Dear member
i use femwater coupled with GMS.
i want to modelize an excavation. i put the head in the bottom of the
excavation as constant head(equal to the elevation) but the level of
aquifer near the excavtion is constant.
do you now how to modelize the excavation with GMS.
Date: Wed, 27 Jun 2007 05:39:49 -0000
From: "pun_mahesh" <pun_mahesh@...>
To: cpkumar@...
Subject: Exporting Flow files
Namaste Mr. Kumar,
This is Mahesh Pun, a graduate student of Environmental Engineering.
Currently i am using GMS software. Currently i am trying to model a
watershed basin of mid-west america. I am using WASH123D (1D
river/stream, 2D overland, and 3D subsurface flow), modeling of water
flow in an integrated presperctive. Currently it runs on super-
computer, unix environment. I am using (a new user)GMS to generate
geometric and flow files of rivers, overland, and sub-surface. I am
able to create geometric files of these in GMS, extract it from
GMS ,and send it to super-computer and is ready for simulation. But i
can't flow files and extract it from GMS.
Sir if you have any ideas regarding this matter or any advice and
suggestions i could use to solve this problem, please kindly let me
know. I am using all my ideas currently but nothing seems to work.
It was nice to know you through website, an experienced and helpful
person in this field of environment Modeling. I would be waiting for
your reply. Thank you sir.
Sincerely,
Mahesh Pun
M.S. Environmental Engineering
Department of Civil and Environmental Engineering
Department of Biological Systems Engineering
University of Nebraska-Lincoln
pun_mahesh@...
Dear Member,
Based upon the information received, I have initiated preparing the
directory of groundwater hydrologists. You can access the directory at
http://tech.groups.yahoo.com/group/gwmodel/files/
I again request the remaining groundwater hydrologists in this group
to please forward the following details to my e-mail address
cpkumar@... at your earliest convenience.
* Name
* Official Address
* Phone Number
* FAX Number
* E-mail Address
* Website Address
* Area(s) of Specialization
If you press the reply button, then ensure that default group address
is replaced by cpkumar@... in the "To" field, otherwise the
message will go for posting to entire group.
Regards
Kumar
==================================================
C. P. KUMAR
Scientist 'E1'
National Institute of Hydrology
Jal Vigyan Bhawan
Roorkee - 247667 (Uttarakhand)
INDIA
Web Page : http://www.angelfire.com/nh/cpkumar/
==================================================
Dear Member,
I intend to prepare a directory of groundwater hydrologists. After
compilation, I can upload the directory in the Files section of
gwmodel group (http://tech.groups.yahoo.com/group/gwmodel/files/), so
that anyone can refer to it whenever needed. I therefore request all
the groundwater hydrologists in this group to please forward the
following details to my e-mail address cpkumar@... at your
earliest convenience.
********************************
Name
Official Address
Phone Number
FAX Number
E-mail Address
Website Address
Area(s) of Specialization
********************************
If you press the reply button, then ensure that default group address
is replaced by cpkumar@... in the "To" field, otherwise the
message will go for posting to entire group.
Regards
Kumar
==================================================
C. P. KUMAR
Scientist 'E1'
National Institute of Hydrology
Jal Vigyan Bhawan
Roorkee - 247667 (Uttarakhand)
INDIA
Web Page : http://www.angelfire.com/nh/cpkumar/
==================================================
Hello
After doing simulation with femwater; I can’t see the surface of the water
table
And I don’t now if I can cut some cross section
ghassen
thank you
Hello! I'm learning GMS and i have some questions.
1.- How is define the aquifer? I define aquifer like tutorial, but when
convert map --> modflow the simbology of aquifer are the same that wells. Is
ok???
2.- Then run Modflow, I don't undersand the grahic.
Is there somewhere explain de results then run Modflow?
Thanks.
PLEASE SOME COULD HELP HOW TO DEMNSTRATE THE GOVERNING
EQUATION OF TRANSPORT LINK WITH THIS MESSAGE
THANK YOU
EXCUSE MY BAD ENGLISH
I SPEAK FRENCH VERY WELL
Hi there
I am using GMS 4.0 and wondering how to build a 2d and 3d finite
element mesh using imported dxf file or shape file. Any tutoril in
this regard?
Dear all,
I am stuck with FEMWATER transport simulation. I have a well calibrated
regional flow model that I have used to create transport model at a local or
finer scale using the total pressure heads as boundary conditions. My model
now comprises two polygons: the outside boundary with specified head and
flux (recharge) and a tailings impoundment in the centre with specified
flux. I now want to investigate the effects of dispersion on concentrations
of any releases from the dam. I have tried to speciffy the concentration in
tailings impondment but i am just getting zero concentrations in the output.
Please help
Masi
I recentely began to use GMS and i want to import data from surfer. I
do that without problem, but if i use them in the package recharge GMS
can't integrat them and cant proces.
Can some one help me for that.
Thank you very much.
Best regards
Lahoucine HANICH
Universié de Marrakech
Morocco
===========================================================
Please note deadline for applications is June 7th 2006.
Terms of reference may be found in the following documents:
Strategic Study of Groundwater Resources in Prey Veng and Svay Rieng
Phase 2
http://www.seila.gov.kh/english/consult_en.asp?
language=en&pgid=30&title=Consultant
A Senior Hydrogeologist is required (57 person-days)
The Senior Hydrogeologist will be a senior international expert in
the development and application of groundwater models for water-
resources applications. The Senior Hydrogeologist will have overall
responsibility for model development and will oversee the work of
the Intermediate Hydrogeologist. It is envisaged that the Senior
Hydrogeologist will be based overseas and will conduct the majority
of his/her work at home base, communicating with the team in
Cambodia by e-mail. Provision will be made for the Senior
Hydrogeologist to make two visits to Cambodia of 2-3 weeks each.
Model development will be based on the data collected during the
already completed Phase 1 study.
http://203.223.42.59:8080/downloads/SSGWRPVSR_STFS-FinalReport_05-12-
23.pdf
STRATEGIC STUDY OF GROUNDWATER RESOURCES IN PREY VENG AND SVAY RIENG
(PHASE 1) With funding from IFAD-RPRP project, STFS contracted IDE
to carry out the first phase of a strategic study of groundwater
resources in Prey Veng and Svay Rieng provinces. The objective of
the study is to assess the potential for sustainable development of
groundwater irrigation in Prey Veng and Svay Rieng provinces,
considering the availability of groundwater resources and other
environmental constraints. The first phase comprised collection and
interpretation of existing data on groundwater availability and
groundwater use, and recommendations for subsequent phases of the
study.
Other members of the four person team have already been selected.
GEB Development, a respected national consulting and construction
company with strong links to the Cambodian Ministry of Rural
Development, will prepare the bid. GEB Corp may also be contacted
directly at:
GEB Development Corporation
Chhum Bok Village
Kompong Speu, Cambodia
Email1: Landmine_Mapper@...
Email2: geb@...
Please help USDA's National Agricultural Library plan for services to
meet your information needs. Take a moment with your Web browser to
complete NAL's brief online survey
http://osincsurvey.com/run/osl04nal
This survey will be available beginning Tuesday, April 18, 2006.
Please complete the survey by Tuesday, May 2, 2006. NAL plans to
share summary findings from this survey on the NAL Web site,
www.nal.usda.gov. Thank you for helping NAL plan its services.
(Our apologies for any duplication)
This is a brief email to provide information on the upcoming model
calibration and uncertainty analysis course – using PEST – in late summer
2006.
Regards – Matt Tonkin
pest@... <mailto:pest@...>
Calibration and Predictive Uncertainty Analysis Using PEST, San Francisco,
Fall, 2006
In collaboration with the Groundwater Resources Association of California
(GRA) the third annual California PEST Course will be presented at the Savoy
Hotel in San Francisco, September 13th to 15th, 2006. The instructors will
be Dr. John Doherty, the author of PEST, and Matt Tonkin.
For more details visit http://www.sspa.com/PEST/training.html
<http://www.sspa.com/PEST/training.html> or to register for the course,
visit http://www.grac.org/pest.html <http://www.grac.org/pest.html> .
Further info about PEST can be found at pest@... <mailto:pest@...>
. This account is used to circulate occasional information on courses and
software updates. PEST has been freeware since February 2001 and is
available at http://www.sspa.com/PEST <http://www.sspa.com/PEST> .
[Non-text portions of this message have been removed]
Dear mmembers,
I am usingt T-Progress in GMS for markov chain simulation. I try to
draw variogram from my data which having 7 lithotypes. The results show
some it is not permissible. But we I am working with 5 lithotypes it is
giving good results. My question is there any restirction in GMS that
It will not work more than categaries. Thanks in advance.
Snehamoy Chatterjee
III International Symposium on Transboundary Waters Management
Overcoming Water Management Boundaries
Invitation Letter
Dear colleague,
We are organizing the III International Symposium on
Transboundary Waters Management, to be hosted at the University of
Castilla-La Mancha, in Spain, from May 30th to June 2nd, 2006, and
co-organizer by UNESCO and SAHRA.
The Symposium will be focus on the analysis of all Water Management
Boundaries, which impose conditions for water managing. Beside the
natural or physical boundaries, coming from the basin limits or the
differences resources sources (surface, subsurface, or coastal), there
are other human boundaries. These come from the fact that water
resources are coupled with the larger reality of a region, including its
environmental, social, legal, and economic characteristics. This implies
that at various levels of responsibility may appear boundaries, which
must be overcome for a successful water management strategy. These
include boundaries from the international scale, to the national,
regional, local, or even individual scale. The meeting is intended to
provide an integrated forum for TWM, considering both natural and human
boundaries.
This third Symposium will build on the review and analysis of
transboundary basins and aquifer management issues that occurred at the
previous symposiums in November 2002 in Monterrey (Mexico), and November
2004 in Tucson (USA). Topics ranging from quantity and water quality
management, impacts of climate fluctuations, building flexibility and
robustness into compacts, non-conventional water resources, and improved
sharing of data will be considered. Market-based allocation approaches,
ecological conservation, legislation framework, and the need for greater
hydrologic literacy among decision-makers also will be included, in view
of their relevance in the international and interstate water resources
arena.
Keynote speeches and panel discussions by recognized experts will
address a range of topics critical to improved transboundary waters
management. Additionally, we are working on organizing a course on
Isotopes in Hydrology and their potential application to TWM, on May
29th.
Abstracts reception is open up to March 1st. Travel Grants and special
registration rates are available. We would very much appreciate your
participation in the symposium. It promises to be a lively and
interesting event, attended by researchers, policy makers, academics,
and representatives of NGOs from all over the world.
You may obtain more information, at http://www.uclm.es/congresos/twm/.
Let me know any particular question.
We are looking forward to seeing you at this meeting.
Yours sincerely,
Javier González Pérez
Symposium Chairman
Javier.Gonzalez@... /Tfno. +34 926295300 Ext.3282
Fax. +34 926295391
Avda. Camilo José Cela, s/n
13071 Ciudad Real – España (Spain)
[Non-text portions of this message have been removed]
Dear Sir/Madam
I would like to prepare the input files of Modflow (PM5.1)
externally (by another application). The input files are
*.con,*.htc,*.lea and so on.
It's done now, but a problem has occured. In short, Modflow doesn't
look at my input files - bas.dat, bcf.dat and etc. I found out that
I should "regenerate input files" before running modflow.
This may be done by ticking the relative checkbox in run dialog,
while running modflow manually.
1- Is there any way to enforce Modflow to regenerate input files
automatically? (a switch, a preferences or ...)
2- If not, what are the format of these files. (Fortunately they are
text files).
Sincerely,
Groundwater modeling community
We also want everyone to be aware of the last GMS regular training
course that will be taught here in the US this year. The 4-day course
will be in Las Vegas on October 11th - 14th. Details of this basic course
can be found on our website
<http://ems-i.com/Training/gms_training_vegas.html> .
This class will be taught using the new 6.0 version. If you are new to GMS
or your want to learn about the new features of 6.0, please consider
attending
this course.
If you have any questions or would like to register for this class, please
contact
me.
Warm regards
Jeff Davis
EMS-I
***************************************************************************
Environmental Modeling Systems Incorporated
1204 West South Jordan Parkway, Suite B, South Jordan, UT 84095
phone:(801)302-1400 fax:(801)302-1160
email: jeff@...
www: http://www.ems-i.com <http://www.ems-i.com/>
Quote: "Know this for sure: You can pay me now, or you can pay me later!"
***************************************************************************
[Non-text portions of this message have been removed]
Last call! - spaces are still available for two parameter estimation and
uncertainty analysis course to be held in the UK and USA this summer.
Best wishes,
Matt Tonkin, SSP&A
matt@...
Courses: Model Calibration and Predictive Uncertainty using PEST
Shrewsbury, England, September 13-15, 2005
Stony Brook, Long Island, NY, September 19-21, 2005 (near MacArthur Airport
and Port Jefferson)
Principal Instructor: Dr. John Doherty (author of PEST)
Guest Instructor: Jim Rumbaugh (author of Groundwater Vistas) (New
York course only)
Assistant Instructor: Matt Tonkin
This intensive course instructs participants on the automated calibration of
environmental models, and the analysis of the predictive uncertainty
associated with such models. The principal instructor is the developer of
PEST, the industry standard package for model-independent, automated
calibration and predictive uncertainty analysis. The course focuses on the
use of PEST, including the new capabilities added to Versions 8 and 9 this
year. The course includes thorough coverage of the theory and application of
nonlinear parameter estimation techniques in the calibration of different
types of models. There is a strong practical aspect of the course -
participants gain hands-on experience in the use of PEST, including its
advanced regularization and predictive analysis features, in the calibration
of groundwater flow and transport models, surface water quality and quantity
models, as well as other types of models including a vadose zone model and a
biological growth model.
Course Details and Registration
For detailed information on course content visit
www.sspa.com/pest/training.html to download a prospectus, or write to
pest@....
To register on-line for the New York course please visit
www.sspa.com/pest/training.html
To register on-line for the UK course please visit
http://www.esinternational.com/training/CourseDetail.asp?course_id=49
Information about PEST can be found at pest@.... This account was
established for PEST users to obtain information on courses and software
updates. The account is used to circulate occasional information. To be
added to the PEST list write to pest@... with the subject "subscribe".
Please find below an announcement for the release of V10 of PEST and
associated UK and USA courses in parameter estimation and uncertainty
analysis.
Apologies for any double postings, best wishes,
Matt Tonkin, SSP&A, matt@...
PEST Version 10 Beta Release
PEST v10 will be released later this year. A beta version can be downloaded
from ( http://www.sspa.com/pest/download.html) for those interested in
exploring recent developments in model predictive uncertainty analysis.
Enhancements to the capabilities of PEST in v10 include:
* PEST’s SVD-assist scheme has been enhanced, enabling regularized inversion
to be used with highly parameterized models with efficiencies commensurate
with traditional parameter estimation.
* PEST’s predictive analyser is more powerful, with an improved line-search
algorithm and added functionality to encompass the effects of predictive
noise on predictive variability.
* A greatly expanded suite of utility software supports:
* Comprehensive post-processing of PEST results including analysis and
plotting of the resolution matrix and other by-products of the regularized
inversion process.
* Quantification of the contribution to pre- and/or post-calibration error
variance of important model predictions by individual parameters or
different parameter types.
* Data acquisition analysis - assess the value of making extra measurements
of system state (e.g., water level) or of system properties (e.g.,
transmissivity) in terms of predictive error variance reduction, in advance
of acquiring those data.
Moore and Doherty (Water Resources Research, May 2005) show that traditional
predictive uncertainty analyses can underestimate true variability by
neglecting complexity that it is beyond the ability of the calibration
process to capture. PEST Version 10 provides access to the methodologies
presented in that paper that support the analysis of predictive error
variance as an adjunct to regularized inversion.
Courses: Places are still available at the upcoming PEST courses in the UK
and USA
Principal Instructor: Dr. John Doherty (author of PEST)
Guest Instructor: Jim Rumbaugh (author of Groundwater Vistas) (NY
course only)
Assistant Instructor: Matt Tonkin (SSPA)
For more information on the courses visit:
http://www.sspa.com/pest/training.html
To register on-line for the UK course visit:
http://www.esinternational.com/training/CourseDetail.asp?course_id=49
To register on-line for the NY course visit:
www.sspa.com/pest/training.html
Information about PEST plus technical support can be found by writing to
pest@... <mailto:pest@...> . This account was established for PEST
users to obtain information on courses and software updates. The account is
used to circulate occasional information. To be added to this list write to
pest@... with "subscribe" as the subject. To ensure you receive no
future emails write to pest@... with “unsubscribe” as the subject.
[Non-text portions of this message have been removed]
Date: Wed, 8 Jun 2005 19:35:57 -0700 (PDT)
From: "Roshan Singh" <r4roshan@...>
Subject: re: GMS borehole data file format
To: cpkumar@..., cpkumar@...
hiiiii sayit,
i am a masters student at griffith uni brisbane
australia,
doin my thesis in saltwater intrusion in coastal
aquifers of brisbane coastal region. so, i have just
started working on GMS. have finished all the tuts
almost.
i think u can solve my problem at this stage. wht i m
thiking is tht i have imported the Geo-Tiff image of
the region to GMS and then made the 2-D mesh in the
map module. but next i want to create boreholes into
the 2-d mesh as done in the special tut of the GMS
FEMWATER...but i m nable to do it as all the boreholes
are coming at the same point after importing the data
into the GMS.
can u please give me the exact procedure and file
format to import the borehole data into GMS and to
create the boreholes. if i will be able to create the
boreholes then i can assign the regions after that and
make a 3-d mesh from the regions. pls suggest me tht
am i thinking in right direction or nt?
pls help me out of this as time is running out fr
me..if u have any contacts like phone no..i can give u
a call..
thanks
waitin fr ur repluy,
roshan singh.
student
griffith uni
brisbane
australia.
__________________________________
Discover Yahoo!
Stay in touch with email, IM, photo sharing and more. Check it out!
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Dear friend,
Training courses on groundwater modelling are being
regularly conducted by few organisations/firms. I
believe that these courses are quite useful for all
concerned with groundwater flow and contaminant
transport modelling activities. However, in view of
time or money constraints or other reasons, some
persons may be interested only in getting the course
material and tutorial notes without actually attending
the course. I feel that course organisers may consider
providing the course material at nominal cost to the
interested persons and accordingly incorporate the
same in their course announcements.
Just to give an example, I recently had an unpleasant
experience. A Training Course on "Groundwater Flow and
Transport Modeling with GMS" was organized by LaGa
Systems, Hyderabad (India) during April 11-14, 2005 at
Hyderabad, INDIA. I asked Chief Executive, LaGa
Systems, Hyderabad to provide me a copy of
"Comprehensive Course Notes with Tutorial Notes and
Data" of the training course. He informed the cost of
course material as Indian Rupees 1000. After getting
the money, he informed that "We can send only the
course manual for the money you sent. We can not give
the data". I agreed to it and asked him to send
"Comprehensive Course Notes with Tutorial Notes"
without the data. However, I got only the "GMS
Tutorials" and not the complete course manual. I
wonder why major portion of the course material was
removed from the pack (clearly evident from very thick
spiral size inconsistent with the number of pages)
before sending me only the tutorial parts. It may also
be noted that I contributed for their training program
by sending a compilation of GMS discussions for
distribution to the participants.
I hope that better sense prevails and things are made
more transparent and convenient.
Regards
Kumar
__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
Dear group;
I ve just signed to your group. I'm a civil engineer and doing my
master thesis on groundwater modeling. I got borehole logs (about 100
holes) and imported these to GMS. Then created cross-sections between
these holes, but I couldnt create solids. I'm using GMS v.5.0, do u
have any suggestions?
INTERNATIONAL GROUNDWATER CONFERENCE
on Groundwater (Perspectives, Problems and Challenges)
IGC - 2006, New Delhi, February 1-4, 2006
Organized by School of Environmental Sciences, JNU,
New Delhi-110067 in collaboration with
Department of Civil Engineering, Indian Institute of
Technology, New Delhi-110016 & KTH, Stockholm, Sweden
Themes for IGC-2006
TS-1 Water Resources Assessment
TS-2 Recharge Process and Artificial Recharge
TS-3 Water and Environment
TS-4 Models and its application in soft and hard rock
aquifer system
TS-5 Management Aspects of Groundwater
Call for Papers
All abstracts (not exceeding 250 words on a 3.5"
floppy or CD along with a hard copy in duplicate)
should reach Dr. AL Ramanathan, Organizing Secretary,
Conference Secretariat (IGC-2006), School of
Environmental Sciences, JNU, New Delhi-110067 on or
before 15th June, 2005. Acceptance will be
communicated by July 11, 2005. Authors will have to
submit full manuscript of the paper(s) (with original
figures, if any) to the Conference Secretariat by
October 10, 2005. Necessary instructions regarding
preparation of the manuscript(s) will be sent along
with the acceptance and author(s) are requested to
submit the final text in electronic form (CD or 3.5"
floppy).
Please contact for further details:
Dr. AL. Ramanathan
Conference Organizing Secretary (IGC-2006),
School of Environmental Sciences, JNU,
New Delhi-110067, India
+91 (0) 11-26704314 or 26704316
+91 (0) 11-26106501
alr_jnu@..., alrjnu@...
Dr.M. Thangarajan
Conference Chairman (IGC-2006),
NGRI, Hyderabad
+91-040-23434698 (O),
+91-040-27175156 (R)
mthangarajan@..., or
mthangarajan@...
Dr. A.K. Keshari
Conference Co-organizing Secretary,
IIT, New Delhi
akeshari@...,
akeshari@...,
Dr. Prosun Bhattacharya
Conference Co-organising Secretary,
KTH, Sweden
prosun@...
Web: www.jnu.ac.in; www.envisjnu.net
__________________________________________________
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Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
Hi,
I'm actually working with GMS v. 5.0 on chlorinated solvants transport
modeling. I simulate an injection by use a cell with a specified
concentration "specconc" (RT3D).
My problem :
If i use the RT3D mass balance summary file to define the injection
rate (in mg/d), the result is very weak.
For example i calculate an injection rate of 30 mg/d with this data
(mass balance summary files) and an injection rate of 7000 md/d with
flow out multiplied by the concentration in the cell of specified
concentration "specconc".
Can you help me, how does RT3D calculate mass balance summary file ?
Do you think this injection rate result 30 mg/d is correct and exist
in natural conditions ?
Please help me,
With best regards
fabrice
Dear Friend,
I have been compiling selected extracts on GMS
discussion from other mailing lists for past few
months, as given below. I understand that in view of
random and discontinuous placing, many parts may not
be easily comprehensible. Still I think that it could
be helpful to groundwater modellers to some extent.
Regards
Kumar
==================================================
C. P. KUMAR
Scientist 'E1'
National Institute of Hydrology
Jal Vigyan Bhawan
Roorkee - 247667 (Uttaranchal)
INDIA
Web Page : http://www.angelfire.com/nh/cpkumar/
==================================================
Kumar Links to Hydrology Resources:
http://www.angelfire.com/nh/cpkumar/hydrology.html
Google Groups in Hydrology:
http://www.angelfire.com/bc/nihhrrc/google.html
Software User Groups in Groundwater Modelling:
http://www.angelfire.com/bc/nihhrrc/groups.html
==================================================
-----------------------------------------------------------------
* If there is an aquitard between layers, then it is
possible to have a perched aquifer.
Note that I (and others) have had mixed luck using the
LPF package in transient models, but good luck using
it in steady state models.
Sometimes MODFLOW will leave a cell saturated when the
cell directly below it is dried out. I don't know what
causes this, other than perhaps there is a convergence
problem with that cell. I generally ignore these cells
and look at a layer or two below this layer, if the
layers are of the same aquifer, to see what is
happening to the water table. If they are of differing
aquifers, you need to somehow remember to disregard
the wet cell.
* MODFLOW has problems in computing drawdown within
the cell that the well is located in.
The trick is to split the middle layer in which the
well is located in, into 2 layers (so you end up with
4 total layers). Then, place the well in the lower of
the 2 new layers (so it is in the third layer). In
that way, you will have more control in computing
drawdown in the area where the well is.
* You need to insert a node along each point in the
drain arc where you want to assign an elevation to.
There is not a way to "map" elevations from a DEM to
the drain elevations.
The units are a bit confusing. Basically, you are
defining a unit length conductance for the drain arc.
Then, GMS determines how much length of the drain arc
occupies each cell and comes up with the total
conductance to be assigned to each cell.
* Note that in GMS you can now select a polygon
representing a region and GMS will display the total
flux into and out of the polygon at the status bar. It
is not a complete flow budget, but should assist be
able to assist you.
* In GMS 3.1 you can set only a single color for a
pathline. When using the option to color the pathlines
based upon zone codes, you are at the mercy of GMS.
Note that in GMS 5.0 you can now set the color based
upon each zone code. The pathline interface in GMS 5.0
is quite nice. I have included a screen capture of
what it looks like.
* The Stream / Aquifer Interaction Package is much
more complicated than the River Package. Basically, it
is identical to the River Package except that flow is
routed along the stream using Manning's equation to
determine the water surface elevation at each MODFLOW
cell.
So with the Stream Aquifer Interaction Package you
need to define additional information regarding the
stream that you may not have (i.e., Manning's
roughness, stream top elevation, flow rates, etc.). If
you don't have the routing parameters defined
correctly, MODFLOW will have computational problems.
In the River Package you simply define the water
surface elevation of the river at your nodal
locations. Much simplier.
* Note that GMS allows you to "Map" drain elevations
(and other elevations, such as river, stream, etc.)
using a DEM (indirectly).
GMS can import a DEM and will represent this data as
scatter point data. You can then interpolate this
scatter point data to a 2D grid that matches your 3D
grid. Then, GMS can convert the 2D grid to a TIN.
Then, in the TIN Module you can lower the elevations
of the TIN by a fixed amount (if you need to). Then,
within the Map Module, you can tell GMS to use the TIN
for assigning the drain elevations.
* Unfortunately, GMS is unable to convert a grid-based
MODFLOW model into a map-based MODFLOW model. You
would have to do it manually.
* AutoCAD cannot directly read the 3DG (3D grid) files
from GMS. You will need to convert the grid to a DXF
object within GMS first.
From the Map Module, select CAD | Data -> CAD. Then,
select File | Save As. Select DXF as the file type.
GMS will then save the 3D grid as a DXF file that you
can then read into AutoCAD.
* I have never modeled the movement of nitrogen in
groundwater. However, assuming that it can be
transported like other contaminants in groundwater,
you would first start by developing a MODFLOW model to
compute a groundwater flow field, and then use MT3D to
model the transport of the nitrogen in that field.
However, you would need to define advection,
dispersion, and diffusion terms for nitrogen (if they
are applicable) for the MT3D model.
* I have run into problems in the past at cells
containing wells when developing a dewatering model.
Basically, you cannot control (or limit) the amount of
drawdown accurately.
The fix for this is to either:
1. Refine the grid cell spacing around the well
location so that the cell dimensions are smaller and
then ignore the value in the cell containing the well.
You can refer to the drawdown elevation in the
adjoining cells. 2. Place another layer directly above
the well screen.
Both of these approaches work fine. It is just a
malady of MODFLOW model cells containing wells.
* Need to export in ASCII format x, y, and hydraulic
conductivity for each layer of the MODFLOW model. Is
there an easy way of doing this in GMS?
You have to first generate *.txt file using any txt
editor, each row will contain "x"<space or
tab>"y"<space or tab> "k". after preparing this open
the GMS and go file menu and simply press open file.
It will be open and will exported as scatter point.
Exported file will be visible in 2D Scatter menu. For
there you have to do appropriate gridding and export
the layer to 3D Grid.
* GMS "remembers" which cells become disabled after
running a simulation. So, even when you have deleted a
feature arc from the model, GMS will not automatically
re-enable the cells that had dried out. A fast way to
re-enable these cells is to delete the previous
solution from the data tree. If that still fails to
re-enable these cells, then reset the IBOUND values to
1. Here is how you do it:
1. From the 3D Grid Module, select MODFLOW | Global
Options.
2. Select the IBOUND button.
3. From the displayed IBOUND Array dialog, select
Constant -> Array. Define 1 as the value and select
OK. Now all cells will be re-enabled.
4. Switch to the Map Module.
5. Select Feature Objects | Map -> MODFLOW / MODPATH.
This will disable the cells outside of the model
domain.
Finally, even if you have a river arc defined, the
amount of water introduced into the top layer cells
may not be enough to prevent the cells from drying
out. A trick you can do to test this, is to make
certain that you have defined a starting head value
for the MODFLOW model that is sufficiently high to
fully saturate the upper layer.
* GMS does not provide a facility to directly assign
interpolated scatter point data as FEMWATER recharge
data. However, you can work around this limitation
indirectly. By contouring the interpolated recharge
data, in the Map Module you can then define polygons
of equal recharge. Then, GMS will then map this data
to the FEMWATER upper layer faces. With regard to
modeling of drains in FEMWATER, there is not an
equivalent drain element like you have in MODFLOW. The
closest there is in FEMWATER, is the canal option. You
need to define a canal from within the 3D Mesh Module.
Choose the Create Reach tool, and then connect the
nodes where the canal is to be located. Then, double
click on an ending node to terminate the reach. Then,
choose the Select Reach tool and double click on the
reach you created. You can then define the properties
of the canal reach.
* Is GMS useful to compute the concentrations of
elements like radionuclides in groundwater due to
leaching from SOLID radioactive waste dumped in near
surface disposal facilities? (This is similar to
landfill case for conventional pollutants). Is it
possible to use mass leaking or leaching rates as
initial, or boundary conditions instead of
concentration based initial or boundary conditions? Is
it possible to use the flow data generated by the
MODFLOW module of the GMS in some other independent
solute transport models?
I think GMS could do the job assuming some experience
with the interface and the underlying modeling codes.
You could probably use GMS for these evaluations with
some appropriate assumptions regarding source terms.
You will need some independent estimate of the
leaching/dissolution rate from the radioactive waste
source. Mass-inflow sources or boundaries can be
approximated by using a high-concentration source term
with a very low infiltration or injection rate.
Ideally, the infiltration or injection rate will be
low enough to not perturb the flow field. Using this
method, the concentration of the source or boundary
condition will likely not reflect the real system, and
may be physically unrealistic. For example, the
source-term concentration could be above the
solubility limit for the species being modeled. The
critical factor using this method is that the overall
mass be realistic, not the flow rate or concentration.
The flow information generated by MODFLOW is routinely
used in MT3D and RT3D. RT3D might be a good initial
choice for this problem as it allows first-order
degradation rates. It is available within the GMS
environment. You could probably figure a way to get
the flow data from MODFLOW into other solute-transport
models with some pre- or post-processors.
Be aware that radionuclides form daughter products
which may form their own daughter products, etc. These
may be as, or more, important as the original element.
For instance, uranium decay leads to radon which
readily phase transfers. SWIFT accounts for this type
of progression. I'd make sure RT3D can do the same
before going down the GMS road.
SWIFT would likely be a better choice overall,
especially to account for the daughter products. The
models within GMS (MODFLOW/RT3D) could probably
address the limited concerns from the original post. I
agree that he broader issues of model suitability for
the complete problem should drive the code selection.
* Note that GMS supports unit coordinate conversion.
Select Edit | Coordinate Transformation. You should be
able to convert your model to whatever coordinate
system you want. However, I do not recommend having
different coordinate systems for different parts of
the model. Choose one coordinate system and then stick
with it.
* Calibration of the model is often the most time
consuming part of the modelling process (apart from
correct conceptualization of the model domain). I am
guessing that the model you are using within the GMS
pre/post processor is MODFLOW and you coupled it with
the MT3D or MSMT3D. Is this correct? The first thing
to do is to get your flow model right, that is set the
model boundary conditions, geometry of the model,
internal and external stresses acting on the aquifer
(recharge, evapotranspiration, pumping, constant (or
variable) heads, no flow boundaries etc. etc.) right.
This is the base for your contaminant transport
modelling.
You have to set the flow model calibration targets,
(usually water levels in monitoring bores), and a
range of acceptable elevations above and below the
observed values. You have to draw groundwater contour
levels (if possible) for steady state or if you are
doing transient calibration then for selected times.
Compare the simulated groundwater contours to the
observed values. Also, if you are running transient
simulation compare observed and simulated hydrographs
for your monitoring points. Remember that the
hydraulic parameters obtained from the laboratory
studies are not representative of the in situ values.
They can give you an idea about the relative magnitude
of parameters but the calibrated parameters will be
almost always different from the lab values Only after
you have calibrated the flow model you can start
simulation of the contaminant transport.
Again you will have to start from the calibration of
the transport model. You do it mainly by changing
transport parameters (retardation, dispersivity,
porosity, bulk density, decay parameters). If, during
transport calibration you have to change the flow
parameters (e.g. hydraulic conductivity, geometry,
recharge etc, than you will have to re-run the flow
calibration before progressing any further with the
transport. This is just a very brief description of
what you may have to do to calibrate your model. I
would suggest that you read something about the
calibration of the groundwater models before you spend
too much time on running your model. An easy to read
book may be "Applied Groundwater Modelling" by Mary P.
Anderson and William W. Woessner. Another good book
for you would be "A practical Guide to Groundwater and
Solute Transport Modelling" by Karlheinz Spitz and
Joanna Moreno.
* In GMS 5.0, you can ask it to display the stream
direction. From the Map Module, select Display |
Display Options. From the Display Options dialog,
check the box for "Stream Arrows" at the bottom of the
dialog box. Click OK and you will see an arrow in the
center of the arc, showing the stream direction. If
the arrow is too large, you can set the size of the
arrow within the Display Options dialog box.
* It is possible that FEMWATER is not correctly
mapping the recharge. However, you can check the
amount of recharge that is mapped to the FEMWATER mesh
by choosing the "Select Boundary Face" tool and then
double clicking on the top of the mesh. GMS will then
display for you the amount of recharge being assigned
to the face element. Are you seeing any effect from
the recharge? Perhaps the recharge is not enough to
see the mounding effect from recharge and you have a
level water table.
* Make certain that you have the well points defined
in the Map Module BEFORE generating the TIN and mesh.
I have seen situations where the node point looks to
be at the identical location of the 3D mesh node, and
GMS will not map the data to the node.
* I would look at the input to the Dispersion Package.
Something in the input is causing the MT3D model to
diverge, causing the floating point number to exceed
the memory space allocated to storing the number,
thereby creating the NaN exception from the math FPU
(floating point unit). I always try to simplify,
simplify, simplify. Then, add complexity (one step at
a time).
* GMS 4.0 never really did a good job at exporting
shapefiles. You can download the latest release of GMS
4.0 to see if it solves the problem. Otherwise, the
only soultion is to move up to GMS 5.0.
* Here's how I combine coverages, assuming the arcs
you want are in different MAP files (*.map).
1) Open the project, get the grid into GMS.
2) Go to File/Open, and open the first .map file. To
avoid confusion, make sure there are no duplicate arc
names between the two coverages. Rename arcs if
necessary.
3) Go to File/Open, and open the second .map file.
Now you should have arcs (and whatever other objects)
from both coverages.
4) In Map mode, go to the Feature Objects drop-down
menu. Click on the "Coverages..." button. Delete the
arcs that you don't want in the combined coverage.
5) Go to File/Save As. Click the drop-down menu for
"Save as type" and select *.map. Type a new .map file
name into the window. Click the Save button. The new
.map file should have the desired arcs from both of
the original coverages.
I haven't played with this in GMS 5.0, so I don't know
if the sequence is exactly the same. But this is the
basic procedure.
* You cannot model salt water intrusion with Visual
MODFLOW. That's because MODFLOW cannot model salt
water intrusion. You need a model that can support
differing densities of fluids (i.e., salt water and
fresh water). The FEMWATER interface in GMS allows you
to model such situations.
* Assigning streambed elevations:
Two ways I see in approaching this.
1. See if you can set up an ESRI shapefile that
contains a sample arc with the necessary attribute
data, and see if GMS 5.0 supports importing this data.
If so, then you can have a GIS expert store the node
elevation attribute data from the elevation source
using the tools in ArcView / ArcGIS.
2. Write a software program to post-process the Map
file that GMS creates. The Map file is an ASCII text
file, and fairly easy to follow. You can then have
your program look up the elevation data as it runs
into the stream nodes.
However, someone else might have a better, more
elegant way to approach this.
* Assigning streambed elevations
Caroline's tutorial on making the stream arc and
stream node files using DEM elevations. This uses
ArcGis/ArcToolbox and ArcView 3.x with the GridPIG
tools extension.
You start with a shapefile that contains the stream
arcs. Add nodes to the stream arcs by creating a
coverage. Then associate DEM elevations with the
nodes.
1 Open ArcToolbox
2 choose 'export from shapefile'
3 choose 'Shapefile to Coverage'
4 type in the name of the shapefile containing the
stream
arcs as the input file
5 type in the name of the new output coverage
6 click OK
1 Open ArcToolbox
2 choose 'Topology'
3 choose 'Build'
4 type in name of the coverage created in the prior
step
5 choose Feature class 'Node'
6 click OK
1 Open ArcView 3.x with the GridPIG Tools v2.6
extension
active.
2 Add the grid data source for the DEM to the view
3 Add the arcs from the coverage created in the prior
step
4 Add the nodes from the coverage created in the prior
step
5 Make sure the nodes theme is active
6 choose Theme menu
7 choose 'Convert to shapefile'
8 add the new nodes shapefile to the view
9 choose GridPIG Tools
10 choose 'Grid Value to a Point'
11 choose 'no' to use single cell value
12 select the grid data source for the DEM
13 choose 'yes' option for original field names
14 click OK
* None of the simulation programs within the GMS
environment can simulate two-phase air-water flow.
* The first thing that I would suggest is that you
build your solids using the current version of GMS
which is version 5.0. There have been significant
improvements to the program including the stratigraphy
building. Next, I think part of your trouble is that
you are following outdated documentation. You do not
need the 2D mesh module to build a TIN. There is a
new command, "Map->TIN" which builds TINs directly
from your polygons created in the Map module. Although
TINs, meshes, and grids can all be used to represent a
surface in GMS, structurally they are all different.
Meshes and grids are typically associated with a
numerical model whereas a TIN in GMS is solely used to
represent a surface.
* As distributed by the USGS, the STR Package does not
support the FREE format option, which can be specified
in the Basic Package input file. The STR file is
always read in fixed column format, regardless of the
presence or absence of the FREE option, in fields 5 or
10 characters wide. As a result, although the
run-together input that appears in Tore's and Jim's
input files is difficult for human eyes to interpret,
Modflow has no problem reading input like this. In
fact, if you insert spaces to make the input look
better, the values read by Modflow will not be the
values written by GMS -- they will be truncated as a
result of being offset from the columns where Modflow
expects to read the input data. Now if the version of
STR has been modified for GMS to support the FREE
option, that's a different matter.
* GMS has always read in and written out standard
MODFLOW files. If you are trying to read in a model
that was generated outside of GMS, either read in the
*.bas or the *.nam file and GMS will read in the rest.
There should be a similar method for reading in
GMS-generated files into PMWIN.
-----------------------------------------------------------------
__________________________________
Do you Yahoo!?
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Dear Friend,
I have been compiling selected extracts on groundwater
modelling discussion from various mailing lists for
past few months, as given below. I understand that in
view of random and discontinuous placing, many parts
may not be easily comprehensible. Still I think that
it could be helpful to groundwater modellers to some
extent.
Regards
Kumar
==================================================
C. P. KUMAR
Scientist 'E1'
National Institute of Hydrology
Jal Vigyan Bhawan
Roorkee - 247667 (Uttaranchal)
INDIA
Web Page : http://www.angelfire.com/nh/cpkumar/
==================================================
Kumar Links to Hydrology Resources:
http://www.angelfire.com/nh/cpkumar/hydrology.html
Google Groups in Hydrology:
http://www.angelfire.com/bc/nihhrrc/google.html
Software User Groups in Groundwater Modelling:
http://www.angelfire.com/bc/nihhrrc/groups.html
==================================================
-----------------------------------------------------------------
* In my experience, PCG is faster than LMG for small
models but LMG is faster for large models. Of course,
for small models, speed generally is not so much of an
issue.
* DAMP is used as a multiplier to scale the head
change at each iteration, not RELAX. The DAMP
parameter in the PCG solver package is analogous to
the ACCL parameter in the SIP package. Although I
cannot explain precisely what RELAX controls (since
I'm no mathematician), the typical range for RELAX is
0.97 to 1.0. In my experience, setting RELAX=0.97 can
help to achieve convergence, and may speed up
convergence on a "well-behaved" model, but not always.
* I'm sure you've heard "All models are wrong but some
are useful." If you replaced all the wells in a model
with drains, you would expect to get different
results. How is this any different? You have
replaced one package with a different one that is
based on different assumptions so of course, they get
different results. If you want to know which one is
better, examine the assumptions behind the different
packages and see which assumpptions best match the
conditions at the particular region to be modelled.
If none of the available packages do what you need,
write your own package to do what you need.
* The newer LPF package is the way that most other
models work, i.e., you enter Kz and the inter-cell
conductances are computed internally. The way that
MODFLOW88/96 did it with a pre-computed vertical
conductance always struck me as a bit odd; however,
that has been our happy MODFLOW world for about 20
years. So now we have a new option that is
mathematically more correct, but it is still
disconcerting when the computed heads are different.
I guess you'd have to ask a lawyer about who would
win. My sense is that the differences could never be
explained to a jury. It does present the MODFLOW
modeling community with a problem, though. The way
that you did it with MODFLOW-SURFACT is probably the
way that the USGS should have done it as well - adding
the input of Kz in the BCF Package.
* Input of vertical hydraulic conductivity has its
advantages, however, McDonald and Harbaugh got it
correct in keeping a fixed thickness of a cell for the
vertical direction conductance - for
gravity-segregated vertical equilibrium (GSVE), you
have a transmissivity that is conductivity times
saturated thickness which is valid only for the
horizontal direction and not for the vertical
direction (in actuality, the vertical direction
physics changes from GSVE to unsaturated flow which
would lower the conductivity further and that would be
closer to the "fixed thickness" answers that do not
reduce separation distance between 2 cells vertically
even for consideration of a homogeneous case, but that
aside). Nor does the document state where or under
what conditions the use of a "variable thickness for
vertical conductances" option performs better. That's
why I was asking to see if anyone knew why this was
done in the first place.
* I propose that the node location of a cell that
contains the water table should be located at the
water table instead of the center of the cell as is
standard. Comparisons of this formulation to analytic
calculations numerically implemented in the WATQ code
indicate a much improved solution at shallow depths
compared to the calculations of the current LPF
formulation. This formulation does not, however, take
into account the dynamics of drainage from the
unsaturated region above the water table which can be
a major influence. I want to repeat Richard Winston's
point that "All models are wrong". A model is not
intrinsically good or bad. That judgment depends on
what the model is used for. What may be better in one
situation may not be better in another. You have
highlighted this concept in your discussion of GSVE.
MODFLOW still exists for two contradictory reasons; 1)
as the name implies it is modular and hence easily
extensible to specialized situations. 2) It is widely
known and accepted that the code has accurately solved
groundwater flow problems. It is incorrect to extend
the second point to expect MODFLOW to accurately solve
all groundwater flow problems. Once again required
accuracy like good and bad depends on the problem that
needs to be solved. That MODFLOW produces two results
for the same geometry and boundary conditions means
that it approximates the physics of the flow situation
differently. It proper care is taken, the ability to
change the approximation of the physics of flow is a
good thing because the code can be tailored to
specific problems.
* Yes, having flexibility in averaging schemes is a
good thing. The LPF package provides one more
averaging scheme in the vertical direction. It does a
harmonic average of the conductances, as opposed to
the BCF package's harmonic average of vertical
conductivity times area divided by separation distance
as provided in the MODFLOW documentation for the
various fully three-dimensional, and
quasi-three-dimensional alternatives. However, I am
guessing that people are encountering drastically
different and surprising or unexpected results is
because of the vertical direction treatment.
Specifically, the cell thickness varies as a function
of its saturated thickness in the LPF package for
vertical direction treatment. For a simple example,
consider a homogeneous case with two cells where the
cell below is getting drier. The vertical conductance
quickly rises due to the cell below drying up, to such
levels that drain and dry up the cell above (which
also causes the conductance to increase in a cascading
manner) which would be a very different result than
with use of any of MODFLOW's BCF options. Like I
stated earlier, infact, when things dry up, it should
slow down the conductance due to physics change to
unsaturated flow, and even a gravity flow assumption
will not speed it up.
Yes, there is a dilema in GSVE models for vertical
direction treatment because GSVE by its definition,
applies only to horizontal direction flow - I have
seen this in saltwater-freshwater GSVE models with
multiple aquifers as well. And there too, when you
give it specialized treatment, it is due to certain
physically motivated considerations. Otherwise, the
way MODFLOW BCF did it (or a use of grid-block cell
thickness in the LPF package) is the best you can do
with the VE assumptions being used, since conductance
may be smaller than saturated levels due to
unsaturated zone physics - but you don't know by how
much, unless you simulate unsaturated zone physics.
Using saturated thickness instead of cell thickness in
the vertical direction leads to results that are more
removed from this physics.
* This is one of the most challenging groundwater
modelling projects you can find in real-world
modelling... Ideally, you should use a
saturated-unsaturated code, such as FEFLOW or Modflow
surfact or similar. Such codes are able of simulating
perched water conditions.
If you are using traditional MODFLOW, and assuming
saturated conditions, it is a bit more complicated to
simulate such a scenario. You will probably have some
dry cell issues (and perhaps some convergence
problems), but it is possible to simulate the open pit
crossing multiple layers using drain boundary
conditions.
For the upper layers, where seepage faces may occur,
set the drain elevation slightly above the layer
bottom elevation (say 0.1 m above cell bottom
elevation). If you use Visual MODFLOW as the
interface, that's very easy to do using formulas that
will assign the correct elevation even in irregular
layers. In that case, if the head in the pit wall is
higher than the cell bottom elevation, Modflow's drain
package will remove the outcroppng groundwater. The
conductance value (another input to the drain package)
is tipically a calibration parameter, obtained through
matching drain removal rates with real values observed
at the mine site.
I suggest that you also use a solver that is not too
aggressive, such as PCG2, and that you play a bit with
re-wetting parameters and dumping factors until you
obtain a stable solution. We've done several mine
dewatering modelling projects using this approach and
it definetely works for most cases, as long as you
understand the code and it's limitations.
* Dry cells in a multi-layer model are not necessarily
a bad thing unless they do not accurately reflect the
conditions in the field. Perhaps I am stating the
obvious, but just for the record, dry cells occur in
MODFLOW models when the calculated water table is
below the bottom elevation of the grid cell. Since
MODFLOW only simulates saturated groundwater flow, it
does not represent a head value in the unsaturated
cell, so the cell becomes 'dry' and MODFLOW assigns a
'dummy' head value usually in the range of -1e-30 (or
something else easily recognized as a dry cell).
Although the presence of dry cells in a model is often
a hassle because they create problems with the
convergence of the numerical solution, dry cells do
not necessarily indicate a 'problem' or error with the
model. In your case, the dry cells don't appear to be
causing a problem with the solution convergence (or
atleast, you haven't mentioned this problem) and you
are getting a good mass balance, which is a good sign
but doesn't necessarily indicate 'correctness' of the
solution. If the water levels in the second layer of
your model match closely with the observed field
conditions, then the occurance of dry cells in layer 1
appear to be reasonable.
However, if the dry cells are occurring where you
would otherwise expect saturated conditions (based on
water levels in the field) then you probably need to
revisit your boundary conditions to make sure they are
reasonable (conductance values are often the culprit),
check your initial heads and make sure you are not
starting the iterations with dry cells, and make sure
you have enough recharge flux entering the system to
accommodate flux leaving the system through wells,
rivers, and other boundary conditions. If all this
looks good, then Mark Wilsanac gave some very good
suggestions on how to change the solver and rewetting
package settings in order to deal with dry cells. -
Patrick Delaney
* If the river boundary cells are the only place in
your model where water may leave the system, then one
of the most likely causes of the mass balance problem
is the conductance values you are using for the river
cells. Check your conductance values to make sure
they are within reason. The conductance values can be
reasonably estimated using the following formula:
C = (L x W x Kv)/B
where
L = length of the river in a cell W = width of the
river in a cell Kv = vertical hydraulic conductivity
of the riverbed in a cell B = thickness of the
riverbed in a cell
Most of the popular graphical interfaces for MODFLOW
allow you to enter these 'physical' parameters and
will automatically calculate the conductance values
for each river boundary cell.
Another possible cause for mass balance problems could
be the solver you are using (SIP often produces larger
mass balance than other solvers like the PCG or LMG)
or perhaps the convergence criteria for the solver is
not 'tight enough'.
Just as an afterthought, the fact that you have more
water entering the system from the rivers than leaving
the system through the rivers does not, in itself,
indicate a problem with the water balance. This
indicates you have 'losing rivers' because the water
table adjacent to the river is lower than the river
stage. The excess water entering the system from the
rivers may be leaving through other avenues such as
evapotranspiration, pumping wells, drains, specified
head head boundaries, etc. - Patrick Delaney
* Check out if you dont have any dry well cells, or
any other dry boundary cell. If a cell goes dry during
simulation, it becomes inactive for MODFLOW, and any
boundary assigned to that dry cell will be ignored.
That means that your wells may be inactive (even
though you assigned them to be pumping all the time).
That typically produces a noticeble change in the
budget, but sometimes the heads may not change too
much, unless you look at specific well cells very
closely.
My suggestion is to first look into the budget for
changes in well pumping/injection rates. If the total
rate is different from those you entered into the
model, then you have a dry well cell. Zoom in all well
cells to identify which ones have become dry during
that stress period (look in all model layers).
* With a model set up with cell-to-cell size changes
below 50%, there can be instabilities or failure to
converge. This can be due to other reasons, or cell
size change coupled to highly variable conditions in a
transient solution. If a geologic unit pinches out,
that should be represented primarily by changes to
cell properties, and secondarily by changes in cell
dimension (aspect-ratio rules apply vertically as well
as horizontally). Remember to preserve aspect ratios
of each cell below 10:1, and below 5:1 to be safe. It
is acceptable to have a layer with variable properties
from cell-to-cell. It is rarely acceptable to use
MODFLOW cell dimensions to closely simulate physical
variations in layers when they pinch out.
* I have not used the WHS solver sold by waterloo
hydrogeologic. while i therefore cannot comment on
this solver and its claimed superiority to SIP, i feel
quite sure that SIP has been the best performing
solver for almost all models i have constructed over
the past few years, and never had problems with mass
balance which could not be successfully overcome by
using SIP. i do recall a paper published in Ground
Water years ago when WHS proponents at software
developer Waterloo Hydrogeologic compared their WHS to
SIP and PCG (among other public domain solvers). i
felt that sip had been shortchanged and misrepresented
in their analysis in that they had claimed that sip
yielded a much greater mass balance error than that
obtained when using their whs solver. what they had
failed to do in their analysis, was to accordingly
decrease the HCLOSE with their corresponding decrease
in the acceleration parameter. this is the equivalent
of not closing tightly enough on heads, and therefore,
ending up with an excess mass balance error. this was
an improper use of SIP.
I have found that lowering of the acceleration
parameter, and corresponding decrease in the HCLOSE
will yield a very low (acceptable) to zero mass
balance error, but one must be careful in that the
acceleration parameter is not set so low that the
model converges prematurely with insufficient head
change.
* Check all inputs in the flow model first. Make sure
your flows are realistic. Make sure your K's and
recharge are realistic. Refine your grid and use
dispersivity values that will minimize numerical
dispersion. Make sure your grid cell size complies
with appropriate Peclet criteria (as a rule of thumb,
for finite diferences, Pe should be ~ 2; that means
your grid size should be roughly 2* your dispersivity
value, in the area where, for MOC, this can be
higher). I suggest your read some transport modelling
books that explain this in detail. Be careful with
using constant concentrations, they can act as a
source, but also as sinks (if he concentration in
neihbouring cells is higher than the ones you
specified in the constant concentration node).
* When she is referring to inflow, in plane, and
outflow, I think what she is doing is looking at the
color coding for the velocity vectors or pathlines.
When she sees that there are very few arrows or
pathlines with a green color (indicating 'inplane' or
flat horizontal flow in the layer) she gets concerned
for some reason. Most likely the lack of 'in plane'
flow has very little to do with anything she is
concerned about, it just reflects the fact that she
has slight vertical gradients in the model.
WRT to the vanishing concentrations, you could also
suggest her to make sure she didn't input a default
degradation rate of 0.5 or something very high and
then forgot about it, or the other possibility is she
has assigned a sorption coefficient of 1 (mistaking it
for a retardation coefficient), or perhaps just a very
large sorption coefficient of 0.01 L/mg which would
cause the plume not to move at all, thus giving the
impression that it is disappearing from the model,
when in fact it hasn't moved at all. Another
possibility is that she initially assigned
non-conservative values of sorption and decay
coefficients when she set up the transport model
scenario, and she is now trying to modify these values
in the Setup/Transport Engine dialog instead of in the
Input mode (I've seen this problem a few times) or
Visual MODFLOW.
Finally, the fact that the solution solves in two
iterations seems to indicate that the total run time
of the MT3DMS solution may have been left as the
default of 1 day (perhaps she assumed it automatically
picks up the end time of the flow simulation). She
can change this by selecting Run/MT3DMS/Output Times
and entering the desired Simulation Time.
* The simplest way of defining a starting
concentration is to use the Recharge Coverage and
specify a polygon shape that denotes the contaminant
concentration to be applied to the model.
* What to do when your contaminant plume does not
migrate as expected.
When using MT3D or RT3D for a contaminant transport
simulation, if the plume fails to move as expected (or
does not appear at all in your Visual MODFLOW output),
here are a few common causes and their solutions.
Problem #1: Overlay is not active, or masked by
another overlay
Solution #1: As with Head Equipotentials, Particles,
and even Basemaps and other overlays, you must make
the Concentration overlay active in order to see it.
Click the F9-Overlay button at the bottom of your
screen, and ensure the overlay has been checked off
(to make it active). It is also possible that other
overlays are masking your concentrations. To resolve
this, change the Overlay Order setting to User
Defined, then highlight the Concentration overlay, and
use the arrow buttons to move it up the list.
Problem #2: Simulation Output time
Solution #2: In Visual MODFLOW, the Simulation Output
time can be different for your flow and transport
simulations. Check to see that you have defined the
correct simulation time(s) in the Run Menu, by
selecting MT3D (or RT3D) / Output - Time Steps.
Additionally, in the Output Menu of Visual MODFLOW,
ensure that you have selected the Concentration
overlay as the active overlay, then select the Time
button in the left toolbar, to change output times as
desired.
Problem #3: No concentration input assigned, or not
assigned properly
Solution #3: Ensure that you have correctly defined at
least one cell with an Initial Concentration, or a
transport boundary condition of one of the following
types: Constant Concentration, Recharge Concentration,
Evapotranspiration Concentration, or Point Source.
Please NOTE that Concentration values entered for
Concentration Observation Wells are used for
calibration purposes only; they do not contribute mass
to a transport simulation.
Problem #4: Inadequate flow gradient
Solution #4: Before running your transport simulation,
run just the flow simulation (MODFLOW). Using
Pathlines or Velocity Vectors, ensure that there is a
sufficient flow gradient to cause plume migration.
Problem #5: Incorrect reaction parameters
Solution #5: Check the reaction options in the Main
Menu, by clicking on Setup / Numeric Engines /
Transport. Check that the correct Sorption and
Reaction options have been selected.
First order decay rates (dissolved and sorbed phases)
may have a tremendous impact on the plume mass, since
during the simulation, some contaminant mass may be
removed from the model. If the decay rate is too high,
your plume will show very small concentrations, and/or
will not be visible at all at later simulation times.
Decay rates (due to biodegradation or other
mass-removal processes) can be taken from literature
values, but this should be done with caution, as this
parameter is highly site-specific for most compounds.
A good reference on decay rates used in natural
attenuation studies can be found in:
Wiedemeier et al., 1999: Technical Protocol for
Implementing the Intrinsic Remediation with Long-Term
Monitoring Option for Natural Attenuation of Dissolved
Phase Fuel Contamination in Ground Water. Air Force
Center for Environmental Excellence, Brooks, AFB.
This document can be downloaded from:
http://www.afcee.brooks.af.mil/products/techtrans/monitorednaturalattenuation/pr\
otocols.asp
The decay rate (l, or sometimes called Kd, with units
of 1/day), is typically obtained from half-life
values, converted into appropriate units using the
following relationship:
l = ln(2)/t1/2
Where t1/2 = half-life of the compound
In addition, check that your Kd value is correctly
defined in the Species Parameters tab. A very large Kd
value will result in an extremely high retardation
factor, which can result in lack of contaminant
movement through your model.
For typical organic compounds (such as TCE, DCE, PCE,
BTEX, etc.) where linear, reversible sorption can be
assumed, retardation will be calculated using the
following formula:
Retardation = 1+ (Bulk Density/porosity)*(Kd)
Where Kd = Partition coefficient
For hydrophobic organics, Kd can be determined using
the relationship below:
Kd = Koc*foc
Koc - octanol-carbon coefficient
foc - organic carbon fraction in the aquifer
A more detailed overview on Kd's can be found in:
US-EPA, 1999. Understanding variation in Partition
Coefficient, Kd, values. EPA
402-R-99-004A&B. US-EPA Office of Air and Radiation.
This document can be downloaded from:
http://www.epa.gov/radiation/cleanup/partition.htm
* From the Modflow standpoint, water that exits the GW
system through of a drain cell is accounted for in the
budget, but is otherwise not simulated. The situation
for river cells is similar--Modflow does not simulate
any flow in the river, it only simulates exhange
between the GW system and each individual river cell.
So there is no way to route water from a drain cell to
a river. The Streamflow Routing (STR) Package, on the
other hand, does simulate flow in surface-water
streams, accounting for flow rates in the stream and
calculating stream stage, which is then used as the
external head in the GW/SW exchange calculation. If
you want to simulate exchange between drains and
rivers, you could use the STR Package for both types
of features.
* How to import modflow model files to gwvistas 4?
Select File/New and click the MODFLOW button. On the
next dialog, click browse to go find the name file
(*.nam). If this is an older MODFLOW88 dataset, then
browse to find the *.bas file. Some datasets
(especially those that were created without the use of
a preprocessor) can be troublesome.
* I want to input separately 2 sets of recharge into a
modflow model: (1) Effective recharge from rainfall,
and (2) urban leakage (same format as the (1)), which
will overlap. Since both components are fairly complex
and over a long time (1200 Stress Periods), I would
like to keep them as independent as possible (avoiding
the data compilation option, if you see what I mean).
It is possible to do what you want using just the
Recharge package. Here is how you do it.
Define each recharge distribution for each stress
period using parameters. You can use one set of
parameters for the rainfall and another for the urban
leakage. With each parameter, you can use multiplier
arrays and zone arrays to define the spatial
distribution of the recharge. Then, for each stress
period, use the parameters for that stress period to
apply recharge from both rainfall and urban leakage.
MODFLOW-2000 will add the contributions from all the
parameters you use in a stress period to determine the
total recharge.
You should be able to do this with any reasonably
up-to-date GUI for MODFLOW-2000. If you are using a
GUI and you can't figure out how to do this, contact
the GUI developer for assistance. If you aren't using
a GUI, you can check the input format in the Online
Guide for MODFLOW-2000 at
http://water.usgs.gov/nrp/gwsoftware/modflow2000/MFDOC/guide.html
or in the original MODFLOW documentation as modified
in "Time-varying-parameters.pdf" (distributed with
MODFLOW-2000).
* Since I know you are using Modflow VKD (based on
MF96, not MF2K) and that the wells package is almost
certainly being used for many abstraction wells, I
suggest 2 routes:
1. A FORTRAN utility to combine two recharge files - a
days work? 2. To use a MF package that you aren't
already using - but with some manipulation e.g. the
rivers package. By setting the stage of the river as
above any elevation in the model (1000m?) and the
conductance equal to the quantity you want to recharge
for that SP - with a 1 m difference between stage and
bottom elevation you will get the appropriate amount
leaking (recharge) to each cell.
You can achieve the same result with the drains
package by specifying 2 drains in each cell. The trick
is to have one with a positive conductance and the
other negative, but the same value. Make the
difference in elevation 1m and the magnitude of the
two conductance values the quantity you want to
leak/abstract. If the elevation is outside the range
of variation in the model, you end up with a constant
recharge/abstraction from the model.
For composite/trick boundary conditions of this type I
suggest drawing figures for them like those in the
MF88 book, it will help to understand what I'm trying
to say.
* Design the shoreline?
Depending if you are using FEMWATER or MODFLOW, it is
handled differently. With FEMWATER, you want the
boundary of your 3D mesh to follow the shoreline. With
MODFLOW, you are working with a 3D grid. So, you need
to mark the cells that contain the shoreline with a
fixed head boundary condition, and the cells outside
this area will be disabled.
If you are attempting to model the interaction with
the sea bed, then you will need to set the top
elevations of the mesh or grid to match that of the
sea bed. However, generally you end your model at the
shoreline.
* MT3D Performance
What you need most depends on where your bottle-neck
occurs. You need to monitor CPU and RAM usage on the
computer during the MT3D run. If you run Windows 2000
or XP, you can right click (for a right-handed
pointing device) on the Taskbar (grey bar at bottom of
screen), then select Task Manager in the menu pop-up.
Once Windows Task Manager opens, select the tab
labeled "Performance". "Performance" shows CPU usage
graphically and memory usage in numeric form. If the
"CPU Usage History" (top graph) stays maxed at 100%,
then a CPU speed increase should help. In parallel,
observe the "Physical Memory" values. If the
"Available" value becomes a small fraction of the
"Total", AND the "Commit Charge, Total" exceeds the
"Physical Memory, Total" then you are likely to have a
RAM-limited condition. In this case, more RAM would
help. With 300,000 cells, consider 1 Gbyte or more. If
both things are happening (unlikely), then upgrading
CPU and RAM should help. Be aware that upgrading one
component sometimes results in the other becoming the
limiting condition. That is why it is "unlikely" both
limits are happening simultaneously. Usually one tops
out before the other. If you run Win98... consider
upgrading the OS.
* There are various things that you have to do to get
Surfact running in Vista 3:
1. You can only have a limited number of packages.
For example, if you are doing contaminant transport
modelling then you have to turn some other pacakges
off, otherwise Surfact will not run e.g. you can turn
the cell by cell flow packages off (just type 0 into
the packages number in Model - Modflow - Packages).
Another pace you can turn packages off is in the
output control: Turn off the drawdown unit.
2. You have to modify some things in the Model -
Modflow options and some in the Modflow - Surfact
options. These are:
Model - Modflow - Packages: change modflow version to
surfact; change solver to PCG4; and untick
automatically reset package units
Model - Modflow - BCF package: tick the box to use
the BCF4 package
Model - Surfact - Packages: add a unit number (one
that you have not yet used) and tick the box for BCF4;
add the unit number to PCG4 and tick the box (use same
unit number as shown in Model - Modflow- Packages);
add a unit number and tick box to RSF4 is you want the
model to simulate surface seepages (and remeber to
turn this unit on in Model - Surfact - RSF4 package).
Model - Paths to models: set modflowwin32 option to
DO NOT USE; put in correct path for surfact in the
modflow box.
I can't think of anything else right now - I always
forget one thing and spend a couple of hours wondering
why surfact won't run. If you have any difficulties
it would be helpful to know if the surfact Dos window
displays and if so, what it says in the window.
* The most common problem when using SURFACT is
setting up the program file. Select Model/Paths to
Models. Change the MODFLOWwin32 Option at the top to
"do not use". That tells Vistas that you are not
using one of our model DLLs. Then change the MODFLOW
program from MFWIN32.DLL to whatever your SURFACT
program is (usually it is msft.exe).
* I believe that if you are using the latest version
of SURFACT (V2.2) that problem 1. below is no longer
an issue. It used to be that SURFACT could only open
a limited number of files but that is no longer the
case. Also, if you upgrade to Vistas Version 4 and
SURFACT V2.2 the link between the two programs is
easier to establish. The same holds true for all of
the other versions of MODFLOW that Vistas supports
(MODFLOW88, MODFLOW96 in double precision,
MODFLOW2000, MODFLOWT, MODFLOW-SURFACT, SEAWAT, and
SEAWAT2000).
* VS2DI or VS2DT, being a Richards equation-based
models have certain PROs and CONs when used for
groundwater recharge estimation:
Pros: the Richards equation models are the most
theoretically based and allow representation of the
flow processes in porous mediums more realistically
than the water-balance models. They have been well
tested against field and laboratory experiments and
proved to provide good correlation with observed
results.
Cons: the major complicity of the Richards equation,
comparing to the saturated flow models, is that its
coefficients are non-linear functions of the pressure
potential. To approximate these functions, three
different algebraic equations are usually used (named
after their authors): Brooks and Corey's, Gardner's,
and van Genuchten's. Richards equation can be solved
with a very limited number of boundary conditions. The
condition for water at the boundary can be specified
either as the flux of water across the boundary, the
head at the boundary or as a combination of specified
head and specified flux. The Richards equation with
these boundary conditions is a nonlinear partial
difference equation that has no close-form or
analytical solution. To solve the Richards equation,
a finite-difference method of numerical approximation
is applied in VS2DI. Searching for a best numerical
method for the Richards equation became a special
field in hydrologic science, particularly in 1980's,
however, almost all implemented approaches cannot
assure that the model will unconditionally converge
and simulation results will be obtained. It is an art
to get the model to work correctly (produce results
for the whole simulation period with a good water
balance) when you have varying flow boundary
conditions in your profile. Our experience also proved
that applications of Richards equation-based models to
highly heterogeneous soils with variable hydraulic
properties can be extremely difficult to execute and
time consuming.
These days there more and more examples when less
sophisticated in flow equation but much more advanced
in terms of weather/plant effects water-balance model
HELP is used to estimate groundwater recharge.
* I will suggest you keep the north and south boundary
as variable head boundary. This I am suggesting you
treating there is no river, lake etc. If these
features are present on north or south side of model
domain, then you have look for another type of
boundary. Regarding limited observation well data and
that too is limited to layer1, then it will not be
possible to do any realistic modelling. If there is no
scope of generating additional data, i would like to
suggest that you confine your modelling activity to
first layer only.
* What makes a good correlation depends on what your
expectations are. If you are conducting exploratory
research, maybe 0.2 isn’t bad. If you are testing a
known process having some natural variability, 0.6
might be acceptable. But if you are calibrating
instruments, maybe 0.9 isn’t good enough.
If you don’t have any clear expectations, how do you
tell if a correlation is good? The answer comes in
three parts.
1. Value - Square the correlation coefficient (called
the coefficient of determination or just R-square).
R-square is the proportion of variation in the
dependent variable (y) that can be accounted for by
the independent variable (x). You might be able to
decide how good your correlation is from a gut feel
for how much of the variability you wanted your model
to account for.
2. Significance - Every calculated correlation
coefficient is an estimate. The “real” value may be
somewhat more or somewhat less. You can conduct a
statistical test to determine if the correlation you
calculated is different from zero (or some other
number if it’s relevant). The larger the calculated
correlation and the greater the number of samples, the
more likely the correlation will be significantly
different from zero. For example, a correlation of
0.59 (R-square of 0.35) would be significantly greater
than zero based on about 25 samples, but a correlation
of 0.01 wouldn’t be significant with 250 samples.
3. Plots - You should always plot the data used to
calculate a correlation to ensure that the coefficient
adequately represents the relationship. Specifically,
the data should be linearly related and free of
outliers. There are a few other things to look for
(e.g., hidden trends, autocorrelation) that I won’t go
into here.
So, the reviewer who said that “the "R square" value
of 0.35 has no significance and is just as good or as
bad as say 0.01” would only be correct if she looked
at a statistical test of whether the value was
significantly different from zero. R square does not
need to be more than any particular value to draw a
comparison. Remember, too, that “no relationship” may
also be an important finding.
* If you are considering GUI's for your project, you
may want to look at Visual MODFLOW Pro. In
particular, if cell splitting, or grid refinement is
an issue for you. Visual MODFLOW includes two
distinct features that help users with this.
1) Cell refinement tool
2) Grid smoothing tool
1) Cell refinement/splitting tool: You'll need no
more than a few clicks to edit your grid in a very
flexible manner. To split your cells, just click on
'Refine by ...", and specify how many times you want
the cell to be split into (2, 3, 4...). Then, select
the area you need to refine with your mouse.You can
apply this to one row or column, or all cells in the
domain - whatever you wish. The same applies for
splitting layers and coarsening the grid.
2) Grid smoothing tool: After grid refinement, you may
want to use the grid smoothing routine to produce a
smooth transition between coarser areas to highly
discretized ones. Again, just a few clicks. This is
actually a perfect tool to help you better understand
the effects grid size and refinement will have on your
model results.
Another feature that may be useful for you is Visual
MODFLOW Pro's batch capabilities. It will allow you
to prepare all data input files in different model
projects and run them in 'batch mode'.
* The interpretation method is different according to
the geology. You have methods for porous media, others
for fissured aquifer, others for double porosity
media. Methods also vary according to the type of
aquifer (confined or unconfined; semi-confined with a
leaky aquifer...) and corrections can be made
according to the type of well (partially penetrtaing
well; pumping well with head loss; skin effect and so
on). Finally, boundary effects (barrier or recharge)
may affect significantly your interpretation.
In order to remain pragmatic I would suggest you to
start with the simplest method : the Theis formula,
(or even the Jacob approximation if your pumping time
is big enough) and check wether you get a good fit or
not with realistic parameters. Even a fissured
unconfined aquifer can be interpreted with Theis when
your radius of influence is wide so that the fissure
network can be assimilated to an homogeneous
equivallent porous media and the depletion of the
water level is moderate compared to the thickness of
the aquifer. This should give you a rough estimate of
your transmissivity, which is in many cases,
sufficient.
If you need more accuracy you can use specific
softwares. You will find on the net many softwares
proposing many different methods. You don't need Pest
as they have their own fitting engine. AQTESOLV for
instance proposes methods with well storage effect.
However, as soon as a software proposes its own
adjustement, it's becoming very difficult to know
what's you're doing and you end up playing a video
game. So be carefull, especially if you lack
experience in this domain, not to use complex methods
with many parameters which will end in a perfect fit
but with irrealistic results. In my company (French
geological survey)we use ISAPE, a software which is no
more commercialised, but whose philosophy is to let
the user propose realistic values and where you can
add or remove well effects or boundary influence. I
wish this approach were more widespread.
* I think your scenario will represent two different
geologic materials with peculiar intrinsic properties.
Hence, I suppose this will require two separate
simulations. To the best of my knowledge, MODFLOW 2000
only allow one K matrix values per layer per
simulation and this is incorporated within the flow
package. However, if the introduction of the permeable
barrier is controlled along defined specific paths or
unique relatively smaller area(s), then you can use
one simulation with two stress periods and incorporate
Horizontal Flow Barrier Package in the second period
to account for the permeable barrier distribution.
This is not suppose to be of much problem especially
if you incorporate your modflow with GIS package like
GRASS GIS.
* Sophisticated modeling programs like Visual Modflow
Pro, or any of a number of similar packages, will run
properly with a variety of inputs that may not be
physically realistic - and thus provide garbage for
output. With that in mind, here are some thoughts on
your questions:
1) You may divide a single aquifer into more than one
layer if there is some reason to look at vertical
stratification within the aquifer. For example, a
thick aquifer may have different hydraulic or
transport properties in different vertical zones. You
may also divide a single aquifer into several layers
if you want to examine the vertical flow patterns due
to pumping from different zones within the aquifer.
2) The top of Layer 1 could be the ground surface,
the water table (not as common because it can move
vertically), or the top of the uppermost aquifer or
aquitard of interest depending on the physical system
being modeled.
3) You'll need to assign boundary conditions no
matter what the size of the physical system is. If
you don't have natural physical boundaries, one
strategy is to assign boundary conditions at a
distance far enough away from the area of interest to
minimize the effects of boundary assumptions on the
solution.
* It is appropriate to use a single layer if you feel
that it is reasonable to ignore vertical flow in your
model. Assuming that you would be using the Layer
Property Flow (LPF) Package of Modflow-2000, and if
the aquifer represented by layer 1 is not overlain by
a confining unit, then specifying the top of layer 1
as ground surface is reasonable. The reason that you
would be better off this way than specifying the water
table elevation as the layer top is that the LPF
Package only provides two options with respect to the
confined/unconfined status of a layer: Confined or
Convertible. If the head in a cell goes above the
specified top of a convertible layer, the cell is
treated as confined. Every model needs to have at
least one fixed head, either as a constant-head cell
or as a fixed external head (such as the stage at a
river cell), or the solver will not be able to reach a
solution. You may need to expand the domain of your
problem to encompass a fixed head.
* 1- Model design depends greatly on your project
goals. For example, you could have one aquifer, but an
overlying layer (and/or underlying layer) as well. Or,
you could be modelling just 1 aquifer, but split it up
into several layers in VMOD to provide more detailed
flow information (i.e. if the aquifer is 100 feet
thick, having just 1 layer will not provide very
detailed output. You can subdivide the 1 "real-world"
layer into 10 "model" layers, all with the same
hydrological properties, in order to obtain more
detailed output). Or, you can simply design a 1-layer
model if that is all your project requires.
2- In Visual MODFLOW, Layer 1 represents the uppermost
layer of your profile, and the top of Layer 1 is
therefore the ground surface. Layers in Visual MODFLOW
represent soil layers (or conceptual soil
layers)....the location of groundwater in these layers
is determined by your model inputs, and the resulting
calculations of the flow model.
3- The assignment of boundary conditions is a question
that often goes beyond the scope of Technical Support,
and enters the realm of Extended Modeling Support.
However, to provide you with some guidelines:
-If you have no "obvious" water inputs (streams,
rivers, lakes, injection wells, recharge from
rainfall, etc.), you can try assigning an upgradient
equipotential line, and downgradient
equipotentialline, using Constant Head Cells at the
upgradient and downgradient edges of your model, to
represent the regional water table (other boundaries
may be more appropriate, depending on your specific
model domain and objectives). You can then add
additional inputs (extraction wells, contaminant
sources, etc.) to the model region, which will be
influenced by your regional flow gradient.
4- I would recommend taking some time to run through
the Tutorials included with your Visual MODFLOW
software (the PDF instruction files are located on
your installation CD-Rom, and the files are
automatically copied to the Tutorial subfolder in your
Visual MODFLOW program folder). These tutorials are
designed to teach you how to work with your software,
and how to design a model, import data for model
inputs, run the various packages, calibrate your
model, examine your output in 2D and 3D, and export
data.
* You can use the field interpolator program in the
PMWIN package. Using the field interpolator you can
interpoltae the field data in txt file to the grid
point of your model. On the other hand, you can import
any dxf file which illustrate the changes in hydraulic
properties to help you in the graphical interface.
* Upwind discretization always has an artificial
diffusion term no mater how refined your grid is (even
thought it diminishes with grid refinement). Central
discretization always produces an artificial
dispersion term that causes "wigles" however you can't
control it with grid refinement. For almost any Pellet
number the upwind scheme will produce positive
coefficients for your coefficient matrix, while that
isn't true for central differences. However central
differences has "second order accuracy" while upwind
only has first order. You can visualize numerical
diffusion and dispersion mathematically by deriving
the "equivalent or modified equation" see
http://widget.ecn.purdue.edu/~jmurthy/me608/main.pdf
for some cool notes on this (as good as any book I've
read).
Physically you can visualize numerical diffusion by
imagining a 1D discretization of a domain | : | : | :
| where | are faces and : is the center of the cells.
If your initial property is 1 on a given cell say i
and 0 on all others it would look like this:
| 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0
So using upwind with a courant = v dt / dx of say 0.5
and a velocity from left to right after the first time
step the accurate solution would be something like
(zooming on cell i):
| 0 { 0.5 | 0.5 } 0 |
Note that I have created a new cell delimited by the
{} brackets this "new cell" that doesn't exist in our
domain is exactly half of cell i and alf of cell i+1.
The property's value will be 0.5 inside this new cell
and 0 outside it (meaning that cell i and i+1 would
have half with 0.5 and half with 0). This would be the
accurate solution because a courant of 0.5 makes the
property shift half a cell every time step. However we
are bounded to our initial discretization so the
solution we will obtain will be:
| 0 | 0.5 | 0.5 |
so you can see than instead of having a 0.5 of
property in a volume the size of a cell we have 0.5 in
a volume the size of 2 cell thus lowering the
concentration. This happened because the definition of
concentration is C = lim vol ->0 DM/DVOL and we
implemented it as DM/DVOL. If we would diminish the
size of our grid so that currant = 1 we could obtain
the exact solution. So the smaller your grid is the
more accurate your solution will be. This is the
physically correct way of solving the diffusion
problem another way is to use higher order schemes
witch usually maintain the sharpness of the gradients
but usually remove mass from all the wrong places
(even thought they conserve it). Looking at the same
example a central differences discretization would
derive something like:
| -0.25 | 0.75 | 0.25 |
Cell i-1 will produce a negative property because the
concentration al the face between i-1 and i is 0.5
cell i +1 will obtain the accurate concentration of
0.25 (0.5 in half the volume of a cell). But we are
producing the famous "wigles" close to the properties
gradient. There are smarter second order schemes like
qwick or TVD schemes.
* In visual MODFLOW there is provision for importing
MODFLOW files (*.bas files). In PMWin there is
provision for conversion of MODFLOW88/96 (*.nam). I
have tried to import *.bas file in Visual MODFLOW and
found that model data is not correctly coming to
model. These options may be available in GMS but I am
unable to locate the exact sub-menu. Number of options
is available for opening different format files In the
FILE menu. But It does not permit opening of *.bas or
*.nam files. This option must be in different menu.
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In one of the contaminant transposrt problems..I calculated the
unknown
concentrations by solving the matrix equations using matlab".I did a
material
balance on the solution by back calculating for the full
concentration of flow.
How can I figure it out that the solution is pointwise as well as
step wise
stable. What is meant by point wise stability?
thanx.
Regards.
Reet
I`ve just taken ground water modelling course..so probably my qns
will sound very basic types to you people.
Qn::When we solve for the unknowns(concentrations at different nodes
after a particular time) using upstream spatial weighing with crank
nicholson(theta=0.5) for different sized meshes(coarse, fine, medium)
and by using central spatial weighing with crank nicolson or fully
implicit .
What will be the impact of upstream versus central spatial weighing
on numerical dispersion as the grid size is refined.
Can this be defined numerically by using peclet number and courant
number?
Can anyone please explain it with physical aspect as well as
numerical.
qn2::What will be the impact of crank nichoson temporal weighting
(theta=0.5) and fully implicit temporal weighting(theta =1)on
numerical dispersion as the time step is refined.??????
time step being refined means..courant number c=q*delta(t)/deta(x)
will also become less thus monotonous.
Thanx allot.
Reet
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