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