Urban gully erosion in sub‐Saharan Africa: A case study from Uganda

Abstract

The study examined gully erosion in Koboko, North‐western Uganda, initially a war refugee camp, which progressively turned into a permanent rural town. A repeatable, low‐cost methodology to quantify gully properties in data‐scarce, resource‐limited urban contexts is developed, which integrates collection of existing hydrological, land use data, topographic surveys, hydrological and hydraulic modelling, and interviews to local inhabitants and stakeholders. Four main gullies have developed in the last 10–15 years along the eastern, hillside of Koboko, with width‐to‐depth ratios not exceeding 3 and maximum scour depths of 9 m. Their length ranges between 270 and 460 m in the most densely populated area and is mostly unstable, especially for slopes exceeding 3%. Causes of the gullies include urban road development, changes in urban land cover to impervious surfaces, and inadequate planning of the urban drainage system. The gullies hamper the safety of people and buildings and increase health risks in an already vulnerable community. Slope–area and slope–road length thresholds suggest Koboko to be less susceptible to gullies compared to other reported urban contexts and support the anthropogenic origin of the observed gullies. The analysis allowed to design mitigation measures that still self‐sustain after 3 years of implementation. Results upscaled at country level can be used to predict which other urban centres in Uganda may be susceptible to gullying. Gullying in rapidly developing urban areas in sub‐Saharan Africa clearly show the co‐evolution of a social and a geomorphic system, which should be accounted for in urban planning to avoid adverse societal effects.

GUEST EDITORIAL—SPECIAL ISSUE: Mapping and modelling soil erosion to address societal challenges in a changing world

“…Hewett, Simpson, and Wainwright (2018) developed a tool for communicating and visualizing erosion risk to infrastructure in Britain by combining hydrological, geomorphological, and participatory action research principles. Zolezzi, Bezzi, Spada, and Bozzarelli (2018) developed a low‐cost, repeatable methodology to quantify gully properties and to suggest appropriate mitigation measures in Uganda, combining observations with stakeholder interviews. They further up‐scaled their method to provide a country‐scale map of urban areas under the threat of urban gullying and described drivers of evolution of gullies in a sociogeomorphic system.…”

Urban Expansion and Erosion Processes in an Area of Environmental Protection in Nova Lima, Minas Gerais State, Brazil

“…Accelerated soil erosion could even become more severe in urban areas with high population growth and high rainfall intensity. Soil erosion has assumed destructive dimensions in many parts of the world, especially in the urban environment Rotta and Zuquette, 2014;Guerra et al, 2018;Zolezzi et al, 2018). In tropical regions, water erosion is prevalent.…”

Rapid assessment of abrupt urban mega-gully and landslide events with structure-from-motion photogrammetric techniques validates link to water resources infrastructure failures in an urban periphery

“…Earth surface hazards that occur abruptly (within a few hours) are of particular concern from a safety and damage perspective because there is little time for warnings and other emergency response measures. The literature mainly characterizes the formation of mega-gullies as a result of landscape changes such as deforestation, road construction, and urban development (Archibold et al, 2003;Adediji et al, 2013;Makanzu Imwangana et al, 2015;Zolezzi et al, 2018), although there have been studies documenting abrupt megagully formation in tropical environments (e.g., Moeyersons et al, 2015). In both agricultural and urban areas, gully formation is associated with rain-generated runoff (Valentin et al, 2005).…”