Abstract
The objective of this paper is to assess quantitatively the potential recharge of shallow aquifers in the Senegal River delta in context of semi-arid climate, of massive irrigation development and of modification of hydrologic and hydrogeological characters after dams building. Quantitative estimation of recharge potentialities have been based on hydrological balance and groundwater table fluctuation calculations and on isotopic tracers techniques of the water molecule (δ18O, δ2H and 3H). This different methodological approaches used to estimate recharge rates have been useful, valuable and complementary. They give results fairly homogeneous and very interesting with indications accurate enough on recharge rates and on recharge spatio-temporal variations in shallow aquifers in alluvial plain (rate varying between 0-37% of annual rainfall) and dunes formations (rate varying between 0-44% of annual rainfall). Results indicate that recharge variations in term of proportions and of distribution are not only depending of volume and frequency rainfall or groundwater depth but also depending of soil and subsoil surface conditions, human activities (water withdraw, irrigation, market gardening, etc.) and evaporative demand. This recharge knowledge in terms of proportions and distribution in shallow aquifers is often very useful to propose groundwater resources management model and to define strategies to exploit them sustainably especially when groundwater resources are very unproductive and often very salty as in Senegal River delta.
Highlights
The Sustainable management of groundwater resources to meet human and ecosystem needs would require a more accurate recharge estimate under varying land use/cover conditions in different periods
We found that hydro-agricultural perimeters, ricegrowing areas when they are flooded, over several weeks, contribute to intensify the vertical percolation and maintain in charge the upper compartment of the alluvial aquifer (GA0083)
The results indicate that recharge proportions in dunes and alluvial plain are conform to those defined by the exponential model (Table 9) and practically by all other methods
Summary
The Sustainable management of groundwater resources to meet human and ecosystem needs would require a more accurate recharge estimate under varying land use/cover conditions in different periods. Knowledge of the groundwater origin and its renewal rate is essential in the management of shallow aquifers in semi-arid zone especially when they are in hyper-salty fluvio-deltaic environments, at which the irrigation practice is almost permanent This is all the more problematic in the delta, as the volumes of water consumed and reinjected into the environment have increased considerably in recent decades to meet agricultural needs, further increasing the sensitivity and fragility of groundwater resources and soils. Estimating recharge under these conditions is essential when groundwater resources are increasingly exposed to climate changes effects and environmental conditions, as is the case of Senegal River delta. Estimating recharge, in these environments types, is to evaluate in a relevant way: what is known and what is measurable. Moctar Diaw et al.: Quantitative Estimation of Recharge Potentialities of Shallow Aquifers in Senegal
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