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maximum number of nodes


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We want to do some high resolution flow and transport modeling using MODFLOW and MT3D from within GMS. We are looking at about 10^6 nodes. Is this feasible? If not, could any of the three be recompiled for more nodes?


It seems like it should be alright but keep in mind that there are quite a few things that could cause memory problems. The way the memory is allocated creates certain restrictions, but a lot has to do with your model. A basic MODFLOW model might run fine with that many nodes but if you then add a number of observation wells then it might run out of memory.

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  • 4 weeks later...


I have been told "Really the only limitation to GMS is your RAM, the more RAM that you have the larger models you can run". That was , of course, true before anyone thought you would have more than about 2 GB of RAM. Now that RAM is becoming cheaper it is easy to get more RAM in a PC than it can really use. I have 3 GB of RAM but I find monster models usually hit a wall when editing time steps or saving, rather than when running MODFLOW - I really hate the dreaded black exclamation mark in a yellow triangle obove "OK" which means you MODFLOW simulation has disappeared.

You have said, in other correspondence, that there is about a 2GB limit per process. If you have a multi-core CPU (say a quad-core), can GMS be spread over the multiple cores (giving you 8 GB of RAM working on GMS rather than just 2)? If so is it done by the OS or by GMS?

I know the sensible solution would be to reduce the number of cell/time steps by breaking the model up in to sub-grids or running several models over fewer time steps, but this is not always easy when the data is linked to another grid model (which might have been fine for a 2D surface model but becomes huge when you turn it in to a 6-layer groundwater model).

I suppose the ultimate question is, what is the highest-spec, stand-alone GMS machine (cores, RAM, OS) that it is currently worth setting up, to build and run monster models?

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