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## 3D vs Quasi 3D

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• Can anyone explain to me the difference between a 3D modflow model and a quasi-3D modflow model? Thanks, Ashley
Message 1 of 4 , Mar 5, 2009
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Can anyone explain to me the difference between a 3D modflow model and a quasi-3D modflow model?

Thanks,
Ashley
• In a quasi-3D model, the confining units are not represented by model layers. Instead, the vertical conductance between the aquifers is set to a low value to
Message 2 of 4 , Mar 5, 2009
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In a quasi-3D model, the confining units are not represented by model
layers. Instead, the vertical conductance between the aquifers is set
to a low value to simulate the resistance to flow due to the confining
units.

ashley.phillips75 wrote:
>
> Can anyone explain to me the difference between a 3D modflow model and
> a quasi-3D modflow model?
>
> Thanks,
> Ashley
>
>
• Quasi-2D models and quasi-3D models are properly defined to classify analytical solutions for groundwater flow in layered aquifer systems. Modflow borrowed the
Message 3 of 4 , Mar 6, 2009
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Quasi-2D models and quasi-3D models are properly defined to classify
analytical solutions for groundwater flow in layered aquifer systems.
Modflow borrowed the term 'quasi-3D model', but it is used somewhat
differently.

And somewhat confusing, in my view. Let me give an example:
When you make a fully 3-dimensional numerical model, for example when you
simulate the flow to a partially penetrating well in an aquifer that is
represented by many model layers, then Modflow terminology tells that this
is a quasi-3D model when the confining layer is represented by a low
conductance. So a model can be fully 3D, and a quasi-3D Modflow model at
the same time.

Kick Hemker

Richard B. Winston wrote:
>In a quasi-3D model, the confining units are not represented by model
>layers. Instead, the vertical conductance between the aquifers is set
>to a low value to simulate the resistance to flow due to the confining
>units.
>
>ashley.phillips75 wrote:
>>
>> Can anyone explain to me the difference between a 3D modflow model and
>> a quasi-3D modflow model?
==========================
C.J. (Kick) Hemker
Elandsgracht 83
1016 TR Amsterdam
The Netherlands
tel: +31 20 6228 711
fax: +31 20 6234 628
mail: hemker@...
http://www.microfem.com
==========================
• Ashley: Quasi-3D usually means that the model represents leaky, confining layers with purely vertical (1D) flow connections between the aquifer layers
Message 4 of 4 , Mar 6, 2009
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Ashley:

Quasi-3D usually means that the model represents leaky, confining layers
with purely vertical (1D) flow connections between the aquifer layers
surrounding each confining unit. The equations govening the simulated
flow rely upon specfication or computation of "leakance" (equal to
vertical hydraulic conductivity of the confining unit divided by the
vertical thickness of the unit), area-of-flow (i.e., the plan-view area
of the grid cell), and the difference in head vertically between the
aquifer units above and below the confining unit.

Fully-3D means that each confining layer is represented in exactly the
same way as each aquifer layer. The porous media being simulated are
continuously discretized and represented by the standard governing
equations, written in 3D form.

Hope this helps.

Bob Schreiber

Robert P. Schreiber, P.E., BCEE, D.WRE
VP & Groundwater Subdiscipline Leader

CDM
One Cambridge Place
50 Hampshire Street
Cambridge, MA 02139 USA
email:schreiberrp@...
Phone and Fax: (617) 452-6251
Cell: (617) 512-6819
Alternate email: schreiberrp@...

________________________________

From: gwmodel@yahoogroups.com [mailto:gwmodel@yahoogroups.com] On Behalf
Of ashley.phillips75
Sent: Thursday, March 05, 2009 1:39 PM
To: gwmodel@yahoogroups.com
Subject: [gwmodel] 3D vs Quasi 3D

Can anyone explain to me the difference between a 3D modflow model and a
quasi-3D modflow model?

Thanks,
Ashley
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