Transcript a gis based tool for regional groundwater risk assessment in poorly

GIS-based TOOL FOR REGIONAL GROUNDWATER
RISK ASSESSMENT IN POORLY PRODUCTIVE
AQUIFERS
Janmaizatulriah JANI, David N LERNER, Steve WISE
Catchment Science Centre
University of Sheffield, UK
GroPro - Groundwater Protection
Plans and Implementation in a North European Perspective
Korsør, Denmark 15-17 September 2008
Research Background
GIS based modelling
•GIS use for surface hydrology
•Groundwater hydrology only consider vertical pathways
Groundwater risk assessment
Vertical outputs;
•More local risk
•High pollutant
concentration
High pollutant
concentration
Horizontal outputs;
•Change location of
risky area as pollutant
transported
•Pollutant
concentration decrease
Research aim and objectives
General Aim
To extend GIS based groundwater risk assessment by
including the analysis of horizontal pathways of pollutant
Overall objectives
•To develop a GIS-based geological model
•To utilise geological model for groundwater hydrology
analysis
•To analyse risk of groundwater
Initial modelling: GIS based geological
modelling
Objective
To represent subsurface geology using GIS tools
Tests
• Reconstruction of geological map
• Reconstruction of subsurface contours map and
cross section
Conceptual diagram of GIS based geological
representation
Top of geological unit
One unit of geology
Fault line
t
∆d1
∆d3
∆d2
Outcrops
Stack of planes
∆d –displacement
t - thickness
Reconstruction of geological map: Dove valley
of the Don catchment, UK
Dove valley
Geology of Dove;
•Carboniferous rock – Middle Coal
Measures, Lower Coal Measures
•Geology beds – steady North Easterly,
•Varies in thickness and dip direction
•Numerous faults – dip about 5°
M.R
© Environment
Agency
Don catchment, UK
Coal
Middle Coal
Measures
O.R
W.E.R
e.g. Stratigraphy units
Modelling assumptions
• Re-categorise of rock groups;
– Sandstone rock
– Mudstone/Siltstone rocks
• Geological beds are planar
• Constant dip angle - 4 °
• Constant strike
• Uniform thickness
• Vertical faults displacement
Simplified version of geology map
Mudstone/siltstone rocks
rocks
Derived fromSandstone
1:50000 scale BGS
Digital Data under
Licence 2008/08 British Geological Survey© NERC
Model outcrops
Original geology map
Mudstone/siltstone
sandstone
Model 2
All Faults
Model Faults
Predicted total area of sandstone rocks
Item
Strike
Thickness
Sandstone rock
Area (km2)
True values
30 °- 70 °
Varies
47
Model 1
55°
Uniform
32 (68%)
Model 2
45 °
Uniform
36(76.5%)
Model 3
60 °
Uniform
26(55%)
Matched outcrops: model 2
matched
mudstone/siltstone
Actual mudstone not
predicted
Actual sandstone not predicted
matched sandstone
% matched outcrops
Model
Model 1
Model 2
Model 3
Rock type
Matched
(km2)
Unmatched
(km2)
Sandstone
18
29
Mudstone/siltstone
25
15
Sandstone
20
27
Mudstone/siltstone
24
16
Sandstone
14
33
Mudstone/siltstone
27
%
Matched
49
13
51
47
Geological view – Cross section of Silkstone Coal
0.30
Fault lines
Elevation (km)
0.20
0.10
0.00
0.0
1.0
2.0
3.0
-0.10
-0.20
-0.30
Distance (km)
4.0
5.0
model 1
model 2
model 3
actual
Conclusions
• The best model prediction - model 2
• Less accuracy of model prediction are due to;
– Insufficient geological inputs
– Simplification and assumptions
– Model do not replicate real geology
Application of methodologies;
• Potential of using GIS for geological modelling
• Capability to model;
– Limited subsurface information
– Important of details geological description
• Provide extra geological views
Next Future works
Can GIS model groundwater flow?
•Groundwater hydrology analysis
•Identification of groundwater catchment, flow
directions and groundwater discharge points.
•Analyse groundwater risk
Thank you for your attention