Combining Sewage And Storm Models

I have For  the same network 2 Models one is Storm run using SWMM solver (the flows in the models are catchment areas with time depth graph) and the other is sewage run using GVF-Convex (the flows in the models are sewage flow entered as population and sanitary loading with extreme flow setups for the peak factor calculations), the question is how i combine them keeping the SWMM solver running (sewage flow are peaked and fixed in the manholes) ?!!

  • Hello Diaa,

    You will only be able to compute the model with one solver at a time.
    Is the network a Combined Sewer Overflow (CSO)? In other words, does the sewer flow and storm flow combine into the same piping system, or do they stay in separate systems?

    If you want to know how to import one submodel into another, the following article will help with that process.

    Combining models with Submodel Import

    If the sewer and storm flow remain in separate systems, then I recommend creating different scenarios for each system, which will allow you to compute the storm system with the SWMM solver and the sewer system with the GVF-Convex solver.

    If the sewer and storm flow combines in the same piping network, then are you saying that you want to compute this system with the SWMM solver? If this is what you want to do, then I would recommend validating and computing to see what changes need to be made to get the SWMM solver to compute. The following article explains the differences between the solvers.

    Differences between solvers: GVF-Convex vs. GVF-Rational vs. Implicit vs. Explicit (SWMM)

    In addition to the above questions, it would be helpful to see your model. You can upload the model files with one of the methods in the following article.

    Sharing Hydraulic Model Files on the Haestad Forum



    Craig Calvin

    Bentley Technical Support

  • To add to Craig's response -

    I see you mentioned that you are using extreme flow factors to model peak flow conditions with the sewage part of the network, with the GVF-Convex solver. The peak flows you get with that analysis are in steady state (a snapshot in time), whereas the SWMM solver computes an unsteady simulation, introducing the element of time. So, the steady state peak flows are not compatible with an unsteady simulation. You would not want to simply assign the respective peak flows to your manholes for use with the SWMM solver, since those peak flows only occurred during the peak flow conditions, not for the whole day.

    The peak flows from extreme flow factors are usually used to size the pipes for worst-case conditions, whereas the SWMM solver would be used for assessing existing system performance.

    If you want to use the SWMM solver after designing/sizing pipes with the peaking factors, you would need to develop load patterns to assign to your unit loads, to simulate how the loads vary during the day (or longer period, if desired). You might have a different pattern for different conditions that you want to simulate.


    Jesse Dringoli

    Technical Support Manager, Haestad Products
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

  • Dears Craig & Jesse

    Thanks For Your Fast reply, i appreciated. The Network I am talking about is exiting one (all the data i have for it is only a sewage model with population and unit sanitary loads with solver GVF-Convex ) that carries sewage flow and in the construction phase the contractor connected the storm catch basins to it. so i need to simulate the most worst case that all pipes are fully loaded with the peak sewage flow while the exact storm event is happening. 

    I know that both engines will not run together, for that i tried to convert the peaked flow to a fixed one but i faced a problem that i can't get the peaked flow for each manhole to define it as inflow (wet) fixed flow.

    Thanks a lot in advance

    Diaa Abdelrahman 

  • Hello Diaa,

    Creating separate scenarios is a good approach to test your network.

    The first scenario can be "only the sewer network" with unit sanitary loads and population to determine sanitary flow through the network. You can use the GVF-Convex Solver for this.

    The second scenario (child of the first) can be "sanitary network + the storm flow". In this you can use the additional data of storm inlets using Active Topology Management to add the additional elements (catchments, catch-basins, conduits etc.) and add your storm events and specify them for your catchments. For this you can use the Implicit Solver which can model combined (storm + sewer) systems.

    If you are doing this, the flows in your model would be more realistic as per the storm events specified.

    Alternatively, you can simply add the wet inflow to the manholes based on the peak inflow calculated. What problem are you facing specifying this? You can specify "Fixed" flow type in it. Can you share a snapshot or elaborate on the problem?

    Hope this helps.


    Yashodhan Joshi

    Bentley Technical Support