# EGU2012 5720 presentation

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```					Geometrical model of the
Baltic artesian basin

Juris Sennikovs, Janis Virbulis,
and Uldis Bethers
Laboratory for Mathematical Modelling of Environmental
and Technological Processes
UNIVERSITY OF LATVIA
Contents of presentation
1.   Description of Baltic artesian basin
2.   Algorithms of geometrical structure model
3.   Highlights of geometrical structure
4.   Examples of groundwater flow model results
5.   Summary
Motivation

There exist several local modelling studies of ground water
flow for the parts of the Baltic artesian basin (BAB)

The aim of the present work is the development of a closed
hydrogeological mathematical model of the whole BAB

This presentation focuses on the development of the
geometrical model of the BAB
Area of study                            Baltic artesian basin
(BAB) is a multi-layered
Crystalline bedding                      and complex
reaches surface                          hydrogeological system
up to 5000 m deep

BAB fully covers the
territory of Latvia,
Lithuania and Estonia,
parts of Poland, Russia,
Belarus as well as large
area of the Baltic Sea,
including island of
Depth                     Gotland.
~5000 m          Depth
<500 m   It is the main drinking
Area - 484000 km2                    water source in the
Baltic countries
Volume - 579000 km3
Average thickness- 1.2 km
Scheme of integrated model system development

Hydrogeological
Information base           Geometry model
model

Closed 3D spatial model,       • 3D mesh
Geological data        which includes geological      • equations
Monitoring data        structure and properties of    • numerical method
geological materials           • boundary conditions
• calibration
• solutions

• input                •Objects(layers, faults,
• update               materials)
• storage              • Automatic mesh generation    • Result: groundwater flow in
• access               • Stratigraphy (hronological   BAB
• remote access(web)   generation)
Data sources                      1. Stratigraphic information from boreholes in Latvia
and Estonia
Unification      of        the
heterogeneous      information
2. Maps of height isolines of geological layers for
from different sources with           Latvia and Lithuania
uneven data coverage, are          3. Maps of sub-quaternary deposits in Latvia and
performed. Algorithms are             Lithuania
developed for this purpose         4. Maps of fault lines on the crystalline basement
considering    the     priority,      surface in Latvia, Lithuania and Estonia
importance and plausibility of     5. Buried valley data from Latvia and Estonia
each of each data sources in
6. Earth topography data
integrating topography and
lithology data as well as
7. Baltic sea depth data
borehole data                      8. Data from published geological cross-sections,
information from books and other sources.
Model construction algoritms

Database of                Filtering
Subquaternary rock data
boreholes
(MySQL)

Parameters        Borderline           Isolines           Fault lines         Set of points   Set of thicknesses

Line

“Law”
3D surface                        2D triangular
mesh                                   Table
2D
Outer border                         3D surface                                  triangulation

Geological
Layer
Set of 3D
surfaces             stratification                   thickness

Volume mesh                                   External sources       DATA/Result
(models)
Algorithm
3D volume mesh
Geometry generation – automated scripting
The construction of the geometric mesh is
implemented by specially developed script
in Python.

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.
Mesh
•Finite element (FE) method was
Typical lines
employed for the calculation of the 3-
Model border
dimensional groundwater flows with
free surface.
Border of the                                     •3D mesh was constructed layer-
geological
material                                          wise.
•The triangular mesh in horizontal
plane was constructed including
characteristic lines such as rivers,
borders of countries and areas of
presence of geological layers.
•Fault lines are also taken into
account considering the
displacements along the fault
•Most of the 3D finite elements are
Rivers   triangular prisms. Pyramids and
tetrahedra are used near the fault
lines and wedge lines of geological
layers.
Edges of triangular mesh coincide with
the line data
•Finite element (FE) method was
Mesh                                    employed for the calculation of the 3-
dimensional groundwater flows with
free surface.
•3D mesh was constructed layer-
wise.
•The triangular mesh in horizontal
plane was constructed including
characteristic lines such as rivers,
borders of countries and areas of
presence of geological layers.
•Fault lines are also taken into
account considering the variable
displacements along the fault
•Most of the 3D finite elements are
triangular prisms. Pyramids and
tetrahedra are used near the fault
lines and wedge lines of geological
layers.

Finite element mesh, view from the top.

Higher resolution of mesh in areas with
sufficient geological data
Example of model construction sequence – basement

Faults

Isolines - Latvia

Boreholes - Latvia         Isolines - Lithuania
Example of model construction sequence – basement

Boreholes - Estonia

Isolines – Baltic sea

Final level data at
points
Russia, Belorus
Example of model construction sequence – basement
Interpolation to 2D mesh

Interpolation of faults
Geological structure
Quaternary             Geological structure consists of 42 layers
distinguished on the basis of each geological
Paleogenic/Neogenic    unit hydraulic properties and geological data
Cretaceous             resolution. The number of layers are allowed to
Jurassic
Triassic               vary across the domain.
Permian
Carboniferous
It includes aquifers and aquitards from Vendian
42 layers

up to the Quaternary deposits.

Quaternary sequence is treated as four layer
Devonian        structure with variable number of layers across
the domain.

Fault displacements are incorporated into the
model taking into account data from the
published structural maps.
Silurian

Ordovician           Four reconstructed regional erosion surfaces
(upper Ordovician, Devonian, Permian and
Cambrian
Quaternary) are included into the model.
Vendian
Geological structure      Quaternary
sequence
Regional erosion
surface

Tectonic faults
Level, m

Wedging out of layers

Distance, km

Vertical exaggeration 200:1
Vertical section
from soutwest to northeast along line A-B
Vertical cross section from south to north

South, Vilnius                   Rīga                   North, Kohtla-Järve
Quaternary

Devonian

Ordovician/Silurian
Level, m

Cambrian/Vendian

Distance, km

Vertical exaggeration 300:1
Distribution of piezometric head in south-north vertical crossection

South, Vilnius                   Rīga                        North, Kohtla-Järve

Upper layers

Regional aquiclude D2nr
Lower Devonian aquifers

O-S, aquicludes

Cm-V aquifers
Distribution of head in D3gj layer, schematic flow directions

Main
discharge
areas

Main
recharge
areas
Summary
Data for the bulding of regional model of Baltic artesian basin has been
collected and prepared

Geometry model of the Baltic artesian basin geological structure is
developed, consisting of 42 layers

3D finite element mesh for the groundwater flow and mass transport
calculations are prepared.

Automated script for the generation of the geological structure and 3D finite
element mesh was prepared allowing for the paralel, repeatable and
documented building of the model.

The present work has been funded by the European Social Fund project „Establishment of
interdisciplinary scientist group and modelling system for groundwater research”
(Project Nr.2009/0212/1DP/1.1.1.2.0/09/APIA/VIAA/060)
Thank You
for attention!

The present work has been funded by the European Social
Fund project „Establishment of interdisciplinary scientist
group and modelling system for groundwater research”
(Project Nr.2009/0212/1DP/1.1.1.2.0/09/APIA/VIAA/060)

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