By Annelieke Duker,1 Eyasu Yazew Hago,2 Stephen Hussey,3 Mieke Hulshof,4 Ralph Lasage,5 Moses Mwangi 6 and Pieter van der Zaag 1,7 *

  1. IHE Delft, The Netherlands
  2. Mekelle University, Ethiopia
  3. Dabane Water Workshops, Bulawayo, Zimbabwe
  4. Acacia Water, Gouda, The Netherlands
  5. IVM, VU Amsterdam, The Netherlands
  6. South Eastern Kenya University, Kitui, Kenya
  7. TU Delft, The Netherlands

* Corresponding author: p.vanderzaag@un-ihe.org

Regions with below 500 mm of annual rainfall, such as the (semi-)arid lands (see map below), have limited socio-economic development options. This is mainly due to lack of water. However, the river beds of many seasonal (also known as ephemeral) rivers and streams that crisscross the lands form shallow groundwater reservoirs, which are recharged every time the rivers flow. Communities draw water during the dry season using scoop holes, hand pumps, dug wells and other simple means. This nature-based water storage has a distributed storage potential that is currently under-utilised in many regions of Africa, in particular for productive purposes such as agriculture (Lasage et al., 2008; Love et al., 2011).

Aridity zones in Africa. Almost two-third of the continent is covered by ASALs where sand rivers are common and water shortages inhibit food production

An example of the large potential of water from the river bed of seasonal rivers are the Shashe, Tuli and Sashane rivers in arid southern Zimbabwe. They contained sufficient water for irrigation even after the extremely dry 2015-2016 rainy season affected by El Nino. Yet it remains a major challenge for people to access this water and use it for productive purposes (Critchley and di Prima, 2012). There is an urgent need for technologies that are tailored to the specific conditions, while being robust and affordable.

Here we make a case for low-cost low-lift solar powered pumps that are scaled to draw water from the river beds for irrigation purposes, as is done in the Sashane irrigation gardens in southern Zimbabwe. The technology allows farmers to access water for supplementary irrigation, and mitigate the risk of sub-optimal rainfall during the rainy season, which is highly and increasingly unpredictable as a result of climate change. Moreover, it enables farmers to extend the cropping season into the dry period and harvest a second (cash or staple) crop.

Some farmers currently use conventional motor pumps, but these often have too high a discharge, and wells are pumped dry. Also fuel costs, the logistics of getting the fuel to site and maintenance requirements limit their usefulness, while carbon emissions and oil leaks have negative environmental impacts. Manual irrigation pumps on the other hand do not provide sufficient water for irrigation at scale.

A schematic of a sand dam (source: MetaMeta)

Solar pumps for water abstraction from river beds of seasonal rivers could make more water available to an increasing number of farmers in a sustainable manner. With water use increasing, a so-called sand dam (i.e. wall across the river in the sand) could be built that would gradually increase the thickness of the sediment layer in the river (through heightening the dam in stages), increasing the volume of water stored and making more water available for use.

The sustainable use of this nature-based storage can be fostered through the creation of a community monitoring device that ensures that all water users have correct and symmetrical information on actual groundwater levels – a critical element in sustainably managing such a common pool resource (Ostrom, 2008).

Improving access to the shallow groundwater of sand rivers, while ensuring adequate operation and management, is a ‘no-regret’ intervention. With limited financial investments and no environmental costs it provides real opportunities to boost production. It climate-proofs food supply chains in arid and semi-arid Africa through access to nature-based water storage that is currently largely unused.

Considering that 1/5 Africa is covered by arid and semi-arid lands, and assuming that 1% of these lands are suitable for agriculture and suitably located near a sand river, would mean that sand rivers can provide nature based water storage for 6 million ha of irrigation in Africa. This is significant compared with the 13 million ha irrigated area that existed in 2010 (You et al., 2010), and more so because located in areas where access to water is needed most!

References

Critchley, W., di Prima, S., 2012. Water Harvesting Technologies revisited. Deliverable 2.1 of the FP7 project Water Harvesting Technologies: Potentials for Innovations, Improvements and Upscaling in Sub­Saharan Africa. Vrije Universiteit, Amsterdam, The Netherlands, 113pp.

Lasage, R., J. Aerts, G.-C.M. Mutiso and A. de Vries, A. 2008. Potential for community based adaptation to droughts: sand dams in Kitui, Kenya. Physics and Chemistry of the Earth 33: 67-73.

Love, D., P. van der Zaag. S. Uhlenbrook and R. Owen, 2011. A water balance modelling approach to optimising the use of water resources in ephemeral sand rivers. River Research and Applications 27 (7): 908–925

Ostrom, E., 2008. The challenge of common-pool resources. Environment: Science and Policy for Sustainable Development, 50(4), pp.8-21.

You, L., C. Ringler, G.C. Nelson, U. Wood-Sichra, R.D. Robertson, S. Wood, Z. Guo, T. Zhu and Y.Sun, 2010. What is the irrigation potential for Africa? A combined biophysical and socioeconomic approach. IFPRI Discussion Paper. IFPRI, Washington DC