1. ## Maximum Volume

I feel like I'm missing something in InfoSWMM here. I ran into a problem trying to determine storage volume required at a pump station. I have flow entering a storage node, which is then pumped out at a constant rate. I make the storage node some arbitrarily large size then run the model. I look at the Storage Volume Summary Report and see the reported Maximum Volume in MG. This should be the volume that I will need to storage for the given inflow hydrograph and outflow pump rate. I then convert that to cubic feet and divide by the depth of my storage tank to get the cross sectional area required at the top and bottom of the storage tank to hold that Maximum Volume. I then re-run with the storage resized to check that it indeed does not flood and I see that the Maximum Volume has changed. There is no flooding to account for this. So if the inflows are the same and the pump rate is the same, why does the Maximum Volume in the Storage change, depending on the cross sectional area of the storage? I'm missing something. I need to determine a storage volume required. I recreated this with just a simple model to replicate the problem and eliminate any other issues.

2. Hello Ross, I am looking at your model. The volume of a storage node is based on both the cross sectional area of the storage node AND the area of the connecting links. I was going to suggest that you connect the storage node or Wet Well to a dummy link so the Storage Node will ONLY have the area you entered. The pump does not add any storage,
Regards,
Bob Dickinson

3. Aha! Thanks, Robert. This makes sense and the model you sent behaves how I wanted. I'll try applying this method to my actual models to size storage.

4. In a case you might not miss anything, the Maximum Volume in the Storage would still change as the maximum volume is the peak volume at the time to peak during the hydrograph period. The hydraulic principle of the change is that i) the cross area change would cause the change of water head in the tank, ii)the velocity and the flow went through the link just before entering the tank would be then changed accordingly, therefore iii) create different peak volume.

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