Supporting Information for
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Use of Flow Modeling to Assess Sustainability of
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Groundwater Resources in the North China Plain
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Guoliang Cao1,3, Chunmiao Zheng2,3,*, Bridget R. Scanlon4, Jie Liu2, and Wenpeng Li5
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School of Water Resources & Environment, China University of Geosciences,
Beijing, 100083, China
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Center for Water Research, College of Engineering, Peking University, Beijing
100871, China
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Department of Geological Sciences, University of Alabama, Tuscaloosa, AL 35487
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Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at
Austin, Austin, TX 78758
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China Institute of Geo-environmental Monitoring, Beijing100081, China
(*corresponding author: czheng@pku.edu.cn; phone: +86 10 82529073; fax: +86 10
82529010)
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Flow Model Setup
The SRTM (Shuttle Radar Topography Mission) [Rabus et al., 2003] elevation
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data at 90 m resolution were aggregated to the model grid and used as the model top
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elevation. Borehole data were not obtained in this study. As an alternative, four
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aquifer units’ bottom elevation contour maps were digitized and then interpolated into
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the model grid as needed by the layer-property flow (LPF) package [Harbaugh et al.,
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2000] of MODFLOW-2000.
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One reason for combining aquifer units I and II into one single model layer is
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that units are hydraulically connected in the piedmont area and in cones of
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depression due to pumping wells’ penetrating both units. Moreover, during
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post-development, parts of aquifer unit I in the piedmont area dewatered. If a separate
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layer had been used to represent this unit, the best way to deal with this by
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MODFLOW is to use the multi-node well (MNW) package to distribute the total
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pumping of a well automatically. However, available data for hydraulic conductivity
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for the shallow aquifer zone did not distinguish between aquifer units I and II. A
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different number of active cells were used in each layer to represent their distinct areal
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extent. Layer 1 (shallow aquifer zone) has 34329 active cells and layers 2 and 3 (deep
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aquifer zone) have 32451 cells each.
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The definition of a set of appropriate boundary conditions (BCs) for each layer
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was part of the model calibration process considering the magnitude and direction of
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flow across the boundaries. Combinations of specified-head and specified-flow
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boundaries were set for layer 1. A specified-head boundary was defined along the
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eastern boundary, coincident with the coastline of the Bohai Sea, assuming the
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shallow aquifer zone is hydraulically connected with the sea. Specified-flow was used
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for the boundary between the mountain area and the plain to represent lateral flow
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from the Yan and Taihang Mountains assuming that lateral flow only occurs in the
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shallow aquifer zone. To simplify model construction and calibration and considering
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the available data, the southeast boundary along the Yellow River was also defined as
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a specified-flow boundary. Initial flow rates along boundary segments determined
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using the Darcy’s Law were tested and validated during the model calibration process.
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Lateral boundaries for layers 2 and 3 were assumed to be no-flow.
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The spatial distribution and application times of irrigation are unknown.
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Considering that reconstructions of groundwater dynamics and evaluation of
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groundwater depletion are the primary goals of this study, recharge from precipitation
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and irrigation return flow (including irrigation from surface water and groundwater,
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leakage from water diversion canals) were combined to represent total areal recharge.
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Because river recharge represents a small fraction of total input/output, rivers were
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not simulated explicitly in this study, and groundwater discharge to rivers were
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combined with aquifer pumpage.
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Statistical pumpage data are available from 1980 through 2008 in annual
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bulletins for each municipality and province and from previous estimates [Ren, 2007;
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Zhang and Fei, 2009]. In the NCP, the volume of groundwater pumped for irrigation
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per metric ton of grain production is ~ 450 m3 based on statistical data on total
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groundwater pumpage and total grain yield from 1980 through 2008. Total
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groundwater pumpage before 1980 was estimated based on total grain yield assuming
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that irrigation pumpage per unit of grain yield remained uniform over the entire NCP.
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Groundwater abstraction data collected in this study include annual pumpage
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estimates at the province-level; thus it was necessary to redistribute these pumpage
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data to active cells in the model. The planting area for wheat and corn covers
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approximately 50% of the total land area and 70% of the total cultivated area [Xu et
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al., 2005; Han et al., 2008]. In 2000, 835,400 wells were used over the Hebei
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Province, which means ~ 4.4 wells/km2 [Zhang and Li, 2005]; thus, water withdrawal
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from each model cell should represent water discharge from ~ 16 pumping wells. This
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was achieved in the simulation by locating one “virtual” pumping well in each active
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model cell, which accounted for all the simulated water withdrawal in that cell. To
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simplify the model input process, all recharge terms in each cell in layer 1 were
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converted to volume rates and combined with pumpage in that layer into one term;
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this term and pumping in the other two layers were input into the model through the
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well (WEL) package.
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Evaporation from the water table was simulated by the linear segmented
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evapotranspiration (ETS) package which uses a user-defined segment line to
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conceptualize the relationship between water table evaporation and hydraulic head
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[Banta, 2000]. Compared with the evapotranspiration (EVT) package, the ETS
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package can more closely represent the actual nonlinear relationship between ET and
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water table depth [Doble et al., 2009]. ET extinction depth was assigned to 4 m
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uniformly across the NCP, and the potential ET, calculated using the
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Pemnan-Monteith equation [Yang et al., 2009], was converted to the maximum ET
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rate required by the ETS package. The segmentation (Figure S1) is based on field
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measurements of ET at different water table depths in the NCP [Li, 2008].
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Groundwater budgets in the shallow and deep aquifer zones were calculated
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separately using the Zonebudget program [Harbaugh, 1990], which is designed to
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compute subregional water budgets for MODFLOW.
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Additional Literature Cited in the SI
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Banta, E. R. (2000), Modflow-2000, the US Geological survey modular ground-water
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model-documentation of packages for simulating evapotranspiration with a
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segmented function (ETS1) and drains with return flow (DRT1).
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Doble, R. C., C. T. Simmons, and G. R. Walker (2009), Using MODFLOW 2000 to
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Model ET and Recharge for Shallow Ground Water Problems, Ground Water,
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47(1), 129-135.
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Han, S. M., Y. H. Yang, Y. P. Lei, C. Y. Tang, and J. P. Moiwo (2008), Seasonal
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groundwater storage anomaly and vadose zone soil moisture as indicators of
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precipitation recharge in the piedmont region of Taihang Mountain, North China
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Plain, Hydrol. Res., 39(5-6), 479-495.
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Harbaugh, A. W. (1990), A computer program for calculating subregional water
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budgets using results from the US Geological Survey modular three-dimensional
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finite-difference ground-water flow model, Open-File Report 90-392, U.S.
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Geological Survey, Reston, Virginia.
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Harbaugh, A. W., E. R. Banta, M. C. Hill, and M. G. McDonald (2000),
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MODFLOW-2000, The U. S. Geological Survey Modular Ground-Water
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Model-User Guide to Modularization Concepts and the Ground-Water Flow
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Process, Open-File Report 00-92, U.S. Geological Survey, Reston, Virginia.
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Li, J. (2008), The synthesize analysis of the diving evaporation coefficient (in
Chinese), Ground Water, 6, 27-30.
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Rabus, B., M. Eineder, A. Roth, and R. Bamler (2003), The shuttle radar topography
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mission--a new class of digital elevation models acquired by spaceborne radar,
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Isprs. J. Photogramm, 57(4), 241-262.
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Ren, X. (2007), Water resources assessment of the Haihe River Basin (in Chinese),
China Water Power Press, Beijing.
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Xu, Y., X. Mo, Y. Cai, and X. Li (2005), Analysis on groundwater table drawdown
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by land use and the quest for sustainable water use in the Hebei Plain in China,
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Agr. Water Manage., 75(1), 38-53.
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Yang, G., Z. Wang, H. Wang, and Y. Jia (2009), Potential evapotranspiration
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evolution rule and its sensitivity analysis in Haihe River basin (in Chinese), Adv.
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Water Sci., 3, 409-415.
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Zhang, S., and L. Li (2005), Water Resouces in China (in Chinese), Sino Maps Press,
Beijing.
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Zhang, Z., and Y. Fei (2009), Investigation and Assessment of Sustainable Utilization
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of Groundwater Resources in the North China Plain (in Chinese), Geological
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Publishing House, Beijing.
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Figure S1. Evapotranspiration segments, defined by intermediate points which are
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based on the proportion of the ET extinction depth and the proportion of the
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maximum ET rate, used in the ETS package and measured for sandy loam and clay in
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the piedmont region in the NCP [Li, 2008]. ETm in the x-label is maximum ET rate.
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