Ponds in Series

[MasterBase]

A coworker has modeled a series of 3 ponds separated by 2 roads and 2 sets of large box culverts(with a weir) to equalize the 2 upstream ponds. The final outfall is a small stone box culvert under a railroad track. When I take out the road crossings and model this as one large pond with several subcatchments I get a 100year elevation 2.5' higher than he does.

Since the storm elevations back up into the upstream ponds; his theory was to add the upper ponds elev-areas to the lower ponds to make it more realistic.

We are in debate as to whether ponds in series automatically account for other ponds volumes as the elevation rises into one another or whether his method is accurate, I feel like he is double dipping on storage and getting false results. We are using the Dyn-Stor-Ind Method.

Please help

 

[Twinkie]

That is the purpose of the Dyn-Stor method.

http://www.hydrocad.net/dsi.htm

 

[MasterBase]

Thanks, his concern is when you put in the areas just for the individual ponds, that the calculations show a storage area reflective of that basin instead of the total physical storage at that elevation.

 

[gbam]

Should you not model each basin separate but in series (A->B->C)? This way you could potentially get difference WSEs in each Pond at the same time step.

 

[MasterBase]

They are 3 separate basins linked to one another with a simple link in series. Each pond has multiple sub areas. When routed the 100yr was 4-5 feet into the other basins, so he added those upstream areas into the lower pond thinking it would be more accurate since the elevation rises that high. What he isn't realizing is that the water surface in the lower pond accounts for storage in the upstream ponds, though the storage number doesn't say that when you click on the lower pond. I believe what Twinkie said I just need to convince my co-worker that his logical thought process is double dipping with storage

 

[psmart]

MasterBase, when you say "Simple link in series", do you mean a separate link node? If so, this will break the pond-to-pond tailwater capability.

Just use three ponds, each routed directly to the next: A->B->C

Enter the available storage within each pond. This is the volume that is directly controlled by the pond's outlet device(s). Don't include the volume for any other nodes, upstream or downstream. These volumes are accounted for separately in their respective nodes, and should not be double-counted.





Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[MasterBase]

See the link, I believe I did it the way you said. Thanks

 

[psmart]

Looks good to me: 3 ponds in a row with direct pond-to-pond routing.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[gbam]

Quick question:

Is it possible to get reversing flow when/if the pond elevation downstream is higher than the upstream pond? If yes, you may need to use additional software to evaluate that scenario; Interconnected Pond Routing (ICPR) or similar. I do not use HydroCAD so maybe Peter can answer if HydroCAD handles that scenario.

 

[beej67]

I know hydrocad will handle backflow if you switch to Simultaneous Routing method, but it also has a tendency to explode unless you massage it a bit. Not sure how that's handled in Dyn-Stor-Ind.



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[MasterBase]

I had it as Sim Route previously and the elevations were 2' higher

 

[psmart]

DSI is the recommended routing procedure for most tailwater situations. SimRoute tends to be less stable, and is needed only to model reversing flows.

To be clear: Tailwater means that the discharge is reduced by the downstream water surface elevation, but water is always flowing in the same direction from A to B. Reversing flows means that the flow actually changes direction, flowing first from A to B, and then from B to A.

For details see

http://www.hydrocad.net/tailwater.htm

Masterbase: When you say the elevations were 2' higher with SimRoute, I'm guessing there were warning messages in one of the models? The warnings are intended to identify modeling issues (such as oscillations) that may compromise the results. Please review and resolve any warning messages before you draw any conclusions from the results.


Peter Smart
HydroCAD Software

http://www.hydrocad.net