Review of MAR practice in Africa Girma Y. Ebrahim, Jonathan Lauze, Karen Villholth

Outline Introduction Objectives of MAR Types of MAR Review of MAR practice in Africa

Introduction Managed Aquifer Recharge (MAR) is a method that is gaining attention as a means of storing excess water during periods when seasonal supply is higher than demand MAR is the purposeful recharge of water to aquifers for subsequent recovery or environmental benefit This has certain advantages over surface storage in tanks or reservoirs such as reduced land use, decreased risk of contamination and reduced loss of evaporation MAR has been identified in many places as both a practical and necessary strategy for achieving water security and resilience or efficient management are needed to artificially recharge the aquifer for aquifer storage and recovery, and simultaneously preventing seawater intrusion.

Objectives of MAR Source: Dillon et al. (2009)

Adapted from Gale (2005), published in Dillon et al., 2009)

Common MAR types Several methods of introducing water into an aquifer exists such as injection wells, infiltration basins , galleries etc. Main criteria demand for water, adequate source of water available for recharge, suitable aquifer for storage and recovery of the required volume

Spreading method Require permeable surface soils to get high infiltration rates and to minimize land requirements Sufficient land area for surface infiltration exists Where evaporation losses are minimal Require unconfined aquifer so that infiltrated water recharges the aquifer without causing groundwater-mounding problem Where there is no impermeable surface between the surface and the aquifer The unsaturated zone should also be free of contaminants If water quality improvement through Soil-Aquifer-Treatment (SAT) is desired Where the topography is relatively flat (<5% is the most suitable) The aquifer should be sufficiently transmissivity to accommodate lateral flow of the infiltrated water away from the recharge area and the storage coefficient should be high enough to accept more recharge Whenever possible, surface infiltration systems are preferred, because they offer the best opportunity for clogging control

Injection method If the bottom restricting layer is not too deep (less than 3 m, for example), trenches can be used to drain the perched water and send it down to the aquifer Confined aquifers, where the impermeable layer is deeper than 40 m In areas where there is no sufficient land for spreading method Where evaporation is high Where depth to groundwater is deep The aquifer should have sufficient transmissivity and the storage coefficient should be high enough to accept more recharge For injection techniques, the recharged water needs to be highly treated, as this system is used to recharge directly into the aquifer

Sand dams Suitable in seasonal rivers with sandy sediments and accessible bedrock Sand dams should be constructed in geological environments where the weathering products contain a substantial amount of sand and gravel Bedrock consisting of granite, gneiss and quartzite are more favourable Sand dams should be sited in catchment with slope preferably in the range of 1-5% Storage capacity of sand dams is a function of specific yield of river riverbed material Sand dams should be sited in less erosive areas Sand dams provide reliable sources of water for communities living in remote, rural areas.

Induced bank filtration This process is performed when the surface water quality needs improvement. The streambed and aquifer sediments are used as a medium for removing contaminants from the surface water bodies The technique is useful for removal of sediment from the surface water bodies, metals, pathogens and some other organic contaminants. The system has to installed in perennial streams and lakes, which are in hydraulic connection to the adjacent aquifer system.

Overview of worldwide MAR applications Droughts are frequent in most African countries and climate change will likely increase the frequency of drought. However, the extent of MAR practice in Africa is very low compared to other continents. Source: marportal.un-igrac.org

MAR in Africa Among the 1100 case studies only 42 case studies are found in Africa. At present only 8 countries in Africa are using MAR namely Egypt, Ethiopia, Kenya, Morocco, Namibia, Nigeria, South Africa and Tunisia. Among the 42, 10 are found in Kenya and 13 in South Africa Given the climatic variability and drought conditions and problem of food security WHY MAR practice is very limited in Africa? Sand dams provide reliable sources of water for communities living in remote, rural areas.

Review of MAR practice in Africa - objective The objective is to compile and synthesize MAR experiences in Africa in order to gauge the viability of MAR approaches and inform the modalities of future MAR projects on the continent Given the climatic variability and drought conditions and problem of food security, MAR practice in Africa is very limited Not sure that holds. I think it is more of a capacity (technical and fiancial issue). Consdier reformulating.

Main MAR types in Africa

MAR in Africa per country

Source of water for MAR in Africa The Williston, case study South Africa demonstrate a very good example where groundwater from the adjacent compartment is used to recharge another compartment used for domestic water supply.

MAR implementation in Africa over time Implementation of MAR is increasing over time in Africa

Sectoral use of MAR Number of MAR projects per final water use of MAR water (in 8 cases there were no data so these were excluded from the figure)

Challenges MAR challenges include little unsaturated zone thickness, site selection and infrastructure design, mixing of recharge water with poor water quality in the aquifer, and clogging. Site Selection and Design Unsaturated zone thickness at site Site selection (3 sand dams + infiltration basin Egypt on clay soil Infrastructure design Operation and maintenance Mixing of recharge water Clogging

Conclusions MAR is not widely practiced in Africa and is concentrated in only eight African countries. At least four factors may limit wider application of MAR in Africa: 1) lack of awareness and hydrogeological uncertainties (poorly understood aquifer and geochemical properties), 2) lack of financial resources, 3) lack of capacity, 4) lack of enabling policy frameworks. Inter-annual climate variability 32 out of the 41 case studies are located in geographic regions with medium to high and high inter-annual rainfall variability. MAR contributes to better control of irregular and scarce water resources, ensures adequate water supplies in regions of high variability in water availability.

Conclusions Soil type Our results shows that 51% of the reviewed case studies are located in sand clay loam Challenges clogging is identified as the main challenge in Africa. This is consistent with main challenge in MAR application worldwide. Data gaps Data limitations severely constrain the guidance, which can be generated to improve future implementation of MAR in Africa

Recommendations Explore expansion of MAR in geographic regions of high inter-annual climate variability Increase awareness towards MAR and strengthen capacity Develop MAR implementation guidelines tailored to Africa (resource-constrained context) and promote its adoption and adherence Promote research, monitoring and evaluation Research, monitoring and evaluation help to identify technologies that works Water shortages can, for a large part, be solved by storing excess water during wet seasons and making it available during dry seasons

Thank you!!