Alioune Kane

Large Dams and Uncertainties: The Case of the Senegal River (West Africa)

This article examines the environmental and socioeconomic consequences of hydraulic infrastructural changes along the Senegal River valley and estuary. During the 1980s, two dams were built along the valley floor to facilitate hydroelectrical production and regular water supply for crop irrigation. In 2003, a breach was dug across Barbary Spit to alleviate flooding in the nearby Saint-Louis city. Although these structures helped regulate the river flow, they also resulted in a series of unforeseen impacts. The study examines these, after on-site measurements (topometry, water salinity, piezometry), analysis of hydrological data, field observations, and surveys with dam managers, state regional directions, and local stakeholders. It stresses the urgency of elaborating models of hydraulic management to limit the negative consequences of the hydraulic constructions. These models should consider the variety of water uses in the middle valley and delta, and also the water safety and quality (salinity) downriver from Diama Dam.

Cartographie du potentiel en eau souterraine du bassin versant de la Lobo (Centre-Ouest, Côte d’Ivoire) : approche par analyse multicritère

RÉSUMÉ Ce travail aborde le problème d’accessibilité en eau potable dans les zones fissurées de la Côte d’Ivoire notamment en saison sèche. Sur le bassin versant de la Lobo, le problème se pose avec plus d’acuité puisque les retenues aménagées pour l’alimentation en eau des populations ne sont pas correctement alimentées ces dernières années et sujettes à une très forte eutrophisation. L’approche pluridisciplinaire (télédétection, analyse multicritère et système d’information hydrogéologique à référence spatiale) a été adoptée. La cartographie des sites potentiels en eau montre que la quasi-totalité du bassin de la Lobo possède une bonne et excellente disponibilité en eau souterraine (93% de la superficie totale). Cette bonne disponibilité en eau souterraine est due à une faible pente et à une bonne densité de fracturation qui entrainent une bonne infiltration des eaux dans l’aquifère. L’identification des sites potentiels montre que près de 72% de la superficie du bassin est favorable à l’implantation d’ouvrages à gros débits. Dans l’ensemble, ces aquifères présentent une bonne accessibilité avec cependant, une exploitabilité médiocre. Editeur Z. W. Kundzewicz; Edithur Associé M.D. Fidelibus

Universities as Solutions to Twenty-First Century Coastal Challenges: Lessons from Cheikh Anta Diop Dakar University

The past 30 years have brought radical changes to coastal zones in West Africa. These areas have experienced rapid urban expansion and business growth, along with widespread overexploitation of natural resources. This chapter illustrates the process undertaken by a Senegalese university to shift its goals in order to increase understanding of the complex social-ecological systems affecting one another in West African coastal areas. This adjustment in university priorities has led to valuable contributions to national research and development systems, helping to facilitate sustainable management of coastal areas in this region.

Management of a Tropical River: Impacts on the Resilience of the Senegal River Estuary

Tropical rivers are under constant pressure and are subjected to flood control policy and planning. The Senegal River has been, for more than thirty years, under multiple types of management and planning. That has become recently more important because of significant hydro-climatic variability that has occurred during recent years. Higher levels of winter rainfall have resulted in frequent occurrence of flooding which guided Senegalese authorities to create an artificial opening on the sand of spit so-called Langue de Barbarie. The major consequence of this has been the closing of the old mouth of the Senegal estuary 25 km downstream of the town of Saint-Louis. However, two new mouths have opened themselves recently within 150 m of the current mouth. The increasing vulnerability in the Senegal River estuary has been one of the main impacts of the watershed management of the Senegalese northern River accordingly. The developments of Senegal River management policy have been based on the concept of remedying the consequences of climatic events; then, the utilization of water resources presented risks that are far greater than expected.

Morphological and Hydrodynamic Changes in the Lower Estuary of the Senegal River: Effects on the Environment of the Breach of the ‘Langue De Barbarie’ Sand Spit in 2003

The Senegal River estuary and its coastal interface, the ‘Langue de Barbarie’, a long sandy spit shaped by the littoral dynamics, are located in Sahelian zone. Their instability results in considerable risk to their hydrological, climatic and ecological balances. The ecosystems there have suffered severely from the effects of drought and reduced freshwater inflows. Dams have partly dealt with the problem of water availability, especially in the upper basin. But the effects of their management on the environment have often been criticized. The breaching of the Langue de Barbarie sand spit on 4 October 2003 was justified by the imminent flooding of the city of St. Louis. It allowed the rapid escape of the flood waters of the Senegal River and thus saved St. Louis. The initial channel of 4 m width is now 2 km wide, with significant changes to the environment. This rapid evolution of the breach was accompanied by major impacts on the environment. Today, the lower estuary of the Senegal River is at a critical stage of its history with the accumulation of vulnerability factors such as the development of a marine dynamic, the over-salinization of water and lands and the rapid morphological change of the Langue de Barbarie sand spit caused by severe coastal erosion. In socioeconomic terms, despite the attempts of the communities to adapt through the development of activities such as salt extraction or the move of market-gardening activities towards less disadvantaged areas, the situation remains alarming, in view of the impoverishment of the local communities.