When modeling storm sewers and catch basins, does the model count storage in pipe?

[hydroponder]

I am modeling a storm sewer system that will connect to an underground array of pipe (storage) before outletting to existing storm sewer. I originally setup the model to model the array of pipes as a pond and just used one catchment for the inflow of the storm sewer to the storage pipes. For the second model, I modeled all of the storm sewer and catch basins and then routed them to the same "pond" (storage pipes) as above. My results are close, but different. I am wondering if the hydrocad model counts the storage in the pipes routed from one catch basin to another? If so, I may be double counting some storage and would like to make a correction if needed.

There is only one connection to the array of pipes, so I wonder if I just model the inlet pipe to the storage pipes as an orifice it would not count the pipe storage, but would like to keep it all in there if possible.

Thoughts?

 

[psmart]

When you use a culvert outlet, the pipe is evaluated as a outlet control device, without allowing for storage in the pipe.

To use a pipe for storage, you would include it as a storage definition for the pond. This assumes the presence of a separate outlet control (such as a weir, orifice, or smaller pipe) that will restrict the outflow and create a level pool (a pond) within the larger pipe(s).

The differences in your two scenarios could be due to the use of a single subcatchment vs. several smaller subcatchments. There could also be very slight time lags in the CB's that are offsetting the individual hydrographs. I would need to see the two scenarios to know for sure.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[hydroponder]

Thanks Peter. That is what I suspected, but wanted to make sure. I think I have it dialed in now.