# Ascertaining the maximum hydraulic grade when we have a pump and wetwell modelled in civilstorm

We have created a storm water model wherein we have a series of ditches and pipes that drain to a sump (in civilstorm terms a wet well) from there a pump is continuously pumping out. For the extent of area that we have we know that for sure there will be overflow, but we wanted to know when there is an overflow what will be the maximum hydraulic gradient line in the entire conveyance system. But our model is showing just the overflow discharge we could not see the maximum hydraulic gradient line. Can we know if there is a way that exists to ascertain the maximum HGL in civilstorm for this condition?

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Hello Scott,
Thank you for the response. We have the color code turned on, the issue is it is showing the maximum hydraulic gradient line as max operating elevation of wetwall for the entire conveyance system. As there is an overflow, it is supposed to show the actual maximum hydraulic gradient line, but it is not showing the maximum hydraulic gradient line beyond the top of wet well. We tried increasing the wet well top for that case it is again showing maximum hydraulic gradient line upto the wet well. Our intention is to view the actual maximum hydraulic gradient line for the conveyance system which we know for sure that will be more than the top of wet well as there is a overflow. So would like to know how to get that information from civilstorm.

Thank you!
Regards,
Shobana P.

• Sorry, I just saw your reply now. Please see the tips in my previous answer. If you are extending the top of the wetwell and still seeing the maximum HGL equal to the wetwell top elevation, then the software may be predicting that water would continue pooling up that high. If the surface area spreads out above the actual sump top, then you may need to use a different approach to simulate that increase in surface area.

I would also recommend looking at some graphs of HGL of the surrounding area to see if perhaps they are unstable, causing the unexpected high max HGL. Review the mass balance error in the Calculation Summary as well. If the results are observed to be unstable and/or a high mass balance error is seen, this will need to be addressed first before results can be scrutinized. These articles can help (I recommend using the Explicit (SWMM) solver for most situations):

If your wetwell is enclosed and you need to model surcharging, you may need to extend the top even further using the "chimney" approach described here. However, my understanding is that your wetwell is being used to simulate a depression in the land which acts as a pond. So, the depth-area or pond element approach may be better as it enables you to model the larger surface area above the real top of the sump (whereas the wetwell models vertical side walls unless you use the depth-area approach)

The 2D Modeling feature is another option to explore.

Regards,

Jesse Dringoli
Technical Support Manager, OpenFlows
Bentley Systems, Inc.

• Sorry, I just saw your reply now. Please see the tips in my previous answer. If you are extending the top of the wetwell and still seeing the maximum HGL equal to the wetwell top elevation, then the software may be predicting that water would continue pooling up that high. If the surface area spreads out above the actual sump top, then you may need to use a different approach to simulate that increase in surface area.

I would also recommend looking at some graphs of HGL of the surrounding area to see if perhaps they are unstable, causing the unexpected high max HGL. Review the mass balance error in the Calculation Summary as well. If the results are observed to be unstable and/or a high mass balance error is seen, this will need to be addressed first before results can be scrutinized. These articles can help (I recommend using the Explicit (SWMM) solver for most situations):

If your wetwell is enclosed and you need to model surcharging, you may need to extend the top even further using the "chimney" approach described here. However, my understanding is that your wetwell is being used to simulate a depression in the land which acts as a pond. So, the depth-area or pond element approach may be better as it enables you to model the larger surface area above the real top of the sump (whereas the wetwell models vertical side walls unless you use the depth-area approach)

The 2D Modeling feature is another option to explore.

Regards,

Jesse Dringoli
Technical Support Manager, OpenFlows
Bentley Systems, Inc.

Children
• Hello Jesse,

I have the same scenario that Shobana is experiencing. Although I have an add on question.

I have a system of ditches connected to a wet well. I have a pump connected to the wet well to pump out the flow in.

My question is if Civil Storm considers the volume of storage upstream of wet well as:

a. Only wet well storage

b. Wet well storage + Storage in dtiches

Thanks,

Naga

• Nagarajan,

Channel elements are not storage elements, though the volume of water is still accounted for in the mass balance and dynamic equations. I would need to understand what you mean when you say “considers”. Volume from the ditch enters the wetwell and the wetwell elevation rises accordingly, triggering any attached pump to turn on when it reaches the on elevation. So in that sense, the “storage” in the ditch is “accounted for”. If you're referring to the volume results shown in the wetwell node, that would be the volume just for the wetwell.

Does the wetwell exist in the real world?  Or are you trying to use it just to connect the pump?  This situation could be modeled with the pond element instead - Modeling Ponds With Pumps - where the pond elevation-area (or elevation-volume) curve is configured to include the storage of the depression (or what you were modeling as the wetwell) and the surrounding ditch (replacing at least part of the ditch/channel element).

I hope this helps,
Larry

• Thanks for your quick response Larry.

To answer your question on the wet well, there is a pump station and so i have considered the volume of the sump in the pump station as the volume of the wet well. The ditches are the inlet to this pump station sump.

My intention with my earlier question was to check how Civil Storm calculates the overflow volume from a wetwell. Does it do this by:

a. Overflow volume = Total inflow volume - Volume pumped out - Volume of wet well

b. Overflow volume = Total inflow volume - Volume pumped out - Volume of wet well - Volume stored in the ditches

I hope this clarifies. Thanks for helping out. Please let me know if there are further questions.

• My intention with my earlier question was to check how Civil Storm calculates the overflow volume from a wetwell. Does it do this by:

a. Overflow volume = Total inflow volume - Volume pumped out - Volume of wet well

b. Overflow volume = Total inflow volume - Volume pumped out - Volume of wet well - Volume stored in the ditches

If I'm understanding your question correctly, it would be 'a'. Overflow volume is flow that leaves the system from overtopping, regardless of whether or not excess volume is being stored in an adjacent conduit or channel element.

For example if the water surface elevation reaches the top of the wetwell and you have 100 gpm coming out of the wetwell from a pump, and 120 gpm coming into the wetwell from an upstream channel element, the overflow rate would be 20 gpm. Over a period of time this would become a volume value. Now, during this time when the wetwell is overflowing, the depth in the upstream channel may rise or fall and the storage volume in the channel would change accordingly, but that volume would not be part of the overflow, as the overflow is only the flow that leaves the wetwell's top.

If this doesn't answer your concern, please explain a bit more about what you want to determine and perhaps some background on why (are you seeing something off in the results in your model which prompted this?)

Regards,

Jesse Dringoli
Technical Support Manager, OpenFlows