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C Callipari

Representing large storage basins in 1d

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Hi,

I am attempting to model a storage basin within a 1d network, connected to a 1d stormwater network, within a 2d model. The basin is triangular in shape and has 1:4 side slopes. I have created an NA table for the changing surface area with elevation, and applied it to a 1d_nwk pit (type R at the moment, since there is no option for triangular pits). The model runs without instability but the hydrograph of the 1d basin is all over the place.

Any suggestions? Thanks!

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Hi,

Is the storage basin connected solely to your 1D pipe network? If so then I don't think you need to specify an "R" pit (I believe these are more often used for modelling a connection between the 1D pipe network and the 2D floodplain). You should be able to leave the "Type" attribute blank (i.e. it is a node instead of a pit channel), and use your NA table to specify the extra storage at that node. I wouldn't have thought the shape of your node (i.e. triangular) would be relevant, as this would be accounted for in your NA table.

I'm not sure if that will have any bearing on your problems but hope it helps!

Cheers

Richard

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Hi,

I would model the detention basin as a NA table, culvert (outlet) and 2d_bc (SX). I have attached screen shot of a general configuration.

You could do something similar using pits i guess, but i feel this way gives you a bit more control over the 1D/2D boundary cells.

If you are still having problems with stability things to check may be:

1) That the NA table is being correctly inputted, this can be done using the .eof file (written to the 1d results directory). If you open this file in a text editor and search for the node name you should find an entry that looks something like:

Node TC_PC_3540.2

Elevation (m) 3.579 3.621 3.663 3.704

Surface Area (m2) 10.0 19.8 27.1 32.4

2) Check the topography of the 1d/2d SX cells, flow should be able to leave the cells. If the "z" flag is used on the SX line this will lower the cell centre not the cell sides. Much better to use a z_sh layer to smooth the topography than to use the z flag.

Hope this helps

Phillip

post-220-1261095540_thumb.jpg

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Thankyou Richard, Phillip for your suggestions. I thought I'd share my response to the problem:

Whilst the 1d storage basin (represented as a pit with an NA table, connected to incoming and outgoing pipes in the 1d_nwk) appeared to be working without instability, the flow hydrograph through the basin seemed very unusual (extreme oscillations).

However the stage hydrograph of the 1d basin showed reasonable operation when compared to the 2d stage hydrograph (obtained from a PO point on top of the basin)- that is, peaks in the 2d water level followed 1d pit surcharges.

Osciallations in the pit flow hydrograph may be attributed to the rapid filling/emptying of the basin (the basin is fairly small compared to the flow over the floodplain) and the associated behavioural changes in connecting pipes.

So for anyone else modelling a similar basin, I'd suggest comparing the stage hydrographs in the 1d and 2d alongside the flow hydrograph.

Cheers

Chiara

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