Stabilisation of urban gullies by managing rainwater at parcel scale

Abstract

Urban gullies (UGs) are an increasingly urgent concern in many cities of the Global South. Rapid and largely unplanned urban expansion, combined with inadequate drainage infrastructure, erodible soils, and intense rainfall, have led to the formation of thousands of large UGs —often several tens of meters wide and deep and extending over hundreds of meters— in cities across the Democratic Republic of the Congo. These gullies cause loss of life, destroy housing and critical infrastructure, and further exacerbate the vulnerability of already marginalized populations. The situation is particularly severe in Kinshasa, where more than 800 UGs have already been recorded, threatening over one million people.A wide range of initiatives has been implemented to stop UG expansion. These include large-scale engineering interventions led by the state or non-governmental organizations, such as concrete reinforcement of gully heads and canalizing the gully channel. However, many measures are expensive and/or often fail.Nevertheless, emerging evidence highlights promising strategies for urban gully prevention and control. A key principle is to prevent rainwater from leaving individual parcels by installing water retention structures, as the accumulation of runoff along roads is a primary driver of gully initiation and expansion. A critical requirement for success is that a majority of households actively participate in such initiatives. Improving risk awareness and creating synergies between UG control and water accessibility will therefore be crucial to achieving this.Here we aim to demonstrate the effectiveness of such a strategy. For this purpose, we installed water retention structures in a representative catchment in Kinshasa affected by UGs. This is done in close collaboration with local stakeholders. By monitoring and studying participation rates as well as the resulting hydrological effects (e.g., through the involvement of local students), we will develop actionable guidelines to this growing problem in Kinshasa and elsewhere, thereby enhancing both urban resilience and water security in vulnerable neighborhoods.