15% of Sub-Saharan Africa

This solution can be applied where sand rivers occur that have a width of at least 50 m, a thickness of the sand layer of at least 3m, with soils adequate for crop cultivation on its banks (which is mostly the case) and where each year at least one flow event occurs. The best evidence of the existence of water in the dry river bed is rich riparian vegetation along these rivers, which is particularly conspicuous during the long dry season.

The sand river alliance is still investigating the full potential, but our current knowledge is that some 15% of Sub-Saharan Africa is crisscrossed by these sand rivers, hosting at least 100 million people in 20 million households. If 5% would live close to large enough sand rivers, and would each cultivate 0.5 ha, then this would amount to an irrigated area of 500,000 hectares! Our solution is scalable, and if these households are successful, some will expand their fields and other households may join in. So the scope is huge!

The yellow parts of Africa have sand rivers that regularly flood

Why is it not used yet

There are two mean reasons why these sand river aquifers are underutilised.

First, sand rivers often occur in areas where the majority are pastoralists, who may be less inclined towards arable agriculture. But this is inevitably going to change if Africa’s population is projected to double in 25 years. More food (and fodder!) will need to be produced as the demand for it will increase accordingly.

Second, knowledge to “read” sand rivers, its potential water sources, and to hand-drill a well-point (an inexpensive and effective technology of accessing this water) is often lacking. Where the sand river aquifers are currently utilised, mostly expensive hand pumps (mainly for domestic use) or simple scoop-holes are used. The latter are cumbersome: they easily cave in, or fall dry as the pump discharge is often too large. This is not so with the 3-5 m deep well-points that the sand river alliance developed.

What is the impact for smallholder farmers?

The impact can be tremendous; our solution has the potential to transform vulnerable households into climate-robust prosperous livelihoods. A family intensively cultivating 0.5 ha with permanent access to irrigation water, can obtain at least two but possibly three harvests per year. Farm income will fluctuate because in particular vegetables have fluctuating market prices, but there will be seasons with high prices and large incomes. Average net profit per 0.5 ha per season may thus fluctuate between $200 and $1,000.

The cost of the initial setup is $500, which includes construction of a well-point ($100), a low-capacity water pump and hosepipes ($350; cheap small fuel pump; a small solar pump costs $500 extra), and vegetable seeds and fertilizers to cultivate the first irrigation crop of about 2,000 m2 ($50). The payback period of the $500 investment will fluctuate with market prices but may be two to four cropping seasons, i.e. within two years. A set-up with a solar-pump is double the price and thus the pay-back period will be longer (but note that the running costs will be lower).

A Sunflower pump in a farm plot along the Limpopo river in Mozambique near Chókwè

Potential for local businesses

Small businesses may be interested in providing services to prospective sand river irrigators: siting and hand-drilling a well-point (the estimated average cost of $100 includes a 30% profit margin), and selling pumps and the usual farm inputs. But also providing advice which crops to grow, which irrigation method to use etc. Both rural hardware stores as shops specialising in farm inputs may therefore be interested


To make our proposed solution work three bottlenecks need to be addressed:

  1. Technical knowledge: local professionals need to “read” sand rivers, and know where the water potential is securest, where to site the well-point and how to hand-drill such a well.
  2. Management of natural resource: the new irrigators will need to be trained in, not only irrigation techniques, but also in observing and monitoring the state of their water resource, through regularly measuring the water level in their well-point. Also, there may be regulatory requirements (water permits), although in many countries small-scale irrigation below 1 ha are allowed. In the beginning there are not likely to be problems of water scarcity, but if the solution becomes popular, the water system may reach its limits. Then the irrigators along a river stretch will need to make institutional arrangements, e.g. at which groundwater level abstractions will need to be decreased. This is not only an issue for the irrigators, but also for the competent local water authority.
  3. Assisting farmers with making the initial investment: once the solution is locally known, it may attract farmers who are able to self-finance the initial investment, e.g. through selling small ruminants, or mobilizing funds from relatives. But many will not be able to raise the required cash. Then solutions have to be found; this can be in the form of bank loans of lease-to-buy arrangements. High interest rates coupled with lack of collateral inhibit poor farmers in large parts of Africa to take out a loan, and lease-to-buy schemes may be too risky for service providers. Some of the risks may have to be covered by local development programmes. Remember that conventional irrigation development is very costly (smallholder irrigation schemes in Africa typically cost as much as US$10,000 to 20,000 per hectare to construct, and most of the time is not recovered from the irrigators). Converting these amounts to individual 2,000 m2 farms, could make a case for regular irrigation development programmes opening a window to support this new type of individual farmer-led irrigation development.

Environmental sustainability and trade-offs

Trade-offs in development always occur. One of the most significant trade-offs will be that if the solution becomes popular, water for irrigation will compete with water for the riparian vegetation. This is a real trade-off as the riparian vegetation provides essential (ecosystem) services to local residents (fire wood, fruits, honey, etc.). Locally, rules will have to be made as to which part of the riparian vegetation should remain protected.

In some sand rivers, sand harvesting occurs, the sand being used in the construction industry. Here issues may arise between irrigators and sand harvesters. The sand river alliance has not (yet) found any evidence, however, that the sand harvesting has indeed affected the volume of water needed for irrigators. Sand harvesting may even offer a development option, whereby local youngsters earn sufficient cash for a well-point and a pump, and thus embark on a farming career!

Upstream-downstream tradeoffs and conflicts are less likely to occur, as the water captured by sand rivers (namely during high flood events) may be considered a nuisance by downstream actors.

A further issue is the impact of over-abstraction. Over abstraction of aquifers generally has a very large time horizon (decades are the norm), leading to immense lowering of groundwater levels, which will take years to restore. This is generally very difficult to address and there are few success stories where aquifers have indeed been restored. In the sand rivers the situation is, however, different! Here the resource will be re-filled near-instantaneously each time a flow event occurs. The system is re-set completely. This fortunate situation allows groups of irrigators to make mistakes and learn, and, together with regular monitoring of the resources, may lead to irrigators adopting arrangements that avoid over-abstraction in subsequent years.

Shashane river, Zimbabwe