This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Modeling pipe storage in SewerGEMS

I need to model filling/emptying patterns of a sanitary sewer tunnel whose outflow will be controlled by a pump station at the downstream end. How can I specify a no-flow outfall so that the wastewater starts filling the tunnel? Or can this not be done in SewerGEMS? I tried setting the tailwater elevation of the outfall higher than the tunnel crown, but the model still simulated flow out of the network as the sum of the inflows.

Parents
  • We may need some additional information for this, such as a diagram of what is being modeled and/or the model files you are working with. Included in this information would be what the outflow of the tunnel is. For instance, is the pump station directly connected to the tunnel? If not, what elements are between the tunnel and the pump station?

    For the outfall, you might consider an elevation-flow curve.

    Other options for modeling the tunnel would include using the pond element. There are options for the pond to be modeled as a pipe volume. Ponds require outlet structures, such as culverts, risers, etc. Pumps are not allowed as part of the outlet structure, so if the pump station is directly connected to the tunnel, this may not be the best option.

    If the pump station is directly connected to the tunnel, you may want to consider modeling this as a wet well.

    If this doesn't help, more information will be needed on what is being modeled in this system and the general setup. You can also send the model you have using the following information:

    There are two options for sharing your model files on BE Communities. If you would like the files to be visible to other members, compress the files into a zip file and upload them as an attachment using the ‘Advanced Reply editor’ before posting. If your data is confidential, you can follow the instructions in the link below to send it to us via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley.

    communities.bentley.com/.../bentleysecurefilesupload.aspx

    If you upload the model using the confidential sharefile link please let us know in this post so we know to retrieve the file.  

    Regards,

    Scott Kampa

    Bentley Technical Support

  • Thank you, Scott. I uploaded the model to Sharefile.

    Basically, we have a 20,000 LF, 21.3-ft tunnel, with 6 dropshafts. The tunnel will be used to divert excess flow from a sanitary trunk sewer and store it until it can be pumped back to the trunk sewer. I have modeled the dropshatfs as bolted manholes. The d/s end of the model has a wet well (approx. 25,000 gal) and a pump. I'll be looking at filling patterns first, so I added a pump curve that basically has the pump off all the time. The model is sending the excess flow as an overflow to the wet well, so I cannot see the backwater effect on the tunnel. Thanks again for looking at this.

  • Hello,

    Let me step back and ask what you are expecting in terms of results. Are the pipes supposed to slowly fill over time? Should they become surcharged? If the conduits are only expected to reach a certain elevation, you might be able to try a place a stop control structure on one of the downstream pipes with a weir just above the expected elevation. This could conceivably keep flow from reach the outfall, as long as the results are well-balanced and the inflows correct.

    For the model layout itself, are the elevations and pipe sizes accurate to what you have in the field? Also, you have hydrograph inflow at all of the entry points (modeled as manholes). I just want to make sure the input there is correct as well.

    Lastly, was there a reason that you wanted to try to model this in two steps (zero outflow first, then include pumped flow)? If it is possible to include the pumped flow as well, you might end up with reasonable results in comparison to trying to model a case where there is no allowable outflow.

    Regards,

    Scott

  • The tunnel will be used for storage of excess wastewater during storm events, so we're expecting it to start filling slowly (at some point it'll be surcharged). Wastewater will not be pumped out during the high flow event. Once the storm has passed and the levels in the main trunk sewer (from where the excess flows were diverted) are within permit limit, then the pumps will be turned on and we'll start emptying the tunnel.

    The hydrographs entering the manholes (they are in reality drop structures since it's a deep tunnel) are correct.

  • Hello,

    In looking over the options, you may want to consider modeling the tunnel as a pond with a pump attached to it. One pump type available in CivilStorm is Pipe Volume, which allows you to enter the pipe information (size, length, slope, etc.). You can then have the pump connected to the the pond outlet structure, similar to the layout below:

    The pond outlet structure property "Has Control Structure?" would be set to No. This means that there are no composite outlet structure for the pond and flow from the pump will be based on the pump.

    Please give this a try and see if that improves the results.

    Regards,

    Scott

    Answer Verified By: Sushma Choure 

  • Thank you, Scott for all your help. Will I be able to enter hydrographs at various points along the pond or will I be limited to an inlet only?

  • Hello,

    You might be able to model each pipe segment as a separate pond. There would be no control structure on these, as with the suggestion above, but some sort of connection, like a conduit would be needed. In the end, it might be simpler and offer a similar solution to simply model this as a single pond with all inflow going to it.

    It may be worth doing a sensitivity analysis to see if, for instance, modeling this as two ponds is similar to modeling it as one pond. I will say that you likely see that the results will be more stable when modeling this as a single pond.

    Regards,

    Scott

    Answer Verified By: Sushma Choure 

Reply
  • Hello,

    You might be able to model each pipe segment as a separate pond. There would be no control structure on these, as with the suggestion above, but some sort of connection, like a conduit would be needed. In the end, it might be simpler and offer a similar solution to simply model this as a single pond with all inflow going to it.

    It may be worth doing a sensitivity analysis to see if, for instance, modeling this as two ponds is similar to modeling it as one pond. I will say that you likely see that the results will be more stable when modeling this as a single pond.

    Regards,

    Scott

    Answer Verified By: Sushma Choure 

Children
No Data