Floods with silver linings: Redefining how aquifers replenish in dryland Africa

Sean Furey provides GDI with an insight into the research work that has been carried out across Africa which aims to reap the greatest benefits from the continent’s aquifers
Floods with silver linings:  Redefining how aquifers replenish in dryland Africa Floods with silver linings:  Redefining how aquifers replenish in dryland Africa Floods with silver linings:  Redefining how aquifers replenish in dryland Africa Floods with silver linings:  Redefining how aquifers replenish in dryland Africa Floods with silver linings:  Redefining how aquifers replenish in dryland Africa

In the African drylands, it is the floodwater that is critical for focused recharge along ephemeral river valleys and depressions in the landscape

Drilling for water is only useful if there is good water to be had now and into the future. Since 2013, researchers in the UK-funded programme Unlocking the Potential of Groundwater for the Poor, have been working all over Africa to understand better the continent's aquifers and how their hidden wealth can be used to benefit everyone. Now after years of patient work, exciting results and resources are emerging.

One is that the Africa Groundwater Atlas, curated by the British Geological Survey now has downloadable GIS maps for 38 countries. They are quite large scale, so not detailed enough for individual borehole siting, but a good starting point for identifying where major aquifers are. This supports the wealth of other useful information, in English and French, on the soils, climate and groundwater use in all 52 of Africa's countries.

Meanwhile, a major finding published in the leading science journal Nature in August overturns our understanding of how aquifers are recharged in Africa's drylands. In humid areas of the continent, like the tropical Congo Basin, there is a direct relationship between the rain that falls on an area of rainforest and what percolates down into the soil and rock. Not so in the Savannah's and scrubland of the Sahel, the Horn of Africa and Savannah's of East and Southern Africa.

Analysis of the precious few long groundwater records, combined with local studies in Niger, Ethiopia and Tanzania have shown that here rainwater is only able to percolate into the aquifer in well-defined locations, like ponds and riverbeds, and only after very intense storms. As a hydrogeologist that used to work on the chalk aquifers of South East England, this is almost is a polar opposite. In the UK, nice steady drizzle over the winter may be unpleasant for most people but it is heaven for ducks and water resource managers, because the soil gets saturated and water flows down into cracks and pore-spaces of the underlying rock, then on to providing baseflow for rivers and wetlands.

In the African drylands, it is the floodwater that is critical for focused recharge along ephemeral river valleys and depressions in the landscape. In parallel to this work, research on climate change indicates that in these areas of West and East Africa, rainy seasons are likely to come later and have fewer rain days - but with the same or more volume of rainfall. The inference from this is that when it does rain, it will rain harder - and more of it will find its way into the ground.

So, looking ahead, the role of aquifers in acting as a buffer between periods of flood and drought will become more and more important. This makes managed aquifer recharge look increasingly important to capture floods, both to protect lives and property from damage and to have that water available through the long dry seasons.

One such low-cost opportunity is the way that road drainage is designed so that instead of dumping storm water into already swollen rivers, they divert the water into infiltration ponds and ditches, which farmers can then use when the storm subsides.

Tropical and sub-tropical climates around the world are always challengingly variable, and these extremes look set to expand, but for drillers and water users at least there is this one silver lining.

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