dsd-nl 2014 - imod symposium - 11. high resolution global scale groundwater modelling, rens van...
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High Resolution Global Scale Groundwater Modelling
Department of Physical Geography – Faculty of Geosciences
Rens van Beek
Inge de Graaf, Edwin Sutanudjaja, Yoshi Wada & Marc Bierkens
Limits to global groundwater consumption: effects on low flows and groundwater levels
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De Graaf et al., 2014
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Simulated water stress index for 2000 (Wada et al., 2011)
Towards a high resolution global hydrological model
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Global-scale simulations at 5 arc minutes (~10 x 10 km at equator)
River discharge Domestic water use
What has been the effect of abstractions on groundwater levels?
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• Simulation of groundwater head dynamics;
• Lateral flow (exchange between cells) cannot be ignored at finer spatial resolutions.
Challenges to the construction of a physically based global-scale groundwater model: • Quality of available global datasets:
- Surficial hydro-lithology; - Aquifer thickness estimates.
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Model lay-out
• 5’ resolution; • Steady-state; • Offline coupling to MODFLOW; • Coupling to iMOD under construction.
Sutanudjaja et al., 2011
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Land-surface model
Available global datasets
Gleeson et al. 2010
Hartmann and Moosdorf 2012
Hydro-lithology
Conductivity
Model Input
Groundwater recharge
Surface water levels • Imposed as average long-term levels for
lakes, reservoirs and lakes; • Based on discharge for rivers and imposed
by means of the RIVER package using uniform conductivity;
• DRAIN package is used where no main river channel is available.
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range Land surface
Sediment basin
50 m
Floodplain elevation
range
1) 𝐹′ 𝑥 = 1 − 𝐹 𝑥 − 𝐹𝑚𝑖𝑛
𝐹𝑚𝑎𝑥 − 𝐹𝑚𝑖𝑛
F’(x) is spatial frequency distribution of elevation above the floodplain 2) Associated Z-score
𝑍 𝑥 = 𝐺−1(𝐹′ 𝑥 )
Where G-1 is the inverse of the standard normal distribution.
Sediment basin aquifers: delineation and depth (1)
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3) Using case studies in the US
• range of aquifer thickness
• average coefficent of variation
• Aquifer thickness is assumed to be log-normally distributed (positive skew)
4) 𝑙𝑛𝐷 = 𝑈(𝑚𝑖𝑛;𝑚𝑎𝑥)
𝑌 𝑥 = 𝑙𝑛𝐷 × (1 + 𝐶𝑣𝑙𝑛𝐷Z x )
𝐷 𝑥 = 𝑒𝑌(𝑥)
dmax
dmin
Sediment basin aquifers: delineation and depth (2)
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Cumulative probability of aquifer depth
Average simulated aquifer thickness
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Transmissivity (m2d-1)
0.5 5 15 40 >100
𝑇 𝑥 = 𝑘0𝑒−𝑧//λ
𝐷(𝑥)
0
𝑑𝑧
Aquifer-scale transmissivities
Steady-state water table depth
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Validation on groundwater wells
0.25-2.5 320- 640 > 640
Observed GW heads
Sediment basins
All wells
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Validation on groundwater wells
0.25-2.5 320- 640 > 640
Observed GW heads
Sediment basins
All wells
Relative residuals
𝑅𝑟𝑒𝑙= 𝐻𝑠𝑖𝑚−𝐻𝑜𝑏𝑠
𝐻𝑜𝑏𝑠
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0.01 0.1 1 10 100 1000 Years - Months years decades centuries millennia
Flow paths and travel times
• Suitable method to develop aquifer schematization and properties for data poor environments;
• The large scale-distribution of groundwater levels is captured; starting point to assess groundwater level fluctuations;
• Confirms the relevance of including lateral flow in global scale hydrological models at finer resolutions.
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Conclusions
What is the effect of past and future abstractions on groundwater levels?
Major limitations, currently being addressed: • Steady-state;
• Single, unconfined layer;
• Coupling of surface and groundwater.
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Thank you for your attention
http://www.hydrol-earth-syst-sci-discuss.net/11/5217/2014/hessd-11-5217-2014.pdf
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Europe USA
Validation groundwater depths