Abhatoo - Centre Nationale de Documentation

Mountain-front recharge is the recharge of groundwater occurring in the piedmonts of highelevation mountains often receiving more precipitation due to orographic effects. This type of recharge is the major source of groundwater replenishment in many semi(arid) basins. The Tensift basin in central Morocco hosts the large alluvial plain of Haouz with its vast phreatic aquifer of more than 6000 km2. Groundwater in the Haouz plain is the main source of water for the socio-economic activities in the area. This groundwater originates from the adjacent High-Atlas ranges. Despite the importance of mountain-front recharge for the socio-economic development in the area, it was never investigated with care but only incorporated in a very limited regional-scale studies providing highly speculative conclusions. The aim of the present study is the close investigation of recharge sources in the mountain-front area of the High-Atlas of Marrakech at the local scale, with an emphasis on infiltration within wadi channels.
Hydrophysical data (piezometry, sediment water content and heat), hydrochemical (major ions) and environmental tracers (stable isotopes of water) from field campaigns and experiments were used in this study. The data acquired was analyzed by analytical methods and modeling (heat transport modeling). Coupled groundwater fluctuation measurements and environmental tracers (¹⁸O, ²H, and major ions) were used to identify and compare the natural mountain-front recharge to the anthropogenic irrigation recharge. Within the High Atlas mountain front of the Ourika Basin, Central Morocco, the groundwater fluctuation mapping from the dry to wet season showed that recharge beneath the irrigated area may be higher than recharge along the streambed. A conceptual model of seasonal groundwater recharge sources in the study area was established. These findings highlight that irrigation practices can result in the dominant mountain front recharge process for groundwater. The hydrochemical evolution of groundwater in the mountain-front area is controlled mainly by water-rock interactions through mineral dissolution, silicate weathering and ion exchange. The strong relationship between groundwater and mountain water, enhanced by traditional irrigation, and the ecological agriculture practiced in the area preserved the excellent quality of groundwater. Streambed water content and temperature were continuously logged over a year for the Rheraya intermittent wadi. Over the entire year, the calculated total potential recharge based on heat transfer modeling was 425 mm/m². During winter and spring when the alluvium has a higher water moisture, this recharge is predominantly generated by floods. Normal streamflow generally generates low infiltration but contributes to wetting the sediment. During the summer, brief flashfloods over dry sediment result in shallower and slow wetting from infiltration, despite of their higher peak streamflow.
Results from this study can be incorporated in future management schemes for the water resources preservation in the Tensift basin.