Quantifying the direct impacts and risks of large urban gullies in the Democratic Republic of Congo

peer reviewedLarge urban gullies (UGs) cause major infrastructural damages and often claim casualties in many tropical cities of the Global South. Nonetheless, our insight into this new type of geo-hydrological hazard remains limited to some case studies and the overall impacts remain poorly quantified. Here, we aim to bridge this gap by making a first assessment of the number of persons affected by urban gullies at the scale of the Democratic Republic of Congo (DRC). We used Google Earth imagery in combination with local news sources and earlier research to identify 25 cities in DRC where UG occur at a significant scale (at least ten UGs). This list is likely exhaustive. Next, for each of these cities, we used Google Earth imagery and other high resolution satellite images to map all visible UG, evaluate their expansion rate and inventorize detectable damages to houses and roads. In total, >2,000 UGs were mapped across the 25 affected cities. Overall, the problem of UGs in DRC is especially acute in the cities of Kinshasa, Mbujimayi, Kikwit, Tshikapa and Kananga. Over 90% of these gullies were active during the observation period (typically from 2002 to 2020). Next, we assessed the total number of persons that are directly affected, as well as the number of persons currently at risk. Using available high resolution population density data and taking into account the current position of urban gullies, we estimate that around 68,700 people were directly displaced due the formation and expansion of UGs over the last 15 years. This corresponds to an average of ca. 4,300 persons per year. By considering the population that lives in the direct vicinity (<100 m) of an UG, we estimate that around 1.3 million people in D.R. Congo are currently at risk and/or experience significant impacts because of UGs (e.g. reduced land value, problems with trafficability, stress). This number has doubled over the past 10 years (2010-2020) and will likely continue to increase as a result of urban expansion and climate change. Overall, this research shows that urban gullying is a very serious problem in the Democratic Republic of Congo, but likely also in many other countries of the Global South. More research is needed to better understand this processes and, ultimately, to prevent and mitigate its impacts. The results and the database of this study provide an important step towards this

Strategies Des Resiliences Urbaines Face A La Production Des Services De Base En Eau Potable, Electricite Et Assainissement Dans Les Quartiers Batumona A Kimbanseke Et Talangay A N’sele/Rd.Congo

La réflexion sur la problématique des résiliences urbaines liées à l’approvisionnement en eau potable, électricité et assainissement dans les quartiers BATUMONA à Kimbanseke et TALANGAY à N’sele est basée sur le fait que la périurbanisation rapide des pays en voie de développement est liée à une consommation excessive de la ressource foncière pour l’habitat BEAUGARD & HALLEUX, (2015) ; ANGEL & ali,(2016).Le concept de résilience urbaine paraît savant et, est  très mal connu par les sujets enquêtés. Cette situation se justifie probablement par le niveau très bas d’instruction des sujets enquêtés dû à l’insuffisance de moyens financiers, au faible revenu (salaires toxiques), dont le dénominateur commun est la précarité de conditions de vie de la population et leurs conséquences néfastes TREFON, (2O11), MABIN, BUTCHER & BLOCH, (2013) ; ANGEL & ali, (2016). Il s’agit là, d’une conséquence de l’urbanisation rapide et de la répulsion du centre-ville, en raison de la forte pression foncière, de coûts élevés de la vie pour les ménages à faible revenu à Kinshasa en général et en particulier dans l’aire d’étude à Kinshasa-Est. Il y a lieu de faire également référence à l’inexistence de politique de planification urbaine WATSON, (2009), BINZANGI & FALANKA, (2014).Globalement, l’aire d’étude fait face à une croissance extraordinaire de son contenant et doit être gérée rationnellement, pour assurer sa durabilité environnementale. Malheureusement, l’état actuel des sites étudiés est confronté à des précarités à outrance des conditions de vie urbaine. Cette précarité a engendré la pauvreté urbaine de masse qui a ouvert la voie aux vulnérabilités des conditions de vie urbaine et celles des habitants. Face à la crise économique persistante, les sujets enquêtés ont développé d’autres stratégies de survies appelées «  résiliences urbaines ». Les sujets enquêtés éprouvent de difficultés énormes de tous ordres qui constituent des conditions majeures de viabilité et vivabilité environnementales urbaines. Ces difficultés constituent des facteurs limitant de possibilités de la plupart des ménages enquêtés dans l’aire d’étude, à prévenir les risques environnementaux et leurs aléas sur les vies humaines. A ce titre, les difficultés précitées soustraient l’aire d’étude des exigences de durabilité environnementale urbaine

The origin and control of mega-gullies in Kinshasa (D.R. Congo)

This study aims to investigate the relation between mega-gully (> 5 m width) distribution and urbanization in Kinshasa (D.R. Congo), to establish what governs mega-gully location and plan form and to illustrate the concepts behind mega-gully treatment. For this purpose, the diachronic distribution of mega-gullies has been mapped in Kinshasa. All mega-gullies have been reported in ArcGis 9.3 on the orthorectified SPOT 2007 image. A newly elaborated DEM enables the mega-gullies to be placed in their natural topographical context. The GIS inventory on the SPOT 2006/2007 anaglyph indicates the mega-gully situation in the high town of Kinshasa 5 years ago: 308 mega-gullies with a cumulated length of 94.7 km, a mean drainage density of 0.4 km km− 2 and an average width and depth of 17 m and 6 m respectively. On the WorldView 1 (WV1) coverage, the number of mega-gullies has more than doubled between 2007 and 2010 from 160 to 334. The study shows that mega-gullies only develop within the urbanized perimeter of the high town of Kinshasa and only 5 to 10 years after incipient urbanization. The study also indicates that neither the location, the plan form or the downslope course of mega-gullies in Kinshasa are controlled by the natural topography. Forty-three point eight percent of the mega-gullies in Kinshasa are ‘axial’, occupying urban structures which function as artificial runoff drainage lines: roads, tarred or not, with or without side-road trenches, gutters in all forms and materials from concrete to sand, also foot paths and further all artificial runoff drainage lines. The study reveals that every mega-gully is directly or indirectly induced by human activities, but that every gully also finally ends to grow after an initial phase of sudden development. Mega-gully treatment follows two principles, often combined. The first is to stop the alimentation of the mega-gully head with water. The second includes a complete stabilization of the channel and walls inside the mega-gully. This study emphasizes that gully prevention can basically be achieved by control of the runoff discharges in the artificial stream network, as well as beside the roads

Démarrage et longueur de la saison de pluies dans la région de Kinshasa et risques induits

peer reviewedLa détermination et la prévision du démarrage de la saison de pluies sont des questions cruciales à travers la RDC en général et en particulier dans l’hinterland de la ville de Kinshasa étant donné que l’agriculture y est pluviale. Elles permettent de déterminer le calendrier agricole, particulièrement le semis, et influence le rendement. La question qui se pose toujours est celle de savoir s’il y a un changement climatique dans la région de Kinshasa qui se traduirait par la variation de la saison des pluies de 1961 à 2010. Et si c’est le cas, quels en sont les impacts sur l’activité agricole et autres ? Cette étude mène une analyse de la variabilité interannuelle et décennale de la saison des pluies à partir de deux séries chronologiques dans la région de Kinshasa. [...

Contribution of Remote Sensing in the Estimation of the Populations Living in Areas with Risk of Gully Erosion in Kinshasa (DR Congo). Case of Selembao Township

info:eu-repo/semantics/publishe

Assessing urban gully occurrence at the scale of Africa

peer reviewedThe rapid and typically uncontrolled growth of many African cities leads to a plethora of problems and challenges. One of these is the formation and expansion of large urban gullies (UGs) in many (sub)tropical cities. UGs typically lead to the destruction of houses and other infrastructures, displace large numbers of people and often claim casualties. As the formation of such gullies is strongly linked to land use and rainfall intensity, the problems associated with UGs are likely to aggravate in the near future as a result of continued urban expansion and climate change. However, this newly emerging geo-hydrological hazard hitherto received very little research attention. Several studies report on the occurrence and impacts of UGs. Yet, they remain limited to specific local case studies. A clear understanding of the patterns, impacts and driving factors of UGs at larger scales is currently lacking. To address this gap, we aim to better understand the spatial patterns and UG occurrence at the scale of Africa.In order to achieve this, we are documenting cases of UG occurrence across Africa through the visual analysis of very high spatial resolution satellite imagery. This mapping already allowed us to identify more than 3,500 UGs in 11 countries (mainly across D.R. Congo, Angola, Republic of the Congo, Nigeria and Mozambique). Using on this database, we develop a logistic regression model that accurately simulates the likelihood that UGs occur within (peri-)urban areas across Africa. Our preliminary results show that a combination of rainfall characteristics, topography, soil type and variables describing the land use/urban context can already robustly explain why certain cities are extremely susceptible to the problem and others not. Overall, our dataset and model are first crucial steps to better understand the current and future risks of UGs across Africa

Effectiveness of measures aiming to stabilize urban gullies in tropical cities: Results from field surveys across D.R. Congo

peer reviewedUrban gullies are a rapidly growing concern in many tropical cities of the Global South. Various measures are already implemented for their stabilization. However, an overview of these measures and their overall effectiveness is currently lacking. We aim at addressing this gap by documenting existing initiatives to stabilize urban gullies in D.R. Congo and assessing their overall effectiveness. To this end we conducted extensive field campaigns in Kinshasa, Kikwit and Bukavu and combined our terrain observations with data on gully expansion rates (derived from series of satellite imagery). In total, we characterized present and past stabilization initiatives for 398 urban gullies. For 69 of these gullies, the effect of a specific measure on gully expansion rates could be estimated. Results show that for the large majority of gullies, various measures have been implemented. Yet, these are mainly ad-hoc measures installed by the affected population. More structural measures based on larger engineering works were observed for only 20–30% of gullies. The huge efforts invested in the installation of measures strongly contrast with their overall low impact. Among all strategies, only the deviation of runoff resulted in significantly lower expansion rates after installation. The numerous initiatives that rely on the sparse means available seem to have limited effects. This does not imply, however, that they are completely ineffective and should be abandoned. Based on our findings, we formulate recommendations for further research on how to effectively prevent and stabilize urban gullies, taking into account the difficult environmental and socio-economic context