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Integrating MODFLOW and GIS technologies for assessing impacts of irrigation management and groundwater use in the Hetao Irrigation District, Yellow River basin XU Xu1,2, HUANG GuanHua1,2† & QU ZhongYi3 1
Center for Agriculture Water Research, China Agricultural University, Beijing 100083, China; Chinese-Israeli International Center for Research and Training in Agriculture, China Agricultural University, Beijing 100083, China; 3 Water Conservancy and Civil Engineering College, Inner Mongolia Agricultural University, Hohhot 010018, China 2
Due to severe water scarcity, water resources used in agricultural sector have been reduced markedly in Hetao irrigation district. Application of water-saving practices (WSPs) is required for the sustainable agricultural development. The human activities including WSPs and increase of groundwater abstraction can lower down the groundwater table, which is helpful to the salinity control. Meanwhile, an excessively large groundwater table depth may result in negative impact on crop growth and fragile ecological environment. In this paper, the Jiefangzha irrigation system in Hetao irrigation district was selected as a typical area, a groundwater flow model based on ArcInfo Geographic Information System (GIS) was developed and implemented to quantify the effect of human activities on the groundwater system in this area. The pre- and post-processing of model data was performed efficiently by using the available GIS tools. The time-variant data in boundary conditions was further edited in Microsoft Excel with programs of Visual Basic for Application (VBA). The model was calibrated and validated with independent data sets. Application of the model indicated that it can well describe the effect of human activities on groundwater dynamics in Jiefangzha irrigation system. groundwater flow modeling, MODFLOW, GIS, water-saving practices, irrigation district
1 Introduction The Hetao irrigation district (Hetao), located at the upper reaches of the Yellow River basin, is one of the three largest irrigation districts of China[1]. It has a typical arid and semi-arid continental climate. The irrigation water is drawn from the Yellow River, while the groundwater is mainly for domestic and industrial use. Excessive water diversions from the river and poor irrigation have caused severe water logging and salinity. Due to more severe water scarcity in the Yellow River basin, the irrigation water drawn from the Yellow River to Heao has been required to cut from 5.2×109 m3/a to less than 4.0×109 m3/a. Therefore, diversified water saving practices (WSPs) have been taken in irrigation districts to improve both water conveyance efficiency and water use effi-
ciency[2]. Application of WSPs and the increase of groundwater abstraction will cause a decline of groundwater table, thus leading to the control of water logging and salinity. However, an excessive lowering of the groundwater table may result in negative impacts on crop growth and on fragile ecological environment due to reduced capillary rise as referred to in previous researches[3]. These impacts seem to be major when the groundwater table depth is greater than 3 m. Therefore, it is essential to investigate the impact of human activities on groundwater dynamics, mainly irrigation WSPs and the increase of groundwater abstraction in the Hetao area. Received July 2, 2009; accepted August 4, 2009 doi: 10.1007/s11431-009-0328-5 † Corresponding author (email:
[email protected]) Supported by the Chinese 11th Five Years’ Research Programs (Grant Nos. 2006BAD11B06, 2007BAC08B02) and the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA100207)
Citation: Xu X, Huang G H, Qu Z Y. Integrating MODFLOW and GIS technologies for assessing impacts of irrigation management and groundwater use in the Hetao Irrigation District, Yellow River basin. Sci China Ser E-Tech Sci, 2009, 52(11): 3257―3263, doi: 10.1007/s11431-009-0328-5
The groundwater flow model is an appropriate tool to assess the effect of proposed future human activities on groundwater dynamics. Coupling the geographic information system (GIS) technology to process-based groundwater model can facilitate hydrogeological and hydrologic system conceptualization and characterization. Strategies for GIS and model integration can be categorized as loose coupling, close coupling and embedded coupling. The advantage of loose coupling can facilitate further changes in the model independently. Contrarily, the embedded coupling and closing coupling require significant investment in programming and data management. Both approaches impose more constraints when changes are needed[4]. Consequently, the loose coupling is selected for this study. Various studies have confirmed the appropriateness of coupling the GIS and groundwater flow modeling[5−8] and shown that most strategies and methods to couple a groundwater flow model with GIS are specific to the study area. Some new GIS functions could further support the requirements of process-based approaches in addition to the overlay or index operations. However, there are few studies on the impacts of WSPs on groundwater dynamics using a coupled GIS and groundwater flow model. In view of improving the knowledge on Hetao water use and groundwater dynamics, the main objectives of this study are to develop an integrated methodology based on loose coupling of a groundwater flow model and GIS to assess the impacts of irrigation WSPs and the increase of groundwater abstraction on the groundwater dynamics in the Jiefangzha irrigation system (JFIS) in the Hetao irrigation district, in the upstream of the Yellow River basin.
2 Study area The main part of the JFIS, located at the southeast of the main drainage ditch and northwest of the main canal, is selected as the case study area (Figure 1). It is bounded by the fourth sub-main drainage ditch and Yongji sub-main canal in the east, and by the first sub-drainage ditch and Wulahe sub-main canal on the southwest border. The JFIS is the second largest system in the Hetao with a total area of 215,700 ha. It has a flat topography, with a gradient of about 1/5000 from southeast to northwest. The study area has a typical arid to semi-arid continental climate. The mean annual precipitation is only 3258
Figure 1 The study area, locations of the observation wells used for model calibration and validation and groundwater flow directions in the first aquifer group.
155 mm, with 70% of rainfall occurring during July to September. The mean annual evaporation is about 2000 mm. Irrigation is essential during the entire crop growing seasons and surface basin irrigation is the major irrigation method. Canal seepage and field percolation cause the rising of the groundwater table. Groundwater is either used by the crops through capillary rise or, due to the poor drainage system, is discharged by evaporation. The latter results in severe problems of salinization[1]. The appropriate target groundwater table depth in crop growing seasons is 1.5 to 2.0 m. However, drainage conditions are not adequate to achieve these target depths. Groundwater table depth greater than 3.0 m would bring about negative impacts on crop growth and fragile ecological environment. This basin is underlain by Quaternary sediments, mainly lake sediments and alluvial deposits of the Yellow River. The Quaternary systems become thicker from south to north where regional subsidence has occurred. The thickness of Q4 is about 6 to 25 m, while that of Q3 ranges from 35 to 240 m in the southeast-to-northwest direction. The deposition properties for Q4 are mainly clay-sand in the south and clay with interlayers of silt sand in the north, while the deposition properties for Q3 consist of fine-medium sand, fine sand and silt sand with clay interlayers. The upper layer of Q2 (Q22) is underlain as a layer of stable muddy clay with a thickness of 20 to
Xu X et al. Sci China Ser E-Tech Sci | Nov. 2009 | vol. 52 | no. 11 | 3257-3263
40 m, which acts as a relatively low permeable layer preventing vertical flow.
3 Methodology MODFLOW-2000[9], developed by the US Geological Survey was selected to simulate the behavior of groundwater flow in the study area because it is a well-documented, extensively tested and verified model that can be readily incorporated into studies for optimal water resources management. The model consists of a main program and a large number of highly independent subroutines called modules. The modules are grouped into packages which deal with single aspects of the simulation. The packages including Recharge (RCH), Well (WEL), River (RIV), Drainage (DRN) and Evapotranspiration (EVT) were used in this study. The Visual MODFLOW is a powerful MODFLOW pre/post processor[10], and the version 4.2 was used to simulate three-dimensional unsteady groundwater flow. The ArcInfo version 9.2 (Environmental Systems Research Institute, ESRI) with Access databases (Microsoft) was used to aid the development of model. The data acquired
Figure 2
in disparate formats and scales were converted to digital format and processed to form a GIS database (Figure 2). The lengthy process of spatial database development included converting the data to digital format, building the geodatabase and finally editing the data. The GaussKrueger projection and Beijing1954 Coordinate System were selected to integrate the different spatial data. Physical and hydrogelogical data were used to develop a conceptual model by using the available ArcInfo tools. The topology, subtype and domain were created in geodatabase. The relationships were created between feature classes, tables, or feature classes and tables. The geodatabase was connected with a database management system (DBMS), i.e. Access for efficient management of the GIS database. Figure 2 shows the flow chart to develop the groundwater flow model of JFIS. The data files of aquifer-system stress factors were further processed in Microsoft Excel with Visual Basic for Applications (VBA) programs to obtain the acceptable format data. The output of MODFLOW data, e.g. the spatial distribution of groundwater table depths, was analyzed based on Spatial Analysis tools and 3D Analyst tools with the arid of VBA programs.
Schematic procedure for data processing and construction of groundwater flow model.
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Groundwater flow modeling
The first aquifer system (Q3 and Q4) was discretized into two sub-aquifers, i.e., the first and the second subaquifers. A uniform rectangular grid with square cells of 200 m was adopted. The first layer representing the Q4 is a low-permeable layer, while layers 2 to 4 refer to the Q3 aquifer, and have higher permeability, with uniform hydrogeological parameter values and uniform spacing. It is assumed that the aquifer is horizontally isotropic with its horizontal hydraulic conductivity being 10 times larger than the vertical one. The horizontal hydraulic conductivity for first layer varies with values of 0.3 m/d to 1.0 m/d in the north-south (N-S) direction and the specific yield is in a range of 0.02 to 0.08. The layers 2 to 4 have the same hydraulic conductivity varying from 4 m/d to 18 m/d in the N-S direction, and their specific yield and storage coefficient vary respectively from 0.06 to 0.13 in the N-S direction and from 0.00028 to 0.0038. In the southeast boundary (Figure 1), the main canal was defined as a river boundary condition using the RIV Package in the first layer during the irrigation period (i.e. from May to early November). For layers 2 to 4, no flow boundary conditions were assumed. In non-irrigation period, flux boundary conditions for all layers were considered using the WEL Package, considering the relatively steady lateral flow from the Yellow River in the southeast according to hydrogeological survey[11]. In the northwest, the main drainage ditch was considered as a drain boundary for the first layer. Non-flow boundary was assumed for the lower layers according to hydrogeological investigation[11]. The first sub-main drainage ditch and the upper reaches of Wulahe sub-main canal form the southwest boundary, and they were simulated by using a drain boundary and a flux boundary for the first layer, respectively. While no flow boundary conditions were defined for the lower layers due to the horizontal groundwater flow direction approximately parallel to these boundaries. Similarly, the east boundary, consisting of the fourth sub-main drainage ditch and the upper reaches of Yongji sub-main canal, was considered as a drain boundary and a flux boundary only for the first layer, respectively. And no flow boundary condition was defined for lower layers. Initial values of groundwater levels in the first subaquifer were obtained by using the interpolation technique for May 1, 2004 and May 1, 2005 for model cali3260
bration and validation, respectively. The recharge rate of canal seepage from the main and sub-main canals was assigned to the cells using the RCH Package. Recharge from field percolation, rainfall and melt water was combined in a single effective rate, Re used in the RCH Package. The seepage along the lateral and lower-order distribution canals were embedded in Re as well. Thus, combining the irrigation water use, rainfall, and soil types, 73 recharge zones were defined using the extract and overlay functions. The amount of melt water recharge, which occurs in April, was estimated as the product of the specific yield Sy by the changes in water table depth. During the non-frozen period, groundwater evaporation is related to the evaporation demand of the atmosphere and the groundwater table depth. The EVT Package was used to calculated groundwater evaporation. Combining the land use, soil types and climatic Thiessen polygons, evapotranspiration zones were produced in polygon format based on extract and overlay functions. And 57 evaporation zones were determined. During the frozen period, evaporation values were estimated as the product of Sy and the changes of water table. Ground water, exploited for the industrial, domestic and livestock use was estimated with the pumping WEL Package. Only the main and sub-main drainage ditches were considered. Groundwater flow to drains was modeled using the DRN Package. Groundwater head data from twelve observation wells (Figure 1) were used for model calibration relative to the period from May 1, 2004 to April 30, 2005. This period was divided into twelve stress periods where computations were performed using a one-day time step. Monthly stress period was defined in primary During the irrigation season i.e. from May 1, 2004 to October 31, 2004 each period had a month duration while out of this season the stress periods ranged from 10 to 60 d according to specific conditions. A trial and error method was used in the calibration process with root mean square error (RMSE), standard error of the estimate (SEE) and model efficiency (EF) being the criteria. The calculated monthly groundwater table depths were in good agreement with the measured data of the selected 12 observation wells used for this process. The values of RMSE, SEE and EF were 0.21 m, 0.028 m and 0.98, respectively. The coefficient of determination R2 was equal to 0.98. The model was validated with data of six different observation wells (as
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shown in Figure 1) for the period from May 1, 2005 to April 30, 2006. The simulated monthly groundwater table depths agreed well with the measured data with RMSE= 0.24 m, SEE= 0.031 m, EF= 0.98 and R2 = 0.97.
5 Model application The canal system improvement will reduce water conveyance loss. The water use efficiency in field will be increased by the application of water-saving irrigation technologies[12]. Therefore five scenario alternatives were supposed as shown in Table 1, corresponding to the combination of different values of the conveyance ratio (a), the ratio of the deep percolation water to the irrigation water in field (c) and amount of groundwater abstraction by the year 2020. Here, both a and c values were calculated as an integrated values. In this study, we assumed that the ratio of seepage loss to the total canal water loss is a constant. The components of groundwater balance for irrigation period (i.e. from May to early November) were calculated for 2004 and the five scenario alternatives. In 2004, the recharge from irrigation water and evaporation of groundwater were the main factors for the variations of groundwater levels. The canal seepage and field percolation were 98.5 mm and 76.6 mm which accounted for 54.7% and 42.6% of the total recharge in irrigation period, respectively. The recharge from the precipitation only amounts to 4.9 mm. The main output of water from the aquifer was the groundwater evaporation which was 124.8 mm and accounted for 85.7% of the total discharge in irrigation period. Groundwater abstraction and discharge by drainage ditches only account for 5.7% and 8.6%, respectively. Results show that a 8.9 mm to 38.1 mm reduction of groundwater evaporation can be achieved as the irrigation water decreases by 8.6% to 34.2% for alternatives 1 to 5, compared to the situation of 2004. This implies the
alternatives can significantly reduce groundwater evaporation and thus are helpful to salinity control. While the proportion of exploitation to total discharge increases from 5.7% to 19.2%, the recharge from the irrigation water decreases by 12.8 mm to 95.9 mm, equal to 7.3% and 54.8% of that in 2004. The areas for different groundwater table depths were calculated in crop growing period (i.e. from June to August), without considering the canal and residential area. The areas with groundwater table depth less than 1.5 m were 51.5%, 46.4% and 40.3% of the total area in June, July and August of 2004, respectively. This indicates the groundwater table in certain area is close to the root zone, which may lead to salinization. Application of WSPs and increasing abstraction can reduce the area with groundwater table depth less than 1.5 m to 35.1%, 26.8% and 20.1% in June, July and August, respectively, for alternative 5. The area with appropriate groundwater table depth[1] i.e. between 1.5 m and 2.0 m for crop growth shows a slight change as the application of WSPs and increase of groundwater abstraction. The proportion of area with depths larger than 3 m was about 3% in 2004, but it increases to 14.5% to 23.5% during the period of June to August for alternative 5. This may negatively impact the local ecological system. Figure 3 shows the spatial distribution of groundwater table depths in July for different alternatives. In 2004, most area with groundwater table depth less than 1.0 m was in the northwest part. Most area in the southeast part had groundwater table depth close to or over 1.5 m. Only a small amount of area in the central and southern part had depth of water table over 3.0 m. Application of WSPs can increase the area with suitable groundwater table depth in the northwest part as shown in Figures 3 (b)—(d), while in the southeast part, groundwater table declines resulting in an increase in area with depth close to or above 3 m.
Table 1 Present situation and scenario alternatives for different water-saving practices and groundwater abstraction in JFIS Ratio of percolation water to Ratio of percolation water to Ratio of outflow to Item irrigation water in field for irrigation water in field for inflow of canal system autumn irrigation period c2 crop growing period c1 Present situation 0.50 0.24 0.40 Alternative 1 0.54 0.21 0.37 Alternative 2 0.57 0.18 0.34 Alternative 3 0.63 0.15 0.30 Alternative 4 0.69 0.12 0.27 Alternative 5 0.75 0.10 0.25
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Groundwater exploitation (104m3/a) 1633 4436 4436 4436 4436 4436
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Figure 3 The spatial distribution of groundwater table depths in July, where (a), (b), (c) and (d) are corresponding to the situation of 2004, alternatives 2, 3 and 5, respectively.
Application of high-level WSPs such as alternatives 4 and 5 may result in much more decrease of water table depth, which may lead to negative impact on crop growth and ecological environment. Therefore, alternative 3 with an improved integrated conveyance ratio of 0.63, and a percolation water ratio of 0.15 for crop growing period and 0.3 for autumn irrigation period, respectively is a reasonable WSP for the JFIS. The implementation of this comprehensive water-saving practice will result in a reduction of 23.7 mm for groundwater evaporation and a reduction of 104.3 mm for river water use. 3262
6 Conclusion We have developed a methodology by integrating the groundwater flow model and GIS technology to analyze the impact of water saving practices on groundwater dynamics of the Jiefangzha irrigation system (JFIS). Data sets collected in JFIS have been used to calibrate and validate the model. Five scenario alternatives corresponding to different WSPs have been proposed to simulate the groundwater dynamics with considering groundwater abstraction by the year 2020. Results show that
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groundwater table will decline markedly with the application of WSPs, which is helpful to salinity control. The alternative with an improved integrated conveyance ratio of 0.63, and a percolation water ratio of 0.15 for crop 1
growing period and 0.3 for autumn irrigation period, respectively is a reasonable WSP for this area. Based on this WSP, 23.7 mm of groundwater evaporation will be reduced and 104.3 mm of the irrigation water will be saved.
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