Improving safety and resilience for erosion-affected communities in the Democratic Republic of the Congo

Areas across the Democratic Republic of the Congo (DRC) suffer from erosion as the result of heavy rain falling on unconsolidated soil. Towards the end of 2020, the UN asked WSP to find solutions at eight sites where erosion gullies were getting worse, creating dangerous situations for nearby communities. At one site, a gulley had consumed the main N40 road near the airport – leading local people to cut the perimeter fence and walk on to the airfield to get past the obstruction.

Kananga is situated in the Kasai-Central Province within the DRC. It is the fourth most populated area in the country with an approximate population of 1.45 million. The area has its dry season between June and July with a lengthy wet season for the rest of the year. 

With the airport site prioritised for emergency works, we surveyed all eight locations – carrying out geotechnical and hydrological studies. Other gullies in the area had been rehabilitated by local contractors using concrete. We decided against this option because of the time required for fixing reinforcing bars and allowing concrete to cure, as well as the availability of skilled workers required to achieve a good-quality result. 

Instead, we opted to use gabion baskets and rock mattresses to line channels through the gullies. We reshaped the ground to ensure there were no steep gradients, using vegetation and geotextiles on the surrounding slopes to prevent further soil erosion. At the end of the channels, we used more gabions and PVC-coated mesh to form dissipation basins for water to flow into safely.

Sourcing materials was a challenge: mesh and other materials had to be imported from countries such as Botswana and South Africa. However, we were able to use locally sourced stone to fill the gabions – with people from the community employed to sort pieces of the correct size from local quarries. Before construction begins, we will run a two-week workshop with the contractor focusing on the quality of work required and the technique for building the gabions.

With the design for the erosion gullies now completed, our team hopes construction will start this year. This won’t mark the end of the challenge, though, as the gullies will remain susceptible to further erosion from heavy rain during construction, meaning that careful monitoring will be required to keep workers safe. Once construction is complete, the restored gullies will safeguard local communities from the impact of further erosion.