Sand dams are a simple, low cost and low maintenance, replicable rainwater harvesting technology. It’s a solution that focuses on community ownership and self supply that involves significant community contribution and locally supplied skills.
They provide a clean, local water supply for domestic and farming use and are suited to arid and semi-arid areas of the world. A sand dam is a reinforced concrete wall (or a similarly robust and impermeable weir) typically built 1 – 5 metres high across a seasonal sand river. When it rains the dam captures soil laden water behind it – the sand in the water sinks to the bottom, whilst the silt remains suspended in the water.
Excellent Development and Africa Sand Dam Foundation
Sand dams, rain water harvesting, water conservation, aquifer recharge, climate change adaptation
Sand dams are a simple, low cost and low maintenance, replicable rainwater harvesting technology. It’s a solution that focuses on community ownership and self supply that involves significant community contribution and locally supplied skills. They provide a clean, local water supply for domestic and farming use and are suited to arid and semi-arid areas of the world. A sand dam is a reinforced concrete wall (or a similarly robust and impermeable weir) typically built 1 – 5 metres high across a seasonal sand river. When it rains the dam captures soil laden water behind it – the sand in the water sinks to the bottom, whilst the silt remains suspended in the water. Eventually the dams fill with sand – sometimes after only one rainfall or over 1 – 3 seasons. 25 to 40% of the volume of the sand held is actually water. A mature sand dam can store millions of litres of water – refilling after each rainfall providing a year round supply to over 1,000 people. Because the water is stored within the sand, evaporation losses are very low, the sand filters the water and water-vector diseases such as malaria are controlled.
Sand dams are the lowest cost form of rainwater harvesting and its robust nature and very low operational and maintenance costs make it particularly suited to remote and poorly served regions. The technical barriers to adoption are low: The technical skills required have and can be developed locally. It is a solution that is scaleable and has a broader application for use as a rural and game park road crossing to replace less effective culvert bridges. Sand dams provide significant environmental benefits such as aquifer recharge, increased downstream flows in the dry-season, rejuvenation of river ecologies and moderation of floods. As such, it contributes to ecosystem services and climate change adaption.
This is a drylands solution. Although Kenya has the highest concentration of dams, examples are found throughout world’s dryland regions. Sand dams can only be built on seasonal rivers with sufficient sandy sediment and where the bedrock or impermeable layer is accessible in the river bed.
The solution was initiated in Machakos and Makueni counties of Kenya by Joshua Mukusya, a visionary farmer and development worker, in 1978. He worked with a range of agencies to develop and implement the technology. In 1990, staff trained by Joshua set up SASOL to pioneer sand dams in the neighbouring county of Kitui. In 2002, Joshua teamed up with Simon Maddrell, Excellent Development’s director, to establish Excellent Development Kenya, now Utooni Development Organisation (UDO) to scale up the work. Sadly, last year, Joshua passed away. In 2010, Excellent Development formed a strategic partnership with the Kenyan NGO, Africa Sand Dam Foundation (ASDF), to support the wider uptake beyond Kenya. Today, ASDF, SASOL and UDO are the three NGOs with the most experience of building successful sand dams, approx. 130 dams / year, although many other NGOs have adopted the technology. Excellent Development funds ASDF with implementation and in partnership with ASDF, supports wider adoption.
A majority of the world’s rural poor, often with the lowest access to clean water, live in dryland regions. In our experience, the problem most commonly prioritised by dryland communities is the lack of water and the time required to collect it. Sand dams provide a clean, reliable water source, close to their homes. The very low cost of operating and maintaining sand dams means they are well suited to remote, poorly served regions. Because it is a low cost technology that requires a major community contribution and the knowledge and skills of locally trained artisans, it’s a solution particularly suited to community ownership and self-supply. This contributes to effective implementation. The second biggest and related problem in drylands is growing enough food to eat and sell. Sand dams save farmers hours every day that they can invest in improving their farms to grow more food and create the potential for farmers to irrigate trees and crops, water livestock and generate an income.
The solution’s direct impacts are
• Improved access to water for people, crops and livestock in water scarce environments
• Reduced time required to collect water
• Reduced water-related disease
• Aquifer recharge and rejuvenation of ecology
As well as providing water for domestic purposes, sand dams create potential for wider development. These long term indirect impacts include: improved agricultural production and irrigated vegetable gardens and tree nurseries, which in turn significantly improve incomes; improve nutrition and improve school attendance. By storing and retaining water within a watershed, sand dams regulate the flow of water, provide protection against storms, erosion and floods and build resilience to drought and climate change. In 2010, an independent evaluation of the work SASOL and UDO noted the importance of strong community engagement and the integration sand dams within wider food security and development programme in order to realise these long term impacts.
Key indicators of the direct impacts are
• Number of households provided with new/improved drinking water
• Proportion of population with sustainable access to an improved water source
• Reduced distance and time spent in fetching water
• Reduced water borne and water related diseases
Sand dams provide a year round local water source and so create potential for wider development. Key indicators of these indirect impacts include
• Improved livestock production
• Increased horticulture farming
• Improved income for households around the sand dam
• Improved school attendance and
• Increased food production
In addition to these quantitative measures, semi-structured discussions and interviews create qualitative measures of change and allow community groups to reflect on the work, identify what has worked and what hasn’t and plan further work together
As a drylands solution, it will be of most interest to other dryland farmers including pastoralists. It should also interest all those who are working with dryland farmers to improve their water and food security or whose work is impacted by food and water issues: implementers, policy makers, funders and researchers. In addition, the solution should be of interest to people with an interest in:
• dryland game reserves,
• rural road engineering,
• drylands agroforestry,
• peace building and conflict management
• aquifer recharge, green water credits and payment for environmental services and
• climate change adaptation and disaster risk reduction.
Public works programmes would transform dry rural areas by implementing ‘sand dam bridges’ over seasonal rivers and streams – there are a number of isolated examples of this working in Kenya – one of which, supplying a piped network of water kiosks, had a yield of 40 million litres per year. The same technique could also create a sustainable environment for animals, plants and insects in game reserves throughout Africa and elsewhere. Even more developed countries like Australia or Jordan could significantly benefit from sand dams.
In order to upscale this solution, there is a need for greater awareness and advocacy of the technology and its benefits amongst these groups. Nothing generates interest in sand dams more than exposure to successful examples and talking to those responsible through peer to peer learning visits: community to community; NGO to NGO and country to country.
There is a need to pilot and document the solution’s application in new contexts / countries and for new ‘sand dam champions’ who are in a position to influence decision makers and create government and funding policies to enable rapid adoption. There is also a need to invest in research, learning resources and training to create a cadre of technical advisors and to better understand the design, construction, impacts and potential of sand dams
Do adapt the application to the context. Although sand dams are technically replicable, their application in new contexts requires careful understanding and consideration. Excellent Development has developed a framework tool to help agencies identify the political, economic, social, technical, legal and environmental factors that should be taken account of when introducing sand dams to a new context.
Do site sand dams correctly. There are 2 pre-requisites for a suitable sand dam site. 1) Sand dams must be built on a seasonal river with sufficient sandy sediment. These conditions are only found in drylands. 2) A site must have accessible bedrock in the river bed to anchor the dam to.
Do design and build sand dams correctly. When correctly designed and built, sand dams last 50 years or more. In order to rebuild a resilient sand dam, there are two golden rules for design: 1) sand dams must be built on an impermeable and/or rock base at least 1.5m wider than the flood width of the river and 2) they must allow the river to continue flowing in the same direction as before.
Do support terracing, tree planting and conservation farming in the wider catchment. This conserves soil and water on farms, increases aquifer recharge and base flows into the dam and reduces the amount of silt in the sand dam aquiver.
Don’t short cut community ownership. Communities better understand and are able to implement solutions to their problems if they are central to the planning of the solution. Genuine community commitment and ownership from initial planning to on-going management is vital to realise the intended benefits and full potential created by a dam. Legal registration and agreements to safeguard community access and water rights help this
Don’t build a sand dam in isolation. An independent evaluation in 2010 of SASOL and UDO’s work found the long term impacts on poverty, food security and incomes were greatest when sand dams were integrated within a wider community development programme aimed at improving food production, livestock management and land management practice.
Sand dams are the world’s lowest cost method of capturing rainwater in dry rural areas by a factor of 3 to 30 times compared to rain water harvesting tanks, earth dams, haffirs and rock catchments. In Machakos County, Kenya, the cost of materials and technical support for a dam using 250 bags of cement is £4,400 and £7,300 for a 500 bag dam. Costs rise by up to 50% in more remote regions or countries. Sand dams require a lot of hard work. Community members collect the required stones, sand and water, support construction and terrace the land around the dam. If this in-kind contribution is included the costs would rise by 100%. In Kenya, with a long tradition of building sand dams, it takes from 6 to 12 weeks to plan and prepare for construction and 2 days to 2 weeks to build the dam. In other areas, with less experience and/or less community commitment, building a dam may take 6 months or more
Although many organisations have built sand dams in Kenya, the overwhelming majority, approximately 1,000 in total, have been built by three organisations: UDO, SASOL and ASDF. All three organisations host learning visits for staff from other organisations. Excellent Development has supported learning visits by 10 organisations including staff from WaterAid, the RAIN Foundation, the Dabane Trust (Zimbabwe), the Mennonite Central Committee (Tanzania and Mozambique) and the Christian Committee of Mozambique (CCM). ASDF and Excellent Development have also provided in-country technical support to Dabane Trust, CCM and WaterAid Uganda. A number of organisations including UNEP, Vrije Universiteit Amsterdam, TU Delft, Acacia Institute, SamSamWater and SASOL have studied sand dams in Kenya including their impact on hydrology and aquifer recharge. These agencies plus the RAIN Foundation have also promoted awareness, advocated for wider adoption and written technical guides and websites.
Ian Neal, Technical and Development Manager, Excellent Development, Unit 59 The Market Building, 195 High Street, Brentford, UK, TW8 8LB, email: firstname.lastname@example.org or +44 20 8232 9050. Website: www.excellent.org.uk.
A consortium of Dutch agencies led by the RAIN Foundation has written a sand dam manual and two websites (www.sanddam.org and www.bebuffered.com) that promote rainwater harvesting technologies including sand dams. Several other agencies have written sand dam manuals or technical briefs from VSF Belgium, WaterAid, Practical Action and Erik Nissen-Petersen.