Kabul Basin Aquifer Recharge, Revision 2: Data Review and Feasibility Study Elements

Agency for International Development (USAID) to review existing technical documentation for the implementation of an Aquifer Recharge System (ARS) in the Kabul River Basin. The study aims to determine if a full feasibility study addressing the implementation of an ARS in the Kabul River Basin would be a logical step forward. An ARS, also known as a Managed Aquifer Recharge, is the practice of optimizing recharge of an aquifer under controlled conditions to store water for later extraction or to achieve environmental benefits. Water is typically added to an aquifer by infiltration via surface structures such as ponds, basins, galleries, and trenches or injection via wells. There are many potential sources of recharge water, including stormwater, treated wastewater, and water from surface watercourses or aquifers. The Kabul River Basin is located in central eastern Afghanistan and covers between 54,000 km2 and 86,000 km2, divided into four to eight sub-basins. Groundwater in this basin is generally confined to three water-bearing strata: the Logar Aquifer, the Paghman Aquifer, and the Allowdin Aquifer. The Logar Aquifer has a loamy cover layer of at least 10 m thickness, which is very sandy and therefore permeable. The Paghman Aquifer is associated with the Paghman major river system and has a thickness of up to 100 m. The Allowdin Aquifer has a cover layer of reworked loess of several meters thick, which has a certain protective effect on the underlying aquifer. Groundwater recharge in the Kabul Basin is primarily provided by surface infiltration from the Paghman, Kabul, and Logar River systems. Calculations indicate the annual recharge rate is on the order of 380 Mm3/yr. The basin is balanced, with recharge and withdrawal approximately equal. However, certain sub-basins within the Kabul Basin are at a water deficit, while others have a water surplus. Tetra Tech identified several areas that will require clarification or resolution during any subsequent feasibility study, including the status of proposed dam construction and design plans, and the current status of documented infrastructure projects regarding drinking water supply. The study concludes that there are no documented geologic or hydrogeologic conditions that would preclude the recommendation of a feasibility study for the Kabul Basin. The benefits of ARS include improved maintenance of wetlands, opportunity for storage of water in times of surplus to meet need in times of demand, prevention of salt-water intrusion, increased water availability for irrigation use, and augmentation of drinking water supplies. Managed aquifer recharge also has the potential to improve water quality through natural processes, such as the removal of nutrients, degradation of chemicals, and pathogen die-off. However, there are limitations to ARS, including hydrogeological, environmental, or cost constraints. In some cases, direct use of stormwater or treated wastewater for irrigation or other non-potable uses may be preferable to managed aquifer recharge. The study notes that there are a number of environmental, health, and social issues associated with the process that need to be considered. The study recommends that a full feasibility study be conducted to determine the feasibility of implementing an ARS in the Kabul River Basin. The study also identifies key pre-feasibility study elements and data requirements needed to move forward, including a detailed review of the hydrogeology of the basin, a thorough assessment of the water balance, and a comprehensive evaluation of the environmental, social, and economic impacts of the project.