Managed groundwater recharge at the farm scale in pre-Saharan Morocco

Abstract

The oases of the pre-Saharan basin of Wadi Ferkla in southeastern Morocco receives low and erratic rainfall (annual average of 141 mm and inter-annual standard deviation of 70 mm). From the 1980s, surface water and groundwater are increasingly used due to the expansion of irrigation, mainly along two wadis, namely Wadis Ferkla and Satt originating in the High-Atlas and the Anti-Atlas Mountains, respectively. Their flows reach the Ferkla's irrigated perimeters only when the volume of the flood events exceed upstream evaporation, withdrawals and riverbed's infiltration. Nowadays, these irrigated perimeters exert significant pressure on groundwater resources, through numerous drillings equipped with pumping systems, most of them being powered by solar energy. This increasing water demand situation incentivizes individual farmers to design and implement innovative techniques to increase water access for their farms. For instance, the spreading of floodwaters – an ancestral and collective irrigation practice in traditional oases – is currently being modernized by individual farmers. The new technique consists in partially diverting flood flows into earthen basins. The stored water either infiltrates to recharge local aquifers, or is pumped for flood irrigation of date palms. An experimental protocol was set up to characterize groundwater recharge below one of these on-farm basins equipped with a recharge well. Barometric probes were installed in the basin, in the recharge well and in neighboring boreholes to automatically monitor water levels. A topographic survey of the monitoring points and of the basin aimed at deriving piezometric levels from water levels measurements and estimating the height-surface-volume curves of the basin. After 7 months of continuous monitoring, 3 flood events were recorded. The establishment of the basin water balance at a fine time-resolution allowed estimating its different components including the infiltration rate influencing groundwater recharge. An analytical modeling of this process was developed to assess its effect on groundwater level variations. This approach aims to contribute to a broader reflection on securing water management in this fragile oasis ecosystem.