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Modflow 2000-transient model result


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Hi, I have a question about head of the transient model. 

I am simulating model with 4 layers /top-clay, 2-aquifer, 3-clay, 4-aquifer/ which are all confined. Is it right about all layers confined?

I built conceptual model using the Borehole-Solid, Map-Modflow and 3D grid with  Modflow 2000, LPF package, PCG solver. I think, aquifer is confined, so pressure water level in Layer 1. So, I could not understand transient computed head. Because, when ortho mode on and layer 1,  around all pumping wells get dry, drawdown is very high /2000, 3000m/. Layer 2-head and drawdown is ok. Which layers head is correct? Initial head from Steady state head and using Starting head-3D dataset to Grid.

Thank you

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When you have a confined layer, it typically doesn't dry out.  Therefore, if it *should* dry out, there is a good chance that you are going to see unrealistic heads in the model for that layer.  You might want to make Layer 1 be unconfined and see how that goes.....or the Layer 2 head may be more appropriate to use (depending on what you are trying to show and how close it is to Layer 1 in the other cells).

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Thank you for replying. 

I've made Layer 1 be unconfined. it's same dry cells. 4 Layers have 1 water level /SWL-starting head in layer 1/, so simulated head should be 1 that is same at all layers. Is it right or false? my simulated head did not same when ortho mode on. Head is different in each layer. 

I want to how much drawdown will be after 40 years during pump. what should i do. I am beginner modeler.

Layer 1 -green -clay-Kh 0.001m/d, Ss 0.001                                                                                    Top - 1000masl  /approximately/                     Static water level 850-1040masl

                                                                                                                                                   Bot1 - 800masl /approximately

Layer 2 -purple-sandy clay or sandstone aquifer-Kh 3-12m/d, Ss 0.008-0.03                           Bot2 - 750masl /approximately

Layer 3-red--clay-Kh 0.001m/d, Ss 0.001                                                                                   Bot3 - 700masl /approximately

Layer 4-purple-sandy clay or sandstone aquifer-Kh 3-12m/d, Ss 0.008-0.03                           Bot4 - 650masl /approximately

Specified head are west, north and east. /orange/

Recharge-5.4e-6 m/d

Pumping rate -total 28PB -87448m3/d

I've attached some image. 

Thank you.


layer 1 head.JPG

layer 2 head.JPG

Steady state head.JPG

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You've provided some good information.  However, I can only provide you my thoughts based on what I see.  It is unclear to me which layer(s) you are pumping in.  Based on the K of layer 1, that wouldn't be a great layer to withdraw water from, compared to Layer 2.  It is not shocking to see Layer 1 cells drying out around the wells, based on the low K value.

I'm not seeing anything really wrong with your head results.  They will not be exactly the same (which is how you have upward/downward gradients in an aquifer).

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Helo, try using MODFLOW-NWT instead of MODFLOW-2000. Its excelent in handling problems with cell drying/rewetting. In the LPF package set all layers to convertible. If insist on using MF-2000, maybe try different timestepping scheme to avoid overshoots.

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