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SENSITIVITY ANALYSIS OF THE STABILITY OF GROUNDWATER FLOW SYSTEMS. M.J.M. Vissers M. van der Perk, P.F.M. van Gaans.

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sensitivity analysis of the stability of groundwater flow systems

SENSITIVITY ANALYSIS OF THE STABILITY OF GROUNDWATER FLOW SYSTEMS

M.J.M. Vissers

M. van der Perk, P.F.M. van Gaans

Universiteit Utrecht, Centre for Geo-Ecological Research, Faculty of Geographical Sciences, P.O. Box 80115, 3508 TC Utrecht, The Netherlands, phone: +31 30 2532988, fax +31 30 2535050, m.vissers@geog.uu.nl

groundwater flow is important for spatial planning and groundwater quality assessment
Groundwater flow is important for spatial planning and groundwater quality assessment.

Configuration of pathways of point and diffuse source pollution:

  • Temporal
  • Spatial
hydrological systems analysis
Hydrological systems analysis!

Toth (1962): A flow system is defined as a set of flow lines in which any two flow lines adjacent at one point of the flow region remain adjacent throughout the whole region

How to operationalize this definition?

How to quantify stability?

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Automatic?

Uncertainty?

Manual delineation of groundwater flow systems by interpretation of particle tracks(Engelen and Kloosterman, 1996)
methods
METHODS
  • Groundwater model
  • Define groundwater flow systems
  • Monte Carlo analysis of stability
study area
Ice-pushed ridge in the east, “flat” in the west

Mainly Agricultural land use, eastern part cultivated in the 1920’s

Study area

Drinking water well

Observation well

Height lines on moraine

Stream / Ditch

Overijssels Canal

Wetlands

City / Industry

Heathland

Forest

Grass

study area1
Study area
  • Drenthe clay in the west forms base at –30m NAP
  • Sandy unconsolidated aquifer
groundwater model
Groundwater model
  • MODFLOW
  • 18 x 12 km
  • 50 x 50 m cells
  • 6 layers
  • Drainage network
  • Calibration
define groundwater flow systems
When a discharge area is “continuous”, the flow lines towards it will remain adjacent throughout the region

Identified by a 3-cell buffer around discharge cells

Define groundwater flow systems
define groundwater flow systems1
Size of recharge area may be too small  take minimum of 50 cells

Groundwater divide can be present “within” a groundwater flow system

Define groundwater flow systems
groundwater flow systems and transit distance
Groundwater flow systems and transit distance

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X-coordinate

transit time
Transit time

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transit time1
Transit time

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groundwater flow systems can be identified
Groundwater flow systems can be identified
  • Configuration of pathways:
    • In space: groundwater flow system & characterization
    • In time: travel distance and age at specified depths
  • Uncertainty….
sensitivity analysis
Sensitivity analysis
  • Recharge
  • KH/KV
  • Drainage resistance
  • Drainage level
  • Recharge & Drainage level (Monte Carlo)
drainage resistance parametric analysis

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Drainage resistanceParametric analysis
recharge parametric analysis
RechargeParametric analysis

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monte carlo analysis recharge drainage level
Monte Carlo Analysis (recharge & drainage level)

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conclusions
Conclusions
  • Hydrological systems analysis can be applied to groundwater model results
  • Uncertainty in flow is not only caused by parameter errors, heterogeneity etc.
  • Climatic variations and human factors are very important in natural flow systems
  • Uncertainty can be mapped, flow systems are quite stable
  • The combination of maps can be used for many purposes

m.vissers@geog.uu.nl