The present study aims at understanding the role of the structure and the geometry of the weathering profile on the hydrodynamic behavior of hard rock aquifers. We first described 2D geophysical cross sections of weathering profiles realized and validated on an experimental site. Next, we implemented five long-term pumping tests in wells drilled at various locations of these cross sections. Finally, we chose the appropriate analytical solutions to determine the hydrodynamic parameters in consistence with the structure and the geometry of the weathering profile. Results reveal that land covers, weathering type and thickness, presence of no flow boundaries, etc. are all factors that explain the flow regime, which appears therefore much less unpredictable. In other words, the 2D geophysical data are enough to locate the best permeable areas, or the areas where the structure of the aquifer without impervious boundaries and with leakage favor a good long-term behavior of the well. The values of aquifer's transmissivity vary between 5.10 −3 and 4.10 −5 m 2 /s. The storage varies between 0.06 and 7.10 −7. The variability of these parameters from site to site reflects the high heterogeneity of hard rock aquifers.

Abstract:This study aims to estimate the groundwater storage change of hard rock aquifers in the face of change. For this, the approach developed consisted initially in the implementation of 5 Magnetic Resonance Soundings (MRS) around the observation wells realized and monitored from 2014 to 2015 in the Sanon experimental site. In a second step, we determined the storage change using the MRS data and the water table fluctuation method. The MRS data show that the water content varies spatially from 4.5 to 1.3%. The maximum value is recorded at the central valley where a piezometric dome is observed. The specific yield varies from 2.4% in the central valley to 1.3% at the outlet. The renewed water resource is estimated at 116 mm in the central valley and 32 mm at the outlet, which corresponds respectively to 13 and 3% of the annual rainfall. The renewed water resource is consistent with the annual recharge. Thus, the combination of the MRS geophysical approach and water table fluctuation method is an efficient, fast and cheaper (compared with long-term pumping test) tool for the estimation of groundwater storage changes.

This study aims to characterize water table fluctuations and estimate groundwater recharge in the Tougou catchment located in the Sahel zone of Burkina Faso. Water table fluctuation and groundwater budget approaches are developed on an experimental site equipped with observation wells. The trends of water fluctuations in the different layers of the weathering profile are similar. There is a time-lag response of groundwater recharge to the daily precipitation occurrences. The interaction between the upper (clayey alteration) and lower (transition zone-fractured schist complex) parts of the weathering profile shows that generally the hydraulic head in the upper part is higher than that of the lower part due to difference in drainage porosity. The latter varies at the catchment scale between 0.006 and 0.009 and is inversely proportional to the saturated thickness of the clayey alteration layer. The groundwater recharge is annually estimated between 36 and 49 mm, which correspond to 6% and 9% of mean annual rainfall in the catchment. Annual evapotranspiration was estimated to be about 223 to 443 mm.

I S S N 2 3 4 7 -3487 V o l u m e 1 3 N u m b e r 1 0 J o u r n a l o f A d v a n c e s i n P h y s i c s | ABSTRACTThis study aims at assessing the relationship between soil water stock and the yield of agricultural practices in Tougou catchment located in northern Burkina Faso. It is a region that has experienced a significant and continuous degradation of its natural resources, especially soils, due to the climate variability and the rapid increase of the population. Areas allocated to subsistence agriculture are increasing at the expense of pastoral land. This degradation causes a change in processes and mechanisms that control ecological systems. In order to provide solutions to this issue, some agricultural practices have been implemented to improve crop yield. This is particularly the case of traditional techniques:"zaï", "stony line" and "half-moon", which can significantly improve the soil infiltration capacity and yield. Daily monitoring of soil moisture and pressure in experimental plots based on these agricultural practices show that half-moon and Zaï provided good yield with 2180kg / ha and 1070 kg / ha respectively compared to that of the control plot with about 480 kg/ha. These important yields are due in large part to the improvement of the retention capacity of these soils, thus giving to crops the necessary water need for their development even in drought periods Indexing terms/Keywordswater content, yield, agricultural practices, crop, sahelian climate, Tougou, Burkina Faso INTRODUCTIONFor several decades, the increasing of population pressure in arid zones located in the north and south of the Sahara has led to profound changes in the management and use of natural resources and agricultural land [1,2,3] These anthropogenic disturbances result in scarcity of natural vegetation, soil degradation (water and wind erosion), deterioration of the soil water regime, and a decrease in water efficiency for crop production. This has negatively affected agricultural activities in several Sahelian countries. Agricultural yields decline very significantly in this region as a result of climatic hazards and anthropogenic actions [4]. Indeed, according to the fourth report of the Intergovernmental Panel on Climate Change [5], rainfed crop yields could fall by 50% by 2020 in most of these countries. This is unfortunately the case for Burkina Faso where the situation is very pronounced in its Sahelian part. Indeed, according to the assessment provided in 1994 by the Institute for Environment and Agricultural Research of Burkina Faso (INERA) [6], about 90% of arable land in Burkina Faso Sahel is severely degraded, leading to a reduction in useful agricultural land per capita and marginal land use. In addition, the decline in annual rainfall in this region (more than 20%) since the end of the 1960s [7] has resulted in yield reduction of cereal production of about 16-20% [8]. In this region, the degradation of soil productivity results from the unbalance of organic and mineral matter induced by repeated fires, o...

This study aims to estimate the hydrodynamic properties of soils under various agricultural practices in the Tougou catchment in northern Burkina Faso. The methodology adopted is based on the determination of the unsaturated hydraulic conductivity and capillary sorptivity close to saturation. This method relies on the measurement of the transient infiltration flux at the soil surface with imposed hydraulic head varying from-60 to-20 mm. These tests are carried out on control, stony line, half-moon and zai plots. The results show a difference in hydrodynamic parameters according to the agricultural practices. The unsaturated hydraulic conductivity is 33.1 cm/h, 13.1 cm/h, 20.3 cm/h and 4.0 cm/h for zai, control, stony line and half-moon plots respectively. The unsaturated hydraulic conductivity is 33.1 cm/h, 13.1 cm/h, 20.3 cm/h and 4.0 cm/h for zai, control, stony line and half-moon plots respectively. The pores participating to water transfer also differ. The mean size of drainable pores is 43.7, 56.2, 22.3 and 87.2 μm on control, stony line, half-moon and zai plots respectively.