Food security and the socio-economic development in many arid and semi-arid regions in Africa cannot be envisaged without a stable and reliable water supply to support local agriculture. Rural communities in those areas often depend on shallow groundwater resources associated with ephemeral alluvial systems to maintain water supply throughout the year.
However, the potential of these aquifers to support agricultural intensification is often ignored in mitigation efforts. Preservation and harvesting techniques to manage or even enhance the alluvial aquifer storage are used and documented in many areas of the world. But not all techniques are effective, and often infrastructures are built without the necessary understanding of the local geological conditions, resource availability and aquifer dynamics.
May Gobo catchment, in the Tigray highlands of Ethiopia, is used in this research as a case study to analyze both the potential of small alluvial aquifers and the impact of storage enhancements to improve the water availability. Specifically, the effectiveness of two sand dams built in 2013 was evaluated. Fieldwork was conducted within the May Gobo catchment and neighboring areas, and multidisciplinary data collected to assess the critical elements determining the dynamic behavior of the alluvial aquifer. Surface and subsurface geological mapping, petrophysical characterization and the analysis of the chemical processes affecting groundwater were used to build a detailed hydrological model, which defined the characteristics of the aquifer units and their interconnections. Using climate data, the model was used to estimate aquifer recharge and the main recharge mechanisms. Finally, a numerical 3D model was constructed to better understand the groundwater flow and assess the role of the sand dams.
The groundwater model synthesizing all the data and insights gathered in the field has allowed simulations of the dynamic communication between the aquifer units and suggests that the role of the sand dam in the recharge of the river banks is rather limited. However, taken together, the results indicate that there is more potential for water storage in the sand river that is currently being used. Moreover, a substantial part of the storage built with the sand dams is lost through evaporation.
Implementation of the recommendations concerning the use of the resources stored by the sand dam could lead ultimately to better management of local water supply and development of agriculture in this area that today is considered marginal. These conclusions can be extended to other areas with similar characteristics and water resource challenges. The construction of numerical models, integrating all the available knowledge, provides a management tool to test development alternatives for these resources before implementation. This kind of approach should be used by decision-makers to decide on the optimal location and type of infrastructures to support agricultural development through groundwater resources.