Abstract
Rural communities in sub-Saharan Africa commonly rely on shallow hand-dug wells and springs; consequently, shallow aquifers are an extremely important water source. Increased utilisation of shallow groundwater could help towards achieving multiple sustainable development goals (SDGs) by positively impacting poverty, hunger, and health. However, these shallow aquifers are little studied and poorly understood, partly due to a paucity of existing hydrogeological information in many regions of sub-Saharan Africa. This study develops a hydrogeological conceptual model for Dangila woreda (district) in Northwest Ethiopia, based on extensive field investigations and implementation of a citizen science programme. Geological and water point surveys revealed a thin (3–18 m) weathered volcanic regolith aquifer overlying very low permeability basalt. Hydrochemistry suggested that deep groundwater within fractured and scoriaceous zones of the basalt is not (or is poorly) connected to shallow groundwater. Isotope analysis and well monitoring indicated shallow groundwater flow paths that are not necessarily coincident with surface water flow paths. Characteristics of the prevalent seasonal floodplains are akin to “dambos” that are well-described in literature for Southern Africa. Pumping tests, recharge assessments, and hydrometeorological analysis indicated the regolith aquifer shows potential for increased utilisation. This research is transferrable to the shallow volcanic regolith aquifers that overlie a substantial proportion of Ethiopia and are prevalent throughout the East African Rift and in several areas elsewhere on the continent.
Highlights
The availability of groundwater in sub-Saharan Africa and its potential for agricultural use has been increasingly reported in recent years with many authors predicting that a rapid expansion in groundwater exploitation, as occurred since the 1960s in South and East Asia, may be imminent [1,2,3,4].The use of groundwater for small-scale irrigation is increasingly promoted by governments, donors, and non-governmental organisations (NGOs) as an important tool to alleviate poverty, improve food security, boost rural employment and economic development, promote gender equality, and mitigate against increasing climate variability [5,6,7,8]
Prior to promotion of groundwater irrigation in sub-Saharan Africa, we need to improve our knowledge of the aquifer systems; it is commonly expressed in the literature that the hydrogeology of the region is under-studied and poorly understood [11,12,13]
The solid geology is overlain by weathered basalt regolith
Summary
The availability of groundwater in sub-Saharan Africa and its potential for agricultural use has been increasingly reported in recent years with many authors predicting that a rapid expansion in groundwater exploitation, as occurred since the 1960s in South and East Asia, may be imminent [1,2,3,4]. Prior to promotion of groundwater irrigation in sub-Saharan Africa, we need to improve our knowledge of the aquifer systems; it is commonly expressed in the literature that the hydrogeology of the region is under-studied and poorly understood [11,12,13]. Conceptual models of the Quaternary basalt hydrogeology were developed by Nigate et al [26] who investigated large public supply springs in the Gilgel Abay catchment (the major tributary of Lake Tana), within which is located most of the Dangila study site. When it is considered that regolith overlies a great deal of the crystalline basement and more recent volcanics, notwithstanding the unconsolidated sediments that cover approximately 25% of Africa [36], the extent of the shallow geology with potential for manually excavated or manually drilled wells that may support small-scale irrigation becomes pervasive [37]. Aquifers considered “shallow” and “very shallow” have a wide distribution within Ethiopia, underlying approximately 50% of the country [23]
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