[en] Urban gullies (UGs) are a growing concern in many tropical cities of the Global South. Addressing this new geo-hydrological hazard requires good insights into the rates and controlling factors of this process. Therefore, we investigate the expansion rates of a representative sample of UGs in Kinshasa (n = 17) and Bukavu (n = 29), two contrasting cities in D.R. Congo. We reconstruct long-term (10–17 years) expansion rates, making a distinction between headcut retreat and sidewall widening, and analyse the environmental factors potentially explaining these rates. Total expansion rates varying between 12.6 and 863 m2y-1. Most of this expansion happens through sidewall widening. In Kinshasa, which is mainly characterized by sandy soils, contrasts in expansion rates are mainly correlated to the characteristics of the upslope drainage area of the gullies. Especially the road density and a hypothetical runoff index (combining drainage area, land use and soil characteristics) explain a significant part of the observed variation. In Bukavu, such trends are less apparent. This is likely because the clayey nature of the soils provides more resistance against gullying, resulting in overall smaller and less actives UGs. Furthermore, the already low infiltration rates of these soils probably make the relative impact of urbanization on runoff production smaller. Our results also indicate that UGs located in recent landslides have higher gully expansion rates. The mechanisms behind remain poorly understood. Overall, our work opens promising perspectives to model and predict gully expansion rates in urban settings but may also guide efforts aiming to stabilize UGs.
Disciplines :
Earth sciences & physical geography
Author, co-author :
Ilombe Mawe, Guy ; Université de Liège - ULiège > Sphères ; Université de Liège - ULiège > Faculté des Sciences > Doct. scienc. (géographie) ; Université Officielle de Bukavu > Géologie ; Université de Kinshasa > Géosciences
Lutete Landu, Eric ; Université de Liège - ULiège > Sphères ; Université de Kinshasa > Gestion de ressources naturelles
Imwangana, Fils Makanzu; Université de Kinshasa, Geoscience Department, Kinshasa, Congo ; Geological and Mining Research Center, Geomorphology and Remote Sensing Laboratory, Kinshasa, Congo
Hubert, Aurelia ; Université de Liège - ULiège > Département de géographie > Géomorphologie et Géologie du Quaternaire
Dille, Antoine; Royal Museum for Central Africa, Department of Earth Sciences, Tervuren, Belgium
Bielders, Charles L.; Université Catholique de Louvain, Earth and Life Institute - Environnemental Sciences, Louvain-la-Neuve, Belgium
Poesen, Jean; KU Leuven, Department of Earth and Environmental Sciences, Leuven, Belgium ; Maria-Curie Sklodowska University, Institute of Earth and Environmental Sciences, Lublin, Poland
Dewitte, Olivier; Royal Museum for Central Africa, Department of Earth Sciences, Tervuren, Belgium
Vanmaercke, Matthias ; Université de Liège - ULiège > Département de géographie > Géomorphologie et Géologie du Quaternaire ; KU Leuven - Katholieke Universiteit Leuven [BE] > Géographie
Language :
English
Title :
What controls the expansion of urban gullies in tropical environments? Lessons learned from contrasting cities in D.R. Congo
ARES - Académie de Recherche et d'Enseignement Supérieur
Funding text :
This research was funded by the Belgian ARES-PRD project PREMITURG (PREvention and MITigation of Urban Gullies). Special thanks to all students and colleagues who helped us during the field data collection, including Patrick Nlandu Wandela, Cinamula Mitima Justin, Chibeye Espoir, Bwirhonde Peke, Lubunga Ndobano as well as to the numerous local stakeholders who provided further information on the gullies and the Civil protection of South Kivu. We further wish to thank the anonymous reviewers for their constructive feedback.
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