Cell Size Zones in 2d Mesh

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Cell Size Zones in 2d Mesh

Ski907
Is there a preferred method, or perhaps some trick to quickly develop 2d meshes with different "zones" of cell sizes? For example when modeling a reservoir and dam system, it can be desirable to dynamically model flow through the reservoir to capture the effects of attenuation. Typically I use a cell size on the order of 2-5 feet on and downstream of dams, but this is excessively fine for modeling a reservoir.

In some cases it would be easy to simply link a storage area, or a 2D area to a hydraulic structure on the dam, but in a particular model I'm working on, there are three open channel spillways which activate at different stages, and the entrance draw-down effects likely influence each other- so I'd like to model the dam and reservoir together. Ideally I'd like to have one big mesh with 2 foot cells around the dam and 50 foot cells out in the reservoir, but hand editing the mesh with the tools I'm aware of to accomplish this is not feasible. Any tricks out there folks have had success with?

I did try and make 2 separate meshes and link them together with a SA connection, which worked, but there is some anomalous stuff going on around the boundary conditions, and just doesn't seem as clean as using one big mesh.
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Re: Cell Size Zones in 2d Mesh

Toby
Check out the free plugin to QGIS, RiverGIS.  http://rivergis.com/ras2d_geometry.html  It might do the trick for you.  
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Re: Cell Size Zones in 2d Mesh

Lonnie A
In reply to this post by Ski907
One "trick" I use is just to draw a zig-zagged breakline in the area I want smaller cells and then edit the breakline cell spacing to the resolution I'm looking for.
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Re: Cell Size Zones in 2d Mesh

Ski907
Wow- this works wonders. Somehow I missed that you could change the cell size along breaklines. I will also try out the RiverGIS model in QGIS as I'd like to have a little more "control". For right now the breakline trick fits the bill. Thanks!
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Re: Cell Size Zones in 2d Mesh

cameron
We use some custom scripts to create cell sizes that vary.  You could also use SMS which has added the option to generate RAS meshes.