River Catchments Stabilisation

Back to Conserving Terrestrial Ecosystems

Most of the rivers that flow through Malilangwe originate beyond the boundaries of the reserve. As a result, the health of these river systems depends not only on conservation efforts within Malilangwe, but also on land-use practices in the surrounding communal areas.

Why Restore River Catchments?

Over the past three decades, large areas of natural vegetation have been cleared for agriculture in the Chitsa, Chizvirizvi, Fair Range and Chipimbi resettlement areas. In many places, cultivation has extended across natural drainage lines, increasing surface runoff and accelerating soil erosion. The effects of this degradation are now being felt downstream within the reserve.

Excessive runoff from surrounding catchments is causing widespread erosion and flooding, threatening important habitats and ecological processes. The dambo grasslands associated with the Chiloveka, Benzi and Mahande Rivers—key grazing areas for white rhinoceros and other wildlife—are being damaged by expanding rills and gullies that drain and dry out these wetlands. At the same time, thousands of tonnes of sediment are washed into the Malilangwe Reservoir each year. This sedimentation may contribute to prolonged blooms of toxic algae, creating risks for both wildlife and people.

Without intervention, these impacts are likely to worsen, making catchment restoration a critical conservation priority.

Using Vetiver Grass to Combat Erosion

One of the most effective and sustainable tools available for controlling erosion is vetiver grass (Chrysopogon zizanioides). Used extensively in tropical and subtropical regions around the world, vetiver provides a natural, low-cost solution for stabilising agricultural landscapes and reducing runoff.

Unlike earth banks and other engineered structures that attempt to block water flow, vetiver hedges act as living, porous barriers. They slow the movement of water across the landscape, allowing sediment to settle while still permitting runoff to pass through. This makes them less vulnerable to failure during heavy rainfall events.

A vetiver hedge consists of dense, upright clumps of grass with an exceptionally deep and robust root system. Within the first year after planting, roots can extend two to three metres into the soil, helping to anchor slopes and strengthen vulnerable ground. As runoff slows behind the hedge, sediment gradually accumulates on the upslope side, creating natural terraces that further reduce erosion and improve water infiltration over time. Importantly, the cultivars used for erosion control are sterile and non-invasive, ensuring they do not spread into natural ecosystems.

Malilangwe’s Use of Vetiver

Malilangwe and its partners have established more than 50 kilometres of vetiver hedge along a contour lines at approximately 1 metre elevation intervals in the Chitsa Communal Land as the first phase of a long-term programme to restore the Chiloveka River catchment.  The broader goal is to systematically stabilise agricultural fields throughout the river catchments surrounding the reserve, working progressively around Malilangwe’s boundary and addressing the most vulnerable areas first.

The performance of the vetiver system is monitored annually, and our latest field observations have produced encouraging results. Although approximately 20% of the hedges were lost during 2024 as a result of heavy grazing pressure and exceptionally dry conditions, the majority have remained intact and continue to function effectively. Preliminary measurements indicate that the hedges are successfully slowing runoff and trapping sediment within active gullies; measurements taken in 2026 show that, on average, approximately 10 centimetres of soil has accumulated behind the hedges, with some locations recording up to 30 centimetres. These deposits grow as additional soil is captured during successive rainfall seasons.

Monitoring is ongoing, and the results will form the basis of a scientific publication evaluating the effectiveness of vetiver as a catchment restoration tool. By working beyond the reserve’s boundaries and partnering with neighbouring communities, Malilangwe is addressing environmental challenges at their source and helping to secure healthier catchments for both people and wildlife.