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RE: Outlet to a Pond Flows

Ref: http://communities.bentley.com/products/hydraulics___hydrology/f/5925/t/101651

Hello Scott,

I have an additional questions with regards to my model. I have been reviewing some of the information and confirming with hand calculations and came across something which does not make sense. In my model my K-6 catchment outlets to CB-1 which then has an orifice restriction that forces the water to pond at the node. 

As a check I took the runoff hydrograph from K-6 and transferred it into Excel. I then routed it through a 'pond' (catchbasin with ponded area in my case) and produced an outflow hydrograph which would discharge into the underground system. After this was completed I then copied the outflow hydrograph produced by SewerGEMS for my catchbasin into Excel for comparison. 

I have included my graph of inflows and outflows which I produced from excel as well as the outflow I obtained from SewerGEMS. I noted that there is a discrepancy in the outflow curves where SewerGEMS appears to be discharging for a longer period resulting in a larger outflow volume. I then went back into my spreadsheet and calculated total volumes of the inflow, outflow, and outflow from sewergems, here is how they compared:

Inflow = 78.26m3

Outflow = 78.24m3 (slightly different due to some assumptions in my routing spreadsheet)

Outflow from SewerGEMS = 95.32m3

As you can see the graph which I copied from SewerGEMS for comparisons appears to have invented additional flow at the catch basin node. Other than the discrepancy at the end of the graph they are almost identical which was what I was looking for. I was wondering if you had ever seen this before or know what would be causing it?

Any information or help would be greatly appreciated. Thanks again for the help on the above issue I had wondered if the outlet was summing the other catchments as well but was looking for confirmation. If you have any questions or need more information please let me know.

Thanks again,

Ryan

  • Hello Ryan,

    Could you please provide the model for this? 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.

    http://communities.bentley.com/content/bentleysecurefilesupload.aspx

    If you send the model, please post here so we know it is available.

    Thanks,
    Scott
  • Scott,

    I have uploaded the newest version of the model via Sharefile. The model has changed since I created this topic but still has the same thing happening. For some reason if you calculate the total outflow from the catchment versus the total outflow from the CB, they are not equal. This also leads to the CB ponding to more depth than it should and therefore is erroneous information.

    Thanks,
    Ryan
  • Hello Ryan,

    I see element K-6, but I don't see the catch basin you reference in your original description (CB-1). Could you confirm if we have the right model? Thanks.

    Regards,
    Scott
  • Scott,

    Sorry k-6 was incorrect above. The model is correct. In the model K-1, K-2, and K-3 all outlet into CB-1, CB-2 and CB-3 respectively. At these catch basins will be where the discrepancy occurs. As far as I can tell they all have a variation in the total volume, while the magnitude varies.

    Ryan
  • Hello Ryan,

    Sorry, but can you send the spreadsheet as well? I don't see that among the files you provided already. You can send it to the same link if you want. Thanks again.

    Regards,
    Scott