Over the decades, rapid urbanization has reshaped the face of many African cities, attracting millions of people to rapidly expanding centers. But beneath this apparent dynamic, another movement, more discreet and more worrying, works the soil in depth. In the Democratic Republic of Congo, a long-ignored geomorphological phenomenon now threatens the balance of several metropolises. These are the urban ravines which, slowly but surely, are eating away at the foundations of neighborhoods and endangering the lives of millions of inhabitants.
A study led by the Catholic University of Louvain has mapped the entire phenomenon on a country scale for the first time. It identified 2,922 active urban gullies in 26 Congolese cities. Researchers have shown that these training courses, invisible on official plans, already affect more than half of the urban centers studied. In Kinshasa, 868 ravines wind through neighborhoods, often on the immediate edge of homes.
Unlike landslides or floods, these gullies do not strike in an instant. They expand slowly but continuously, hollowing out the city from the inside. Between 2004 and 2023, they caused the displacement of around 118,600 people. Since 2020, the pace has accelerated, forcing more than 12,000 residents per year to abandon their homes, according to the study published in Nature.
Urban ravines in the DRC reveal systemic fragility
Under the influence of tropical rains, sandy soils and steep slopes form a terrain conducive to erosion. But in the city, these natural characteristics are not enough to explain the explosion of the phenomenon. It is human choices that amplify the consequences. Rapid urbanization, the absence of water evacuation networks and the disappearance of plant cover have transformed urban landscapes into hydraulic traps.
In expanding neighborhoods, roads are often built without a soil study or sanitation plan. As a result, they become direct channels for runoff water, which accumulates, hollows, then collapses into gullies. According to data analyzed by KU Leuven researchers, 98% of the identified gullies are connected to the road network, either by running alongside a roadway or by directly receiving its drainage.
The most affected populations live in peripheral areas, often informal, where the authorities are slow to intervene. In these neighborhoods, residents see the cracks widening week after week, without means to stop them. In 2022, around sixty people lost their lives due to these collapses, according to data relayed by New Atlas.
The study conducted by the University of Kinshasa and the Official University of Bukavu also reveals even more worrying data. In 2023, more than 3.2 million people lived in areas at direct risk of gully expansion. Among them, more than half a million already live in areas where the ground could give way at any time.
What science suggests to stop the spiral of destruction
Stabilizing a gully is expensive. Sometimes more than a million dollars per site, according to estimates from the African Geological Research Center. Faced with these amounts, prevention remains the only possible solution on a large scale. You still need to know where to intervene, and above all how. This is precisely what a more precise mapping of the phenomenon allows today.
By combining topographical data, road density, soil nature and changes in urbanization, the researchers modeled the most vulnerable areas. This approach paves the way for more resilient urban policies. It would make it possible to anticipate risks from the design stage of projects, to install suitable drainage systems, or even to preserve areas of protective vegetation.
However, the integration of urban gullies into disaster risk reduction plans remains marginal. Gina Ziervogel, geographer at the University of Cape Town, emphasizes the importance of engaging with residents of threatened areas. Their observations, their daily experience in the field, can feed into solutions adapted to local realities. She advocates for more inclusive urbanization, where land and water management would no longer be relegated to the background.
In fact, urban ravines act as a revealer. They expose the flaws of rapid and haphazard development models. They also reflect, more broadly, the tensions between demographic growth, urban poverty and political inaction. If nothing is done, the fault line will continue to widen.
