Could sand dams offer a reliable source of water?

On a busy market day in Lemishami village, Letilia Lekula herds his goats to a dry, sandy riverbed with a stone wall built across it. The animals wait patiently as he pulls a wooden trough from a nearby thicket and then starts digging in the sand.

After about five minutes Lekula hears a splash. The sound is now so familiar to his goats that they circle around him as he scoops water from the hole in the sand into a trough for them to drink.

For the pastoralists of Lemishami in Ol Donyiro ward, which lies 115 kilometres (71 miles) from the town of Isiolo in Kenya’s arid eastern region, the sand dam is a lifesaver.

Built across the Raap River, the simple wall catches water and silt that flows down from a nearby mountain range. As sand accumulates at the wall, it traps water and holds it through much of the dry season.

Months after natural ponds and rivers have dried up, the sand dam remains a reliable source of water.

Only a few years ago, villagers could rely on the year-round flow of the Ewaso Ng’iro River. Now, however, with upriver communities using more water for farming, the river has all but disappeared between March and August. The area’s rainfall is too sporadic to keep the river topped up.

“It’s been dry for the better part of the year,” Lekula said. “The rain is unpredictable. Nowadays it’s both very heavy and only lasts a few days.”

Lekula’s village got the sand dam as part of the Isiolo County Adaptation Fund (ICAF), a project funded by the U.K. Department for International Development through the London-based International Institute for Environment and Development.

Set up in 2012, the fund worked with communities in Ol Donyiro, which is classified as a water-stressed region, to understand the challenges they face.

After Isiolo communities proposed sand dams as a solution to their water shortage problems, the fund constructed and rehabilitated a dozen sand dams across the parched county at a cost of 5.1 million Kenyan shillings ($50,000).

The sand dam in Lemishami is so effective that the pastoralists no longer feel the need to move their households, or manyattas, every year in search of water. Children can stay in school and women don’t have to walk 30 kilometres to find water for their families, residents say.

While the sand dam doesn’t provide enough water for all of the community’s cows, which have been moved to more remote grazing fields, the villagers can keep a few goats at home for milk and meat.

“Now the manyattas and schools are settled,” said Lekula. “We have enough water for our households, school and goats, and have enough time after watering our animals to buy food from the market.”

CATCHING WATER

Like several other wards in the region, Ol Donyiro has no substantial groundwater and gets only between 300 and 350 millimetres (12 to 14 inches) of rain each year, according to Junius Njeru, an engineer with the water ministry in Isiolo County.

But the ward also has some fortunate geography. It is the endpoint for floodwater coming from the rainy Nyandarua Mountains. Every time it rains on the mountains, the overflow brings water and silt down to the area’s dry riverbeds.

Normally the floodwater would quickly disappear once it reached Ol Donyiro, Njeru said. But now the sand dams that sit across some of the area’s riverbeds catch the water during the rainy season and hold onto it through the dry season.

At 1.5 metres (5 feet) high and 1 metre (3 feet) wide, the Lemishami sand dam holds about 50,000 cubic metres (1.7 million square feet) of water, which experts say should sustain five villages for three months.

“Storing water together with the sand reduces the rate of the evaporation, enabling the water to last longer than it would have in an open area,” Njeru explained.

The sand also helps clean the water when it reaches the dam. “Sand acts like activated carbon in a normal water supply,” Njeru said. “The water comes down as muddy but it’s filtered as it passes through the sand.”

Lekula is grateful that the sand dam has brought reliable water to his community, their livestock and the area’s wildlife. But he remembers struggling to find water and fears that even the sand dam will run dry if it does not rain soon.

Njeru says the pastoralist shouldn’t worry, because the dam relies on rain from the wet mountains, not the dry area around Lemishami village.

“As long as the rainwater is flowing into the rivers from upstream, the sand dams will always have water,” he said.

This article is published in collaboration with Trust.org (Thompson Reuters Foundation) . Publication does not imply endorsement of views by the World Economic Forum.

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Author: Sophie Mbugua is a journalist based in Nairobi, Kenya. 

Image: Boys from Nalepo Primary School carry water collected in plastic bottles and cans. REUTERS/Noor Khamis.