L'homme et l'eau dans le bassin du lac Tchad = Man and water in the lake Chad basin

The Alau dam was constructed with high hopes : to supply potable water to the Maiduguri metropolis, and to supply water to irrigate the Jere bowl for the production of rice. This study, based on field observation and literature search, confirms that several years after its construction, the reservoir behind it fails to fill up to an expected level, precluding the achievement of the two objectives. It is discovered that the reservoir loses water to the unconsolidated sands at its floor, and to the Bama ridge, the outermost beach of the Mega-Chad, on its northeastern margin. Field observation also reveals that a topographical divide exists between the Alau reservoir and the Alau (natural) lake which prevents the two to function as one body of water at a low level as envisaged by the planners. Finally, it is found that the reservoir basin is not adequately confined and a small rise would flood extensive areas in the region (the restraining dykes notwithstanding) and thereby compounding the problems of seepage and evaporation both of which are considerable in the area. The preoccupation of the planners is to divert water from the larger Yerdzeram river to fill the reservoir and make it possible to release water for urban and irrigation needs. In fact, some water was diverted this way during 1992 as an experiment, while an elaborate dyke construction to divert more water to the reservoir is going on in the Sambisa swamps. However, it is contended that while additional water might improve the level of the reservoir, it would not solve the inherent problems which is largely a legacy of the processes associated with the Mega-Chad. These are : excessive seepage into loose sand at the floor, side and along any canal that may be built ; flooding of an extensive area should the water level rise more than the current level, another metre may be more than enough ; and the topographic divide between the Alau reservoir and lake... (D'après résumé d'auteur