenance of the dam and organises meetings of farmers. In dry periods, it is important to manage water resources in such a way that downstream areas have enough water. When a series of dams are built on the same watercourse, an inter-dam committee may be required to manage the distribution of water and avoid conflicts between the users of the different dams.
Well-constructed small-scale dams last at least 50 years with a certain amount of upkeep. A high standard of technical planning and construction is required for small-scale dams to avoid subsequent damage. Depending on the natural characteristics of the watershed, small-scale dams may require additional SWC/SPR measures upstream to protect them from siltation.

These small-scale dams are suitable for use in narrower valleys, as a considerable volume of water can be impounded with a relatively short structure. They are not as well suited to wide, gently sloping valleys, as very long dikes are required and this increases the cost.

Location

Location: Mali, Mali

No. of Technology sites analysed:

Geo-reference of selected sites
  • n.a.

Spread of the Technology: evenly spread over an area (approx. 0.1-1 km2)

In a permanently protected area?:

Date of implementation: 10-50 years ago

Type of introduction
Masonry dam (PIPRO-DB)

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

  • Cropland
    • Annual cropping
    Number of growing seasons per year: 1
  • 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
  • chemical soil deterioration - Cn: fertility decline and reduced organic matter content (not caused by erosion)
  • biological degradation - Bc: reduction of vegetation cover
  • water degradation - Ha: aridification, 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
They can range in length from 100 to 200 m, and the dam wall is usually between 2 and 4 m high.

Technical knowledge required for field staff / advisors: high
Technical knowledge required for land users: low
Main technical functions: control of dispersed runoff: retain / trap, control of concentrated runoff: retain / trap, increase of infiltration, increase / maintain water stored in soil, increase of groundwater level / recharge of groundwater, water harvesting / increase water supply
Secondary technical functions: increase in organic matter, increase in nutrient availability (supply, recycling,…), sediment retention / trapping, sediment harvesting, increase of biomass (quantity), promotion of vegetation species and varieties (quality, eg palatable fodder)

Dam/ pan/ pond
Depth of ditches/pits/dams (m): 2-4
Length of ditches/pits/dams (m): 100-200
Author: PIPRO-DB

Establishment and maintenance: activities, inputs and costs

Calculation of inputs and costs
  • Costs are calculated:
  • Currency used for cost calculation: n.a.
  • Exchange rate (to USD): 1 USD = n.a
  • Average wage cost of hired labour per day: n.a
Most important factors affecting the costs
The cost of small-scale dams varies greatly depending on the physical characteristics of the site, the size of the structure and the local availability of materials. In Dogon country, in Mali, the PDRT project constructed dams with cyclopean concrete costing an average of around 20 million CFA francs and between 3 and 5 million CFA francs per hectare. The internal rate of return of the dams built averaged 17% (Nill & Kobilke, 2002). Larger dams built in the Beledougou area cost 100-140 million CFA francs. Helvetas Swiss Intercooperation reports costs of around 20 million CFA francs for areas of 10-80 hectares (PASSIP, 2012).
Establishment activities
  1. At the planning stage, the condition of the valley upstream and downstream and all user groups must be taken into account. The question of land tenure must be settled before construction begins. The question of project ownership and upkeep must also be clarified. (Timing/ frequency: None)
  2. In order to avoid conflicts, it is essential to take into account all the user groups, livestock keepers in particular (Timing/ frequency: None)
  3. Construction of dam (Timing/ frequency: None)
  4. Watering corridors must be established to prevent animals from damaging the crops (Timing/ frequency: None)
  5. well-organised management committees must be set up to ensure efficient crop production and oversee maintenance work (Timing/ frequency: None)
Maintenance activities
  1. A management committee controls the opening and closing of the gates. It organises the maintenance of the structure and the implementation of any additional measures necessary to protect the gabion structures and stone bunds. It also collects and manages funds for the maintenance of the dam and organises meetings of farmers (Timing/ frequency: None)
  2. Depending on the natural characteristics of the watershed, small-scale dams may require additional SWC/SPR measures upstream to protect them from siltation. (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: subtropics
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?
  • Yes
  • No

Occurrence of flooding
  • Yes
  • No
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
x
good
education

poor
x
good
technical assistance

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

poor
x
good
markets

poor
x
good
energy

poor
x
good
roads and transport

poor
x
good
drinking water and sanitation

poor
x
good
financial services

poor
x
good

Impacts

Socio-economic impacts
Crop production
decreased
x
increased

fodder production
decreased
x
increased

risk of production failure
increased
x
decreased

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

demand for irrigation water
increased
x
decreased

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

contribution to human well-being
decreased
x
increased


The water impounded by small-scale dams makes it possible to farm a much larger area in the valley bottoms and ensures better yields in the rainy season and also in the off-season. The production of food staples and market garden output increases significantly. More intense production ensures employment all year round, which improves the stability of local communities, increases their income and raises their standard of living.

Ecological impacts
water quantity
decreased
x
increased

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

groundwater table/ aquifer
lowered
x
recharge

soil moisture
decreased
x
increased

soil cover
reduced
x
improved

soil loss
increased
x
decreased

nutrient cycling/ recharge
decreased
x
increased

beneficial species (predators, earthworms, pollinators)
decreased
x
increased

Off-site impacts
reliable and stable stream flows in dry season (incl. low flows)
reduced
x
increased

downstream flooding (undesired)
increased
x
reduced

downstream siltation
increased
x
decreased

Cost-benefit analysis

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

Long-term returns
very negative
x
very positive

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

Long-term returns
very negative
x
very positive

Climate change

Gradual climate change
annual temperature increase

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

not well at all
x
very well
local windstorm

not well at all
x
very well
drought

not well at all
x
very well
general (river) flood

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

not well at all
x
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?
  • Yes
  • No
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 small-scale dams create water reserves. When there is not enough rain or during dry spells in the rainy season, the dams retain enough water for crops throughout their growth cycle. If rain-fed crops fail, production in the valley bottoms can mitigate these losses. In wet years, the dams regulate the flow of water, preventing heavy floodwaters from causing damage to land downstream.
  • The water impounded by small-scale dams makes it possible to farm a much larger area in the valley bottoms and ensures better yields in the rainy season and also in the off-season. The production of food staples and market garden output increases significantly. More intense production ensures employment all year round, which improves the stability of local communities, increases their income and raises their standard of living.
  • In the dry season, the recharged water table makes a second and even third crop harvest possible, increasing the availability of food, providing income for farmers and guaranteeing work all year round.
  • Replenished water tables not only improve crop output, they also reduce the time and effort that women devote to fetching water and make it easier to water livestock.
Weaknesses/ disadvantages/ risks: land user's viewhow to overcome
Weaknesses/ disadvantages/ risks: compiler’s or other key resource person’s viewhow to overcome
  • A high standard of technical planning and construction is required for small-scale dams to avoid subsequent damage. In order to maximise the value of the investment, well-organised management committees must be set up to ensure efficient crop production and oversee maintenance work.

References

Compiler
  • Dieter Nill
Editors
Reviewer
  • Deborah Niggli
  • Alexandra Gavilano
Date of documentation: Oct. 7, 2014
Last update: May 28, 2019
Resource persons
Full description in the WOCAT database
Linked SLM data
Documentation was faciliated by
Institution Project
Key references
  • Good Practices in Soil and Water Conservation. A contribution to adaptation and farmers´ resilience towards climate change in the Sahel. Published by GIZ in 2012.: http://agriwaterpedia.info/wiki/Main_Page
This work is licensed under Creative Commons Attribution-NonCommercial-ShareaAlike 4.0 International