Modelling of seawater intrusion using FEFLOW
C. P. Kumar
With reference to my earlier queries (did not get any response at that time), a recent response from Mr. Alessandro Casasso is placed below.
Regards
Kumar
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C. P. KUMAR
Scientist 'E1'
National Institute of Hydrology
Jal Vigyan Bhawan
Roorkee - 247667 (Uttarakhand)
INDIA
Web Page : http://www.angelfire.com/nh/cpkumar/
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Re: Modelling of seawater intrusion
Monday, September 22, 2008 3:52 PM
From: "alessandro.casasso" <alessandr...@yahoo.com>
To: "C. P. Kumar" <cpk...@yahoo.com>
Have you found any answer to you questions? I'm working at a MS thesis about Feflow modelling of a shallow aquifer in Venice. I will not try to model salt pans - too difficult even to think where they are.
About rainfall and evapotranspiration: I've got rainfall and temperature data. I calculated ET with Blaney-Criddle formula, but I found that results are overestimated. I tried to reduce risults by comparing modeling results with real results (in the area I'm studying, I can get results from 11 piezometers..) and I found that BC formula results can be divided by 3. I found that ET estimation is one of the most difficult parts of shallow aquifers modeling...
I've got no idea about brackish water in rivers. In my model, I assigned the tidal oscillations (1st type boundary conditions) also to a channel of Venice lagoon that encloses my modeling domain.
I developed a relation between TDS and conductivity (I've got specifical conductivity measures), but I did a very rude approximation. As I'm modeling a peninsula, I thought that seawater contains most NaCl , so conductivity (microSiemens per cm) is dominated by NaCl concentration. Conductivity is linked to NaCl concentration in this way: - every ion has an equivalent conductivity, that is the specifical conductivity for a concentration of 1 equivalent/liter (for NaCl, 1 equivalent = 1 mole); - this equivalent conductivity is also linked to concentration by Onsager formula; - specifical conductivity = equiv conduct x concentration [mole/liter]
I visited your site some time ago, I found it very interesting. Sorry for my English, I have to improve it. About my tip on TDS-conductivity: as we say in Italy "here I tell it, and here I deny it" :-) I'm only a MS student and I got these advice reading a laboratory chemistry manual...
See you soon on this forum,
Alessandro Casasso
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Date: Sun, 20 May 2007 20:03:41 -0700 (PDT)
From: "C. P. Kumar" <cpk...@yahoo.com>
Subject: Modelling of seawater intrusion
To: hydf...@yahoogroups.com, hydrolo...@yahoogroups.co.in, gwm...@yahoogroups.com, gw...@yahoogroups.co.in, rhydr...@yahoogroups.com, fef...@yahoogroups.co.in, sea...@yahoogroups.co.in, coa...@googlegroups.com
Dear Group Member,
I am grateful to the following members/experts for their interesting/useful observations/comments/suggestions on my report "Modelling of a Coastal Aquifer using FEFLOW" (available at ftp://ftp.wasy.de/FEFLOW/Goa.pdf ).
(1) Reinhard Zapata (Waterloo Hydrogeologic, Canada)
(2) Krishnaiah C. (India)
(3) S.V.N.Rao (Roorkee, India)
(4) V.V.S. Gurunadha Rao (Hyderabad, India)
(5) Michael Jorgensen (Australia)
I am prompted to seek further suggestions for the following issues in modelling the seawater intrusion in coastal aquifers.
(a) How to model the effect of salt pans on groundwater in coastal areas?
(b) How to incorporate the evaporation from open water surfaces (e.g. to define time-variant boundary condition in case of rivers) and evaporation from shallow groundwater table?
(c) How to model the effect of brackish water in rivers (due to tidal backwater effect from sea) on groundwater in coastal areas?
(d) How to develop correlation between resistivity values and TDS and between resistivity values and hydraulic conductivity.
(e) Suitability of Kriging, Akima and Inverse Distance Weighting techniques for interpolation/regionalization of different parameters/variables.
Any suggestions for the above will be helpful for extension of this (or similar) study in future.
There is a small errata in the report - title of figure 7 may be read as "Measured Values of Hydraulic Conductivity (*10E-4 m/s)" - the multiplier was missing.
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/
==================================================
cassius
order to determine the hydraulic conductivity, storativity etc.
(b) A greater value of evapotranspiration can be assigned to the open
water surface (where ET rate should be much higher than in
groundwater) using "Join" when you are assigning "In/Out flow on Top/
Bottom".
(c) No idea about it.
(d) In my thesis (about Adriatic Sea) I supposed that the only solute
in water is NaCl.
Electrical specific conducitvity (microSiemens/cm) of water (were you
talking about groundwater or terrain resistivity?) increases with the
salt concentration (mg/l) with an almost linear correlation:
NaCl Concentration (mg/l) ~ conductivity (microSiemens/cm) * 0.58 -
130
So you can determine some couples of electrical conductivities and
salt concentrations and then use a fitting procedure (minimum
squares?).
I found it no so far from reality...
(e) I use kriging technique because I think that Akima "invents"
"strange" values far from the points where the value (of hydraulic
conducitvity, etc) is known
Regards,
Casasso
PS: my thesis is coming to an end, I'm going to be a real engineer!