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jrwbell

1d_bc:QT (Q pits only)

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Hi.

I would like to use a 1d_bc:QT polygon to apply inflow from RAFTS .LOC to the top of Q pits. i.e. take into consideration the depth-discharge relationship referred to in the pit database such that surcharge appears in the 2D domain.

I note the manual has "C", "O" and "P" flags, however, can anyone tell me whether the "P" flag will apply QT (uniformly distributed underneath the polygon to relevant nodes) to top of Q pits or will it "only direct flow into the bottom of pit channels".

cheers

Justin

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Hi Justin

I would use a Read MI SA Pit == command this will distribute the flows within a region and apply flows to any 1d nodes connected to the 2d domain.

It is my understanding that the assign pit capacity is then used and any surcharge flows applied to the 2D domain. (If this is incorrect can someone post another reply)

Regards

David

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Hi Justin

I would use a Read MI SA Pit == command this will distribute the flows within a region and apply flows to any 1d nodes connected to the 2d domain.

It is my understanding that the assign pit capacity is then used and any surcharge flows applied to the 2D domain. (If this is incorrect can someone post another reply)

Regards

David

Hi

I've been using 2D_SA polygons to apply the inflows to 1d_nwk pit objects (Type="Q"; Conn_2D="SX" or "SXZ" though I think there are other settings you could use.) to assign catchment flows to pit surfaces. If multiple pits fall inside the SA polygon then the flow hydrograph is split equally between the pits.

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Hi All

Yes, to utilise the pit depth-discharge curves for gully traps/drains you'll need to apply the inflow to the 2D domain which then feeds into the 1D domain via the pits using the allocated curves. The best way is to use the Read MI SA PITS command, and yes, the inflow hydrograph is equally shared amongst the pits within the SA polygon.

For very large events, there can be problems with applying large flows to only a few 2D cells, however, we're looking into having a variation of Read MI SA PITS where if all cells are dry, the flows are assigned just to the pit cells, but once wet it spreads the flows over the wet cells and any remaining dry pit cells - this works very nicely and will be in the 2010 release.

There is also the SXL option (for the 1d_nwk Conn_2D attribute) that some modellers like which depresses the pit cells down slightly so as to ensure a good depth of water, and therefore a larger flow from the depth-discharge curve feeding into the 1D domain.

Cheers

Bill

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Thanks Everyone.

I have decided to try 1d_bc:QT|P via a polygon so as to apply inflows to the bottom of the pits. My logic for this approach is because I'm not modelling every pit and pipe in the drainage system so it's therefore reasonable to apply inflows at the bottom of the pit channels. I have also used the same approach at some locations too, as point objects (can I do this?).

My follow-up question though is I've encountered the following error at some pits underlying my 1d_bc:QT|P polygon, but at not all pits: ERROR - All 1D nodes within 1D QT region to be assigned a flow are a H boundary or a 2D SX link. The error is written twice at the particular pit, yet there's no error in the next pit above or below that fall under the same polygon.

Anyhow, if anyone can shed light on this then that'd be appreciated:

a) can i use point objects with a |P flag (or doesn't it matter); and

B) what might be causing that error at particular pits but not others under the same 1d_bc:QT|P polygon?

cheers

Justin

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