Routing Velocity Calculation
    • 22 Aug 2022
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    Routing Velocity Calculation

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    Article summary

    If the flood routing model is to going be used with a water quality simulation, then an approximate formula must be used to calculate nodal velocities.

    The node types forming the flood routing model are:

    The velocity is then used to determine flow area at each timestep. This value is stored in the Mode results field for the node and will be used for future water quality runs.

    The following options are available to specify velocity as a function of flow.

    Power Law Function

     

    For Q > Qo

    V = Vo + a( Q - Qo )b

    (1)

    and for Q £ Qo

    V = Vo

    (2)

    where:

    V = Velocity defined in the Rating Curve (VQ Rating)

    Vo = Minimum Velocity

    Q = Flow defined in the Rating Curve

    Qo = Minimum Flow

    a = Velocity Scaling Parameter

    b = Velocity Power Parameter

    The second formulation is introduced to avoid potential problems when the flow dips initially, possibly attaining a negative value; a property associated with the Muskingum algorithm.

    These parameters are defined in the data fields topics for each of the flood routing node types.

    User Supplied Relationship

    In this case you provide a rating curve relating velocity and flow and the Flood Modeller linearly interpolates between these values.

    Derivation from Section Geometry

    This method is only available for the VPMC Cross-Section node.

    The velocity is determined from the supplied section details using Manning's equation in the usual way.


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