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www.excellent.org.uk
Sand Dams & Drylands:
Small solutions; big impacts.
Simon Maddrell
Founder, Excellent Development
www.excellent.org.uk
About Excellent Development
• Supports community-led rainwater harvesting and sustainable
agriculture in rural drylands.
• Pioneers of the application of sand dams in different contexts:
Eight countries with agricultural and pastoral communities • Kenya (Ukambani & Northern Rangelands), Tanzania, Sudan, Chad,
Zimbabwe, Mozambique, Swaziland & India.
• Enabled communities to construct 900+ dams since 2002
• Almost 1 Million people with access to clean water.
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Where do sand dams work?
Sand Dams are a drylands solution requiring:
• Sufficiently seasonal rivers
• Sufficiently sandy sediment
• Accessible bedrock
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Technical sustainability – life cost
• Along with sub-surface dams are the most cost-effective form of
rainwater harvesting in drylands (UNDP).
• Virtually zero operation and maintenance costs: • Last over 50 years
• 5% need one-off repairs
• 2% failure rate (80% of which have been repaired)
Built in Mwala District, Kenya, 1957. Drank 2013
Built 1985
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Technical sustainability – design
Breaking the rules to manage dryland seasonal river flows:
• Enabling the river to flow in the same way as before: • Central spillways.
• Dams not always straight.
• Managing river floods with multiple spillways.
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Social sustainability – community ownership
• Community registered, built and managed.
• If there is a hand pump – communities
charge for water and maintain the pump.
2 Million days invested in self-help projects since 2002
7
Saving 2-10 hours per day enables communities to invest in sustainable development of their land.
Sustainable Land Management
2 Million days invested in self-help projects since 2002
Saved nearly 1 Billion hours collecting water since 2002
Social sustainability – reinvesting time
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Environmental sustainability
Virtuous Cycle of Soil & Water Conservation
Terraces
Sand Dams
Trees
Maintain water
& soil in farms
Water for people,
livestock,
vegetables
& tree nurseries
Retain more
water & soil in
farms
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Advantages of sand dams
Water protected from:
• Contamination.
• Evaporation.
• Disease vectors, such as
Bilharzia-carrying snails,
and mosquitoes.
Water yields up to
40M litres per annum
Multi-Use Water Source
Clean water for people
Saving time:
bringing clean water*
to within 30-90 mins
of people’s homes.
Nearly 1 Million People since 2002
Multi-Use Water Source
Irrigation of smallholder farms
• Demonstration farms.
• Vegetable plots.
• Tree nurseries.
• Community plots and
individual plots.
Nearly 1 Million Trees since 2002
Water for livestock & wildlife
Multi-Use Water Source
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• Primarily a sub-surface dam (6m deep & 0.9m high)
• Created an earth dam wing by scooping out the bend
Sand dam in Rajasthan, India
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• Sand dams are recharging 3 govt. tube wells in one village in
Rajasthan – doubling output and removing salinity.
• 100 smallholder farmers irrigating more land and producing
vegetables for the first time.
Recharge & salinity reduction in India
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Potential of sand dam road crossings
Potential to leverage infrastructure investments
for the benefit of water supply and agriculture
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Sand dams as rural road crossings
Sand Dam road crossing, Machakos, Kenya
Serves nine villages with est. 40M litres/annum
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Problems with culvert bridges in drylands
• Culverts unable to handle seasonal river flows
• Exacerbated by blockages from river flotsam
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Sand dam rural road crossing
Makueni County, Kenya
• Road crossing with four commercial
farms next to the dam.
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Water for year-round smallholder irrigation
Makueni County, Kenya in November 2014
• Commercial farm growing ‘out of season’
maize, vegetables, papaya etc.
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Sand dams:
Small solutions; big impacts.
Simon Maddrell
Founder, Excellent Development
www.excellent.org.uk
Small dams support smallholder farmers
• More than 2 billion people depend on smallholder farms,
which provide 80% of the foodΨ
• Smallholder farmers are 71% of the world’s poorest people*
75% of the world’s poor live in drylands§
• The World Bank acknowledges that small-scale dams &
smallholder farmers are an essential part of the solution to
global hunger and poverty.
Small-scale dams:
Sand dams, check dams, sub-surface dams, water-spreading weirs
* UNEP 2013 Ψ IFAD 2011 § UNCCD