Building Riverbeds from Sand Dams

kenya

globally, 500 million smallholder farmers provide up to 80 percent of food consumed in most of the developing world. Most of these farmers rely on rain-fed agriculture. In the drylands, climate change is causing more droughts and floods as well as shorter, more unpredictable rainfall. It is reducing the ability of these farmers to grow food. Eighty-four percent of Kenya is drylands, and the rainfall is increasingly unpredictable, variable, and infrequent. And when it rains, up to 85 percent of the water may be lost as runoff, washing away fertile topsoil and seeds and undercutting food production.

Makueni County in Kenya is typical. An estimated 57 percent of the households lack access to an improved water source. On average, women and children spend four and a half hours a day collecting water. In times of drought, it takes up to 12 hours, which leaves little time to invest in sustainable land management and food production. It is not surprising that Makueni County has a Human Development Index of 0.558 and that 31.1 percent of its children are underweight. But a study conducted in Kenya in 1999 showed that where sand dams were built, households suffering from malnutrition declined from 32 to 0 percent, and incomes significantly increased.

Guided by the principle that poverty alleviation in drylands can only be achieved through sustained investment in soil and water conservation, Excellent Development began working with self-help groups in Makueni in 2002, with the sand dam as the technology of choice. A sand dam is a reinforced concrete wall that is built across a seasonal sandy river. During the rainy season, the river carries silt and sand downstream. The heavy sand accumulates behind the dam, while the light silt washes over the dam. Within one to four rainy seasons, the dam fills with sand. But, up to 40 percent of the volume behind the dam is water, trapped between sand

particles and protected from evaporation. A mature sand dam stores up to 20 million liters of water. The dam is replenished with each rainfall, but even without regular rain, it can supply over 1,000 people with a year-round local water source.

Sand dams differ from other dams. Their spillway is in the middle, not on the side of the dam. This allows the river to continue flowing normally, which reduces soil erosion. In fact, a sand dam is not really a dam— rather, it is the creation of a new and higher riverbed that acts like a sponge to soak and store the water and protects it from evaporation and contamination. The aquifer is replenished from the water stored behind the dam, and the river flow is slowed down, which reduces flooding in the lower catchment. Sand dams are invaluable in areas with seasonal rivers and sandy sediments.

Altogether, 111 self-help groups have constructed 366 dams with help from Excellent Development and its strategic partner, Africa Sand Dam Foundation (ASDF). Sand dams supply water for domestic and agricultural use. Livestock can drink from beneath the dam—often from a specially built trough. The banks of the sand dams also sustain the vegetation, tree planting, and other greening activities around the dams. Best of all, water collection now only takes 30 minutes, saving people between 4 and 11.5 hours a day. Time saved from collecting water creates the opportunity for people to invest in sustainable land use techniques like terracing, tree planting, and reclaiming gullies. This improves soil and water conservation, restoring degraded land and enabling improved food production.

Excellent Development and ASDF provide support for people to achieve food security through climate-smart agriculture. This support involves establishing seed banks with improved drought-resistant seeds, diversifying crops, zero grazing of livestock, composting, using manure and planting cover crops, inter-cropping, setting up vegetable nurseries, and planting trees on farms. Between them, the self-help groups, Excellent Development, and ASDF have built over 1,400 kilometers of terraces and planted 860,487 trees on farms. The impact on the community is visible. A 2013 Normalized Difference Vegetation Index study of Makueni County shows that there is significantly greater vegetation during drought, drought resilience, and recovery from droughts where sand dams have been built.

Excellent Development and Africa Sand Dam Foundation (ASDF) have supported pilot programs of the technology in another six countries. But with only limited funds, scaling up the activities remains a challenge.