Investigation of a lysimenter using the simulation tool SiWaPro DSS and adaptation of this program to Vietnamese requirements

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HANOI UNIVERSITY OF SCIENCE

DRESDEN UNIVERSITY OF TECHNOLOGY

PHAM THI BICH NGOC

INVESTIGATION OF A LYSIMETER
USING THE SIMULATION TOOL SiWaPro DSS
AND ADAPTATION OF THIS PROGRAM
TO VIETNAMESE REQUIREMENTS
MASTER THESIS

Supervisors:
Prof. Dr. Ing. habil. Peter Wolfgang Graeber
Dipl. Ing. Rene Blankenburg
Technical University Dresden
Institute for Waste Management and Contaminated Site Treatment

Hanoi - 2008


ACKNOWLEDGEMENTS
Two years have passed and marked a historical pathway toward my Master degree.
The two years were full of challenges, hopes, inspiration and wonderful support
from many people. I would like to thank you all for a big variety of reasons:
My first greatest thanks go to my tutors Prof. Dr. Ing. habil. Peter Wolfgang
Graeber and Dipl. Ing. Rene Blankenburg for having guided, supported and accompanied me through the process of this Master thesis. Thanks also for having greatly
contributed to the thesis with your vast experience and advice.
Many thanks to Prof. Dr. Bilitewski, Assc. Prof. Dr. Bui Duy Cam and Assc. Prof.

Dr. Nguyen Thi Diem Trang for making great efforts to establish and design the
training program frame for this master course and develop it, so I can have a chance
to join this course.
My acknowledgements go also to all teachers from Hanoi University of Sciences in
Vietnam and Institute for Waste Management and Contaminated Site Treatment in
Germany for giving me lots of valuable and interesting lectures and helping us to
understand more clearly and have a thorough grasp of specific knowledge during
this master course.
My grateful thanks to Dr. rer. nat. Axel Fischer, Mr. Christian and Mrs. Hoang Phan
Mai for helping and supporting during my time in Dresden and Pirna, Germany.
Thanks also to Pham Hai Minh for all administrative support during the Master
course time.
I also would like to express my gratitude to:
 The Committee on Overseas Training Project, Ministry of Education and
Training for having granted the scholarship that supported this Mater thesis

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 Hanoi University of Sciences and Institute for Waste Management and Contaminated Site Treatment (IAA) for providing all materials and equipments
that I used during the course.
 Vietnam National University, Hanoi and Technical University Dresden and
German Academic Exchange Service (DAAD) for supporting this Master
training program in which I attended.
Thanks to all the classmates for their nice and warm company for the encouragement and support.
And last but not least, special huge thanks to my family (my parents in law, my parents, my husband, my son and my brothers and sisters) and all my friends (especially Mrs. Ha) and my relatives for thinking of me, helping me, and encouraging me in
my pathway to a Master degree.
I love you all.
Hanoi, 10th December 2008
Pham Thi Bich Ngoc.

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SUMMARY
The main objective of this thesis is to use SiWaPro DSS to model and simulate the
water flow process in the unsaturated zone with the available data from the lysimeter number 302 in Juelich, Germany.
The unsaturated zone is the portion of the subsurface above the ground water table.
It contains air as well as water in the pores. This zone plays an important roll in
many aspects of hydrology, such as infiltration, exfiltration, capillary rise, recharge,
interflow, transpiration, runoff and erosion. Interest in this zone has been increasing
in recent years because the movement of water along with contaminants in this zone
have been affecting the groundwater and the subsurface environment.
Water flow is concerned with movement of water in unsaturated porous media.
In order to handle water flow process under steady state or transient conditions in
the unsaturated zone, a useful computer program is used to model and simulate this
process. This program combines the simulation module SiWaPro for numerical
modeling of water flow and contaminant transport in variably saturated media with
additional simulation and parameter estimation tools, data sources for the simulation and a graphical user interface.
The computer-based decision support system SiWaPro DSS software is a program
for modeling and simulating the processes as water flow, solute transport, bio degradation and sorption in variably saturated porous media.
In SiWaPro DSS, the discretization of the modeling area is realized using finite
elements with the GALERKIN method. SiWaPro DSS contains the 2D triangular
mesh generator EasyMesh 1.4. The mesh generator allows the generation of meshes
with varying element sizes and irregular mesh boundaries. Currently, the generator
allows flexible space quantization at modeling time given by the user.
To validate SiWaPro DSS, the means of measurement data from a lysimeter experiment are used. Lysimeters are devices for measuring the characteristic properties

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of the soil water balance, amounts of seepage water and their quality. In this thesis,
lysimeter 302 located in Juelich, Germany is used for calibrating model.
The Juelich lysimeter 302 was established in August 2001, the monoliths were taken out from Munich-Neuherberg in June 2001 and the installation of the measurement devices occurred and the data logging started on December 10th 2001. This
lysimeter is run by the Research Centre in Juelich (FZJ). This lysimeter is a large
undisturbed lysimeter with 2m2 in area and 2,4m in depth including 0,8m of reference material. The three suction cups are installed together with tensiometers, TDR
and temperature sensors at 3-different depth layers distance from upper edge of the
lysimeter in turn as 0,85m; 1,15m and 1,8m.
To model the water flow of the lysimeter in SiWaPro DSS, the finite element mesh
of the lysimeter is constructed with the column of 1,6m in width and 1,6m in height
(excluding 0,8m of reference material). The lower boundary condition is a first kind
boundary condition that allows outflow only. A second type boundary condition is
applied at the upper boundary of the column of lysimeter. It is a transient boundary
condition using time – variable boundary conditions to simulate precipitation in the
model. Three soil water sampling device layers are applied as first kind boundary
condition, and as the lower boundary condition, only outflow is allowed. The column of the lysimeter soil is divided into 5 layers; each of the soil layers is described
in its hydraulics with 11 parameters.
To calibrate model, two data sets of 11 soil hydraulic and van Genuchten parameters with different initial pressure head and boundary condition of three suction cup
layers as well as different amount of nodes and elements in the mesh are used. Because the time is short – besides, one model took from 25 hours to 50 hours for running; some models took much more time, then they were stopped before they finish.
So there are only 10 models were run. After getting the result from simulation of
each model, the simulation result was checked and analyzed and then the data set
was changed or finite element mesh of the lysimeter was adjusted or the software

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was reconsidered. The simulation results that were shown in diagrams in section 4.1
are the best model, but the results still show some difference of output between simulation and measurement because input data which took from lysimeter station are
not well documented and some soil parameters which are estimated by the person
who operate the lysimeter are different from the fact. The result shows that total

inflow and total outflow of lysimeter are in balance. That means the model and finite element mesh of the lysimeter is designed well. Outflow of the suction cup
layer number 3 in the simulation is almost the same as measurement. Outflow of the
suction cup layer number 1 and lower boundary condition in simulation are the
same as measurement in the first year. But in the second year, outflow of the suction
cup layer number 1 in simulation is higher than measurement; opposite to the outflow of the lower boundary condition the simulation one is lower than measurement. Outflow at the suction cup layer number 2 is different increasing by time between simulation and measurement. The differences come from the data mentioned
as above.
The SiWaPro DSS program have been introducing to Federal Environmental Bureaus and Consulting Companies in Germany. These Bureaus and Companies can
use this software tool primarily for leachate forecasts with respect to the German
soil protection law. In Vietnam it also can be apply similar to Germany, but it takes
a bit time for Vietnamese to familiar with it. For Vietnamese to apply this software,
the GUI and help system were initially translated into Vietnamese.
Therefore, it can be said that SiWaPro DSS is one of the useful tools for leachate
forecast. However, it should be applied for a wide variety of contaminants if the
software is revised to adapt with not only all available data but also a few available
data. The lysimeter is good for calibrating the model and will be better if the data is
documented well and frequency.

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TABLE OF CONTENTS
ACKNOWLEDGEMENTS ..................................................................................... 1
SUMMARY .............................................................................................................. 3
TABLE OF CONTENTS ......................................................................................... 6
ABBREVIATIONS .................................................................................................. 8
LIST OF FIGURES ................................................................................................. 9
LIST OF TABLES ................................................................................................. 11
LIST OF DIAGRAMMS ....................................................................................... 12
1.

INTRODUCTION .......................................................................................... 13

2.

FUNDAMENTALS OF SOIL HYDROLOGY ............................................ 15
2.1 Definition of soil and unsaturated zone ....................................................15
2.2 Soil hydraulic parameters .........................................................................16
2.3 Soil water balance .....................................................................................19
2.4 Soil water flow .........................................................................................22

3.

MATERIAL AND METHODS ..................................................................... 23
3.1 Theoretical approaches and methodology ................................................23
3.2 Finite element method ..............................................................................24
3.3 Lysimeter ..................................................................................................30
3.3.1 General information about lysimeter ...................................................... 30
3.3.2 Juelich lysimeter station description ....................................................... 32
3.3.3 Description of the Juelich lysimeter number 302 .................................. 34
3.4 Water flow model .....................................................................................37
3.5 Description of the finite element mesh of the lysimeter ..........................38
3.6 Description of software SiWaPro DSS ....................................................40
3.6.1 General ........................................................................................................ 40
3.6.2 Layout and Structure ................................................................................. 40
3.6.2.1 Graphical user interface (GUI) and Help System ............................. 41
3.6.2.2 Mesh Generator ..................................................................................... 43
3.6.2.3 Weather Generator ................................................................................ 44

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3.6.2.4 Database Layer ...................................................................................... 44
3.6.2.5 Pedotransfer Functions ......................................................................... 45
3.6.2.6 Import and Export Interfaces ............................................................... 49
3.6.3 Manual SiWaPro DSS Mesh Generator ................................................. 50
3.6.3.1 Create a simple 2D mesh ...................................................................... 51
3.6.3.2 Definition internal curves ..................................................................... 53
3.6.3.3 Inserting a background image as construction basis ......................... 56
3.6.3.4 Boundary condition editor .................................................................... 57
3.7 Data sets for calibrating the model ...........................................................62

4.

3.7.1

Time space .............................................................................................. 62

3.7.2

Evaporation ............................................................................................ 62

3.7.3

Inflow ...................................................................................................... 62

3.7.4

Outflow ................................................................................................... 63

3.7.5

Soil hydraulic parameters ..................................................................... 63

RESULTS ........................................................................................................ 66
4.1 Simulation results .....................................................................................66
4.2 Extension and adaptation to Vietnam requirements .................................71

5.

DISSCUSSION AND CONCLUSIONS ........................................................ 75

REFERENCES ....................................................................................................... 76
STATEMENT UNDER OATH ............................................................................. 79
APPENDICES ........................................................................................................ 80
Appendix 1: Precipitation using for simulation................................................80
Appendix 2: Brief of output of simulation for 784 days ....................................85
Appendix 3: Data from measurement ...............................................................89
Appendix 4: Data from simulation for the days equivalent with measurement
days ...................................................................................................................90

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ABBREVIATIONS
BbodSchG

German Soil Protection Law

CART

Classification and Regression Trees

CART

Classification and Regression Trees

DSS

Decision Support System

Eq

Equation

FE

Finite Element

FZJ

The Research Center in Juelich

GMDH

Group Method of Data Handling

GSF

The National Research Center for Environment and Health

GUI

Graphical User Interface

LUA NRW

The North Rhine-Westphalia State Environment Agency

NIPP

National Institute of Plant Protection

PFT

Pedotransfer Function

SiWaPro

Sickerwasserprognose / Leachate Forecast

SKE 1

Soil water sampling device layer 1 at 0,85m distance to upper edge of
the lysimeter

SKE 2

Soil water sampling device layer 2 at 1,15m distance to upper edge of
the lysimeter

SKE 3

Soil water sampling device layer 3 at 1,80m distance to upper edge of
the lysimeter

SKE

Saugkerzenebene / Soil water sampling device layer

TDR

Time domain reflectometry

vGP

van Genuchten Parameter

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LIST OF FIGURES
Figure 1: The unsaturated zone compares with the saturated zone .........................16
Figure 2: Division of soil fraction sizes, German (left) and American (right). ........17
Figure 3: Dicretization / meshing of area to be modeled. ........................................25
Figure 4: Boundary conditions and discetization of a simple model for groundwater
flow (from Chris McDermott, 2003) .........................................................................26
Figure 5: Boundary conditions and discretization for a simple column model .......26
Figure 6: Stress applied to the top of the rock column causes deformation.............27
Figure 7: Mesh in details ..........................................................................................28
Figure 8: Pressing of the stainless steel bottom plate (left) and lifting of a readily

filled monolithic lysimeter (right). ............................................................................31
Figure 9: Lysimeter covered with grass (left), the round surface of the Lysimeter
(middle) and lysimeter cellar with complete instrument (right) ...............................31
Figure 10: The lysimeter system at the Büel measurement site ................................32
Figure 11: Cross-section of a guideline lysimeter surrounded by a control plot .....32
Figure 12: The lysimeter station in Munich-Neuherberg .........................................33
Figure 13: The instrument for measuring the wind speed (right) and the rainfall
(left)at lysimeter station ............................................................................................33
Figure 14: Simplified sketch of the lysimeter and boundary conditions in the upper,
lower and 3 suction cup layers at lysimeter 302 in Juelich ......................................35
Figure 15: The schematic composition and the arrangement of measurement
devices .......................................................................................................................36
Figure 16: Structure of SiWaPro DSS ......................................................................41
Figure 17: Graphical user interface (GUI) of SiWaPro DSS ...................................42
Figure 18: SiWaPro DSS help system .......................................................................43
Figure 19: Search options for database access ........................................................45
Figure 20: GeODin interface form for data import ..................................................50
Figure 21: First start of the mesh generator ............................................................51
Figure 22: Define the modeling domain ...................................................................52

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Figure 23: Edit node properties ................................................................................52
Figure 24: Generated mesh ......................................................................................53
Figure 25: Define internal curves .............................................................................54
Figure 26: Generated mesh with internal curves .....................................................55
Figure 27: Convex internal curve (left) and concave internal curve (right) ............56
Figure 28: Adjusting graphic ....................................................................................56
Figure 29: Construction with a background image ..................................................57

Figure 30: Boundary nodes of the generated mesh ..................................................58
Figure 31: Selected nodes for assigning material number .......................................61
Figure 32: Selected nodes for assigning initial pressure head .................................61
Figure 33: Dialogue box of language options ..........................................................74

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LIST OF TABLES
Table 1: Nodal Coordinates ......................................................................................28
Table 2: Soi properties and van Genuchten Parameters using for Simulation ........39
Table 3: Switching surfaces for the assignment of the at the beginning of boundary
conditions ..................................................................................................................58
Table 4: Properties of the boundary conditions .......................................................59
Table 5:Submitted soil hydraulic parameters of the lysimeter at FZ Juelich ...........64
Table 6: Soil layer list of the lysimeters ....................................................................64
Table 7: Parameter limits and maximum allowable concentrations of pollutants in
ground water (according to Vietnam standard TCVN 5944-1995 and German
standard) ...................................................................................................................72

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LIST OF DIAGRAMMS
Diagram 1: Graphic of total inflow to the lysimeter surface ....................................63
Diagram 2: Graphic of total inflow to lysimeter surface comparing with total
outflow .......................................................................................................................67
Diagram 3: Graphic of outflow at SKE 3 comparing between Simulation and
Measurement .............................................................................................................67
Diagram 4: Graphic of outflow at SKE 1 comparing between Simulation and

Measurement .............................................................................................................68
Diagram 5: Graphic of outflow at lower comparing between Simulation and
Measurement .............................................................................................................69
Diagram 6: Graphic of outflow at SKE 2 comparing between Simulation and
Measurement .............................................................................................................70
Diagram 7: Graphic of total outflow comparing between Simulation and
Measurement .............................................................................................................70
Diagram 8: Graphic of inflow comparing between Simulation and Measurement ..71

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1.

INTRODUCTION
The unsaturated zone (vadose zone) plays an important roll in many aspects of
hydrology, such as infiltration (the movement of water from the soil surface
into the soil), exfiltration (water evaporation from the upper layers of the soil),
capillary rise (water movement from the saturated zone upward into the unsaturated zone due to surface tension), recharge (the movement of percolating
water from the unsaturated zone to the subjacent saturated zone), interflow
(flow that moves down slope), transpiration (water is uptaken by plant roots)
(Dingman S.L., 2002, p. 220), runoff (the movement of water/rain-water
across the surface soil and entering streams or other surface receiving water)
and erosion (wearing away of soil by the action of water, wind, glacial ice, etc.
on the soil surface) (Simunek J. et. al., 1994, p. 1). Interest in this zone has
been increasing in recent years because the movement of water along with
contaminants in this zone have been affecting the groundwater zone as well as
the subsurface environment. One of the interested areas is to predict the water
movement and water quality in unsaturated zone that is recommended to use
computer models.

The past several decades have seen considerable progress in the conceptual
understanding and mathematical description of water flow and solute transport
processes in the unsaturated zone. A variety of analytical and numerical models are now available to predict water and/or solute transfer processes between
the soil surface and the groundwater table. These models are also helpful tools
for extrapolating information from a limited number of field experiments to
different soil, crop and climatic conditions, as well as to different tillage and
water management schemes (Simunek J. et. al., 1994, p. 1).
A useful computer model that allows predicting water and solute transfer
processes in vadose zone is the computer-based decision support system SiWaPro DSS. This program combines the simulation module SiWaPro for nu-

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merical modeling of water flow and contaminant transport in variably media
with additional simulation and parameter estimation tools, data sources for the
simulation and a graphical user interface.
The main objective of this thesis is to use SiWaPro DSS to model and simulate
the water flow process in the unsaturated zone with the available data from lysimeter number 302 in Juelich, Germany. As mentioned above, the SiWaPro
DSS can be used also for modeling and simulating the water flow process in
the saturated zone and the solute transport process (including bio degradation
and sorption) in the unsaturated and saturated zone, but this thesis does not
consider these processes because of time limitation.
Before focusing on the main objective (discussed in the chapter 3 and 4), the
fundamentals of soil hydrology will be discussed with the basics of soil physics and soil water of the unsaturated zone that are relative to the model (see
chapter 2).
The Juelich lysimeter and lysimeter station description are also mentioned as
an overview to understand more about the model (see chapter 3.3).
Furthermore, the demands by law (thresholds for contaminants in groundwater), the graphical user interface and help system of SiWaPro DSS should be
translated into Vietnamese and adapted to Vietnamese requirements (see chapter 4.2).
Hopefully, initial achievement of the study in this thesis will prepare the

ground for an application SiWaPro DSS into leachate forecasting in Vietnam.

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2.

FUNDAMENTALS OF SOIL HYDROLOGY

2.1 Definition of soil and unsaturated zone
There are several definitions of soil and the unsaturated zone in some science
books and websites, but within the scope of this thesis only a short compilation
of important terminology concerning soil and unsaturated zone which will be
used in the following chapters as well as relevant to content of the thesis is
considered.
Soil:
Soil is an extraordinarily complex medium, made up of a heterogeneous mixture of solid, liquid, and gaseous material, as well as a diverse community of
living organisms (Jury W. & Horton R., 2004, p. 1).
Soil is a rather thin layer over the earth’s surface consisting of porous material
with properties varying widely. It can be seen as a sand-silt-clay matrix, containing inorganic products of weathered rock or transported material together
with organic living and dead matter (biomass and necromass) of the flora and
fauna (Lanthaler C., 2004, p.13).
Unsaturated zone:
The zone between the earth’s surface and the groundwater surface is to speak
of the unsaturated zone, also called zone of aeration (Lanthaler C., 2004, p.14;
quoted from Ward R.C., 1975).
The unsaturated zone is the portion of the subsurface above the ground water
table. It contains air as well as water in the pores (see Figure 1). Its thickness
can range from zero meters, as when a lake or marsh is at the surface, to hundreds of meters, as is common in arid regions (Unsaturated zone flow project,
2001).

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The unsaturated zone is the subsurface zone in which the geological material
contains both water and air in pore spaces. It is different from the saturated
zone, in which all pores
in the aquifer are filled
with water (see Figure
1).
Figure 1: The unsaturated zone compares
with the saturated zone
(Unsaturated zone flow
project, 2001)
As discussed by J. Goldshmid in the book titled Pollutants in Porous Media
(Yaron B. et. al., 1984, p. 208), the unsaturated zone is the buffer between human activity and ground water sources. As such, it serves two functions: as
reactor and as storage reservoir. Unlike from a storeroom, it is almost impossible to retrieve a pollutant from the unsaturated zone. A pollutant that enters the
topsoil is transferred by the water movement through the big reactor, and if it
does not decompose, or become consumed by vegetation, or attached to the
soil material, it will finally reach the aquifer and contaminate groundwater
supplies.

2.2 Soil hydraulic parameters
Determine water and solute transport with numerical modeling needs information about soil hydraulic parameters. Before go to the SiWaPro DSS for modeling and simulating water flow in vadose zone, getting more knowledge about
soil hydraulic properties is important. This section will talk about some soil
hydraulic properties that are related to the model.

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Soil fractions:
According to the size, particles of a soil framework can be divided into two
classes:
the clay fraction < 2 μm in diameter,

-

has been formed as a secondary product from the weathering of rocks (primary minerals) or from transported
deposits,
the non-clay fraction > 2 μm, can be

-

divided into the subclasses: silt, sand,
and gravel (Marshall T.J. et. al., 1996,
p. 4)
Size limits can differ between the German
and the American classifications; therefore,
limits are not natural but defined by man.
Figure 2 show the 2 classification systems
of German and American. The system of
American coming from the United State
Department of Agriculture uses 50 μm as
Figure 2: Division of soil
fraction sizes, German (left)

the limiting size between silt and sand; the
system of German takes limits of 63 μm

and American (right) nomen-

between silt and sand.

clature. Where Bloecke is

According to (Lanthaler C., 2004, p.15)

Block; Steine is Stone; Kies

another size dependent classification: coarse

is Gravel; Schluff is Silt and

soil has a size of > 2 mm and fine soil < 2

Ton

mm. This is based on a suggestion by Atter-

is

Clay

(from

SCHEFFER 2002, p. 157)

berg (1912) to use the number 2 as a limit
between fractions.

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Particle density:
Particle density, ρm, is the weighted average density of the mineral grains making up a soil:
m 

Mm
Vm

(Eq. 1)

where Mm is mass of mineral grains
Vm is volume of mineral grains
Bulk density:
Bulk density, ρb, is the dry density of the soil:
b 

Mm
Mm

Vs
Va  Vw  Vm

(Eq. 2)

where Vs, Va, Vw, are volume of soil, air and liquid
Porosity:
Porosity, Φ, is the proportion of pore spaces in a volume of soil:


Va  Vw
Vs

(Eq. 3)

Volumetric water content:
Volumetric water content or simply water content in soil, θ, is the ratio of water volume to soil volume:


Vw
Vs

(Eq. 4)

Degree of saturation:
The degree of saturation, or wetness, S, is the proportion of pores that contain
water:
S

Vw


Va  Vw 

(Eq. 5)

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2.3 Soil water balance
Soil as an important storage medium can also be explained systematically in
the following soil water balance, where ΔW, the change of the amount of water stored in a certain period, is according to (Marshall T.J. et. al., 1996, p.
248) composed of:
W  P  I  ( A  D  E)

(Eq. 6)

Precipitation (P) and irrigation (I) are balanced against the amounts of losses
of surface runoff (A), underground drainage (D), and evapotranspiration (E)
during a given period. Usually, quantities are given in mm. A can be negative
when water runs from soil to the surface and D is negative when (ground) water gets to the root zone.
Precipitation (P)
The only natural input in this system is precipitation and its appearance can be
divided into a liquid (drizzle, rain, dew) and a solid type (snow, glaze, frost,
hale). The geographical variations, the regional pattern of precipitation and its
distribution during a year/month with different variability (regime) are the
most important aspects for hydrology and soil hydrology. Rainfall intensity
(amount of precipitation divided by duration) is relevant in catchments areas
of rivers/streams susceptible to floods. Whenever precipitation is collected
with any type of rain gauge, uncertainties about the amounts occur due to
wind influence (especially in mountain areas), the topography and site around
the gauge, rain drop size, the material and condition of the gauge itself or
splash and gauge errors (Ward R.C., 1975, p. 16-34).
Irrigation (I)
While some areas have more than enough rainfall, agricultural land in other
areas has to be irrigated. Not only arid and semi-arid regions are irrigated but
also sub humid areas where irrigation supplements natural rainfall. Irrigation

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aims to recharge soil to the field capacity in the layer from which roots absorb
water. The amount of water applied depends on weather, soil, plant, and economic conditions. Insufficient water supply leads to a decrease of yield but too
much irrigation will increase losses of percolation (and can cause a higher water table and salinization of soil) and evapotranspiration, see below (Marshall
T.J. et. al., 1996, p. 268-271).
Surface Runoff or Overland Flow (A)
In case that the rainfall rate exceeds the infiltration rate, the surplus water travels over the ground surface without infiltration to reach a stream channel and
finally the outlet of the drainage basin. On most soils covered with vegetation
this is a rather rare phenomenon. The following conditions are relevant for
overland flow and the infiltration capacity, respectively: saturation of
soil/topsoil, agricultural practices, freezing of the ground surface or when soils
show a hydrophobic nature (Marshall T.J. et. al., 1996, p. 261-264, Ward R.C.,
1975, p. 240).
Underground Drainage (D)
The amount of water percolating through soil to the water table and recharging
groundwater is to be considered as the underground drainage. Water flows
downward to the groundwater table, and drainage soil water content decreases
after infiltration have stopped (Ward R.C., 1975, p. 193).
(Kutílek M. & Nielsen D.R., 1994, p. 133; Ward R.C., 1975, p. 166) defined
infiltration as a process of water (precipitation) entering soil through the surface. (Kutílek M. & Nielsen D.R., 1994, p. 133) denoted the flux density of
water across a topographical soil surface as the infiltration rate (formerly described as infiltration capacity, infiltration velocity and infiltrability). The rate
determines the maximum water amount infiltrating soil under specified conditions in a given time, not limited by the rate of supply. Soil surface condition
substantially affects infiltration (Marshall T.J. et. al., 1996, p. 134).

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According to (Kutílek M. & Nielsen D.R., 1994, p. 176-178) two cases are
important: soil water redistribution occurs when water percolates from wetted

topsoil to the drier subsoil; secondly, the process of drainage to the groundwater level when wetting front is not far from groundwater level or reaches it,
water flows at/near steady state conditions. Excess water is able to move directly from the topsoil to the groundwater after infiltration has ceased.
Evapotranspiration (ET): Evaporation and Transpiration
Evaporation (E) is the water loss from bare soil or a free water surface to the
atmosphere and is not the same for these two kinds of surfaces because their
properties are different, for example the surface roughness, the area of airwater interface, the heat capacity and heat conductance leading to different
surface temperatures. Water extracted from soil by roots to the dry organic
matter of plants and then transported to the atmosphere is called transpiration
(TR). These two processes often cannot be separated and are then unified in
the term evapotranspiration ET = E + TR. Furthermore, a distinction has to
be made between the actual and potential evaporation/evapotranspiration; the
actual E or ET (ETa) reflects the real amount of evaporation resulting from
given meteorological conditions of a surface providing limited quantity of water for soil and plants; it is highly dependent on the water and energy supply.
In contrast, the potential E or ET (ETp) describes the maximal amount of
evaporation that is possible under given meteorological conditions. Maximal
evaporation will occur when enough water is supplied, for example above
areas of surface water (Kutílek M. & Nielsen D.R., 1994, p. 182-218, Ward
R.C., 1975, p. 95-124).
(Marshall T.J. et. al., 1996, p. 393-395) provides another balance, which is the
water balance of a lysimeter:
P  I  E  D  A  W

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(Eq. 7)


ΔW can be determined when the container is weighable. When I is known due
to recording and P is measured by rain gauges, E can be determined by balancing input versus output variables.

2.4 Soil water flow
This section deals with the movement of water in unsaturated porous media,
focusing on infiltration, which is the movement of water from the soil surface
into the soil and redistribution, which is the subsequent movement of infiltrated water in the unsaturated zone of a soil.
Infiltration, Percolation
In section 2.3, infiltration water was already mentioned. (Kutílek M. & Nielsen D.R., 1994, p. 133, Ward R.C., 1975, p. 166) define infiltration as a
process of water (precipitation) entering soil through the surface. The term
percolation is used when the downward flow/movement of water through the
unsaturated zone is to be explained. (Kutílek M. & Nielsen D.R., 1994, p. 133)
denote the flux density of water across a topographical soil surface as the infiltration rate (formerly described as infiltration capacity, infiltration velocity
and infiltrability).
Redistribution
Redistribution can involve exfiltration (evaporation from the upper layers of
the soil), capillary rise (movement from the saturated zone upward into the unsaturated zone due to surface tension), recharge (the movement of percolating
water from the unsaturated zone to the subjacent saturated zone), interflow
(flow that moves downslope) and uptake by plant roots (transpiration) (Dingman S.L., 2002, p. 220).

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3.

MATERIAL AND METHODS

3.1 Theoretical approaches and methodology
To model or simulate the water flow process, a water flow model of Juelich
Lysimeter number 302 is developed based on the finite element mesh method.
The principle behind the application of the finite element technique is that everything is broken down into matrices representing the governing equations,
which are then solved for the unknown values (McDermott C.I., 2003, p.8). It
means that the modeled area is divided into smaller elements linked in a mesh.

The shape of the element used in this program is triangle. Nodes at the corners
of the elements define the boundaries of the element. The nodes are numbered
and assigned natural coordinates of the area in question. The elements are
numbered and the nodes assigned to each element recorded (see section 3.2).
The necessary simulation data are collected, documented and verified (see section 3.7). The model input data, which are related to evapotranspiration, precipitation and hydraulic soil, were taken from field monitoring station (Juelich
lysimeter station).
Theoretically, the parameters for model are estimated either from the function
θ(ψ) according to (van Genuchten M. Th., 1980) or from the continuous function k(ψ), relation from (Mualem, 1976) and (van Genuchten M. Th., 1980)
according to (Wösten J.H.M et. al., 2001), where θ(ψ) is water content as a
function of matrix potential and k(ψ) is unsaturated hydraulic conductivity as a
function of the matrix potential. But in this thesis, the parameters for simulation are taken from the report of (Puetz T. et. al., 2004). These parameters are
estimated and checked.
For calibrating the model, the simulated values of outflow are compared with
the amount of water leaching from the lysimeter as well as the water content
measurements at different depths of a soil profile.

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3.2 Finite element method
In SiWaPro DSS, the discretization of the modeling area is realized using finite elements with the GALERKIN method, so understanding about the finite
element method is necessary before going into SiWaPro DSS description. This
section will discuss about the finite element method-detailing object to be
modeled to finite element mesh and principle behind finite element calculations.
Object to be modeled to finite element mesh.
The object / area (from now on area) to be modeled is divided into smaller
elements linked in a finite elements mesh.
The shape of the element is variable, bars, triangle, squares, tetrahedral and
cubes are most commonly used. The boundaries of the element are defined by
nodes usually at the corners of the elements, but sometimes also along the

boundary of the elements and within the element. The nodes are numbered and
assigned natural co-ordinates of the area in question. The elements are numbered and the nodes assigned to each element recorded. More elements are
generated in places of special interest, or where there are expected to be higher
than normal changes in the parameters being included in the model. This
process, known as discretization or meshing is illustrated in figure 3 above.
Once the area has been discretized the construction of a mathematical model to
describe the processes being investigated is undertaken. This mathematical
model is unique to the process being simulated, similar processes having similar expressions. An example is looking for the head (measure of water pressure) distribution in an area, where only boundary values of the head are
known. Illustrated in Figure 4, or a rock under applied stress in Figure 5.

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