Updated 07/06/22

International Emerging Action (IEA)

January 2020 – December 2022

Bostwana

© CNRS

Context

The Okavango Delta is the second largest inland delta in the world after the central Niger delta. Located in northern Botswana, the natural resources of the Okavango Delta support an important tourism industry and a large part of the local population livelihood. The delta is one of the world's major wetlands, heavily dependent on the annual hydrological cycles of a watershed spanning three countries (Angola, Namibia and Botswana), influenced by climate change.

The Okavango is currently an endorheic system. Each year, approximately 11,000 km³ of water irrigates 15,000 km² of desert. The water of the delta, coming from the Angolan mountains, is pure as it crosses a complex system of sandy aquifers and many islands, where it evaporates, leaving huge quantities of salt. The functioning of this massive and very effective natural filter is poorly understood. Waters annually flood the region to a height of 1 or 2 m, in the middle of the southern summer and six months later in the south (May-June) due to the speed of flow and the distance. Despite the uniqueness of this ecosystem, and the economic importance of its water resources, the long-term geological and hydrological evolution of the Okavango Delta is poorly understood. The 3D geometry of the delta, its age (estimated between 12,000 years and 2 million years), its hydrogeological structure and the evolution of its surface morphology in response to hydrological, tectonic and climatic constraints are still unknown.

Field work with tools.

© Olivier Dauteuil

Objectives

This project follows the Tellus-Rift project, the main objective of which was to map the tectonic structure of the delta and show its current deformation using GPS data. This data highlighted the deformation of the delta linked to tectonic activity on the main faults as well as the annual floods of the river. The first results make it possible to determine the presence, in particular in the south of the delta, of uplifted zones, subjected to a gradual drying up and, conversely, in the north, zones in subsidence causing the flood zones to move towards the northeast. In the central part, the GPS data, supplemented by gravity data, seem to indicate a subsidence potentially linked to the storage of water in a deep aquifer, which remains to be determined.

This project aims to build a new model of the long-term morpho-sedimentary evolution of the delta. It will allow for a better understanding of the hydrogeological system in terms of geometry, chemical composition and sensitivity to climate change.

    Partner

    Okavango Research Institute, Botswana

    Scientific coordination: Marc Jolivet, GéoSciences Rennes

     

    Funding

    Institut National des Sciences de l’Univers, CNRS

     

     

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