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

setting elevations

What is the most accurate way to select what elevation to use for my hydrants. my thinking is to set the hydrant elevation 2.5 ft above the ground elevation when I am running my fire flow scenarios since this is usually where it is measured? Would it make sense to have to change that elevation 6.5 ft below the ground elevation to calculate accurate static pressures? If I set my hydrants 2.5 ft above the ground, would it make sense to set the junctions/nodes at ground elevation, or would we want to be consistent? 

  • Hello M, 

    Elevations should refer to the point from where you want to measure the pressure at those nodes, you could use the elevation from where you measured pressure at the hydrant. Other modelers, experts can confirm here what practice they follow. 

    For nodes, junction you would generally set them up at ground elevations, whatever elevation you choose whether center of the pipe or ground elevations be consistent with that. The correct elevation of a node is the elevation at which you want to know the pressure. The elevations are merely used to convert the hydraulic grade line to pressure. 

    What does node elevation represent in WaterCAD, WaterGEMS and HAMMER? 

    Regards,

    Sushma Choure

    Bentley Technical Suppport

  • is it ok to set my hydrants at 2.5 ft above ground and my nodes on the pipe at ground elevation? Note that my hydrants are on the pipe main rather than attached to laterals off the pipe main.

  • Changing the hydrant elevation would change the calculated pressure (the hydraulic grade would stay the same, unless you use an emitter coefficient on the hydrant which could change the flow as the pressure changes)

    Whether or not it is "OK" to use a certain elevation is up to your engineering judgement. As Sushma mentioned, it generally makes sense to set the elevation to the elevation that pressure would be measured from. So, if you would measure hydrant pressure 2.5 m above the ground, then that makes sense. However, I am not sure I understand why the hydrants would be sticking 2.5 m out of the ground. Typically a hydrant opening would be just slightly above ground level.

    As also mentioned in the article, typically you would want to be consistent as well, so if you used ground elevation for hydrants for example, you would probably want to use ground elevation for junctions as well, for consistency. (so that you can keep in mind that pressures shown across the model are as measured from ground elevation).


    Regards,

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

  • thanks that makes sense.