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 1  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. 2 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 3 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 4 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. 5 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 6 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 7 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 8 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 9 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 10 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 11 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 12 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- 13 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. 14 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). 15 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. 16 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. 17 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) 18 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 19
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