The evolution of the Congo- Kalahari Watershed: African mega-geomorphology

Includes bibliographical references.Africa's bimodal elevation, low in the north and west, and high in the south and east, is globally unique. The Congo–Kalahari Watershed represents the transition between low and high Africa. This sub–continental drainage divide separates two of the world's large rivers: the Congo and Zambezi Rivers. This study focuses on the large rivers which form the Congo–Kalahari Watershed. The analysis of their longitudinal profiles, through the use of a geographic information system and remotely sensed imagery and elevation data, provides insights into this drainage divide. The creation of a geodatabase on river knickpoints, featuring geographic and geologic attributes for 18 longitudinal river profiles represented by 194 047 elevation points (19 700 km), identifies a total of 380 knickpoints, 243 of which have heights larger than 5 m. It is possible to assign a probable cause to 354 of all the knickpoints identified in this study, highlighting the underlying geology as a significant control with tectonics playing a secondary role. The following rivers are studied: Chambeshi, Congo, Kalungwishi, Kasai, Kwango, Luapula, Lufira, Lukuga, Lulua, Luvua and Wamba (Congo Basin) and the Cubango, Cuchi, Kabompo, Kafue, Luena and Upper Zambezi Rivers (Kalahari Basin). It is argued that the Congo–Kalahari Watershed is a trimodal feature comprising of a western, central and eastern zone. The smooth central region of the divide is the oldest and has been relatively stable since the break–up of Gondwana. The western region is topographically rougher and has undergone substantial change in the Cenozoic becoming bifurcated by the headwater erosion of the coastal rivers. The eastern watershed is the youngest and topographically roughest, having been substantially modified in the Neogene due to tectonic activity associated with the extension of Western Branch. Due to the extensive modification, this eastern zone should be considered a new feature. The acknowledgment of these three landscapes may lead to the conciliation of various interpretations and suggested causes of Africa's present day continental geomorphology

The urban water metabolism of Cape Town : towards becoming a water sensitive city

CITATION: Atkins, F., Flugel, T. & Hugman, R. 2021. The urban water metabolism of Cape Town : towards becoming a water sensitive city. South African Journal of Science, 117(5/6):8630, doi:10.17159/sajs.2021/8630.The original publication is available at https://sajs.co.zaTo improve its resilience to increasing climatic uncertainty, the City of Cape Town (the City) aims to become a water sensitive city by 2040. To undertake this challenge, a means to measure progress is needed that quantifies the urban water systems at a scale that enables a whole-of-system approach to water management. Using an urban water metabolism framework, we (1) provide a first city-scale quantification of the urban water cycle integrating its natural and anthropogenic flows, and (2) assess alternative water sources (indicated in the New Water Programme) and whether they support the City towards becoming water sensitive. We employ a spatially explicit method with particular consideration to apply this analysis to other African or Global South cities. At the time of study, centralised potable water demand by the City amounted to 325 gigalitres per annum, 99% of which was supplied externally from surface storage, and the remaining ~1% internally from groundwater storage (Atlantis aquifer). Within the City’s boundary, runoff, wastewater effluent and groundwater represent significant internal resources which could, in theory, improve supply efficiency and internalisation as well as hydrological performance. For the practical use of alternative resources throughout the urban landscape, spatially explicit insight is required regarding the seasonality of runoff, local groundwater storage capacity and the quality of water as it is conveyed through the complex urban landscape. We suggest further research to develop metrics of urban water resilience and equity, both of which are important in a Global South context.https://sajs.co.za/article/view/8630Publisher's versio