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How to add unit hydrograph and corresponding hyetograph in SewerGEMS for calculating the peak flow for a catchment?

I have unit hydrograph with me for a catchment. I also have hyetograph of the catchment. Where do I input this in SewerGEMS and how should I calculate the peak flow from the catchment using it?

  • Hello Ankit,

    The hyetograph would be entered in the Storm Data window (Components > Storm Data). Create a new storm event (for example time-depth) and on the right side choose to create a new return event, where you can then define the table of time vs. depth (cumulative or incremental). Entering and using storm data is covered in our SewerGEMS training material. If you are new to SewerGEMS, take a look at our New User Learning Resource Guide for SewerGEMS. In particular, see these parts of the training courses (on our YouTube channel): Rainfall | Runoff | Catchment Hydrology

    The unit hydrograph (involved with converting rainfall to runoff) is specified in the catchment properties. In most cases users will use the standard SCS Unit Hydrograph method by selecting Unit Hydrograph as the Runoff Method, then SCS Unit Hydrograph as the Unit Hydrograph Method.

    If you have a custom unit hydrograph, you can define it with the Generic Unit Hydrograph selected as the Unit Hydrograph Method (where you can enter a table of time vs flow to define the unit hydrograph). This is typically used for site/catchment-specific conditions.

    Another option is to select SCS Unit Hydrograph as the Unit Hydrograph Method, then select Dimensionless Unit Hydrograph as the SCS Unit Hydrograph Method. This enables you to enter a custom table of T/Tp vs. Q/Qp. This will still utilize the underlying SCS Unit Hydrograph methodology and is typically used for situations that apply to a wider area (more than just one catchment). Examples of this are the Delmarva Unit Hydrograph as seen here. Also see this.


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.