'Sand dams' store water for dry season in semi-arid Kenya
Simple dams that can be constructed in a day by unskilled laborers may revolutionize Kenyan agriculture by storing millions of liters of water, providing once-parched communities with water for domestic use and irrigation throughout the year.
Makueni, Kenya — Barely a month after heavy rains pounded Kenya, many seasonal rivers in the country’s semi-arid east are already drying up, and residents are preparing for the months-long dry season.
But some, like Paul Masila and other members of the Woni Wa Mbee self-help group, are not worried about the looming dry spell. Instead, they are preparing to plant crops or are harvesting fields they planted before the rains.
The group – the name means “progressive vision” in Kamba, the local langage – have revolutionized the region’s fortunes by finding a way to store millions of liters of water under the bed of the Kaiti River, providing the once-parched community with water for domestic use and irrigation throughout the year.
“Drought will never again be a problem, particularly for future generations,” said Titus Mwendo, a 31-year-old farmer in Miambwani, in the Eastern region’s Makueni County.
The Kaiti, like other seasonal rivers in the region, fills with water only during the rainy season, which usually arrives in December.
“The rest of the year is characterized by scorching sun, dry rivers, dusty roads – only those who are fit can survive,” said Masila, a member of Woni Wa Mbee.
But Woni Wa Mbee and other self-help groups in the area, aided by local non-governmental organizations, have found a way to trap and store the Kaiti’s water in its own sandy riverbed, keeping water available for months after the river has disappeared.
“The water reservoirs are called sand dams,” said Kevin Muneene, chief executive officer of the Utooni Development Organization, one of the supporting NGOs. Over the past two years, the organization has helped 80 self-help groups construct 1,528 sand dams in arid and semi-arid areas of Kenya’s Rift Valley and eastern region.
To make a dam, he said, a high concrete barrier is constructed across a seasonal river. When it rains, the water carries sand downstream, depositing it up to the level of the barrier. When the rains finish, water remains trapped in the piled-up sand for up to a kilometer (0.6 miles) upstream of the dam, depending on the dam’s height.
“A well-constructed sand dam has 60 percent of its volume as sand, while the remaining 40 percent is always water,” said Mr. Muneene, an expert in sand dam construction.
In terms of volume, it is estimated that an average sand dam in a relatively wide stream such as the Kaiti River can hold up to 5,000 cubic meters of water, equivalent to 5 million liters (1.3 million gallons). To boost the volume of water stored, several sand dams can be built along one river.
Those numbers suggest that the 1,528 sand dams already built as part of the project will be able to store up to 7.7 billion liters (2 billion gallons) of water, which can be used to irrigate thousands of hectares of land and supply thousands of households for months after the rains stop.
To use the water, community members scoop out sand from the river bed to expose it. It can then be pumped out for irrigation or other uses.
Over 3,000 households are now using water from the dams to grow vegetables, tomatoes, drought-resistant legumes, fruit trees such as grafted mangoes and oranges, and other crops.
“For the first time, we have had water throughout two years. This is not a common phenomenon in this area,” said Florence Munyoki, the treasurer of Woni Wa Mbee and a smallholder farmer in Utaati village.
“Before the dams were constructed, we could walk up to 12 kilometers (7.5 miles) downstream in search of a place to sink a shallow well. This was time-consuming and very tiring,” said the 52-year-old mother of four.
The sand dam technology is believed to be indigenous to Kenya, though it is now being used in other countries around the world, from Zimbabwe to Brazil to Thailand. The Kenya project is the first time the dams have been built in such large numbers and as permanent structures.
“When we initiated this project, we had our own ideas, such as sinking boreholes. But on consulting community members, they insisted that harvesting and storing rainwater would be a better answer to their prevailing water problems,” said Annie Murimi, the Utooni organization’s development officer.
The NGO donates cement to eligible groups and offers technical assistance. The self-help group members then have to collect construction materials such as stones, which are locally available, and offer unskilled manual labor during construction. Experts say that 250 people can build a sand dam in one day.
“To be eligible for support by our organization, there must be a registered group with objectives geared toward water conservation, food security, and income generation,” Murimi said.
All community members are allowed to access the water for domestic use and for their animals but “irrigation is strictly reserved for group members,” said David Nyala, a member of another self-help group known as Wekwatio wa Kanzoka, or “hope of Kanzoka” in the Kamba language.
The Utooni Development Organization also collaborates with the Kenya Agricultural Research Institute to provide local farmers with a range of certified drought-tolerant seeds and seedlings.
• Isaiah Esipisu is a freelance science journalist based in Nairobi. He can be reached at firstname.lastname@example.org