Modelling
Variably Saturated Flow With HYDRUS-2D 
D. Rassam, J. Simunek, and M. Th.
van Genuchten
Price:
US$80 (excludes postage and handling)
Contact :
Indooroopilly
4068,
Email: david_rassam@virginbroadband.com.au
Fax: 61 7 3376 7454
This book
is your companion to HYDRUS-2D (front cover shown here). It has over 250 pages
(with color illustrations) and comes with a CD that includes 107 examples
demonstrating all capabilities of the software. Click here
to view the Table of Contents.
This book caters for beginners as well as advanced
users. It covers many aspects of the software that are neither discussed in the
Technical Manual nor in the on-line Help. It is structured into eight major
parts:
Introductory Examples: Includes two basic examples demonstrating the basic
capabilities of the software in a step-by-step manner designated for first time
users.
Section 1 takes the user on a journey through all HYDRUS windows. It
covers various aspects that include starting new projects, setting up finite
element grids (including 3 advanced examples on Meshgen),
assigning boundary conditions, running the model, and viewing the results.
Section 2 explains the various output files that HYDRUS produces. It
explains the meaning of the different variables involved, and provides 3
advanced examples on how to manipulate the output data to obtain results that
are not readily available in HYDRUS. There are 3 spreadsheets on the CD that
demonstrate mass balance calculations and show how fluxes are integrated over
parts of a boundary.
Section 3 includes 8 projects on root water uptake.
Section 4 includes 13 advanced example applications;
8 on Vertical Plane Flow, 2 on Axisymmetric Vertical
Flow, 1 on Horizontal Plane Flow, and 2 others shows
extra features in HYDRUS. There are 32 projects on the CD that relate to this
section.
Section 5 is a comprehensive section on inverse parameter
estimation. It demonstrates through 28 examples important issues such as non-uniqueness
of a solution, effect of temporal and spatial distribution of the calibration
data, effect of initial values of the optimized parameters, statistical issues,
and validation of results. This section ends with a list of 15 recommendations
on inverse modelling.
Section 6 relates to trouble-shooting. We demonstrate through many
examples cases where HYDRUS may not perform as well as it should, present
likely reasons, and put forward measures for avoiding such cases. The 20
examples highlight the factors that affect the stability of a numerical
solution, such as, initial and minimum time steps, the density of the finite
element mesh, tolerance limits, limits of the tension interval, and the
hydraulic model. The section concludes with 13 recommendations that help the
user achieve trouble free simulations.
Appendixes: In Appendixes I to V we present theoretical backgrounds
related to soil hydraulic properties, modelling evaporation and the
significance of ‘hCritA’, root water
uptake models, the meaning of scaling factors, and various aspects related to
inverse parameter estimation (such as correlation matrix, confidence limits,
and weighting parameters). Appendix VI presents two basic examples on modelling
solute transport. Appendix VII includes an alphabetical index of HYDRUS
windows with cross-referencing to related pages and examples in the book.
Finally, Appendix VIII includes a list of available toolbars and their meaning.
An alphabetical index is also available. There are 9 projects on the CD that relate
to the appendixes.
EXAMPLES (SECTION 4):
Fluctuating Stream Level: simulates a rising and falling stream bank, a
case where individual simulations have to be conducted for each stage because
of the changing nature of the boundary condition along the stream bank.
Modelling Evaporation: a study of the advance of the
drying boundary and the effects of mesh density on predicted evaporative
fluxes.
Capillary Barrier: shows how this principle works.
Modelling Hysteresis: compares simulations that use
drying, wetting, and hysteretic water retention data and shows its impact on
predictions of water storage (e.g., effect on design of soil covers).
Estimating Flow Rates Inside a Domain: shows
how fluxes across any section in a domain (obtained from the graphical
interphase) can be externally integrated to obtain flow rates (not readily
available in the output files).
Effect of Mesh Spatial Discretization and
Tolerance Limits: shows how mesh density and tolerance limits impact
predicted fluxes and run times.
Simulating Surface Runoff: shows how we use HYDRUS to estimate surface
runoff.
Local Anisotropy: simulates flow along a hill slope with a fault that
acts as a preferential path.
Tension Disc Infiltrometer: shows the advance
of the wetting boundary beneath a disc infiltrometer
with and without a confining ring beneath the disc; we show two alternative
techniques to model the confining ring.
Dewatering of a Cylindrical Pit: demonstrates the use of nodal recharge
and demonstrates how recharge rates are transformed into nodal fluxes.
Steady State Horizontal Flow: shows how we can get a 3-dimensional map
for a steady state water table.
Print Times: shows how we can have up to 5,000 print times.
Running Multiple Sequential Simulations: shows how to run multiple
simulations from the DOS prompt.
RETURN
TABLE OF CONTENTS
Preface
Introductory Examples
Example 1: Project ‘1D-Infil’
Example 2: Project ‘2D-infil’
SECTION 1: A Journey Through HYDRUS
Windows
1.1 Pre-Processing
1.1.1 Main
Processes
1.1.2 Geometry
Information
1.1.3 Time
Information
1.1.4 Print
Information
1.1.5 Iteration
Criteria
1.1.6 Soil Hydraulic
Model
1.1.7 Water Flow
Parameters
1.1.8 Time Variable
Boundary Conditions
1.1.9 Geometry and
Finite Element Mesh Editor
1.1.9.1
Rectangular Grids
1.1.9.2
General Grids, MeshGen
1.1.10 Boundary
Conditions Editor
1.1.10.1 Water flow Boundary
Conditions
1.1.10.2 Material
Distribution
1.1.10.3 Root Distribution
1.1.10.4 Initial Conditions
1.1.10.5 Subregions
1.1.10.6 Scaling Factors
1.1.10.7 Observation Nodes
1.1.10.8 Nodal Recharge
1.1.10.9 Local Anisotropy
1.2 Post-Processing
1.2.1 Graphical Display
of Results
1.2.2 Pressure
Heads
1.2.3 Water Boundary
Fluxes
1.2.4 Cumulative Water
Boundary Fluxes
1.2.5 Soil Hydraulic
Properties
1.2.6 Run Time
Information
1.2.7 Mass Balance
Information
1.2.8 Convert Output to
ASCII
SECTION 2: HYDRUS Output Files
2.1 Output Files
2.1.1 Boundary.out
2.1.2 ObsNod.out
2.1.3 h_mean.out
2.1.4 v_Mean.out
2.1.5 Cum_Q.out
2.1.6 Check.out
2.1.7 Run_Inf.out
2.1.8 Balance.out
2.1.9 Optional Files
2.1.10 Fit.out
2.1.11 A_Level.out
2.2 Examples
2.2.1 Example Project WT-1
2.2.2 Example Project Mbal-2
2.2.3 Example Project Mbal-3
SECTION 3: Root Water Uptake
3.1 Relevant Windows in HYDRUS
3.2 Root Water Uptake Simulations
SECTION 4: Example Applications
Vertical Flow Examples
4.1 Fluctuating Stream Level
4.2 Modelling Evaporation
4.3 Capillary Barrier
4.4 Modelling Hysteresis
4.5 Estimating Flow Rates Inside a Domain
4.6 Effect of Mesh Spatial Discretization
and Tolerance Limits
4.7 Simulating Surface Runoff
4.8 Local Anisotropy
Axisymmetric Flow Examples
4.9 Tension Disc Infiltrometer
4.10 Dewatering of a Cylindrical Pit
Horizontal Flow Example
4.11 Steady State Horizontal Flow
Miscellaneous Examples
4.12 Print Times (up to 5,000)
4.13 Running Multiple Sequential Simulations
SECTION 5: Inverse Solution
5.1 Inverse Solution Options in HYDRUS
5.2 Inverse Modelling of Controlled Laboratory
Column
5.2.1 Simulating Wetting Cycle
‘a’
5.2.2 Simulating Wetting Cycle
‘b’
5.2.3 Optimizing Parameter
‘L’
5.3 Effect of Model’s Initial Parameters on Inverse
Solution
5.4 Long Inverse Trial With a Multiple-Layer Soil Profile
5.4.1 Sensitivity Analysis
5.4.2 Inverse Simulations With Layered
System
5.5 General Rules; Do’s and Don’ts In Inverse
Modelling
SECTION 6: Trouble Shooting
6.1 Infiltration After Long Dry Period
6.2 Intense Infiltration Into a Two-Layered Soil
System
6.3 Simulations With Highly Unstable Initial Conditions;
Drainage of a Saturated
Coarse-Grained Soil
6.4 Infiltration Into a Thick Clay Layer After a Dry
Period
6.5 Simulations With Highly Unstable Initial Conditions;
Very High Pressure
Gradient
6.6 Concluding Remarks
APPENDIXES
Appendix I Soil Hydraulic
Properties
I.1 Water Retention Parameters
I.2 Hydraulic Conductivity Function
I.3 Sensitivity Analysis
Appendix II Concept Related to Modelling Evaporation
II.1 Significance of Suctions at Soil Surface
II.2 The Concept of hCritA
Appendix III Root Water Uptake
III.1 Root Water Uptake Reduction Models
III.2 Root Density
III.3 Root Distribution Functions
Appendix IV Scaling Factors
IV.1 Background
IV.2 Stochastic Scaling Factors
Appendix V Inverse Solution
V.1 The Inverse Method
V.2 Statistical Issues
V.2.1 Distribution of
Residuals
V.2.2 Confidence Limits
V.2.3 Goodness of Fit and
Errors
V.2.4 Correlation Matrix
V.2.5 Weighting Parameters
V.3 Calibration Data
Appendix VI Introductory Examples on Solute
Transport
Appendix VII Index for HYDRUS Windows
Appendix VIII Description of Toolbars
REFERENCES
ALPHABETICAL INDEX
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