Dr Adoté BLIVI, Maître de Conférences Université de Lomé, Centre de Gestion Intégrée du Littoral et de l'Environnement adoblivi@hotmail.com

The coastal zone of Togo is very narrow and covers an area of 1710 square kilometers. It constitutes an essential economic potential of the country due to the concentration of more than 90 % of its economic activities, more than 42 % of its whole population and of that of Lomé. The coastal landscape encompasses the delta system of Volta river in Ghana to which are adjoined the clearly differentiated offshore bars, parallel to the coast and the uninterrupted lagoon systems which run into the alluvial plain of the river Mono. The coastline is located in the current offshore bar at a mean of 2 and 3 meters above average sea level. It is lower, at 1 meter in the barrier crossbar at the level of the lagoon and river mouthpieces.

The climatic regime of the coastal zone depends upon two air currents with two contrasted seasons during the year. The temperatures are consisted throughout the year and vary between 25° and 28° C. The coastal geosystem is fed on by the Volta and Mono rivers. The dams built on the two rivers put a limit on the sedimentary volume drift to the sea : this is what accentuates the sedimentary loss and erosion in the zones of lagoon and rivers mouthpieces. The hydrodynamic regime is conditioned by local and regional meteorological elements, namely the marine winds of the southern ocean which generates swell and waves. These waves create on the coast a current of coastal drifting west to east, which activates the mechanism of the coastal morphosedimentary process. An examination of the sandy coasts where a current withdrawal of the seashore is notice in West and Central Africa shows that this dynamic process is generally the result of human action. It is not linked to the sea transgression correlative to the greenhouse effect. Scientific research as regards climate confirms the greenhouse effect linked to the increase of the CO² content in the atmosphere which could probably be the cause of climatic change with subsequent rise in temperature from 1 to 3°5 C. This phenomenon will lead, among others to a partial fusion of glaciers of the Antarctic and Groenland which will in its turn lead to the rise in the sea level up to many centimeters even to a meter with biophysical consequences in coastal zone. The statistical analysis of available maregraphic data on marshes and ponds, though relatively limited, of the coastal stations of Abidjan, of Takoradi and of Tema, enable us to prove, basing especially on the data of Takoradi, a secular trend, holding the year 1930 as a reference of sea level rise along the West - African coasts that could reach 30 cm in 2030. Working from sea level rise data? (from 1930 to 1969) of the station of Takoradi, and basing on the hypothesis of rythm regularity of meteorological and oceanographical phenomena of which data are not available, we discovered that the rate of mean annual rise is 0,34 cm (Woodworth, 1991). We foresaw three scenarios of sea level rise : one with the current trend (annual rise of 0,34 cm) ; another one, with climatic change, assuming an acceleration rhythm of the sea level twice higher than the current trend (mean hypothesis) ; and a scenario of acceleration rhythm of the sea level four times higher than the current trend (high hypothesis).

The gradual sea level rise will be remark in the zone of lagoon and river mouthpieces of the Volta and of the Mono. These two zones, low enough, will be rapidly submerged under the influence of the simple process of sea level and the sea waters will climb up the plains, the lagoon systems, the valleys up to the steep slopes, and the coming in waters by diffusion under the influence of the tides. Along the coast, submersion by amplified waves will be frequent with restructuring of the coastal profile and lowering of the coastline. They will provoke breaks in short segments of the barrier crossbar because of the strong lamination. The salinisation of the lands, of underground and surface waters will constitute one of the characteristics. The other direct effect corresponding to these manifestations of coastal physical oceanography is the accentuation of the speed of the coastal erosion. The data pertaining to the coastal erosion in the current conditions indicate an annual mean of 5 meters. It is certain that this retreat value of the coastline, in the perspective of climatic changes, will progressively increase to 10 meters per year. The consequences in terms of area of lost land will be important.

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