Technologies

Small Earth Dams [Zambia]

technologies_1331 - Zambia

Completeness: 73%

1. معلومات عامة

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

Key resource person(s)

SLM specialist:
Name of project which facilitated the documentation/ evaluation of the Technology (if relevant)
Book project: Water Harvesting – Guidelines to Good Practice (Water Harvesting)
Name of project which facilitated the documentation/ evaluation of the Technology (if relevant)
Book project: SLM in Practice - Guidelines and Best Practices for Sub-Saharan Africa (SLM in Practice)
Name of the institution(s) which facilitated the documentation/ evaluation of the Technology (if relevant)
International Centre for Research in Agroforestry (ICRAF) - Kenya

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:

نعم

2. Description of the SLM Technology

2.1 Short description of the Technology

Definition of the Technology:

Water harvesting and storage structures to impound runoff generated from upstream catchment areas.

2.2 Detailed description of the Technology

Description:

Small earth dams are water harvesting storage structures, constructed across narrow sections of valleys, to impound runoff generated from upstream catchment areas.

Establishment / maintenance activities and inputs: Construction of the dam wall begins with excavation of a core trench along the length of the dam wall which is filled with clay and compacted to form a ‘central core’ that anchors the wall and prevents or minimizes seepage. The upstream and downstream embankments are also built using soil with a 20-30% clay content. During construction – either by human labour, animal draught or machine (bulldozer, compacter, grader etc.) – it is critical to ensure good compaction for stability of the wall. It is common to plant Kikuyu grass (Pennisetum clandestinum) to prevent erosion of the embankment. The dam is fenced with barbed wire to prevent livestock from eroding the wall. Typical length of the embankment is 50-100 m with water depth ranging 4-8 m. An emergency spillway (vegetated or a concrete shute) is provided on either, or both sides, of the wall for safe disposal of excess water above the full supply level. The dam water has a maximum throwback of 500 m, with a capacity ranging from 50,000 – 100,000 m3.

Natural / human environment: The dams are mainly used for domestic consumption, irrigation or for watering livestock. If the dams are located on communal lands, their establishment requires full consultation and involvement of the local community. The government provides technical and financial assistance for design, construction and management of these infrastructures. Community contribution includes land, labour and local resources. The community carries out periodic maintenance of the infrastructure – including vegetation management on embankment, desilting etc. – and of the catchment areas (through soil and water conservation practices).

2.3 Photos of the Technology

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

بلد:

Zambia

Region/ State/ Province:

Southern Province

Specify the spread of the Technology:
  • applied at specific points/ concentrated on a small area
Comments:

In the study area there are over 293 dams serving a cattle population of 1.1 million and human population of nearly 1 million people

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

3. Classification of the SLM Technology

3.1 Main purpose(s) of the Technology

  • Access to water

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

Cropland

Cropland

  • Annual cropping
Number of growing seasons per year:
  • 1
Specify:

Longest growing period in days: 120; Longest growing period from month to month: Nov-April

Comments:

Major land use problems (compiler’s opinion): water degradation, soil erosion, low surface water availability

3.4 Water supply

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

3.5 SLM group to which the Technology belongs

  • improved ground/ vegetation cover
  • water harvesting

3.6 SLM measures comprising the Technology

vegetative measures

vegetative measures

  • V2: Grasses and perennial herbaceous plants
structural measures

structural measures

  • S5: Dams, pans, ponds
Comments:

Secondary measures: vegetative measures

Type of vegetative measures: aligned: -contour

3.7 Main types of land degradation addressed by the Technology

soil erosion by water

soil erosion by water

  • Wt: loss of topsoil/ surface erosion
  • Wg: gully erosion/ gullying
Comments:

Secondary types of degradation addressed: Wg: gully erosion / gullying

Main causes of degradation: Heavy / extreme rainfall (intensity/amounts), floods

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
Comments:

Secondary goals: rehabilitation / reclamation of denuded land

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

4.1 Technical drawing of the Technology

Technical specifications (related to technical drawing):

Dimensions and main components of a small dam: (1) water body; (2) dam wall (with layers of compacted soil; side slopes 3:1); (3) central core ('key'); (4) grass cover; (5) stone apron; (6) spillway

Southern Province

Technical knowledge required for field staff / advisors: high

Technical knowledge required for land users: high

Main technical functions: control of concentrated runoff: retain / trap, water harvesting / increase water supply

Aligned: -contour
Vegetative material: G : grass

Grass species: Pennisetum clandestinum

Dam/ pan/ pond
Depth of ditches/pits/dams (m): 4.00
Length of ditches/pits/dams (m): 50.00

Construction material (earth): 20-30% clay content

Specification of dams/ pans/ ponds: Capacity 100000.00m3

Dimensions of spillways: 5.00m

Vegetation is used for stabilisation of structures.

Author:

Mats Gurtner, Center for Development and Environment, University of Bern

4.2 General information regarding the calculation of inputs and costs

Specify how costs and inputs were calculated:
  • per Technology unit
Specify unit:

Dam

Specify dimensions of unit (if relevant):

10’000 m3 (44 m long; 8 m deep)

4.3 Establishment activities

Activity Timing (season)
1. Site selection in consultation with community.
2. Dam survey and design: Topographical survey of dam area; using leveling equipment (dumpy level or theodolite); Determination of dam wall dimensions.
3. Dam wall construction: Excavate core trench (usually 4m wide; 2m deep). Excavate and transport clay-rich soil to the dam site. Construct core and embankments (slope angles 3:1). Continuously compact placed soil.
4. Construct lateral spillway(s), 5-30m wide (depending on the flood flow and the return slope).
5. Design and installation of irrigation and drainage infrastructure (in case of crop production).
6. Completion: plant kikuyu grass on dam embank-ment, spillway and irrigation canals and fence of; alternatively line with cement

4.4 Costs and inputs needed for establishment

Specify input Unit Quantity Costs per Unit Total costs per input % of costs borne by land users
Labour Dam and spillway construction unit 1,0 2000,0 2000,0 20,0
Equipment Tools unit 1,0 30000,0 30000,0 20,0
Plant material Seeds unit 1,0 1000,0 1000,0 20,0
Fertilizers and biocides Fertilizer unit 1,0 1000,0 1000,0 20,0
Fertilizers and biocides Biocides unit 1,0 1000,0 1000,0 20,0
Construction material Stone unit 1,0 15000,0 15000,0 20,0
Total costs for establishment of the Technology 50000,0
Total costs for establishment of the Technology in USD 50000,0

4.5 Maintenance/ recurrent activities

Activity Timing/ frequency
1. Catchment conservation to minimise siltation of dam and irrigation infrastructure (continuous).
2. (Re-)planting grass on dam and irrigation infrastructure (annually, using hand hoes).
3. Desiliting of the dam (every 5-10 years): excavate and remove the silt deposited in the dam.
4. Cleaning of dam and irrigation infra-structure (annually): remove trees/ shrubs from dam / canals. If concrete lined: repair of any damages.

4.6 Costs and inputs needed for maintenance/ recurrent activities (per year)

Specify input Unit Quantity Costs per Unit Total costs per input % of costs borne by land users
Labour Maintenance of dam unit 1,0 200,0 200,0
Equipment Tools unit 1,0 2000,0 2000,0
Plant material Seeds unit 1,0 300,0 300,0
Construction material Stone unit 1,0 1500,0 1500,0
Total costs for maintenance of the Technology 4000,0
Total costs for maintenance of the Technology in USD 4000,0
Comments:

Machinery/ tools: machinery, ox-ripper, hoe/pick, shovel

Establishment costs are calculated for a dam with an earthwork volume of 10’000 m3 (44 m long; 8 m deep; side slopes 3:1). 20% of costs are borne by the community (in-kind contribution: labour and local materials such as sand, stones). Construction machinery can include: tipper truck, bulldozer, motor scraper, compactor, tractor, grader

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
Specify average annual rainfall (if known), in mm:

700,00

Agro-climatic zone
  • sub-humid
  • semi-arid

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.
Comments and further specifications on topography:

Slopes on average: Gentle (plains), moderate (plains), rolling (plains) and hilly (valleys)

Altitudinal zone: Also 1000-1500 m a.s.l., range from 300-1200 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):
  • coarse/ light (sandy)
  • medium (loamy, silty)
Topsoil organic matter:
  • medium (1-3%)
If available, attach full soil description or specify the available information, e.g. soil type, soil PH/ acidity, Cation Exchange Capacity, nitrogen, salinity etc.

Soil fertility is medium

5.4 Water availability and quality

Availability of surface water:

poor/ none

5.6 Characteristics of land users applying the Technology

Market orientation of production system:
  • mixed (subsistence/ commercial)
Individuals or groups:
  • groups/ community
Level of mechanization:
  • animal traction
Indicate other relevant characteristics of the land users:

Land users applying the Technology are mainly disadvantaged land users

Population density: < 10 persons/km2

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

Land ownership:
  • communal/ village
  • not titled
Land use rights:
  • communal (organized)

6. Impacts and concluding statements

6.1 On-site impacts the Technology has shown

Socio-economic impacts

Production

crop production

decreased
increased

animal production

decreased
increased
Water availability and quality

irrigation water availability

decreased
increased

irrigation water quality

decreased
increased
Income and costs

farm income

decreased
increased

Socio-cultural impacts

food security/ self-sufficiency

reduced
improved

recreational opportunities

reduced
improved

community institutions

weakened
strengthened

Ecological impacts

Water cycle/ runoff

water quantity

decreased
increased

harvesting/ collection of water

reduced
improved

groundwater table/ aquifer

lowered
recharge
Climate and disaster risk reduction

drought impacts

increased
decreased

6.2 Off-site impacts the Technology has shown

water availability

decreased
increased

downstream flooding

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

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 not 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 not well

Other climate-related consequences

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:

negative

Long-term returns:

very positive

How do the benefits compare with the maintenance/ recurrent costs (from land users' perspective)?
Short-term returns:

neutral/ balanced

Long-term returns:

very positive

6.5 Adoption of the Technology

Comments:

Comments on adoption trend: Records of 1991 indicate at least 537 such dams exist in Zambia. In the study area there are over 293 dams serving a cattle population of 1.1 million and human population of nearly 1 million people.

6.7 Strengths/ advantages/ opportunities of the Technology

Strengths/ advantages/ opportunities in the compiler’s or other key resource person’s view
Small earth dams allow for the diversification of income activities including tree nurseries, brick making, fish farming, raising ducks and geese and thus alleviate poverty

improvement of access to markets will be crucial to support such income generating activities
Saves people’s time by reducing the distance to fetch water for domestic use

clear and equitable water use rights and agreements
Reduced risk of crop failure by bridging prolonged dry periods and as such contribute to food security and climate change adaptation

How can they be sustained / enhanced? combine with water saving cultivation practices such as mulching, pitting etc.
Reduced damages from soil erosion and flooding by storing excessive runoff water

How can they be sustained / enhanced? use an integrated watershed management approach to reduce flood and erosion risk
Possibility for watering cattle near the village reduced soil compaction and erosion

How can they be sustained / enhanced? regulate access of cattle to avoid degradation around the water source and protect water source from pollution

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?
Dams are communally owned requires strong organisation and commitment by community
Risk of siltation de-silting and Catchment conservation is essential
Vulnerability to climate change increase depth and design storage to last at least for two rainy seasons
Evaporation and seepage losses maintain minimum design depth of 4 meters; if seepage is high: provide impervious material on the upstream embankment, i.e. clay or plastic lining if necessary

7. References and links

7.2 References to available publications

Title, author, year, ISBN:

Nissen-Petersen E. 2006. Water from small dams. A handbook for technicians, farmers and others on site investigations, designs, cost estimations, construction and maintenance of small earth dams

Title, author, year, ISBN:

Morris P. H. 1991. Statement of Policy: Progress Review of the Drought Relief Dam Cons/ruction Project, Southern Province. Part 1 — Main Report. Irrigation and Land Husbandry Branch, Department of Agriculture, Chôma

Title, author, year, ISBN:

Sichingabula H.M. 1997. Problems of sedimentation in small dams in Zambia. Human Impact on Erosion and Sedimentation (Proceedings of the Rabat Symposium, April 1997. IAHS Publ. no. 245, 1997

7.3 Links to relevant online information

Title/ description:

The Jesuit Centre for Theological Reflection. 2010. Social Conditions Programme.

URL:

http://www.mywage.org/zambia/main/minimum-wage/comparitive-minimum-wage

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