Transcript Modelling as a tool for groundwater protection

Modelling as a tool for
groundwater protection
Tomas Saks, Aija Dēliņa, Konrāds
Popovs, Jānis Jātnieks, Andis Kalvāns
INVESTING IN YOUR FUTURE
Outline
• MOSYS modelling system (PUMA project)
• Buried valleys of Latvia and Estonia
• Modelling examples
Scheme of integrated model system development
Information base
Geometry model
Geological data
Monitoring data
Closed 3D spatial model,
which includes geological
structure and properties of
geological materials
• input
• update
• storage
• access
• remote access(web)
•Objects(layers, faults,
materials)
• Automatic mesh generation
• Stratigraphy (hronological
generation)
Hydrogeological
model
• 3D mesh
• equations
• numerical method
• boundary conditions
• calibration
• solutions
• Result: groundwater flow in
BAB
The Baltic Basin
Area - 484000 km2
Volume - 579000 km3
Average thickness- 1.2 km
Basin scale groundwater model
Geometry generation – automated scripting
The construction of the geometric mesh is
implemented by specially developed script in
Python.
Scripting has several advantages:
1.flexibility in choosing ways to build the
structure;
2.parallelization in developing/updating of
different structure elements;
3.documented and repeatable structure
building path;
4.possibility to rebuild the structure with slight
or significant modifications at any time;
5.possibility to build, and maintain several
structures of different complexity
simultaneously;
6.extension to the next stages of the model
development – calculation of groundwater
flows and mass transport and model
[auto]calibration.
Groundwater flow modelling
Steady state and transient groundwater flow models. The result of the model is
spatial distribution of groundwater head (h(t)) and spatial distribution of
groundwater flow (derived from the groundwater head field).
Boundary conditions:
1.No-flow conditions are defined for the side boundaries.
2.No-flow boundary conditions were applied on the bottom of the model.
3.Infiltration conditions are applied on the surface (derived from regional climate model
data)
4.Mean or time-dependent discharge values are applied for the water abstraction
wells (where data was available)
Material properties are constant horizontal and vertical hydraulic conductivity (K)
and specific storage (Ss) values for each layer, determined during the calibration
h(t )
Ss
   Kh(t )   q(t )
t
Infiltration
Data from regional climate models (RCM) from
ENSEMBLES project for time period 1961-2010 with
spatial resolution of 25 km was used.
Spatially varying, time-averaged infiltration
distribution was applied proportional to run-off from
RCM models (employing empirical calibration
constant).
Precipitation, mm/year
Evaporation, mm/year
Where infiltration
amount results in heads
above surface level,
remaining water are
considered not
infilrating.
Groundwater flows
are mainly
determined by
infiltration in large
closed basins.
Run-off, mm/year
Examples of results
Rīga
Kohtla-Järve
Height ASL, m
Vilnius
Upper layers
Regional aquiclude D2nr
Lower Devonian aquifers
Distance, km
O-S
Cm-V
Distribution of head, schematic flow arrows
Burried valleys of Latvia and Estonia
• In total 38325
boreholes reaching
the bedrock
surface
• 2306 in
paleoincisions
Burried valleys of Latvia and Estonia
• Boreholes as a
source data
• Probably 4
genetic types
– Burried gullies
– Burried fluvial
channels
– N channels
– N channels in old
fluvial channels
Modelling example
500
6550000
100
100
6500000
-100
50
-300
6450000
-500
20
-700
6400000
-900
6350000
-1100
-1500
-1700
6250000
-1900
6200000
-2100
10
5
2
1
-2300
6150000
-2500
0.5
-2700
6100000
-2900
0.2
-3100
6050000
-3300
6000000
-3500
100000
200000
300000
400000
500000
600000
700000
800000
The impact of the Burried valleys on the groundwater flow
0.1
TDS, g/L
-1300
6300000
Formation top level [m amsl]
Groundwater
mineralization (TDS
in g/l) in Middle
and Lower
Devonian multiaquifer.
300
Modelling example
• Stable dO18
Isotopes in
the Middle
and Lower
Devonian
multi-aquifer
The impact of the Burried valleys on the groundwater flow
Modelling example
• Groundwater flow beneath the Scandinavian Ice sheet
(LGM) and residense time in the Middle and Lower Devonian
multi-aquifer without Burried valleys
Modelling example
• Groundwater flow beneath the Scandinavian Ice
sheet and residense time in the Middle and Lower
Devonian multi-aquifer with Burried valleys
Summary
• Basin scale modelling is a start for an operational
model
• Burried valleys are potentially a connecting conduid
for aquifers and also a potentional recharge sites for
the glacial meltwater intrusion into the deep aquifer
systems
• Therefore good knowledge of distribution and depth
of these erosional features are essential not only for
groundwater safety, but also assessment of the
resources