A study involving the University of Pretoria (UP), along with academics from Great Zimbabwe University, University of Cambridge in the UK and Aarhus University in Denmark, has revealed how Great Zimbabwe – the largest city in Southern Africa during the Middle Ages – stored water in dhaka pits to overcome severe water scarcity and drought.

Professor Innocent Pikirayi of UP’s Department of Anthropology, Archaeology and Development Studies was part of the research team that discovered how, more than three centuries ago, the community of Great Zimbabwe maintained a stable water supply in a region known for periodic droughts and which is presently water scarce.

The study was conducted in the context of growing water security challenges, currently among the most significant global challenges for human subsistence and environmental health. It highlights the importance of effective strategies in terms of water management and conservation today.

“Though fragmented, the growing body of environmental and archaeological records, when integrated with historical and ethnographic information, paint a new, convincing portrait of Great Zimbabwe: a landscape where human settlement, land and water were intimately linked for a long time and, to some extent, continue to do so,” says Prof Pikirayi. “Springs and rainwater fed an urban population of ruling elites, religious leaders, craftsmen and merchants. Water storage facilities were strategically placed to maximise supply and demand.” 

While the research presents new research findings concerning the site and resource management strategies that supported it to expose their impact and legacies on the present landscape, the disappearance of Great Zimbabwe may be linked to extreme climate conditions associated with drought and arid conditions during the second millennium AD, usually termed the Little Ice Age (1350 – 1850 AD).

Researchers found that the people of Great Zimbabwe devised climate-smart methods for storing and managing water in an area known for experiencing three different climate patterns: a hot, dry season; a warm, wet season; and a friendly, dry winter. A steady water supply was critical for the growing urban society, which required a reliable and safe water supply for its citizens, livestock and agriculture.

Along with researchers from England, Zimbabwe and Denmark, Prof Pikirayi unravelled the mystery in an article published in the journal Anthropocene. The researchers explained how they used remote sensing methods such as LiDAR (Light Detection and Ranging) mapping (which examines the Earth’s surface) to probe several large depressions in the landscape. Locals described these as dhaka pits, used to store water for the once bustling capital of the Shona kingdom, which had a population of between 10  000 and 18 000 residents before the city was abandoned in the 18^th century.

The never-before-investigated depressions were originally thought to be sources of clay used for building houses. However, according to Prof Pikirayi, the study shows that the pits must also have been used to store and manage water for the city. There are clear signs, he says, that the depressions have been excavated to assist with the collection of surface water and to retain groundwater seeping from the weathered granite bedrock for use during dry periods.

Using LiDAR mapping, researchers located more dhaka pits than were visible to the eye. These pits were located along streams and rills that drained through Great Zimbabwe’s granite landscape, collecting rainwater from the hills or groundwater where it seeped out. Some of the streams passing through the monumental structures at the foot of the Great Zimbabwe Hill and east of the Great Enclosure and Valley Complexes are still active to this day.

This, combined with the location and construction of the depressions, has convinced researchers that the dhaka pits functioned as a creative system to ensure a stable water supply by storing surface and groundwater that could be used beyond the rainy season and during periods of prolonged aridity. The researchers estimate the pits could store at least 18 000 cubic metres of water at any one time.

They hope that exploring dhaka pits in other areas might also reveal how other medieval communities in the region managed and conserved their water resources.

The article ‘Climate-smart harvesting and storing of water: The legacy of dhaka pits at Great Zimbabwe’ by Innocent Pikirayi, Federica Sulas, Bongumenzi Nxumalo, Munyaradzi Elton Sagiya, David Stott, Søren M Kristiansen, Shadreck Chirikure and Tendai Musindo appears in the journal Anthropocene.