Zahrab

Hi Daniele Do you know why the calculated radius of influence with the Sichardt formula is much smaller than the radius of influence from the model? which answer is correct ? Thanks for any help.

Dear all, I do appreciate if you can help me with this problem: I had a square area with 4 cutoff walls around it. and some wells are going to be inside the area to dry it. first I modeled a cross section in Seep2D to see how the wells dry the area. I attached a picture of results. the results looks fine. but I wonder why when I model it in Modflow, as 3D model, the seepage (vertical gradient) is not as continuous as it was in SEEP2D . I attached image here. it sounds like any cell in one aquifer layer has almost the same head pressure along its depth!!! so should I divide my aquifer to multiple layers to get more accurate results? Thank you for any help.

Perfect. will check it out for more information. Thank you again for helpful insight.

Thank you Sean. sounds like I need to know lots of details to get it work. - can I define drain for those arcs to let them have flow out of my domain if it's necessary. - how people model an area? they always are aware of all boundary around their farm/ field/ wells/ etc? is there any source I can see multiple type of fields modeled in Mod-flow?

Thank you, I will try that as well. I am new in this modelling and face a lot of question for such an example.

Dear all I have trouble modeling a square site with different BC. at one side I have river (I put constant head as BC) and no problem in that for modeling. now, 1) at one side I have rock (no flow coming in or out from site at this side) and 2) at other side of square area I have no BC (I mean the water can flow out of area etc) what is the difference in modeling number 1 and 2? how to difine them in my model? my model currently have active cells in coverage so I think it means all sides I have rock, right? Thank you, Zara

I tried decreasing k for silt to the value 0.0003 runing the model gives no error but it makes both tope layer dry and flow budget is almost zero!!! results sounds too wierd so I think that counts as the model error when I set high discharge for low K . I will try transient model for first parameter to see how it respond. Thank you for helping me.

I don't find image uploading here. here is the image on internet: http://www.freeimagehosting.net/dmx4l http://www.freeimagehosting.net/abzdt http://www.freeimagehosting.net/wvbrk

layer 1 is clay, from +25ft to -19ft, k= 0003 ft/min layer 2 is silt, from -19ft to -83ft, k= 0.003 ft/min. layer 3 is sand from -83ft to -175ft, k= 0.012 ft/min. at 1000ft distance from the job site (which is 100*100ft square area) I defined constant head =20ft all around in layer 3 ( means preimeter of 1100*1100 square ) my goal at first was to see how much dewatering and how many wells I need to make the first layer dry for my excavation area. here I defined 43 MNW in layer 2 with desired discharge 12GPM/well !!! (which is impractical) results shows layer 1 at the middle is dry, layer two has head of -40ft and layer 3 is almost +14ft. I expect GMS tonot allow that much water running out of tsuch layer to my pumps. in this case, it means I always need to know real world discharge from silt/clay/sand and then use model to predict the drawdown I can get for it. right? Sorry for too much explanation

actually in my LPF package, all the layer are mentioned convertible. I made my model getting help from Tutorial:"MODFLOW- Conceptual model approach". Thank you guys for helping me. I wish I could post an image of the results here.

as an example here I have about 40 well in two top layer with discharge of 12GPM/well which means about 480 GPM !!! I know from silt layer it's not possible to get that much water, but my model adjust itself for every discharge I define and give me high drawdown instead.

Thanks for replyin. I have a layer of clay with .0003 ft/min and silt with 0.003 ft/min. there is one layer sand underneath with 0.012 ft/min. at 1000ft distance I have constant head at all direction. those are the only BC I have.

Dear all I am new with GMS. and have trouble modeling multiple pumping well to see the total drawdown. I have three layer of clay, silt and sand. I wanna see how much water I should pump and from which layer to get certain drawdown. so I worked backward. giving discharge I checked the result drawdown. I am interested to use wellpoint system in the silt layer (instead of deep well in sand layer) now the question is, why in modflow I can assign any discharge to the well? I expected MODFLOW to give error saying because of low pearmiability this much discharge is not possible to be taken from clay/silt. but that's not the case. any discharge I put in, the modele solve the problem and give me drawdown for it! I used FEMWATER as well, for the same question, and it also solve for any discharge I define!!! That looks wiered to me this can't recognize the layer can't provid a lot water?!! any help is highly appreciated, Zara