SENSITIVITY ANALYSIS OF THE STABILITY OF GROUNDWATER FLOW SYSTEMS

1
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 [phone], fax 31 30
2535050, m.vissers_at_geog.uu.nl
2
Groundwater flow is important for spatial
planning and groundwater quality assessment.

• Configuration of pathways of point and diffuse
  source pollution
• Temporal
• Spatial

3
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?
4
Manual delineation of groundwater flow systems by
interpretation of particle tracks(Engelen and
Kloosterman, 1996)
5
METHODS

• Groundwater model
• Define groundwater flow systems
• Monte Carlo analysis of stability

6
Study area
Drinking water well
Observation well
Height lines on moraine
Stream / Ditch
Overijssels Canal
Wetlands
City / Industry
Heathland
Forest
Grass

• Ice-pushed ridge in the east, flat in the west
• Mainly Agricultural land use, eastern part
  cultivated in the 1920s

7
Study area

• Drenthe clay in the west forms base at 30m NAP
• Sandy unconsolidated aquifer

8
Groundwater model

• MODFLOW
• 18 x 12 km
• 50 x 50 m cells
• 6 layers
• Drainage network
• Calibration

9
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

10
Define groundwater flow systems

• Size of recharge area may be too small ? take
  minimum of 50 cells
• Groundwater divide can be present within a
  groundwater flow system

11
Groundwater flow systems and transit distance
490
488
(km)
486
e
t
a
n
i
d
r
o
484
o
c
-
Y
482
480
478
210
212
214
216
218
220
222
224
226
(km)
X-coordinate
12
Transit time
490
488
486
e
t
a
n
i
d
r
o
484
o
c
-
Y
482
480
478
210
212
214
216
218
220
222
224
226
X-coordinate
13
Vertical transect age and distance
14
Time
15
Transit time
490
488
486
e
t
a
n
i
d
r
o
484
o
c
-
Y
482
480
478
210
212
214
216
218
220
222
224
226
X-coordinate
16
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.

17
Sensitivity analysis

• Recharge
• KH/KV
• Drainage resistance
• Drainage level
• Recharge Drainage level (Monte Carlo)

18
Drainage resistance Parametric analysis
19
Recharge Parametric analysis
490
488
486
e
t
a
n
i
d
r
o
484
o
c
-
Y
482
480
478
210
212
214
216
218
220
222
224
226
X-coordinate
20
Monte Carlo Analysis (recharge drainage level)
490
488
486
e
t
a
n
i
d
r
o
484
o
c
-
Y
482
480
478
210
212
214
216
218
220
222
224
226
X-coordinate
21
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_at_geog.uu.nl