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Saubhagya Singh

Thickness of aquafer, Aquitard

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I have 2 doubts.

1) How can we give thickness of auifer, is it same as lentgh in Z direction of 3-D grid mapped form modflow?

2) How can we give recharge from auitard. Is seepage face used for same purpose?

Saubhagya

Edited by Saubhagya Singh

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Someone plzz reply....

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The thickness of a layer in a MODFLOW grid is specified in the Global/Basic Package using the Top and Bottom elevation arrays.

There are multiple ways to apply leakage from an aquitard. You can explicitly include the aquitard in your model. You could use the recharge package to apply the leakage to a particular layer. You could also use wells to apply the leakage to a particular layer.

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does seepage face serves the same purpose??

And I am facing one more problem, In most of my MT3D models, contaminant is too much spread from expected, i.e. there is not much spatiel variation in concentration , but expected results are like too high concentration around pond (discharging contaminant) and almost zero far away, but thats not the case?

Can you figure out problem ??

Thanks

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I am simulating a contamination travel model with confined aquifer with one layer. There is a pond in between which is recharging at 0.009m/d and contaminant concentrations is 4000ppm. I have a doubt that for pond should we give starting concentration or specified concentration for whole duration (other than recharge conc.).

For defining aquifer as confined or unconfined, we have to select confined (from confined or convertible) in modflow -> LPF package. right ????

What is horizontal anisotropy? Kx/Ky or Ky/Kx ?

thanks :)

Edited by Saubhagya Singh

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Sorry forgot to mention, I am using Modflow and MT3D.

Edited by Saubhagya Singh

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does seepage face serves the same purpose??

No. A seepage face is usually a free draining face where water exits the model

And I am facing one more problem, In most of my MT3D models, contaminant is too much spread from expected, i.e. there is not much spatiel variation in concentration , but expected results are like too high concentration around pond (discharging contaminant) and almost zero far away, but thats not the case?

Can you figure out problem ??

Thanks

The plume may be too spread out for a variety of reasons. If you are using the dispersion (DSP) package then the values of longitudinal dispersivity affect the spreading. The size of your cells and the method used in the advection (ADV) package can also have an effect on the spreading. Also, it may be that your conceptual model for the site is not correct and the transport model is giving you an indication that your flow model is wrong.

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I am simulating a contamination travel model with confined aquifer with one layer. There is a pond in between which is recharging at 0.009m/d and contaminant concentrations is 4000ppm. I have a doubt that for pond should we give starting concentration or specified concentration for whole duration (other than recharge conc.).

If you believe that the concentration was enter the aquifer over a period of time then you will want to use an MT3D boundary condition to simulate that.

For defining aquifer as confined or unconfined, we have to select confined (from confined or convertible) in modflow -> LPF package. right ????

Yes

What is horizontal anisotropy? Kx/Ky or Ky/Kx ?

thanks :)

see the modflow documentation here: http://water.usgs.gov/nrp/gwsoftware/modflow2000/Guide/lpf.htm

HANIā€”is the ratio of hydraulic conductivity along columns to hydraulic conductivity along rows, where HK of item 10 specifies the hydraulic conductivity along rows. Thus, the hydraulic conductivity along columns is the product of the values in HK and HANI. Read only if CHANI < 0.

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Thanks alot for such detailed replies :)

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I am making a single layered model to study contamination travelling and for defining aquifer as confined I selected confined (from confined or convertible) in modflow -> LPF package, Do I need to specify confining beds??

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I am making a Modflow , MT3D model to study contamination using GMS. I cannot understand why am I getting different results (Different head contours) when I make steady state model and transient model with constant conditions?

plz help....

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I am making a single layered model to study contamination travelling and for defining aquifer as confined I selected confined (from confined or convertible) in modflow -> LPF package, Do I need to specify confining beds??

It is not required.

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I am making a Modflow , MT3D model to study contamination using GMS. I cannot understand why am I getting different results (Different head contours) when I make steady state model and transient model with constant conditions?

plz help....

Check your initial heads. It may be that they are not consistent with your boundary conditions.

A quick work around for this is to make the first stress period steady state.

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But if resulting heads obtained form steady state simulation (option in GMS software) are used as initial head for transient model and keeping all other conditions same , head contours after transient simulation should be same as steady state right?? but it is not the case with me!!

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But if resulting heads obtained form steady state simulation (option in GMS software) are used as initial head for transient model and keeping all other conditions same , head contours after transient simulation should be same as steady state right?? but it is not the case with me!!

Based on your description it seems like it should be working. I am not sure what is going on. You can contact support@aquaveo.com for more help.

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Thanks alot Alan :)

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Can you please tell me how to make specific stress period as steady state?

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Someone plz reply.....

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Steady state check box does not appear in my stress period dialog box... I am using GMS 7.1.. please help me out

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Using a transient modflow model in GMS 7.1 I was able to find the steady state check box in the stress periods dialog box (see highlighted portion of the image below). Perhaps this column is outside of the visible region of the dialoge box in your model? Can you try scrolling to the right to see if this is the case? If you are talking about MT3D, there is not a way to make a stress period steady state in MT3D in GMS 7.1, however this feature will be avalilible in GMS 8.3 http://forum.aquaveo...s-steady-state/.

post-5340-0-68561000-1340233555_thumb.jp

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Thanks Lance, Actually I was making a transient MT3D model, that is why there was no check box for steady state.

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