I keep getting dry cell, help me?

[NUGradStudent]

I have a topography and head values for the top layer. I'm trying to
calculate heads for the rest of the system by putting in no-flow
boundaries and letting it calculate the rest. Many of my cells keep
drying out, while the water level should always remain constant at the
elevation of my top layer. Can anyone help me?

[vivek gupta]

Dear user,

 

In my experience, first you need to check your conceptual model which is the prime factor that influences everything from start to end. If you find it right, then move ahead;

 

Obviously you are having dry cell problem in the unsaturated top layer; I suggest you to recheck your major input data such as; recharge, gw level, K and S, make sure that each and every input cell value is perfectly alright;

 

If it doesn't help, go to Run>Modflow>Rewetting settings and try changing wetting threshold, interval, head and method and see if it helps;

 

If rewetting doesn't solve your convergence problem, here are a few essential things to check:

 

1. How is recharge assigned? In the MODFLOW Run settings for Recharge, try assigning recharge to the "highest active cell in each vertical column". This will allow the incoming recharge to bypass inactive or dry cells in your upper layers, and may improve convergence.

 

2. Layer thickness: If you have a top layer that is thin, and dries out quickly, consider  re-assigning the layer elevations, or combining this layer with the layer below. This will increase the total layer thickness, and will likely reduce the probability of dry cells occurring.

 

I believe this should really help you; try out all options as suggested, and do let us know, i would be happy to respond again....

 

God Bless!

 

Regards,

 

Vivek Gupta

M.Tech (Water Resouces)

Design Engineer

Tahal Groups

Mo.: 09954757624

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[Mohobane, Thabiso]

For the cellls that you want to always have water, then you can issgn them a constant-head have boundary and specify the value.


Regards,

Thabiso Mohobane
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The University of Waikato
School of Science and Engineering
Department of Earth & Ocean Sciences
Private Bag 3105
Hamilton 3116
New Zealand

Mobile: +64 211 033 257
Tel: (07)838 4466 ext. 6169

http://erth.waikato.ac.nz

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