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Water 2017, 9(5), 357; doi:10.3390/w9050357

Shoreline Changes on the Wave-Influenced Senegal River Delta, West Africa: The Roles of Natural Processes and Human Interventions

1
Aix-Marseille University, CEREGE UM 34, Europôle de l’Arbois, 13545 Aix en Provence Cedex 04, France
2
Laboratoire d’Enseignement et de Recherche en Géomatique, Ecole Supérieure Polytechnique, Université Cheikh Anta Diop, Dakar, Sénégal
3
Laboratoire de Morphologie et d’Hydrologie, Université Cheikh Anta Diop, Dakar, Sénégal
4
LEGOS (CNRS-IRD-CNES-University of Toulouse), 31400 Toulouse, France
*
Author to whom correspondence should be addressed.
Academic Editors: Sylvain Ouillon and John W. Day
Received: 24 December 2016 / Revised: 10 April 2017 / Accepted: 12 May 2017 / Published: 19 May 2017
(This article belongs to the Special Issue Sediment Transport in Coastal Waters)
View Full-Text   |   Download PDF [6100 KB, uploaded 19 May 2017]   |  

Abstract

The Senegal River delta in West Africa, one of the finest examples of “wave-influenced” deltas, is bounded by a spit periodically breached by waves, each breach then acting as a shifting mouth of the Senegal River. Using European Re-Analysis (ERA) hindcast wave data from 1984 to 2015 generated by the Wave Atmospheric Model (WAM) of the European Centre for Medium-Range Weather Forecasts (ECMWF), we calculated longshore sediment transport rates along the spit. We also analysed spit width, spit migration rates, and changes in the position and width of the river mouth from aerial photographs and satellite images between 1954 and 2015. In 2003, an artificial breach was cut through the spit to prevent river flooding of the historic city of St. Louis. Analysis of past spit growth rates and of the breaching length scale associated with maximum spit elongation, and a reported increase in the frequency of high flood water levels between 1994 and 2003, suggest, together, that an impending natural breach was likely to have occurred close to the time frame of the artificial 2003 breach. Following this breach, the new river mouth was widened rapidly by flood discharge evacuation, but stabilised to its usual hydraulic width of <2 km. In 2012, severe erosion of the residual spit downdrift of the mouth may have been due to a significant drop (~15%) in the longshore sand transport volume and to a lower sediment bypassing fraction across the river mouth. This wave erosion of the residual spit led to rapid exceptional widening of the mouth to ~5 km that has not been compensated by updrift spit elongation. This wider mouth may now be acting as a large depocentre for sand transported alongshore from updrift, and has contributed to an increase in the tidal influence affecting the lower delta. Wave erosion of the residual spit has led to the destruction of villages, tourist facilities and infrastructure. This erosion of the spit has also exposed part of the delta plain directly to waves, and reinforced the saline intrusion within the Senegal delta. Understanding the mechanisms and processes behind these changes is important in planning of future shoreline management and decision-making regarding the articulations between coastal protection offered by the wave-built spit and flooding of the lower delta plain of the Senegal River. View Full-Text
Keywords: Senegal River delta; Langue de Barbarie spit; delta vulnerability; river-mouth migration; spit breaching; ERA hindcast waves; longshore sediment transport Senegal River delta; Langue de Barbarie spit; delta vulnerability; river-mouth migration; spit breaching; ERA hindcast waves; longshore sediment transport
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Sadio, M.; Anthony, E.J.; Diaw, A.T.; Dussouillez, P.; Fleury, J.T.; Kane, A.; Almar, R.; Kestenare, E. Shoreline Changes on the Wave-Influenced Senegal River Delta, West Africa: The Roles of Natural Processes and Human Interventions. Water 2017, 9, 357.

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