EGU21-15404
https://doi.org/10.5194/egusphere-egu21-15404
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Geomophological and vulnerability analysis of a coastal delta under increased hydrological alteration over the past two centuries: Tana River delta, Kenya, East Africa.

Peter Gitau1, Stéphanie Duvail2, Dirk Verschuren3, and Dominique Guillaud2
Peter Gitau et al.
  • 1Muséum National d'Histoire Naturelle-Alliance Sorbonne Université, Sciences of Nature and Man : evolution and ecology, Geography, France (ngashpeter@gmail.com)
  • 2Institute of Research for Development, UMR PALOC, France. stephanie.duvail@ird.fr, dominique.guillaud@ird.fr
  • 3Limnology Unit, Department of Biology, Ghent University. dirk.verschuren@ugent.be

Coastal deltas worldwide are under risk of degradation due to the increasing impacts of sea-level rise, and continuous human alterations of river basin hydrology. This research highlights the geomorphological changes that have occurred within the Tana River delta in Kenya, an important deltaic ecosystem of high biodiversity value in East Africa.

The geomorphological features (river channels, floodplain, coastal dune system) and their evolution over the past two centuries were described. Aerial and satellite imagery was used to assess the magnitude and distribution of coastal changes from the 1960s to present.  Additionally, sediment cores recovered within the mangrove environment were analysed to establish the succession of sedimentation periods and patterns. Finally, we explored the response of the coastal processes of deposition and erosion under anthropogenic alterations of the hydrological system.

It was established that over the past two centuries Tana River has changed its main channel and outlet to the Indian Ocean on three occasions. A first river avulsion occurred in the 1860s, followed by a second avulsion in the late 1890s that was promoted by human interference through channel expansion and dyke construction. The third change in river course has occurred gradually over the past 20 years, amid human efforts to engineer the river channels.

From the sediment analysis and radiocarbon dating, it is ascertained that the lower deltaic region developed rapidly over the past ~180 years, facilitated by increased sedimentation from the main Tana River. On the other hand, analysis of the coastline changes indicate that there has been increased erosion of the coastal dune system and mangrove vegetation along the former river outlet, leading to rapid marine intrusion into local subsistence farming areas. By analysing the combined impacts of both natural river dynamics and human alteration we highlight how the integrity of the Tana River delta has increasingly become vulnerable under present sea level rise and continued upstream river alteration.

How to cite: Gitau, P., Duvail, S., Verschuren, D., and Guillaud, D.: Geomophological and vulnerability analysis of a coastal delta under increased hydrological alteration over the past two centuries: Tana River delta, Kenya, East Africa., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15404, https://doi.org/10.5194/egusphere-egu21-15404, 2021.

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