Environment & Climate
Sand dams boost food security in rural Zim
IN hot and arid parts of the country, this method of water abstraction from sandy riverbeds is helping villagers to grow their vegetable gardens all year round.
It is mid-afternoon in Zhokwe village in Matabeleland South province, Zimbabwe, and heat is shimmering in the air. It may be autumn, but like other parts of Gwanda district, this southern area is hot and arid. In the dry, sand-filled Senkezane riverbed, Freeman Ndlovu (17) is scooping water from a shallow well that he has made in the riverbed.
He is filling containers that will be loaded on a donkey cart nearby. Ndlovu undertakes the 20 kilometres return trip from his village every other day to fetch water for drinking and domestic use from the river, the closest source of water for him and his family.
About 100 metres from where he is fetching water, a wall has been built across the river to make a sand dam. Around 30 residents from nearby villages provided labour and materials, while the local branch of Practical Action, a non-governmental organisation based in the United Kingdom, gave funding for cement and other costs.
It also funded the construction of an abstraction point with a submersible pump and solar panels. This system draws water to supply two tanks used to irrigate the nearby Ukuphila cooperative garden.
Open sand wells in riverbeds have been used as water sources for centuries throughout the world, but sand dams have improved the concept. Vusa Moyo, a field officer for Practical Action, says they are ideal in areas with sand rivers.
“Gwanda is one of the driest areas in the country, but dry as it is, it has rivers that are filled with sand and that gives us an opportunity to construct sand dams. In an ordinary situation a river has sand, but the depth of the sand is such that the amount of water stored under the sand may not last long, so, therein comes the concept of a sand dam.
“You dam the river by building a wall across it, thereby stopping the sand from flowing down the river along with the rainwater on the occasions that it rains. In doing so, you build up a pile of sand. The higher the level of the sand, the more water you can store under it. Initially the sand dam stores water on the surface, then gradually the sand pile builds up until it is level with the dam wall, and at that level the sand dam is mature,” he said.
On a small scale, a sand dam is considered suitable for rural areas because its construction is simple and the materials are cheap and readily available. Maintenance is easy and minimal, and because sand is a good filter the water needs only normal chlorination.
However, there is the risk that the water table drops too low for water to be abstracted because of poor rainfall, or when water is excessively drawn or pumped. Thembo Moyo, a member of the Ukuphila cooperative who led the construction of the dam, says it is a welcome development.
“Sand dams are very useful. We are now able to plant more vegetables throughout the year as we get adequate water for our garden,” said Moyo.
But some villagers who don’t understand the concept of a sand dam have pulled out of the project. Headman Veli Ndlovu says some villagers, including him, had expected that there would be abundant water upstream, above the wall, to allow for the establishment of another garden. This would have benefitted villagers on the other side of the river.
He blames the failure of the sand dam to store surface water on contractors failing to build the wall deeper into the riverbed, which means some of the water is lost through seepage underneath the wall.
In Nhwali, also in the south of Gwanda, villagers recently completed the construction of a wall for a sand dam in the Nhwali River. A large pool of water with quite a number of fish has formed as a result of the damming of the river, and residents catch them for their own consumption as well as to sell.
Melusi Sebatha (31), who helped with the construction of the wall, says besides the bonus of being a source of fish, the dam has brought relief to the villagers as many of them used to travel long distances with their animals to find water.
“Many villagers would travel distances of over 10km one way to find water for their cattle and donkeys, but now they all come here as it is close,” said Sebatha. Isaac Siziba, chairperson of the Nhwali project, says the area experiences perennial water problems and the villagers have always wanted to find a permanent solution.
“Villagers often clashed over the scarce water from the river and such conflict is obviously not good. Although we have a dam not far from here, it is rather small and it usually runs dry quickly.
“We have always wanted to find a way to fix the problem of water shortage, but money was always a hindrance. So when the people of Practical Action came and told us that they could work with us to help resolve this, we were very quick to welcome them,” said Siziba.
A 2016 report titled Zimbabwe’s Irrigation Potential: Management Models for Irrigation Schemes and a Policy Framework for Efficient Irrigated Agriculture and commissioned by the United States Agency for International Development, said the country’s rainy season had become characterised by “late starts, early cutoffs, inadequate amounts and poor rainfall distribution throughout the season”.
The report also highlighted that Zimbabwe had become more prone to droughts and a major drought happened every three years. It said about 80% of the country “is classified as marginal or unsuitable for intensive crop production, yet these regions encompass large arable land masses”.
Irrigation schemes, at various scales, could mitigate against any shortfalls and result in successful crop production, it added. Felix Chari, an economics expert and independent commentator, says while such irrigation schemes can help smallholder farmers to avert hunger, they sometimes fail for a number of reasons.
“There is a need to make sure that such investments remain sustainable, especially in the smallholder sector, as it often faces problems of lack of adequate training, low productivity and poor market access coupled with high transport costs, all of which at times result in the failure of such initiatives,” said Chari. — Newframe.
*About the writer: Kudzanai Musengi is a Zimbabwean journalist.