(Luận văn thạc sĩ) investigation of a lysimenter using the simulation tool siwapro DSS and adaptation of this program to vietnamese requirements

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 lysime-ter number 30

HANOI UNIVERSITY OF SCIENCE DRESDEN UNIVERSITY OF TECHNOLOGY

PHAM THI BICH NGOC

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 accom-panied 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

 Hanoi University of Sciences and Institute for Waste Management and taminated Site Treatment (IAA) for providing all materials and equipments that I used during the course

Con- 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 ment and support

encourage-And last but not least, special huge thanks to my family (my parents in law, my ents, my husband, my son and my brothers and sisters) and all my friends (especial-

par-ly 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, 10 th December 2008

Pham Thi Bich Ngoc

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 lysime-ter 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 simula-tion 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 de-gradation 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

expe-of the soil water balance, amounts expe-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

tak-en out from Munich-Neuherberg in June 2001 and the installation of the ment 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 refer-ence 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

measure-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 col-umn 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 ters 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 Be-cause the time is short – besides, one model took from 25 hours to 50 hours for run-ning; some models took much more time, then they were stopped before they finish

parame-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

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 si-mulation 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 fi-nite 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 out-flow of the lower boundary condition the simulation one is lower than measure-ment Outflow at the suction cup layer number 2 is different increasing by time be-tween simulation and measurement The differences come from the data mentioned

as above

The SiWaPro DSS program have been introducing to Federal Environmental reaus 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

Bu-a bit time for VietnBu-amese to fBu-amiliBu-ar with it For VietnBu-amese to Bu-apply this softwBu-are, 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

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

3.6.2.1Graphical user interface (GUI) and Help System 41

3.6.2.2Mesh Generator 43

3.6.2.3Weather Generator 44

3.6.2.4Database Layer 44

3.6.2.5Pedotransfer Functions 45

3.6.2.6Import and Export Interfaces 49

3.6.3 Manual SiWaPro DSS Mesh Generator 50

3.6.3.1Create a simple 2D mesh 51

3.6.3.2Definition internal curves 53

3.6.3.3Inserting a background image as construction basis 56

3.6.3.4Boundary condition editor 57

3.7 Data sets for calibrating the model 62

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

4 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

ABBREVIATIONS

BbodSchG German Soil Protection Law

LUA NRW The North Rhine-Westphalia State Environment Agency

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 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

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

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

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 unsa-turated 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 mod-els 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 Si-WaPro DSS This program combines the simulation module SiWaPro for nu-

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 ly-simeter 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 phys-ics 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 ter), the graphical user interface and help system of SiWaPro DSS should be translated into Vietnamese and adapted to Vietnamese requirements (see chap-ter 4.2)

groundwa-Hopefully, initial achievement of the study in this thesis will prepare the ground for an application SiWaPro DSS into leachate forecasting in Vietnam

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 ture of solid, liquid, and gaseous material, as well as a diverse community of living organisms (Jury W & Horton R., 2004, p 1)

mix-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, con-taining 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 dreds of meters, as is common in arid regions (Unsaturated zone flow project, 2001)

hun-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

unsatu-rated 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 man activity and ground water sources As such, it serves two functions: as reactor and as storage reservoir Unlike from a storeroom, it is almost impossi-ble 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

hu-2.2 Soil hydraulic parameters

Determine water and solute transport with numerical modeling needs tion about soil hydraulic parameters Before go to the SiWaPro DSS for mod-eling 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

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

According to (Lanthaler C., 2004, p.15) another size dependent classification: coarse soil has a size of > 2 mm and fine soil < 2

mm This is based on a suggestion by berg (1912) to use the number 2 as a limit between fractions

Atter-Figure 2: Division of soil

fraction sizes, German (left)

and American (right)

nomen-clature Where Bloecke is

Block; Steine is Stone; Kies

is Gravel; Schluff is Silt and

Ton is Clay (from

SCHEFFER 2002, p 157)

M



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:

m w a m s

m b

V V V

M V

Volumetric water content:

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

wa-s

w V

w V V V

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

wa-ter stored in a certain period, is according to (Marshall T.J et al., 1996, p 248) composed of:

)

I P

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) wa-

ter 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

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 eco-nomic conditions Insufficient water supply leads to a decrease of yield but too much irrigation will increase losses of percolation (and can cause a higher wa-ter 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

tra-vels 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 sur-face (Kutílek M & Nielsen D.R., 1994, p 133) denoted the flux density of water across a topographical soil surface as the infiltration rate (formerly de-scribed as infiltration capacity, infiltration velocity and infiltrability) The rate determines the maximum water amount infiltrating soil under specified condi-tions 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)

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 groundwa-ter 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 di-rectly 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 air-water 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

wa-ter for soil and plants; it is highly dependent on the wawa-ter 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:

W A D E I

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

ba-lancing 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 infil-trated water in the unsaturated zone of a soil

Infiltration, Percolation

In section 2.3, infiltration water was already mentioned (Kutílek M & sen 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 infil-tration rate (formerly described as infiltration capacity, infiltration velocity and infiltrability)

Niel-Redistribution

Redistribution can involve exfiltration (evaporation from the upper layers of the soil), capillary rise (movement from the saturated zone upward into the un-saturated 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) (Ding-man S.L., 2002, p 220)

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 eve-rything 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 tion 3.7) The model input data, which are related to evapotranspiration, preci-pitation and hydraulic soil, were taken from field monitoring station (Juelich lysimeter station)

sec-Theoretically, the parameters for model are estimated either from the function θ(ψ) according to (van Genuchten M Th., 1980) or from the continuous func-tion 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 simula-tion 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

3.2 Finite element method

In SiWaPro DSS, the discretization of the modeling area is realized using nite 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 calcula-tions

fi-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 num-bered 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 simi-lar expressions An example is looking for the head (measure of water pres-sure) 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

Approximation of real life situation

Mesh made up of several finite elements described by the nodes and the coordinates of the nodes in the natural coordinate system

Element 22 Node:

Figure 3: Dicretization / meshing of area to be modeled

(Reproduce from McDermott C.I., 2003)

In areas of interest where large differences in pa-rameters are expected the mesh is made finer

54

66

12

22

20m above sea level Sea level

all other heads are not known

Figure 4: Boundary conditions and discetization of a simple model for

groundwater flow (from McDermott C.I., 2003)

Figure 5: Boundary conditions and discretization for a simple column model

(from McDermott C.I., 2003)

Principle behind finite element calculations

The principle behind the application of the FE (Finite Element) technique is that everything is broken down into matrices representing the governing equa-tions, which are then solved for the unknown values The principle equation given is

diffi-us take a look at Figure 6 Let u be the displacement, and f be the forces

in-volved The finite element mesh approximation is shown in Figure 7 In the

mesh, there are 8 nodes, from 0 to 7, and in this case 7 elements

Figure 6: Stress applied to the top of the rock column causes deformation

Figure 7: Mesh in details

(from McDermott C.I, 2003)

Assigning a simple coordinate system, where the units of x and y are meters

and the node 3 is at the position 0,0 Then defining all the nodes of this mesh and the elements as illustrated in table 1

Table 1: Nodal Coordinates

Node x y Element Nodes

Dealing with forces, both the x direction and the y direction are considered

Likewise we have movement in both the x and y direction Therefore every

node has a x component and a y component In a three-dimensional system

this would also include a z coordinate Many systems can be approximated in

2D, by assuming a unit thickness of z the necessity to include variations in the z direction is removed

The force vector f and the movement vector u are then composed of an x and

a y component for every node:

Looking at the sketch, Figure 6, Eq 10 can be defined from the forces by

ap-plying and the movement possibilities If K is known, then the whole system will be solved for the unknown values of f and u From this solution then a

number of other values can be defined, such as strain and stress in the actual elements Should this have been a groundwater example, the unknowns would have either been heads or flux, a solution for all heads and flux would be got, and from the heads the gradient dh/dx could be derived, which coupled with the permeability then gives ground water velocity

3.3 Lysimeter

3.3.1 General information about lysimeter

The term lysimeter is a combination of the Greek words “lusis” = solution and “metron” = measure and the original aim of lysimeter is to measure soil

leaching (Lanthaler C., 2004, p 37, quoted from Muller J.C., 1996, p 9), cording to (Lanthaler C., 2004, p 39), lysimeters are also used for determining actual evapotranspiration and groundwater recharge and therefore for setting

Ac-up a water balance Due to an increase of pollution and contamination of groundwater, the original sense of lysimeters gained more and more impor-tance in the last decades and not only quantitative but also qualitative aspects predominate

According to (Kutílek M & Nielsen D.R., 1994, p 215) the explanation and the use of lysimeters are extended as following:

- soil is hydrologically isolated from the surrounding soil,

- lysimeters are containers filled with disturbed (= artificially filled) or disturbed bare soil or soil covered with natural or cultivated vegetation,

un seepage water is measured directly; vertical water movement is also to be determined,

- percolating water is collected either gravimetrically (=gravitation ter) or through suction cups/a suction plate with a negative soil water pressure head, identical to that in the field next to the lysimeter (= suction lysimeter),

lysime an artificial groundwater level can be simulated,

- lysimeters are either weighable or non-weighable; weighable lysimeters

provide information about the change of water storage W for any time

pe-riod; non-weighable lysimeters collect only the water percolating from the soil column

According to (Lanthaler C., 2004, p.40) there are several criteria that can be applied to classify the lysimeter as following:

- size: small (< 0.5 m²), standard (0.5–1 m²), large (> 1 m²)

- weighability: weighable, non-weighable

- soil filling method: disturbed (backfilled) or undisturbed

(mono-lith/monolithic lysimeter)

- if groundwater occurs: groundwater lysimeter with a variable or

invari-able groundwater level; lysimeter without groundwater contact and with

or without applied vacuum

- vegetation: bare soil, grassland, arable land, forest

- soil fractions: sandy, silty, clayey soil

Figure 8, Figure 9, Figure 10 and Figure 11 below show an overview about

lysimeters

Figure 8: Pressing of the stainless steel bottom plate (left) and lifting of a

rea-dily filled monolithic lysimeter (right)

Figure 9: Lysimeter covered with grass (left), the round surface of the

Lysime-ter (middle) and lysimeLysime-ter cellar with complete instrument (right)

Figure 10: The lysimeter system at the Büel measurement site

(from http://www.iac.ethz.ch/en/research/riet/instruments.html)

Figure 11: Cross-section of a guideline lysimeter surrounded by a control plot

(from http://www.fz-juelich.de/icg/icg-4/index.php?index=155 )

3.3.2 Juelich lysimeter station description

Juelich lysimeter station was established in 1980 It is located in Juelich, near Cologne, Germany There are several types of lysimeter, more than 20 in total

10 lysimeters were used for the research project of German Ministry for cation and Research All lysimeters are weighable Their surfaces consist of bare soil, grassland and arable land

9 Soil thermoelements

10 Grass

Figure 12: The lysimeter station in Munich-Neuherberg

(from http://www.fz-juelich.de/icg/icg-4/index.php?index=155 )

At the lysimeter station, the weather parameters are measured such as rainfall,

wind speed, temperature Figure 13 show the instruments for measuring the

wind speed and rainfall at the lysimeter station

Figure 13: The instrument for measuring the wind speed (right) and the

rain-fall (left)at lysimeter station

3.3.3 Description of the Juelich lysimeter number 302

The Juelich lysimeter number 302 was established in August 2001, the liths were taken out from Munich-Neuherberg in June 2001 and the installa-tion of the measurement devices occurred and the data logging started on De-cember 10th 2001

mono-This lysimeter is run by the Research Centre in Juelich (FZJ)

Based on the classification of lysimeter types mentioned above (section 3.3.1), Juelich lysimeter number 302 is a large undisturbed lysimeter with 2m2 in area

and 2,4m in depth In Figure 14, a simplified sketch of Juelich lysimeter

num-ber 302 is presented together with boundary conditions of upper and lower edges as well as 3 layers of suction cups 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

After the drying of the applied soil, the reference material soil was mented with a thickness of 47 cm Above the reference material, a coarse sand layer (33 cm) was implemented in tiers of 10 to 15 cm (compacted) until the upper edge of the lysimeter On the coarse sand a further water tracer was ap-plied (65% concentrated deuterium oxide D2O) and then sprinkled with Milli-pore-water (Puetz T et al., 2004) The schematic composition and the ar-

imple-rangement of measurement devices are presented in Figure 15

In order to match the amount of precipitation at the reference location nich-Neuherberg, the lysimeter was sprinkled with equivalent amounts of Mil-lipore-water at given times At the measurement layers the outflow or ex-tracted seepage water was sampled for a month and then analyzed

Mu-The lysimeter wasn’t saturated with water at the beginning of the experiment Therefore, a part of the infiltrating water was stored for an up-saturation of the soil matrix

Figure 14: Simplified sketch of the lysimeter and boundary conditions in the

upper, lower and 3 suction cup layers at lysimeter 302 in Juelich

(Puezt T et.al., 2004)

Figure 15: The schematic composition and the arrangement of measurement

devices (Puezt T et.al., 2004)

The scenario-based lysimeter set-up allows observation of its component’s behaviour under most natural conditions Precipitation infiltrates the column through a covering layer of inert material (quartz gravel) in order to achieve

uniform permeation into the reference material At the bottom of the nated layer, suction cups are mounted, which extract pore water by vacuum for the determination of the source term Additional suction cups at different depths of the transport zone can be added for the observation of concentration fronts progressing to the bottom (Puetz T et al., 2004) An inert sand filter with graduated grain sizes helps to avoid negative pressure that is otherwise generated by a capillary fringe Trickling off the sand filter, the seepage water

contami-is collected by a tank at the bottom before it contami-is analysed

Meteorological data are recorded to determine the amount of infiltrating water and to compare with the amount measured at the outlet, thus acquiring infor-mation on the flux regime inside the lysimeter Additionally, lysimeters are weighable for the same purpose Any cover of vegetation on top of the lysime-ter is continuously removed

3.4 Water flow model

The mathematical model behind SiWaPro, the modeling module of SiWaPro DSS, is based on the mathematical model used in SWMS_2D (Simunek J et al., 1994)

According to the (Blankenburg R et al., 2005, p 1) the flow model describing 1-dimensional vertical water flow in the unsaturated zone is given by the RICHARDS equation:

t z

h k

de-The hysteretic parametric model of soil water retention curve is given after (van Genuchten M.Th., 1980) and (Luckner L et al., 1989) by:

The parameters of equation 13 are the porosity Φ, the residual water content

A, the residual air content B, the scaling factor α and the slope parameter n

The unsaturated hydraulic conductivity k(θ) depends on the water content in

the soil The function of unsaturated hydraulic conductivity was modeled by (Luckner L et al., 1989) with:

11)

o

S

S S

S k k



The parameters of equation 14 are the hydraulic conductivity k 0 (θ 0 ) at a known

degree of water mobility S 0 =(θ 0 -A)/(Φ-B), the parameter λ and the

transfor-mation parameter m

The parameters Φ, k 0 and θ 0 must be estimated in advance using lab and/or

field tests The parameter λ in the model may range between 0<λ<1, but it is kept fixed at λ=0,5

3.5 Description of the finite element mesh of the lysimeter

As mentioned in section 3.3.3, the height of the Juelich lysimeter 302 is 2,4m including 0,8m of reference material In the water flow model, the reference material is not concerned, so the column of the lysimeter in the finite element mesh has a height of 1,6m The area of lysimeter is 2m2, diameter of the sur-face area is 1,6m, so mesh of lysimeter has a width of 1,6m

The lower boundary condition is a first kind boundary condition of equation (11), only outflow is allowed in this boundary The flux difference between precipitation and evapotranspiration is applied as a second type boundary con-dition at the upper boundary of the column of lysimeter The transient boun-dary condition with using time – variable boundary conditions is used in the model Three soil water sampling device layers (SKE 1, SKE 2, SKE 3) 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 6 parameters and in 5 van Genuchten metes Their values were taken from the field soil description of (Puetz T et al., 2004) and are listed in table 2

para-Table 2: Soi properties and van Genuchten Parameters using for Simulation