Geometrical model of the baltic artesian basin
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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. Description of Baltic artesian basin

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Geometrical model of the baltic artesian basin

Geometrical model of the Baltic artesian basin

JurisSennikovs, Janis Virbulis, and UldisBethers

Laboratory for Mathematical Modelling of Environmental and Technological Processes

UNIVERSITY OF LATVIA


Geometrical model of the baltic artesian basin

Contents of presentation

  • Description of Baltic artesian basin

  • Algorithms of geometrical structure model

  • Highlights of geometrical structure

  • Examples of groundwater flow model results

  • 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 closedhydrogeological mathematical model of the whole BAB

This presentation focuses on the development of the geometrical model of the BAB


Geometrical model of the baltic artesian basin

Area of study

Baltic artesian basin (BAB) is a multi-layered and complex hydrogeological systemup 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 Gotland.

It is the main drinking water source in the Baltic countries

Crystalline bedding reaches surface

Depth

~5000 m

Depth

<500 m

Area - 484000 km2

Volume - 579000 km3

Average thickness- 1.2 km


Geometrical model of the baltic artesian basin

Scheme of integrated model system development

Information base

Geometry model

Hydrogeological model

  • 3D mesh

  • equations

  • numerical method

  • boundary conditions

  • calibration

  • solutions

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)

  • Result: groundwater flow in BAB


Geometrical model of the baltic artesian basin

Data sources

Stratigraphic information from boreholes in Latvia and Estonia

Maps of height isolines of geological layers for Latvia and Lithuania

Maps of sub-quaternary deposits in Latvia and Lithuania

Maps of fault lines on the crystalline basement surface in Latvia, Lithuania and Estonia

Buried valley data from Latvia and Estonia

Earth topography data

Baltic sea depth data

Data from published geological cross-sections, information from books and other sources.

Unification of the heterogeneous information from different sources with uneven data coverage, are performed. Algorithms are developed for this purpose considering the priority, importance and plausibility of each of each data sources in integrating topography and lithology dataas well as borehole data


Geometrical model of the baltic artesian basin

Model construction algoritms

Database of boreholes

Filtering (MySQL)

Subquaternary rock data

Parameters

Borderline

Isolines

Fault lines

Set of points

Set of thicknesses

Line

“Law”

3D surface

2D triangular mesh

Table

2D triangulation

3D surface

Outer border

Layer thickness

Set of 3D surfaces

Geological stratification

Volume mesh

DATA/Result

External sources (models)

Algorithm

3D volume mesh


Geometrical model of the baltic artesian basin

Geometry generation – automated scripting

The construction of the geometric mesh is implemented by specially developed script in Python.

Scripting has several advantages:

flexibility in choosing ways to build the structure;

parallelization in developing/updating of different structure elements;

documented and repeatable structure building path;

possibility to rebuild the structure with slight or significant modifications at any time;

possibility to build, and maintain several structures of different complexity simultaneously;

extension to the next stages of the model development – calculation of groundwater flows and mass transport and model [auto]calibration.


Geometrical model of the baltic artesian basin

Mesh

  • Finite element (FE) method was employed for the calculation of the 3-dimensional groundwaterflows with free surface.

  • 3D mesh was constructedlayer-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 consideringthe displacements along the fault

  • Most of the 3D finite elements are triangular prisms. Pyramids and tetrahedraare used near the fault lines and wedge lines of geological layers.

Typical lines

Model border

Border of the geological material

Rivers

Edges of triangular mesh coincide with the line data


Geometrical model of the baltic artesian basin

  • Finite element (FE) method was employed for the calculation of the 3-dimensional groundwaterflows with free surface.

  • 3D mesh was constructedlayer-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 consideringthe variable displacements along the fault

  • Most of the 3D finite elements are triangular prisms. Pyramids and tetrahedraare used near the fault lines and wedge lines of geological layers.

Mesh

Finite element mesh, view from the top.

Higher resolution of mesh in areas with sufficient geological data


Geometrical model of the baltic artesian basin

Example of model construction sequence – basement

Faults

Isolines - Latvia

Isolines - Lithuania

Boreholes - Latvia


Geometrical model of the baltic artesian basin

Example of model construction sequence – basement

Boreholes - Estonia

Isolines – Baltic sea

Final level data at points

Additional data Russia, Belorus


Geometrical model of the baltic artesian basin

Example of model construction sequence – basement

Interpolation to 2D mesh

Interpolation of faults


Geometrical model of the baltic artesian basin

Geological structure

Geological structure consists of 42 layers distinguished on the basis of each geological unit hydraulic properties and geological data resolution. The number of layers are allowed to vary across the domain.

It includes aquifers and aquitards from Vendian up to the Quaternary deposits.

Quaternary sequence is treated as four layer 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.

Four reconstructed regional erosion surfaces (upper Ordovician, Devonian, Permian and Quaternary) are included into the model.

Quaternary

Paleogenic/Neogenic

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

42 layers

Devonian

Silurian

Ordovician

Cambrian

Vendian


Geometrical model of the baltic artesian basin

Geological structure

Regional erosion surface

Quaternary sequence

Level, m

Tectonic faults

Wedging out of layers

Distance, km

Vertical exaggeration 200:1

Vertical section

from soutwest to northeast along line A-B


Geometrical model of the baltic artesian basin

Vertical cross section from south to north

South, Vilnius

North, Kohtla-Järve

Rīga

Quaternary

Devonian

Ordovician/Silurian

Level, m

Cambrian/Vendian

Distance, km

Vertical exaggeration 300:1


Geometrical model of the baltic artesian basin

Distribution of piezometric head in south-north vertical crossection

North, Kohtla-Järve

South, Vilnius

Rīga

Upper layers

Lower Devonian aquifers

Regional aquiclude D2nr

O-S, aquicludes

Cm-V aquifers


Geometrical model of the baltic artesian basin

Distribution of head in D3gj layer, schematic flow directions

Main discharge areas

Main recharge areas


Geometrical model of the baltic artesian basin

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 interdisciplinaryscientist group and modelling system for groundwater research”

(Project Nr.2009/0212/1DP/1.1.1.2.0/09/APIA/VIAA/060)


Geometrical model of the baltic artesian basin

Thank You for attention!

The present work has been funded by the European Social Fund project „Establishment of interdisciplinaryscientist 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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