Agricultural Water Management 97 (2010) 1461–1468 Contents lists available at ScienceDirect Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat Water ‘banking’ in Fergana valley aquifers—A solution to water allocation in the Syrdarya river basin? A. Karimov a,∗ , V. Smakhtin b , A. Mavlonov c , I. Gracheva c a International Water Management Institute (IWMI), Tashkent 700000, Uzbekistan b International Water Management Institute (IWMI), Colombo 2075, Sri Lanka c The Institute of Hydrogeology and Engineering Geology, Tashkent 100041, Uzbekistan article info Article history: Received 26 November 2009 Accepted 20 April 2010 Available online 26 May 2010 Keywords: Hydropower irrigation nexus Groundwater irrigation Groundwater recharge River basin management Groundwater modeling Central Asia abstract The Syrdarya river is an example of a transboundary basin with contradictory water use requirements between its upstream and downstream parts. Since the winter of 1992–93, the operational regime of the upstream Toktogul reservoir on the Naryn river – the main tributary of the Syrdarya – has shifted from irrigation to hydropower generation mode. This significantly increased winter flow and reduced summer flow downstream of the reservoir. Consequently, excessive winter flow is diverted to the saline depression called Arnasai, while water for summer irrigation is lacking. This study suggests to store the excessive winter flows temporarily in the upstream aquifers of the Fergana valley and to use it subsequently for irrigation in summer. It is estimated that groundwater development for irrigation could be practiced on one-third of the irrigated land of the valley, and conjunctive use of groundwater and canal water on another third; the rest will remain under canal irrigation. This strategy will lower the groundwater table and create aquifer capacity for temporal storage of excessive water—“water banking”. This use of the term is only one of many concepts to which “water banking” or “groundwater banking” is applied. In this paper, the term is applied for temporary storing of river flow in subsurface aquifers. Pilot modeling studies for the Sokh aquifer – one of the 18 aquifers of the Fergana valley – supported that this strategy is a feasible solution for the upstream–downstream issues in the Syrdarya river basin. Field studies of water banking are required to determine the scale of adoption of the proposed strategy for each aquifer of the Fergana valley. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The growing pressure on water resources in many river basins complicates the trade-offs between upstream and downstream uses. Identifying and implementing suitable water management measures become a challenge. The Syrdarya is an example of a transboundary river basin with contradictory water use require- ments between its upstream and downstream parts (Fig. 1). Since the winter of 1992–93, under increased power demand, the oper- ation of the upstream Toktogul reservoir, located on the Naryn river—one of the two main tributaries of Syrdarya shifted from irrigation to hydropower generation mode, which resulted in significant increases in winter and decreases in summer flow down- stream. Consequences of this dramatic change are excessive winter discharges into the saline depression called Arnasai, and lack of water for summer irrigation downstream of the river. ∗ Corresponding author. Tel.: +998 71 2370475; fax: +998 71 2370317. E-mail address: a.karimov@cgiar.org (A. Karimov). The question that appeared on the agenda of agricultural water management in the region was how to make beneficial use of the excessive upstream winter flows—for downstream irrigation under such circumstances. An analysis of the potential for increasing sur- face storage capacity indicates its limitations (Abbink et al., 2005). The strategy advocated in this study is to store excessive winter flows temporarily upstream – in the aquifers of the Fergana val- ley – and to use it subsequently for irrigation in summer. Such a strategy further referred to here as ‘water banking’ could repre- sent a solution to the new water management environment which emerged in the Syrdarya basin in the early 1990s. The objective of this paper is twofold: (i) to determine the potential of the Fergana valley aquifers to regulate winter flow of the Syrdarya river and (ii) to test water banking using simulation modeling and the example of the Sokh aquifer—one of the 18 aquifers of the Fergana valley. Budgeting of river flow and groundwater is applied to deter- mine the potential for groundwater extraction. Visual MODFLOW simulates water banking in the Sokh aquifer. It is suggested that excessive downstream winter flow could be decreased by target- ing the return flow from the Fergana valley. Groundwater irrigation will lower the water table and decrease the return flow (sub- 0378-3774/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2010.04.011