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Water ‘banking’ in Fergana valley aquifers—A solution to water allocation in the Syrdarya river basin?
Agricultural Water Management 97 (2010) 1461–1468
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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 b c
International Water Management Institute (IWMI), Tashkent 700000, Uzbekistan International Water Management Institute (IWMI), Colombo 2075, Sri Lanka The Institute of Hydrogeology and Engineering Geology, Tashkent 100041, Uzbekistan
a r t i c l e
i n f o
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
a b s t r a c t 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 requirements between its upstream and downstream parts (Fig. 1). Since the winter of 1992–93, under increased power demand, the operation 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 downstream. 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: [email protected] (A. Karimov). 0378-3774/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2010.04.011
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 surface 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 valley – and to use it subsequently for irrigation in summer. Such a strategy further referred to here as ‘water banking’ could represent 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 determine 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 targeting the return flow from the Fergana valley. Groundwater irrigation will lower the water table and decrease the return flow (sub-
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Fig. 2. Ratio of summer/winter flow (Q) in the Naryn river at Uchkurgan.
Fig. 1. Syrdarya river basin (a) and the aquifers of the Fergana valley (b).
surface and drainage outflow). It is estimated that there are free capacities for water banking in the aquifers, and they will increase with groundwater extraction for irrigation. The paper starts from an analysis of the river flow changes within the Syrdarya basin with a focus on the Fergana valley. Then, the potential for both groundwater development and water banking is discussed. Finally, the results of modeling the water banking in the Sokh aquifer are presented. 2. Upstream–downstream issues in the Syrdarya river basin Initially, upstream–downstream issues in the Syrdarya river basin originated in the beginning of the 1960s. Until that time, natural flow of the river met water needs of the users and environmental flow to the Aral Sea. The natural flow regime had high flow in summer and low flow in winter. This regime was suitable for irrigated agriculture—the main historical water user in the region. Expansion of irrigated land in the basin from the 1960s stimulated the development of large storage facilities for regulation of the river flow. The Toktogul reservoir with a total capacity of 19,500 Mm3 was constructed upstream of the Naryn river; the others were the Andijan reservoir (1750 Mm3 ) at the inflow point of the Karadarya river to the Fergana valley, and the Kairakum (2550 Mm3 ) and the Chardara (4500 Mm3 ) reservoirs downstream of the Syrdarya river (Fig. 1). By 1988, the total reservoir capacity of the Syrdarya river basin reached 32,500 Mm3 . This allowed further expansion of the irrigated area to 3.36 million hectares (Mha). About half of this expansion was made possible by the development of the downstream, virgin land where irrigated area increased from 456 to 977 thousand ha (Rubinova, 1979, 1987). Water withdrawal from the river for irrigation amounted to 85% of the total long-term
annual river flow of 37,200 Mm3 /year against 40% before the 1960s, which significantly reduced the river inflow to the Aral Sea. This was the first manifestation of the upstream–downstream conflicts in the basin. The next manifestation occurred in the winter of 1992–93, when the operation of the Toktogul reservoir was changed to maximize hydropower production rather than meeting downstream irrigation needs. This resulted in a shift of the main releases from the reservoir from summer to winter months and in a drastic change in the river flow regime in downstream sections of the river. The river inflow to the Fergana valley (at Uchkurgan flow gauging station) in winter reached 8350 Mm3 /season against 5250 Mm3 /season in average before 1992 (Mustafaev et al., 2006). Summer releases from the Toktogul reservoir decreased from 7750 to 5000 Mm3 /season in average to accumulate flow for subsequent use in winter. As a consequence, from 1966 to 1991 the ratio of summer to winter flow dropped from 2–3 to below 1 (Fig. 2). This change of the river flow below the Toktogul created severe issues downstream (Keith and McKinney, 1997; Abbink et al., 2005; Mustafaev et al., 2006). While hydropower production in the upstream increased by 30%, the shortage of irrigation supplies became large and was estimated at 2000 Mm3 /year or 20% of annual irrigation water demand on average (Mustafaev et al., 2006). Irrigated agriculture downstream of the Toktogul reservoir command area was significantly affected. Between 1990 and 2000, in Mirzachul steppe located on the left bank downstream of the river, cotton yields plummeted by 46% and some of the lands were taken out of production due to the irrigation water shortages and increasing salinity (Kushiev et al., 2005). This has had a direct impact on the downstream agricultural production with estimated losses of around $90.4 million on over 555,000 ha (Keith and McKinney, 1997). Yield of cotton declined in this area below 2 t/ha due to shortage of irrigation water and salinity buildup in the topsoil. Farmers were able to irrigate cotton once or twice a year only, instead of the recommended frequency of four to five times (Djumadilov et al., 2006). The most visible consequence of the shift in the flow regime was however the expansion of the saline Arnasai depression (Fig. 1a) (Kholmatov et al., 2001; Mustafaev et al., 2006). Because of irrigation needs, the downstream Kairakum and Chardara reservoirs accumulate flow starting in October. From January to March when hydropower releases arrive, they are already full. The water passing further downstream is often blocked by the frozen Syrdarya. Another reason is that the dry riverbed below the Chardara reservoirs is occupied by the local population. Expansion of the irrigated agriculture since the 1960s upstream of the Chardara reservoir has resulted in high water diversions upstream and low flow to the river downstream. Under such conditions, the population occupied highly fertile soils in the dry riverbed below the Chardara reservoir for crop production and settlement schemes. This totally changed the shape of the riverbed and reduced the maximum flow capacity
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to 800 m3 /s. Hence, the extra hydropower winter releases from the Toktogul reservoir were forced into the Arnasai depression. Starting from the winter of 1992–93, the total volume of the river flow discharged from the Chardara reservoir into the Arnasai depression exceeded 34,000 Mm3 . The total storage of water accumulated in it was around 40,000 Mm3 (Mustafaev et al., 2006). Its surface water area increased from 2000 km2 in 1991 to 3600 km2 in 2005 and evaporation losses at the rate of 1000 mm/year amounted to 3600 Mm3 /year, i.e., about 10% of the annual flow of the Syrdarya river. Proposals to rectify this new water management situation in the basin primarily focus on the construction of new reservoirs downstream of the Syrdarya river (Mustafaev et al., 2006). However, while the analysis is not yet complete, the efficiency of reservoir water storage under such climatic conditions is questionable. Any new surface storage increases nonproductive losses for regulation of the river flow. There is also a concern that high leakage from the reservoirs proposed in the irrigated zone may raise water tables and increase salinity (Mustafaev et al., 2006). Climate change will also pose new challenges in the future as surface reservoirs have to deal with yet unpredictable flow variability. There is therefore a need to examine alternative strategies, like the one proposed in this paper. The fourfold methodology described in the next section has been used in this study.
water/surface water interactions; however they are the subject of future studies.
3. Data and methods
3.2. Assessment and mapping of the potential for groundwater irrigation
3.1. Analysis of the river flow Analysis of river flow is necessary to understand hydrological interactions between the irrigated areas and the aquifers of the Fergana valley and the Syrdarya river. It is necessary to examine the contribution of other factors, such as return flow from irrigated areas in the valley itself, to the overall river flow regime downstream. This understanding may be inferred from the analysis of observed flow records and water table data. Observed river flow time series at three flow stations – Uchkurgan (on Naryn), Kal and Akdjar (on Syrdarya, Fig. 1b) – were used for this analysis. These data were provided by the Syrdarya Basin Water Management Organization (BVO Syrdarya) and the Hydrometeorological service of Uzbekistan (GlavHydromet) (CAWATERinfo, 2008a,b). The interactions between surface water and groundwater were determined from the ArcView groundwater contour layer created, based on values of water table depth obtained from the State Water Register (‘Vodny Kadastr’), collected by the Information Center of the Institute of Hydrogeology and Engineering Geology (Mavlonov et al., 2006). The return flow to the riverbed was taken from the annual reports of the hydrogeology and land reclamation expedition of the Syrdarya-Sokh Basin Irrigation System Administration (Ganiev, 2008, 2009; personal communication) and the Hydrometeorology service of Uzbekistan (Ivanov, 2008, 2009; personal communication). Transit flow is calculated from the river flow by deducting the water withdrawals from the riverbed. Return flow is taken equal to the drainage flow to the riverbed, since the subsurface flow is much less. Water budgets were compiled for the Syrdarya river reach between Uchkurgan and Akdjar flow gauges. The budget accounts for inflow of the Naryn and the Karadarya rivers, water withdrawal for irrigation and losses from the river between Uchkurgan and Kal flow gauges, and lateral drainage and subsurface inflow to the river between Kal and Akdjar gauges (Fig. 1b). Salinity of the water recharging the groundwater from below 500 mg/l in the natural groundwater recharge zone increases to above 1000 mg/l in the central part of the valley. The blending effect of the recharge and the groundwater can be quantified through the mass-balance studies which can provide qualitative indications of the ground-
Fig. 3. Hydrogeological zoning of the Fergana valley.
The use of groundwater for irrigation in the Fergana valley can reduce return flow to the valley downstream. However, it is necessary to establish which areas of the valley are suitable for irrigation from groundwater. The areas with potential for groundwater irrigation were determined using multiple relevant characteristics and hydrogeological features of the valley. The first was the hydrogeological zoning map of the area which was carried out by the Institute of Hydrogeology and Engineering Geology (Mirzaev, 1974). Three hydrogeological zones within the Fergana valley (Fig. 3) were established by Mirzaev (1974): the natural groundwater recharge zone (A); groundwater spring discharge zone (B), and groundwater upwelling zone with discharge to drainage (C). The eastern, northern and southern parts of the valley constitute the natural groundwater recharge zone (Zone A) with high transmissivity and a deep water table. The central part of the valley representing the groundwater upwelling zone (Zone C) has limited transmissivity and the water table is controlled by means of open drains. Between these two, there is a groundwater spring discharge zone with a shallow water table (Zone B). Other characteristics used in determining areas with potential for irrigation development included (i) transmissivity of the waterbearing stratum, (ii) depth of the water table, and (iii) salinity of the groundwater. Groundwater data (transmissivity, water table depth, salinity) were obtained from the hydrogeological surveys carried out by the Institute of Hydrogeology and Engineering Geology in the Fergana valley (Mirzaev, 1974; Borisov, 1990; Mavlonov et al., 2006). Hydrogeological conditions were categorized into different classes based on transmissivity ranges: (i) poor, with transmissivity less than 100 m2 /d; (ii) low, transmissivity in the range of 100–300 m2 /d; (iii) good, 300–1000 m2 /d, and (iv) high, above 1000 m2 /d. Depth to the water table was also categorized into four classes: (i) above 3 m; (ii) 3–7 m; (iii) 7–12 m, and (iv) below 12 m. Groundwater salinity was categorized into three classes: (i) below 2000 mg/l; (ii) 2000–4000 mg/l, and (iii) above 4000 mg/l. The information on soil types in the valley was obtained from studies of the Uzbek State Design Institute for Water and Land Reclamation (Khasanhanova et al., 2006). The groundwater quality changes as affected by the intensive water extractions and man-
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aged aquifer recharge were not analyzed in this paper and will be subject for future research. Several GIS layers were created using ESRI ArcView 3.2 and Spatial Analyst based on the above data. They include: aquifers of the Fergana valley; depth of the water table; salinity of groundwater; transmissivity of the water-bearing stratum; hydrogeological zoning; and specific yield of deposits of the water-bearing stratum. These layers together allowed zones of varying potential for groundwater irrigation to be identified as shown in Section 4. Apart from identification of areas suitable for groundwater irrigation, the water budgets of the aquifers were analyzed with multiple objectives including determining a potential for groundwater extraction from these areas. Groundwater budgets were analyzed for high flow (1995) and low flow (2001) years for each aquifer of the Fergana valley as described in Karimov et al. (2008) and Gracheva et al. (2009). 3.3. Identification of capacity for groundwater banking The next step is to estimate areas with available free storage capacity, and areas with potential capacity, which could be created by extraction of groundwater for irrigation. Such areas – areas of water banking – were identified using GIS (ESRI ArcView 3.2 and Spatial Analyst). Groundwater storage potential was estimated, based on the specific yield of the water-bearing stratum and the thickness of the aeration zone below a depth of 3 m (Gracheva et al., 2009). Areas suitable for water banking were determined in Zone A with transmissivity of the water-bearing stratum exceeding 300 m2 /d and the water table below 3 m. Areas with potential for water banking after drawdown of the water table below 3 m were determined in Zone B with transmissivity of the water-bearing stratum exceeding 300 m2 /d. It was assumed that groundwater recharge from rivers, main and secondary irrigation canals, as well as from irrigation fields, needs to be stored during winter months in Zone B. Two sources of winter groundwater banking specified are Sokh river for recharge in Zone A and Big Fergana Canal (BFC) in Zone B. The Sokh river flow can be recharged through an infiltration basin, channels of the natural water courses and canals, or by applying winter irrigation. Groundwater banking from BFC can be applied by transportation of winter flow through the canal, dug-wells or the open drainage system.
Fergana Canal (BFC) inside the model area is simulated as a river. Natural recharge, occurring directly as infiltration from precipitation, and seepage from streams of the Sokh river were included in the model. Another form of recharge is excess irrigation. Five scenarios were developed to estimate groundwater extraction and water banking potential. • Scenario 1 simulates current conditions. This scenario assumes ‘no water banking’. Summer extraction of groundwater for irrigation under this scenario is estimated at 117 Mm3 /year. • Scenario 2 simulates groundwater extraction at maximum feasible level determined by annual recharge of 621 Mm3 /year. This scenario also assumes ‘no water banking’. • Scenario 3 simulates groundwater extraction at the same maximum feasible level, but includes ‘water banking’ determined by the winter flow of the Sokh river in a high water year (268 Mm3 /season). • Scenario 4 simulates groundwater extraction at the same maximum level but includes ‘water banking’ determined by the winter flow of the Sokh river in a low water year (144 Mm3 /season). • Scenario 5 simulates groundwater extraction at the same maximum level but includes both water banking’ determined by the winter flow of the Sokh river in a high water year and additional water transportation through BFC in winter. The simulation results for the current scenario were evaluated based on the data cited in Mavlonov et al. (2006). Details of the model compilation and calibration are given in Gracheva et al. (2009). 4. Results and discussion 4.1. Analysis of river flow within the Fergana valley The river flow within the Fergana valley increases in winter and decreases in summer; however, there are differences before and after 1992 (Fig. 4). Before 1992, under the irrigation mode of operation of the Toktogul reservoir, the ratio of summer to winter flow
3.4. Simulation modeling using Visual MODFLOW Simulation modeling is necessary to estimate the actual potential of water banking in the aquifers. The Sokh aquifer selected for groundwater banking modeling studies is formed in the fan of the Sokh river and is composed of 120-m thick shingle deposits. It has a high potential for artificial recharge development and, consequently, for water banking (Mirzaev, 1974; Akramov, 1991). The three-dimensional model of the Sokh aquifer was set up using Visual MODFLOW (Waterloo Hydrogeologic Inc., 2000). Parameters of the model were calibrated manually using criteria of Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Normalized RMSE and mass balance. The details of the model and the input data are given in Gracheva et al. (2009). The surface of the model domain is approximately 2751 km2 . The model has a spatial grid of 150 m and consists of 335 rows and 365 columns. A period of 5 years with a time step of 30 days was used. The three geological strata are represented as five layers in the model. Groundwater in layer 2 is unconfined in Zone A and confined in Zones B and C; it is also confined in layers 3, 4 and 5. The model is bounded on the north by general head conditions governing drainage outflow. The western and eastern boundaries are zeroflow ones lying at the edges of the aquifer. The upstream condition is a fixed-flow boundary, representing underground inflow. The Big
Fig. 4. Syrdarya river flow at the inflow and the outflow nodes of the Fergana valley under (a) irrigation mode (1992) and (b) hydropower generation mode (2001) operation of the Toktogul reservoir.
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Fig. 6. Zoning of Fergana valley by irrigation water sources.
Fig. 5. The structure of the Syrdarya river flow at the Akdjar gauge under (a) the irrigation mode (1992) and (b) the hydropower generation mode operation of the Toktogul reservoir (2001).
was estimated to be 1.27 at the inflow point (Uchkurgan) and 0.86 at the outflow point (Akdjar) of the river (Fig. 4a). The valley was increasing the river flow in winter and in the first half of summer. It also was decreasing river flow from June to August. After 1993, under the hydropower mode of operation of the reservoir, the ratio of summer flow to winter flow has decreased to 0.77 at the inflow point and to 0.40 at the outflow point (Fig. 4b). The Fergana valley has become the consumer of the river flow in summer from May to September and continued to be a source of the river flow in winter from September to April. The causes of this change in river flow can be identified through an analysis of the structure of the flow at the outflow point (Akdjar). Fig. 5 compares monthly discharges of transit flow in the river (releases from Toktogul) with monthly discharges of return flows to the river in 1992 and 2001. Before 1992, the return flow to the riverbed had a maximum from February to May with a peak in April–May of 887–1285 Mm3 /month (Fig. 5a). After 1993, the return flow was at a maximum from November to February and was much less in the summer months than at the previous stage (Fig. 5b). The return flow from the valley to the river in winter months constitutes 40% of the river flow at the outlet of the Fergana valley. The return winter flow from the valley at present amounts to 4000–5000 Mm3 /season. As a consequence, the Syrdarya river flow discharge increases to 1000 m3 /s in winter and falls to 150 m3 /s in summer. While previous studies highlighted hydropower winter releases (Keith and McKinney, 1997; Abbink et al., 2005; Mustafaev et al., 2006), this study found that the superposition of the return flow to the river from the valley, with the winter hydropower releases from Toktogul, created surplus flow which exceeded the capacities of downstream reservoirs (Kairakum and Chardara) and forced the surplus winter flow into the Arnasai depression (Fig. 1a).
able for groundwater irrigation were proposed to be those where transmissivity exceeds 300 m2 /d, water depth is above 3 m and salinity is below 2000 mg/l. Conjunctive use is recommended for areas with transmissivity exceeding 300 m2 /d, water depth ranging between 3 and 12 m, and salinity below 4000 mg/l. Canal irrigation is most suitable under conditions with a water table below 12 m and in areas with a transmissivity less than 300 m2 /d. Isolated wells were recommended for areas with transmissivity in the range of 100–300 m2 /d. The assessment suggests that the potential area for groundwater irrigation is 290,000 ha while for conjunctive use of groundwater and canal water it is 243,000 ha. The system of canals will irrigate the rest of the area. The potential of groundwater extraction for irrigation depends on proper hydrogeological conditions (Zones A and B) and recharge volumes (Table 1). Since groundwater in Zone C is saline and the aquifers have low transmissivity, this zone is not considered in this table. Table 1 shows that the potential maximum annual groundwater extraction is in the range of 5624–6005 Mm3 /year, depending on the year. However, maximum extraction may bring the annual overdraft of groundwater resources to the level of 1885–1955 Mm3 /year.
Table 1 Groundwater recharge of the Fergana valley in high (1995) and low (2001) water years (Mm3 ). Zone Source of recharge
a
S
A
S
577 1320 250 130 1013 768 4056
445.4 97 1074 292 88 88 283 6 557 557 297 297 2744 1336
542 1366 176 289 1113 594 4080
273 650 87 18 0 14 1042
94 242 87 74 14 14 526
368 892 174 92 14 28 1568
249 592 174 179 73 40 1306
94 233 174 5 73 40 619
343 825 348 184 146 80 1926
3739
1885
5624
4050
1955
6005
B
From irrigated fields Leakage from lateral canals Leakage from main canals Precipitation Subsurface inflow Leakage from river Sub-total, Zone B Total (Zones A + B)
b c
Summer. Winter. Annual.
c
101 267 125 99 384 384 1359
From irrigated fields 476 Leakage from on-farm canals 1053 Leakage from main canals 125 Precipitation 31 Subsurface inflow 629 Leakage from river 384 Sub-total, Zone A 2697
a
2001 b
W
A
4.2. Groundwater development potential Fig. 6 shows the results of the zoning of the Fergana valley on groundwater development potential for irrigation. Areas suit-
1995
W
A
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A. Karimov et al. / Agricultural Water Management 97 (2010) 1461–1468 Table 2 Free capacities of aquifer in the Fergana valley. Aquifer
Recharge zone Area (ha)
Almas-Vorzik Kukumbay Kasansay Iskovat-Pishkaran Sokh Altiarik-Beshalish Namangan Isfara Maylisu Karaungur Naryn Chust Pap Andijan-Shahrihan Chimion-Aval Osh-Aravan Nanay Fig. 7. Zones with potential for water banking in the Fergana valley.
This water provides supplies for municipal, industrial and irrigation needs. Groundwater use for municipal water supply and industry amounts to 1760 Mm3 /year in current conditions and is projected to be 2000 Mm3 /year in 2025 (Borisov, 1990). Therefore, groundwater resources available for irrigation now and in the near future are in the range of 3600–4000 Mm3 /year. Extraction of annual groundwater recharge in summer may significantly reduce return flow from the valley to the river. At the same time, there would be a drawdown of the water table. Aquifer recharge would need to be managed to prevent issues related to groundwater depletion, degradation of groundwater quality and high cost of extraction. 4.3. Water banking potential in the Fergana valley The shift from canal to conjunctive use of groundwater and canal water for irrigation will change the groundwater budget because water withdrawals from surface water sources and leakage from the canal systems will both decrease. Groundwater recharge under the new conditions is estimated to decrease from 8200 to 6500 Mm3 /year. Deficits of groundwater recharge can be compensated for by banking the winter flow of the Naryn and small rivers. The distribution of zones with favorable conditions for water banking is shown in Fig. 7 while Table 2 lists their estimated areas and capacity (potential for water banking). The data in Table 2 show that there is a free capacity of over 3000 Mm3 in the recharge Zone A, which could be used for banking
Total
Free capacity (Mm3 )
19,825 2658 4351 19,439 34,589 7366 5196 4385 17,513 3944 28,393 7936 7919 3651 21,223 4349
231 54 30 359 1452 28 77 90 22 5 167 147 16 88 324 71
192,737
3159
of winter flow of small rivers. This capacity is more than the winter flow of small rivers totaling 1000 Mm3 /year. Most of the indicated capacities are located at high altitudes where the flow of the Naryn river cannot be transported by gravity. Capacities in command zone of the canals transferring water of the Naryn river could be created by intensive groundwater extraction for irrigation (Table 3). Table 3 suggests that free capacities of the subsurface aquifers under command areas of canals transporting flow of the Naryn river amount to 769 Mm3 . This study found that additional capacities can be created at 186 Mm3 per m of drawdown by intensive groundwater extraction in the summer season. Together, this would equal nearly half the current shortfall of summer irrigation water. This shows that the physical capacities for groundwater banking do exist. However, careful economic analyses and modeling for each aquifer are required to assess to what extent groundwater banking is economically viable. Also, the groundwater banking will need to be seen in connection with water saving to reduce the return flow to the river. 4.4. Modeling water banking in the Sokh aquifer Simulations of the Sokh aquifer suggest that groundwater development for irrigation with no managed recharge (i.e. no water banking—Scenario 2) lowers the water table (Fig. 8a) and increases the cost of groundwater extraction. The water banking under high (Scenario 3) and low (Scenario 4) water year conditions allows avoiding a significant drawdown of the water table. A combination
Table 3 Availability and potential capacity for groundwater banking in the command areas of the canals from the Naryn river. Aquifer Naryn Naryn Naryn Namangan Namangan Mailisu Andijan-Shahrihan Altyarik-Beshalysh Sokh Isfara Total a b c d
Big Fergana Canal. Big Andijan Canal. Northern Fergana Canal. Big Namangan Canal.
Recharge source (canal) a
BFC BACb NFCc NFC BNCd BFC BFC BFC BFC BFC
Area (ha) 36,859 24,440 23,769 20,228 5371 20,547 4443 17,171 27,561 8828
Capacity available (Mm3 )
Potential capacity per m of drawdown (Mm3 )
158 52 85 181 77 5 0 0 126 85
37 24 24 19 5 20 4 17 28 8
769
186
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Fig. 9. Leakage from the Big Fergana Canal (BFC) under the various scenarios of groundwater development.
in winter under Scenario 2, accordingly. These data show further available capacity for water banking. The modeling studies found a clear correlation between groundwater extraction and total recharge on the one hand and return flow and groundwater extraction, on the other (Fig. 10). The data presented in Fig. 10 illustrate that increasing the groundwater recharge in the hydrogeology Zones A and B from 283 to 587 Mm3 /year would increase the potential for groundwater extraction from 117 to 550 Mm3 /year; this will reduce the return flow from 169 to 69 Mm3 . Fig. 10b provides a simple illustration of how additional groundwater extraction may reduce return flow from the study area to the riverbed. The correlation obtained from Fig. 10 could be applied for groundwater development in the study area. The summary of comparative advantages of the winter water banking and conjunctive use of groundwater and canal water for irrigation in summer is given in Table 4.
Fig. 8. Water table (a), evaporation from the water table (b), and return flow (c) as affected by groundwater extraction and banking in the Sokh aquifer.
of the increased groundwater extraction in summer and managed recharge in winter reduces nonproductive water losses for evaporation and decreases return flow from the study area (Fig. 8b, c). Fig. 8c shows that the model results were approaching the dynamic equilibrium condition at the end of the 5 years of simulation, but had not yet reached it. The results obtained would change a little if the simulations were run for longer periods. Scenario 5 simulates the transit winter flow of the Naryn river through the BFC crossing the study area in the upper part of the Sokh fan. The results suggest that increasing the groundwater summer extraction under Scenario 2 from 117 to 550 Mm3 /season creates a free storage capacity of 10–20 m thickness around the canal, and therefore increases the leakage from it (Fig. 9). Considering that there are other aquifers where this strategy could be applied (Fig. 7), the indicated figures are to be updated for the whole Fergana valley. The data presented in Fig. 9 show that water transportation through the BFC in winter months in Scenario 5 results in a recharge of 140 Mm3 /season, against 46 Mm3 /season under Scenario 1 and 100 Mm3 /season under Scenario 2. In total, winter flow volumes in the range of 252–396 Mm3 /season were recharged annually into the Sokh aquifer. The water table is stabilized in the hydrogeological Zone B at depths of 9–12 m below the surface in summer and 1–4 m in winter as compared to 13–19 m in summer and 6–10 m
Fig. 10. Correlation between (a) groundwater recharge and extraction, and (b) groundwater extraction and return flow for the Sokh aquifer.
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Table 4 The main parameters of simulated scenarios of groundwater development in the Sokh river basin (Mm3 ). Parameter
Scenario 1
Scenario 2
Scenario 3
Scenario 4
Scenario 5
Return flow Evaporation from the water table Leakage from BFK Free subsurface capacity Saving of surface water
228 651 46 6 0
107 316 108 653 521
163 384 108 323 551
133 336 108 588 529
168 389 140 301 486
The data presented in Table 4 illustrate that a shift from canal irrigation in the Sokh river basin to conjunctive water use will reduce irrigation demand for surface water by 486–551 Mm3 /year. Return flow will decrease from 228 Mm3 /year to 133–168 Mm3 /year. The winter flow of the Sokh river recharged into the aquifer would amount to 144 Mm3 in low water years and to 268 Mm3 in high water years. In addition, 96 Mm3 of flow of the Naryn river could be recharged into the aquifer by transportation in winter through the BFC. This will result in 500 Mm3 of groundwater available for irrigation in summer. No drawdown of the water table is expected in the long run under groundwaterintensive development for irrigation in summer and water banking in winter (Scenarios 4 and 5). This strategy will bring regional benefits. The flow of the Syrdarya river will decrease in winter by 300 Mm3 /season and increase in summer by 486–551 Mm3 /year thanks only to the proposed measures in the Sokh river basin. The change in timing of aquifer contributions through the river gains and return flows to the river is confirmed by the river flow analysis and the groundwater modeling. 5. Conclusions Groundwater development for summer irrigation and storage of the winter flow of rivers in aquifers can be a feasible practice for transboundary river basins with vulnerable water resources. This strategy allows reduction of the pressure on river basins in extreme situations emerging from increased water demands and exposed water resources. A shift from the use of canal irrigation to conjunctive use of groundwater and canal water, combined with banking of winter flow reduces return flow from the irrigated zone to the riverbed, reallocates a part of the surface flow from upstream to downstream, ensures improved water supply of downstream water users, and eliminates the threat of drawdown of the water table due to shift to groundwater irrigation. The studies found that the advantage of the proposed approach is the change in timing of the contributions of the aquifers through both river gains and return flows to the river. The change in timing between the groundwater recharge and the return flow is controlled by distance, storage coefficient and transmissivity. This strategy would contribute to sustainable merging of the upstream hydropower and downstream irrigation and environmental needs. Further pilot modeling and field studies are required to examine the economically and environmentally optimal combination of summer extractions and winter banking for each aquifer of the Fergana valley. Acknowledgements The authors gratefully acknowledge the financial support of the OPEC Fund for International Development. Observed flow data used
in this study were provided by the Syrdarya Basin Water Management Organization (BVO Syrdarya) and the Hydrometeorological Service of Uzbekistan (GlavHyromet). Water table depth and other groundwater-related data were provided by the Information Center of the Institute of Hydrogeology and Engineering Geology of Uzbekistan. Soil data were taken from studies of the Uzbek State Design Institute for Water and Land Reclamation. The authors are grateful to Dr. Hugh Turral (formerly, IWMI, Colombo) for his comments and advice. References Abbink, K., Moller, L.C., O’Hara, S., 2005. The Syr Darya river conflict: an experimental case study. http://www.igier.unibocconi.it/files/documents/ events/SyrDarya.pdf. Akramov, A.A., 1991. Regulating Fresh Water Resources in Subsurface Aquifers. Fan, Tashkent, Uzbekistan (in Russian). Borisov, V.A., 1990. Underground Water Resources and their Use in Uzbekistan. Fan, Tashkent, Uzbekistan (in Russian). CAWATERinfo, 2008a. On line data of the Syrdarya river basin. CAWATERinfo: http://cawater-info.net/Syrdarya/index e.htm. CAWATERinfo, 2008b. On line data of the Uzhydromet Center. CAWATERinfo: http://cawater-info.net/bd/index e.htm. Djumadilov, D.D., Anzelm, K.A., Sagimbaev, S., Kulambaev, K., 2006. Salinity on irrigated lands of Aral-Syrdarya water basin. In: Issues of Aral-Syrdarya Basin. Information Bulletin: 5. UNDP Kazakhstan, Kzylorda, pp. 61–70 (in Russian). Gracheva, I., Karimov, A., Turral, H., Miryusupov, F., 2009. Assessment of the potential and impacts of winter water banking in the Sokh aquifer, Central Asia. Hydrogeol. J. 17 (6), 1471–1482. Karimov, A., Turral, H., Mavlonov, A., Rahmatov, N., Manthritillake, H., Borisov, V., Anzelm, K., 2008. Regulating the winter flow of Syrdarya river in aquifers of Fergana valley. J. Water Resour. Kazakhstan 2, 17–26 (in Russian). Keith, J.E., McKinney, D.C., 1997. Option analysis of the operation of the Toktogul reservoir. Issue Paper No. 7. www.ce.utexas.edu/prof/mckinney/ ce397/Topics/Options Toktogul 3.pdf. Khasanhanova, G., Khamzina, T., Ibragimov, R., 2006. Assessment of crop water requirement in Fergana valley. In: Paper Presented in the Regional Conference on Conjunctive Use of Ground and Surface Water Resources of Fergana Valley for Irrigation, Tashkent, 2 November 2006 (in Russian). Kholmatov, E.I., Ishankulov, R., Mavlonov, A.A., Safarov, I., 2001. Arnasai-Aidarkul lake system: ecological problems, today and tomorrow. J. Ecol. Herald 2, 18–23, Tashkent, Uzbekistan (in Russian). Kushiev, Kh., Noble, A.D., Abdullaev, I., Toshbekov, U., 2005. Remediation of abandoned saline soils using Glycyrrhiza glabra: a study from the Hungry Steppes of Central Asia. Int. J. Agric. Sustain. 3 (2), 102–113. Mavlonov, A.A., Borisov, V.A., Djumanov, J.Kh., 2006. Assessment of underground water resources of Fergana valley. In: Paper Presented in the Regional Conf. on: Conjunctive Use of Ground and Surface Water Resources of Fergana Valley for Irrigation, Tashkent, 2 November 2006 (in Russian). Mirzaev, S.Sh., 1974. Underground Water Resources of Uzbekistan. Fan, Tashkent, Uzbekistan (in Russian). Mustafaev, J., Ryabtsev, A.D., Balgerey, M.A., Karlikhanov, O.K., 2006. Diversion of winter flow of Syrdarya below Chardara water reservoir. J. Water Resour. Kazakhstan 1, 5–7 (in Russian). Rubinova, F.E., 1979. Change of Flow of Syrdarya River as Affected by Basin Water Development. Gidrometeoizdat, Moscow, Russia (in Russian). Rubinova, F.E., 1987. Land Development and River Flow Quality in Aral Sea Basin. Gidrometeoizdat, Moscow, Russia (in Russian). Waterloo Hydrogeologic Inc., 2000. Visual MODFLOW User’s Manual. Waterloo Hydrogeologic Inc., Canada.
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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 b c
International Water Management Institute (IWMI), Tashkent 700000, Uzbekistan International Water Management Institute (IWMI), Colombo 2075, Sri Lanka The Institute of Hydrogeology and Engineering Geology, Tashkent 100041, Uzbekistan
a r t i c l e
i n f o
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
a b s t r a c t 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 requirements between its upstream and downstream parts (Fig. 1). Since the winter of 1992–93, under increased power demand, the operation 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 downstream. 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: [email protected] (A. Karimov). 0378-3774/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2010.04.011
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 surface 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 valley – and to use it subsequently for irrigation in summer. Such a strategy further referred to here as ‘water banking’ could represent 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 determine 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 targeting the return flow from the Fergana valley. Groundwater irrigation will lower the water table and decrease the return flow (sub-
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Fig. 2. Ratio of summer/winter flow (Q) in the Naryn river at Uchkurgan.
Fig. 1. Syrdarya river basin (a) and the aquifers of the Fergana valley (b).
surface and drainage outflow). It is estimated that there are free capacities for water banking in the aquifers, and they will increase with groundwater extraction for irrigation. The paper starts from an analysis of the river flow changes within the Syrdarya basin with a focus on the Fergana valley. Then, the potential for both groundwater development and water banking is discussed. Finally, the results of modeling the water banking in the Sokh aquifer are presented. 2. Upstream–downstream issues in the Syrdarya river basin Initially, upstream–downstream issues in the Syrdarya river basin originated in the beginning of the 1960s. Until that time, natural flow of the river met water needs of the users and environmental flow to the Aral Sea. The natural flow regime had high flow in summer and low flow in winter. This regime was suitable for irrigated agriculture—the main historical water user in the region. Expansion of irrigated land in the basin from the 1960s stimulated the development of large storage facilities for regulation of the river flow. The Toktogul reservoir with a total capacity of 19,500 Mm3 was constructed upstream of the Naryn river; the others were the Andijan reservoir (1750 Mm3 ) at the inflow point of the Karadarya river to the Fergana valley, and the Kairakum (2550 Mm3 ) and the Chardara (4500 Mm3 ) reservoirs downstream of the Syrdarya river (Fig. 1). By 1988, the total reservoir capacity of the Syrdarya river basin reached 32,500 Mm3 . This allowed further expansion of the irrigated area to 3.36 million hectares (Mha). About half of this expansion was made possible by the development of the downstream, virgin land where irrigated area increased from 456 to 977 thousand ha (Rubinova, 1979, 1987). Water withdrawal from the river for irrigation amounted to 85% of the total long-term
annual river flow of 37,200 Mm3 /year against 40% before the 1960s, which significantly reduced the river inflow to the Aral Sea. This was the first manifestation of the upstream–downstream conflicts in the basin. The next manifestation occurred in the winter of 1992–93, when the operation of the Toktogul reservoir was changed to maximize hydropower production rather than meeting downstream irrigation needs. This resulted in a shift of the main releases from the reservoir from summer to winter months and in a drastic change in the river flow regime in downstream sections of the river. The river inflow to the Fergana valley (at Uchkurgan flow gauging station) in winter reached 8350 Mm3 /season against 5250 Mm3 /season in average before 1992 (Mustafaev et al., 2006). Summer releases from the Toktogul reservoir decreased from 7750 to 5000 Mm3 /season in average to accumulate flow for subsequent use in winter. As a consequence, from 1966 to 1991 the ratio of summer to winter flow dropped from 2–3 to below 1 (Fig. 2). This change of the river flow below the Toktogul created severe issues downstream (Keith and McKinney, 1997; Abbink et al., 2005; Mustafaev et al., 2006). While hydropower production in the upstream increased by 30%, the shortage of irrigation supplies became large and was estimated at 2000 Mm3 /year or 20% of annual irrigation water demand on average (Mustafaev et al., 2006). Irrigated agriculture downstream of the Toktogul reservoir command area was significantly affected. Between 1990 and 2000, in Mirzachul steppe located on the left bank downstream of the river, cotton yields plummeted by 46% and some of the lands were taken out of production due to the irrigation water shortages and increasing salinity (Kushiev et al., 2005). This has had a direct impact on the downstream agricultural production with estimated losses of around $90.4 million on over 555,000 ha (Keith and McKinney, 1997). Yield of cotton declined in this area below 2 t/ha due to shortage of irrigation water and salinity buildup in the topsoil. Farmers were able to irrigate cotton once or twice a year only, instead of the recommended frequency of four to five times (Djumadilov et al., 2006). The most visible consequence of the shift in the flow regime was however the expansion of the saline Arnasai depression (Fig. 1a) (Kholmatov et al., 2001; Mustafaev et al., 2006). Because of irrigation needs, the downstream Kairakum and Chardara reservoirs accumulate flow starting in October. From January to March when hydropower releases arrive, they are already full. The water passing further downstream is often blocked by the frozen Syrdarya. Another reason is that the dry riverbed below the Chardara reservoirs is occupied by the local population. Expansion of the irrigated agriculture since the 1960s upstream of the Chardara reservoir has resulted in high water diversions upstream and low flow to the river downstream. Under such conditions, the population occupied highly fertile soils in the dry riverbed below the Chardara reservoir for crop production and settlement schemes. This totally changed the shape of the riverbed and reduced the maximum flow capacity
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to 800 m3 /s. Hence, the extra hydropower winter releases from the Toktogul reservoir were forced into the Arnasai depression. Starting from the winter of 1992–93, the total volume of the river flow discharged from the Chardara reservoir into the Arnasai depression exceeded 34,000 Mm3 . The total storage of water accumulated in it was around 40,000 Mm3 (Mustafaev et al., 2006). Its surface water area increased from 2000 km2 in 1991 to 3600 km2 in 2005 and evaporation losses at the rate of 1000 mm/year amounted to 3600 Mm3 /year, i.e., about 10% of the annual flow of the Syrdarya river. Proposals to rectify this new water management situation in the basin primarily focus on the construction of new reservoirs downstream of the Syrdarya river (Mustafaev et al., 2006). However, while the analysis is not yet complete, the efficiency of reservoir water storage under such climatic conditions is questionable. Any new surface storage increases nonproductive losses for regulation of the river flow. There is also a concern that high leakage from the reservoirs proposed in the irrigated zone may raise water tables and increase salinity (Mustafaev et al., 2006). Climate change will also pose new challenges in the future as surface reservoirs have to deal with yet unpredictable flow variability. There is therefore a need to examine alternative strategies, like the one proposed in this paper. The fourfold methodology described in the next section has been used in this study.
water/surface water interactions; however they are the subject of future studies.
3. Data and methods
3.2. Assessment and mapping of the potential for groundwater irrigation
3.1. Analysis of the river flow Analysis of river flow is necessary to understand hydrological interactions between the irrigated areas and the aquifers of the Fergana valley and the Syrdarya river. It is necessary to examine the contribution of other factors, such as return flow from irrigated areas in the valley itself, to the overall river flow regime downstream. This understanding may be inferred from the analysis of observed flow records and water table data. Observed river flow time series at three flow stations – Uchkurgan (on Naryn), Kal and Akdjar (on Syrdarya, Fig. 1b) – were used for this analysis. These data were provided by the Syrdarya Basin Water Management Organization (BVO Syrdarya) and the Hydrometeorological service of Uzbekistan (GlavHydromet) (CAWATERinfo, 2008a,b). The interactions between surface water and groundwater were determined from the ArcView groundwater contour layer created, based on values of water table depth obtained from the State Water Register (‘Vodny Kadastr’), collected by the Information Center of the Institute of Hydrogeology and Engineering Geology (Mavlonov et al., 2006). The return flow to the riverbed was taken from the annual reports of the hydrogeology and land reclamation expedition of the Syrdarya-Sokh Basin Irrigation System Administration (Ganiev, 2008, 2009; personal communication) and the Hydrometeorology service of Uzbekistan (Ivanov, 2008, 2009; personal communication). Transit flow is calculated from the river flow by deducting the water withdrawals from the riverbed. Return flow is taken equal to the drainage flow to the riverbed, since the subsurface flow is much less. Water budgets were compiled for the Syrdarya river reach between Uchkurgan and Akdjar flow gauges. The budget accounts for inflow of the Naryn and the Karadarya rivers, water withdrawal for irrigation and losses from the river between Uchkurgan and Kal flow gauges, and lateral drainage and subsurface inflow to the river between Kal and Akdjar gauges (Fig. 1b). Salinity of the water recharging the groundwater from below 500 mg/l in the natural groundwater recharge zone increases to above 1000 mg/l in the central part of the valley. The blending effect of the recharge and the groundwater can be quantified through the mass-balance studies which can provide qualitative indications of the ground-
Fig. 3. Hydrogeological zoning of the Fergana valley.
The use of groundwater for irrigation in the Fergana valley can reduce return flow to the valley downstream. However, it is necessary to establish which areas of the valley are suitable for irrigation from groundwater. The areas with potential for groundwater irrigation were determined using multiple relevant characteristics and hydrogeological features of the valley. The first was the hydrogeological zoning map of the area which was carried out by the Institute of Hydrogeology and Engineering Geology (Mirzaev, 1974). Three hydrogeological zones within the Fergana valley (Fig. 3) were established by Mirzaev (1974): the natural groundwater recharge zone (A); groundwater spring discharge zone (B), and groundwater upwelling zone with discharge to drainage (C). The eastern, northern and southern parts of the valley constitute the natural groundwater recharge zone (Zone A) with high transmissivity and a deep water table. The central part of the valley representing the groundwater upwelling zone (Zone C) has limited transmissivity and the water table is controlled by means of open drains. Between these two, there is a groundwater spring discharge zone with a shallow water table (Zone B). Other characteristics used in determining areas with potential for irrigation development included (i) transmissivity of the waterbearing stratum, (ii) depth of the water table, and (iii) salinity of the groundwater. Groundwater data (transmissivity, water table depth, salinity) were obtained from the hydrogeological surveys carried out by the Institute of Hydrogeology and Engineering Geology in the Fergana valley (Mirzaev, 1974; Borisov, 1990; Mavlonov et al., 2006). Hydrogeological conditions were categorized into different classes based on transmissivity ranges: (i) poor, with transmissivity less than 100 m2 /d; (ii) low, transmissivity in the range of 100–300 m2 /d; (iii) good, 300–1000 m2 /d, and (iv) high, above 1000 m2 /d. Depth to the water table was also categorized into four classes: (i) above 3 m; (ii) 3–7 m; (iii) 7–12 m, and (iv) below 12 m. Groundwater salinity was categorized into three classes: (i) below 2000 mg/l; (ii) 2000–4000 mg/l, and (iii) above 4000 mg/l. The information on soil types in the valley was obtained from studies of the Uzbek State Design Institute for Water and Land Reclamation (Khasanhanova et al., 2006). The groundwater quality changes as affected by the intensive water extractions and man-
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aged aquifer recharge were not analyzed in this paper and will be subject for future research. Several GIS layers were created using ESRI ArcView 3.2 and Spatial Analyst based on the above data. They include: aquifers of the Fergana valley; depth of the water table; salinity of groundwater; transmissivity of the water-bearing stratum; hydrogeological zoning; and specific yield of deposits of the water-bearing stratum. These layers together allowed zones of varying potential for groundwater irrigation to be identified as shown in Section 4. Apart from identification of areas suitable for groundwater irrigation, the water budgets of the aquifers were analyzed with multiple objectives including determining a potential for groundwater extraction from these areas. Groundwater budgets were analyzed for high flow (1995) and low flow (2001) years for each aquifer of the Fergana valley as described in Karimov et al. (2008) and Gracheva et al. (2009). 3.3. Identification of capacity for groundwater banking The next step is to estimate areas with available free storage capacity, and areas with potential capacity, which could be created by extraction of groundwater for irrigation. Such areas – areas of water banking – were identified using GIS (ESRI ArcView 3.2 and Spatial Analyst). Groundwater storage potential was estimated, based on the specific yield of the water-bearing stratum and the thickness of the aeration zone below a depth of 3 m (Gracheva et al., 2009). Areas suitable for water banking were determined in Zone A with transmissivity of the water-bearing stratum exceeding 300 m2 /d and the water table below 3 m. Areas with potential for water banking after drawdown of the water table below 3 m were determined in Zone B with transmissivity of the water-bearing stratum exceeding 300 m2 /d. It was assumed that groundwater recharge from rivers, main and secondary irrigation canals, as well as from irrigation fields, needs to be stored during winter months in Zone B. Two sources of winter groundwater banking specified are Sokh river for recharge in Zone A and Big Fergana Canal (BFC) in Zone B. The Sokh river flow can be recharged through an infiltration basin, channels of the natural water courses and canals, or by applying winter irrigation. Groundwater banking from BFC can be applied by transportation of winter flow through the canal, dug-wells or the open drainage system.
Fergana Canal (BFC) inside the model area is simulated as a river. Natural recharge, occurring directly as infiltration from precipitation, and seepage from streams of the Sokh river were included in the model. Another form of recharge is excess irrigation. Five scenarios were developed to estimate groundwater extraction and water banking potential. • Scenario 1 simulates current conditions. This scenario assumes ‘no water banking’. Summer extraction of groundwater for irrigation under this scenario is estimated at 117 Mm3 /year. • Scenario 2 simulates groundwater extraction at maximum feasible level determined by annual recharge of 621 Mm3 /year. This scenario also assumes ‘no water banking’. • Scenario 3 simulates groundwater extraction at the same maximum feasible level, but includes ‘water banking’ determined by the winter flow of the Sokh river in a high water year (268 Mm3 /season). • Scenario 4 simulates groundwater extraction at the same maximum level but includes ‘water banking’ determined by the winter flow of the Sokh river in a low water year (144 Mm3 /season). • Scenario 5 simulates groundwater extraction at the same maximum level but includes both water banking’ determined by the winter flow of the Sokh river in a high water year and additional water transportation through BFC in winter. The simulation results for the current scenario were evaluated based on the data cited in Mavlonov et al. (2006). Details of the model compilation and calibration are given in Gracheva et al. (2009). 4. Results and discussion 4.1. Analysis of river flow within the Fergana valley The river flow within the Fergana valley increases in winter and decreases in summer; however, there are differences before and after 1992 (Fig. 4). Before 1992, under the irrigation mode of operation of the Toktogul reservoir, the ratio of summer to winter flow
3.4. Simulation modeling using Visual MODFLOW Simulation modeling is necessary to estimate the actual potential of water banking in the aquifers. The Sokh aquifer selected for groundwater banking modeling studies is formed in the fan of the Sokh river and is composed of 120-m thick shingle deposits. It has a high potential for artificial recharge development and, consequently, for water banking (Mirzaev, 1974; Akramov, 1991). The three-dimensional model of the Sokh aquifer was set up using Visual MODFLOW (Waterloo Hydrogeologic Inc., 2000). Parameters of the model were calibrated manually using criteria of Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Normalized RMSE and mass balance. The details of the model and the input data are given in Gracheva et al. (2009). The surface of the model domain is approximately 2751 km2 . The model has a spatial grid of 150 m and consists of 335 rows and 365 columns. A period of 5 years with a time step of 30 days was used. The three geological strata are represented as five layers in the model. Groundwater in layer 2 is unconfined in Zone A and confined in Zones B and C; it is also confined in layers 3, 4 and 5. The model is bounded on the north by general head conditions governing drainage outflow. The western and eastern boundaries are zeroflow ones lying at the edges of the aquifer. The upstream condition is a fixed-flow boundary, representing underground inflow. The Big
Fig. 4. Syrdarya river flow at the inflow and the outflow nodes of the Fergana valley under (a) irrigation mode (1992) and (b) hydropower generation mode (2001) operation of the Toktogul reservoir.
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Fig. 6. Zoning of Fergana valley by irrigation water sources.
Fig. 5. The structure of the Syrdarya river flow at the Akdjar gauge under (a) the irrigation mode (1992) and (b) the hydropower generation mode operation of the Toktogul reservoir (2001).
was estimated to be 1.27 at the inflow point (Uchkurgan) and 0.86 at the outflow point (Akdjar) of the river (Fig. 4a). The valley was increasing the river flow in winter and in the first half of summer. It also was decreasing river flow from June to August. After 1993, under the hydropower mode of operation of the reservoir, the ratio of summer flow to winter flow has decreased to 0.77 at the inflow point and to 0.40 at the outflow point (Fig. 4b). The Fergana valley has become the consumer of the river flow in summer from May to September and continued to be a source of the river flow in winter from September to April. The causes of this change in river flow can be identified through an analysis of the structure of the flow at the outflow point (Akdjar). Fig. 5 compares monthly discharges of transit flow in the river (releases from Toktogul) with monthly discharges of return flows to the river in 1992 and 2001. Before 1992, the return flow to the riverbed had a maximum from February to May with a peak in April–May of 887–1285 Mm3 /month (Fig. 5a). After 1993, the return flow was at a maximum from November to February and was much less in the summer months than at the previous stage (Fig. 5b). The return flow from the valley to the river in winter months constitutes 40% of the river flow at the outlet of the Fergana valley. The return winter flow from the valley at present amounts to 4000–5000 Mm3 /season. As a consequence, the Syrdarya river flow discharge increases to 1000 m3 /s in winter and falls to 150 m3 /s in summer. While previous studies highlighted hydropower winter releases (Keith and McKinney, 1997; Abbink et al., 2005; Mustafaev et al., 2006), this study found that the superposition of the return flow to the river from the valley, with the winter hydropower releases from Toktogul, created surplus flow which exceeded the capacities of downstream reservoirs (Kairakum and Chardara) and forced the surplus winter flow into the Arnasai depression (Fig. 1a).
able for groundwater irrigation were proposed to be those where transmissivity exceeds 300 m2 /d, water depth is above 3 m and salinity is below 2000 mg/l. Conjunctive use is recommended for areas with transmissivity exceeding 300 m2 /d, water depth ranging between 3 and 12 m, and salinity below 4000 mg/l. Canal irrigation is most suitable under conditions with a water table below 12 m and in areas with a transmissivity less than 300 m2 /d. Isolated wells were recommended for areas with transmissivity in the range of 100–300 m2 /d. The assessment suggests that the potential area for groundwater irrigation is 290,000 ha while for conjunctive use of groundwater and canal water it is 243,000 ha. The system of canals will irrigate the rest of the area. The potential of groundwater extraction for irrigation depends on proper hydrogeological conditions (Zones A and B) and recharge volumes (Table 1). Since groundwater in Zone C is saline and the aquifers have low transmissivity, this zone is not considered in this table. Table 1 shows that the potential maximum annual groundwater extraction is in the range of 5624–6005 Mm3 /year, depending on the year. However, maximum extraction may bring the annual overdraft of groundwater resources to the level of 1885–1955 Mm3 /year.
Table 1 Groundwater recharge of the Fergana valley in high (1995) and low (2001) water years (Mm3 ). Zone Source of recharge
a
S
A
S
577 1320 250 130 1013 768 4056
445.4 97 1074 292 88 88 283 6 557 557 297 297 2744 1336
542 1366 176 289 1113 594 4080
273 650 87 18 0 14 1042
94 242 87 74 14 14 526
368 892 174 92 14 28 1568
249 592 174 179 73 40 1306
94 233 174 5 73 40 619
343 825 348 184 146 80 1926
3739
1885
5624
4050
1955
6005
B
From irrigated fields Leakage from lateral canals Leakage from main canals Precipitation Subsurface inflow Leakage from river Sub-total, Zone B Total (Zones A + B)
b c
Summer. Winter. Annual.
c
101 267 125 99 384 384 1359
From irrigated fields 476 Leakage from on-farm canals 1053 Leakage from main canals 125 Precipitation 31 Subsurface inflow 629 Leakage from river 384 Sub-total, Zone A 2697
a
2001 b
W
A
4.2. Groundwater development potential Fig. 6 shows the results of the zoning of the Fergana valley on groundwater development potential for irrigation. Areas suit-
1995
W
A
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A. Karimov et al. / Agricultural Water Management 97 (2010) 1461–1468 Table 2 Free capacities of aquifer in the Fergana valley. Aquifer
Recharge zone Area (ha)
Almas-Vorzik Kukumbay Kasansay Iskovat-Pishkaran Sokh Altiarik-Beshalish Namangan Isfara Maylisu Karaungur Naryn Chust Pap Andijan-Shahrihan Chimion-Aval Osh-Aravan Nanay Fig. 7. Zones with potential for water banking in the Fergana valley.
This water provides supplies for municipal, industrial and irrigation needs. Groundwater use for municipal water supply and industry amounts to 1760 Mm3 /year in current conditions and is projected to be 2000 Mm3 /year in 2025 (Borisov, 1990). Therefore, groundwater resources available for irrigation now and in the near future are in the range of 3600–4000 Mm3 /year. Extraction of annual groundwater recharge in summer may significantly reduce return flow from the valley to the river. At the same time, there would be a drawdown of the water table. Aquifer recharge would need to be managed to prevent issues related to groundwater depletion, degradation of groundwater quality and high cost of extraction. 4.3. Water banking potential in the Fergana valley The shift from canal to conjunctive use of groundwater and canal water for irrigation will change the groundwater budget because water withdrawals from surface water sources and leakage from the canal systems will both decrease. Groundwater recharge under the new conditions is estimated to decrease from 8200 to 6500 Mm3 /year. Deficits of groundwater recharge can be compensated for by banking the winter flow of the Naryn and small rivers. The distribution of zones with favorable conditions for water banking is shown in Fig. 7 while Table 2 lists their estimated areas and capacity (potential for water banking). The data in Table 2 show that there is a free capacity of over 3000 Mm3 in the recharge Zone A, which could be used for banking
Total
Free capacity (Mm3 )
19,825 2658 4351 19,439 34,589 7366 5196 4385 17,513 3944 28,393 7936 7919 3651 21,223 4349
231 54 30 359 1452 28 77 90 22 5 167 147 16 88 324 71
192,737
3159
of winter flow of small rivers. This capacity is more than the winter flow of small rivers totaling 1000 Mm3 /year. Most of the indicated capacities are located at high altitudes where the flow of the Naryn river cannot be transported by gravity. Capacities in command zone of the canals transferring water of the Naryn river could be created by intensive groundwater extraction for irrigation (Table 3). Table 3 suggests that free capacities of the subsurface aquifers under command areas of canals transporting flow of the Naryn river amount to 769 Mm3 . This study found that additional capacities can be created at 186 Mm3 per m of drawdown by intensive groundwater extraction in the summer season. Together, this would equal nearly half the current shortfall of summer irrigation water. This shows that the physical capacities for groundwater banking do exist. However, careful economic analyses and modeling for each aquifer are required to assess to what extent groundwater banking is economically viable. Also, the groundwater banking will need to be seen in connection with water saving to reduce the return flow to the river. 4.4. Modeling water banking in the Sokh aquifer Simulations of the Sokh aquifer suggest that groundwater development for irrigation with no managed recharge (i.e. no water banking—Scenario 2) lowers the water table (Fig. 8a) and increases the cost of groundwater extraction. The water banking under high (Scenario 3) and low (Scenario 4) water year conditions allows avoiding a significant drawdown of the water table. A combination
Table 3 Availability and potential capacity for groundwater banking in the command areas of the canals from the Naryn river. Aquifer Naryn Naryn Naryn Namangan Namangan Mailisu Andijan-Shahrihan Altyarik-Beshalysh Sokh Isfara Total a b c d
Big Fergana Canal. Big Andijan Canal. Northern Fergana Canal. Big Namangan Canal.
Recharge source (canal) a
BFC BACb NFCc NFC BNCd BFC BFC BFC BFC BFC
Area (ha) 36,859 24,440 23,769 20,228 5371 20,547 4443 17,171 27,561 8828
Capacity available (Mm3 )
Potential capacity per m of drawdown (Mm3 )
158 52 85 181 77 5 0 0 126 85
37 24 24 19 5 20 4 17 28 8
769
186
A. Karimov et al. / Agricultural Water Management 97 (2010) 1461–1468
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Fig. 9. Leakage from the Big Fergana Canal (BFC) under the various scenarios of groundwater development.
in winter under Scenario 2, accordingly. These data show further available capacity for water banking. The modeling studies found a clear correlation between groundwater extraction and total recharge on the one hand and return flow and groundwater extraction, on the other (Fig. 10). The data presented in Fig. 10 illustrate that increasing the groundwater recharge in the hydrogeology Zones A and B from 283 to 587 Mm3 /year would increase the potential for groundwater extraction from 117 to 550 Mm3 /year; this will reduce the return flow from 169 to 69 Mm3 . Fig. 10b provides a simple illustration of how additional groundwater extraction may reduce return flow from the study area to the riverbed. The correlation obtained from Fig. 10 could be applied for groundwater development in the study area. The summary of comparative advantages of the winter water banking and conjunctive use of groundwater and canal water for irrigation in summer is given in Table 4.
Fig. 8. Water table (a), evaporation from the water table (b), and return flow (c) as affected by groundwater extraction and banking in the Sokh aquifer.
of the increased groundwater extraction in summer and managed recharge in winter reduces nonproductive water losses for evaporation and decreases return flow from the study area (Fig. 8b, c). Fig. 8c shows that the model results were approaching the dynamic equilibrium condition at the end of the 5 years of simulation, but had not yet reached it. The results obtained would change a little if the simulations were run for longer periods. Scenario 5 simulates the transit winter flow of the Naryn river through the BFC crossing the study area in the upper part of the Sokh fan. The results suggest that increasing the groundwater summer extraction under Scenario 2 from 117 to 550 Mm3 /season creates a free storage capacity of 10–20 m thickness around the canal, and therefore increases the leakage from it (Fig. 9). Considering that there are other aquifers where this strategy could be applied (Fig. 7), the indicated figures are to be updated for the whole Fergana valley. The data presented in Fig. 9 show that water transportation through the BFC in winter months in Scenario 5 results in a recharge of 140 Mm3 /season, against 46 Mm3 /season under Scenario 1 and 100 Mm3 /season under Scenario 2. In total, winter flow volumes in the range of 252–396 Mm3 /season were recharged annually into the Sokh aquifer. The water table is stabilized in the hydrogeological Zone B at depths of 9–12 m below the surface in summer and 1–4 m in winter as compared to 13–19 m in summer and 6–10 m
Fig. 10. Correlation between (a) groundwater recharge and extraction, and (b) groundwater extraction and return flow for the Sokh aquifer.
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Table 4 The main parameters of simulated scenarios of groundwater development in the Sokh river basin (Mm3 ). Parameter
Scenario 1
Scenario 2
Scenario 3
Scenario 4
Scenario 5
Return flow Evaporation from the water table Leakage from BFK Free subsurface capacity Saving of surface water
228 651 46 6 0
107 316 108 653 521
163 384 108 323 551
133 336 108 588 529
168 389 140 301 486
The data presented in Table 4 illustrate that a shift from canal irrigation in the Sokh river basin to conjunctive water use will reduce irrigation demand for surface water by 486–551 Mm3 /year. Return flow will decrease from 228 Mm3 /year to 133–168 Mm3 /year. The winter flow of the Sokh river recharged into the aquifer would amount to 144 Mm3 in low water years and to 268 Mm3 in high water years. In addition, 96 Mm3 of flow of the Naryn river could be recharged into the aquifer by transportation in winter through the BFC. This will result in 500 Mm3 of groundwater available for irrigation in summer. No drawdown of the water table is expected in the long run under groundwaterintensive development for irrigation in summer and water banking in winter (Scenarios 4 and 5). This strategy will bring regional benefits. The flow of the Syrdarya river will decrease in winter by 300 Mm3 /season and increase in summer by 486–551 Mm3 /year thanks only to the proposed measures in the Sokh river basin. The change in timing of aquifer contributions through the river gains and return flows to the river is confirmed by the river flow analysis and the groundwater modeling. 5. Conclusions Groundwater development for summer irrigation and storage of the winter flow of rivers in aquifers can be a feasible practice for transboundary river basins with vulnerable water resources. This strategy allows reduction of the pressure on river basins in extreme situations emerging from increased water demands and exposed water resources. A shift from the use of canal irrigation to conjunctive use of groundwater and canal water, combined with banking of winter flow reduces return flow from the irrigated zone to the riverbed, reallocates a part of the surface flow from upstream to downstream, ensures improved water supply of downstream water users, and eliminates the threat of drawdown of the water table due to shift to groundwater irrigation. The studies found that the advantage of the proposed approach is the change in timing of the contributions of the aquifers through both river gains and return flows to the river. The change in timing between the groundwater recharge and the return flow is controlled by distance, storage coefficient and transmissivity. This strategy would contribute to sustainable merging of the upstream hydropower and downstream irrigation and environmental needs. Further pilot modeling and field studies are required to examine the economically and environmentally optimal combination of summer extractions and winter banking for each aquifer of the Fergana valley. Acknowledgements The authors gratefully acknowledge the financial support of the OPEC Fund for International Development. Observed flow data used
in this study were provided by the Syrdarya Basin Water Management Organization (BVO Syrdarya) and the Hydrometeorological Service of Uzbekistan (GlavHyromet). Water table depth and other groundwater-related data were provided by the Information Center of the Institute of Hydrogeology and Engineering Geology of Uzbekistan. Soil data were taken from studies of the Uzbek State Design Institute for Water and Land Reclamation. The authors are grateful to Dr. Hugh Turral (formerly, IWMI, Colombo) for his comments and advice. References Abbink, K., Moller, L.C., O’Hara, S., 2005. The Syr Darya river conflict: an experimental case study. http://www.igier.unibocconi.it/files/documents/ events/SyrDarya.pdf. Akramov, A.A., 1991. Regulating Fresh Water Resources in Subsurface Aquifers. Fan, Tashkent, Uzbekistan (in Russian). Borisov, V.A., 1990. Underground Water Resources and their Use in Uzbekistan. Fan, Tashkent, Uzbekistan (in Russian). CAWATERinfo, 2008a. On line data of the Syrdarya river basin. CAWATERinfo: http://cawater-info.net/Syrdarya/index e.htm. CAWATERinfo, 2008b. On line data of the Uzhydromet Center. CAWATERinfo: http://cawater-info.net/bd/index e.htm. Djumadilov, D.D., Anzelm, K.A., Sagimbaev, S., Kulambaev, K., 2006. Salinity on irrigated lands of Aral-Syrdarya water basin. In: Issues of Aral-Syrdarya Basin. Information Bulletin: 5. UNDP Kazakhstan, Kzylorda, pp. 61–70 (in Russian). Gracheva, I., Karimov, A., Turral, H., Miryusupov, F., 2009. Assessment of the potential and impacts of winter water banking in the Sokh aquifer, Central Asia. Hydrogeol. J. 17 (6), 1471–1482. Karimov, A., Turral, H., Mavlonov, A., Rahmatov, N., Manthritillake, H., Borisov, V., Anzelm, K., 2008. Regulating the winter flow of Syrdarya river in aquifers of Fergana valley. J. Water Resour. Kazakhstan 2, 17–26 (in Russian). Keith, J.E., McKinney, D.C., 1997. Option analysis of the operation of the Toktogul reservoir. Issue Paper No. 7. www.ce.utexas.edu/prof/mckinney/ ce397/Topics/Options Toktogul 3.pdf. Khasanhanova, G., Khamzina, T., Ibragimov, R., 2006. Assessment of crop water requirement in Fergana valley. In: Paper Presented in the Regional Conference on Conjunctive Use of Ground and Surface Water Resources of Fergana Valley for Irrigation, Tashkent, 2 November 2006 (in Russian). Kholmatov, E.I., Ishankulov, R., Mavlonov, A.A., Safarov, I., 2001. Arnasai-Aidarkul lake system: ecological problems, today and tomorrow. J. Ecol. Herald 2, 18–23, Tashkent, Uzbekistan (in Russian). Kushiev, Kh., Noble, A.D., Abdullaev, I., Toshbekov, U., 2005. Remediation of abandoned saline soils using Glycyrrhiza glabra: a study from the Hungry Steppes of Central Asia. Int. J. Agric. Sustain. 3 (2), 102–113. Mavlonov, A.A., Borisov, V.A., Djumanov, J.Kh., 2006. Assessment of underground water resources of Fergana valley. In: Paper Presented in the Regional Conf. on: Conjunctive Use of Ground and Surface Water Resources of Fergana Valley for Irrigation, Tashkent, 2 November 2006 (in Russian). Mirzaev, S.Sh., 1974. Underground Water Resources of Uzbekistan. Fan, Tashkent, Uzbekistan (in Russian). Mustafaev, J., Ryabtsev, A.D., Balgerey, M.A., Karlikhanov, O.K., 2006. Diversion of winter flow of Syrdarya below Chardara water reservoir. J. Water Resour. Kazakhstan 1, 5–7 (in Russian). Rubinova, F.E., 1979. Change of Flow of Syrdarya River as Affected by Basin Water Development. Gidrometeoizdat, Moscow, Russia (in Russian). Rubinova, F.E., 1987. Land Development and River Flow Quality in Aral Sea Basin. Gidrometeoizdat, Moscow, Russia (in Russian). Waterloo Hydrogeologic Inc., 2000. Visual MODFLOW User’s Manual. Waterloo Hydrogeologic Inc., Canada.