The Sanaga River is one of Sub-Saharan Africa's largest and greatly regulated rivers. Available flow data for this hydrosystem largely cover the pre-and post-regulation periods. From comparisons between unregulated (hypothetical) and observed scenarios, it has been possible to separate and to quantify hydro-climatic (groundwater þ rainfall) change effects from anthropogenic impacts (especially dam-related alterations). To appreciate shifts in the river regime, discontinuity detection tests and the IHA model were applied to discharge data series reflecting average and extreme flow conditions, respectively. Results obtained principally from the Hubert segmentation method reveal that a major discontinuity occurred in 1970-1971 separating a surplus phase between 1945-1946 and 1969-1970, and a deficient and much contrasted one, from 1971/1972. This implies that the Sanaga catchment is dominantly affected by hydro-climatic changes. However, wide land cover/land use changes experienced here since 1988 have resulted in an increase in surface runoff. Additional quickflows linked to these changes may have partly compensated for the substantial decline in the dry season rainfall and groundwater inputs observed from this date. Although at the monthly scale, dam-related impacts on average flows increase with stage of regulation, the seasonal variability of the river regime remains generally unaffected. A comparison of the IHA statistics, calculated from unregulated and observed streamflow data, show that hydrologic shifts occurring in maximum and minimum discharges are mostly significant from 1971/1972 and are mainly due to the action of dams. Minimum flows appear, however, widely impacted, thus reflecting the prime objective assigned to the existing reservoirs, constructed to supplement flows for hydroelectricity production during the dry season.
The Degradation of Soils in Southern Bamileke : Natural Conditions and Anthropic Factors. Combined with a tortured topographical relief, steep slopes and a harsh climate, the Southern sector of the High Plateaux in the West seems to present a natural milieu that is altogether fragile. But until recent times, no particular menace weighed upon the stability of the slopes in the region. Today, this equilibrium has become precarious, and in places one can see visible signs of degradation in the environment. The causes of this rupture in the equilibrium are to be found in countless and deep changes occurring not only in the social cohesion of the Bamileke, but especially in the economic context. To such an extent that today one is witnessing the wrecking of agrarian techniques that formerly had made of the Bamileke peasants model farmers. Finally, because their agriculture has become speculative, without their production techniques first having been adapted to the new social economic conditions, the farming methods of the Bamileke are in the process of becoming the principal cause in the degradation of their natural environment. If this situation affects in the main the High Lands of the West, the problems seem to be of particular acuteness in their Southern portion.
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