1D river simulations - additional outputs tab
    • 05 Aug 2022
    • 8 Minutes to read
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    1D river simulations - additional outputs tab

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    Article summary

    In this tab, additional outputs and system volume output details are specified.

    RiverSimulationsimagesadditionaloutputs.PNG

    A 1D river simulation will, by default, always save a standard set of six variables. These are:

    • Flow

    • Stage

    • Froude number

    • Velocity

    • Unit mode

    • Unit state

    Pollutant concentrations will be added to this list for a 1D quality simulation.

    Some of these default variables will have no meaning for certain units within a model, e.g. velocity in a reservoir.However, there may be additional variables, not on the default list, that are relevant to particular units and of importance to the modeller. To address this issue, an additional results file can be produced by 1D simulations.

    Additional outputs

    Prior to running a simulation a user can select any variable from a list of additional outputs. These will be saved to the supplementary results file, which has the extension .zzx. It should be noted that multiple selections from the list are permissible.

    Data will be saved to the .zzx file from all units relevant to the selected variables. When the simulation is complete these data will then be available to be output as comma separated variable format files using Tabular CSV in the same way as the default data.

    Available Variables

    The following sections provide definitions of the additional variables that can be saved from an 1D simulation to a zzx file. Any data that is not applicable to the node in question will be given the default null data value of -9999.99.

    Variable

    Description

    Maximum Stage During Save Interval

    This variable is output for all 1D model units. At any time within a simulation this represents the maximum stage that has occurred during the previous save interval.

    Maximum Flow During Save Interval

    This variable is output for all 1D model units. At any time within a simulation this represents the maximum flow that has occurred during the previous save interval.

    Mean Stage During Save Interval

    This variable is output for all 1D model units. At any time within a simulation this is the mean stage over all timesteps within the preceding save interval.

    Mean Flow During Save Interval

    This variable is output for all 1D model units. At any time within a simulation this is the mean flow over all timesteps within the preceding save interval.

    Conveyance

    The conveyance variable applies only to a river section or conduit unit. An array of depths and corresponding conveyance values is calculated for each river section at the beginning of a simulation. During a simulation the conveyance is then calculated by linear interpolation of this relationship at the current depth.

    dh Convergence

    dh convergence is output for all units. It is a measure of the convergence in calculated stage for a selected unit within the model and therefore represents how well the simulation is performing at the selected unit (see Convergence Information).

    dQ Convergence

    dQ convergence is output for all units. It is a measure of the convergence in calculated flows for a selected unit within the model and therefore represents how well the simulation is performing at the selected unit (see Convergence Information).

    Reservoir / River Volume

    Unit volume can be calculated for either a river section or a reservoir unit. For a river section the volume is calculated as the product of average cross-sectional area (of upstream and downstream cross sections) and reach length, and applies to the volume between the node in question and the next node downstream. For a reservoir the volume is calculated by the summing the product of average segment area and segment depth from the user-specified area/elevation relationship over the reservoir depth. This option may be used as an alternative to the "Output approximate system volume" option.

    Operating rule number

    This option applies to structures operating in logical rule mode only. Its value denotes the rule number being applied at the given time.

    Slot Area

    Slot area applies only to a river section unit. A triangular slot can be added to the base of a river section by using the Automated Preissmann Slot option. This aids model stability during periods of low flow. The slot area variable represents the wetted cross-sectional area of the slot. This will be the cross-sectional area of the entire slot when water levels are above the slot height.

    Slot Volume

    Slot volume applies only to a river section unit. A triangular slot can be added to the base of a river section by using the Automated Preissmann Slot option. This aids model stability during periods of low flow. The slot volume variable represents the volume of water contained within the slot. When water levels are above the slot height this will be:

    Slot cross-sectional area x Reach length

    For lower water levels the average slot cross sectional area, between upstream and downstream sections is used in the equation.

    Structure Velocity

    Structure velocity is the average flow velocity through or over a hydraulic structure. It is calculated as:

    Total flow through structure / Total cross-sectional flow area

    This variable applies to variety of structures and for each structure there are a number of different flow scenarios that affect the calculation of cross-sectional area across the unit. These are shown in the table below:

    Structure Type

    Flow regime through structure

    Standard broad crested weir

    Round nosed broad crested weir

    Notional weir

    Sharp crested weir

    Crump weir

    • Dry flow - no flow over structure so zero velocity.

    • Free flow - area calculated assuming critical depth over structure.

    • Drowned flow - area calculated using average depth over structure

    Gated weir

    • Dry flow - no flow over structure so zero velocity.

    • Free flow - area calculation depends on structure being throat or gate controlled.

    • Drowned flow - area calculation depends on structure being throat or gate controlled

    Vertical / radial sluice gates

    • Dry flow - no flow over structure so zero velocity.

    • Gate closed, upstream and downstream level below gate top - no flow over structure so zero velocity.

    • Gate closed, free flow over gate - area calculated assuming critical depth over structure.

    • Gate closed, drowned flow over gate - area calculated using average depth over structure.

    • Free weir flow under gate - area calculated assuming critical depth over structure.

    • Drowned weir flow under gate - area calculated using average depth over structure.

    • Free gate flow - area calculated using standard gated flow equations.

    • Drowned gate flow - area calculated using standard gated flow equations.

    • Free over gate and free under gate flow - area above and below gates summed.

    • Free over gate and drowned under gate flow - area above and below gates summed.

    • Drowned over gate and drowned under gate flow - area above and below gates summed

    Orifice

    • Level above orifice soffit - area of flow assumed to be cross-sectional area of orifice.

    • Level below orifice soffit - area calculated assuming weir flow over orifice invert

    US BPR bridge

    Arch bridge

    • Area calculated from linear interpolation of area / depth relationship

    Surface Area

    The surface area variable applies to both river section and reservoir units. The reservoir surface area is calculated by linear interpolation of the user entered depth / surface area relationship. The river surface area applies to the area between the node in question and the next node downstream is calculated as:

    ((Upstream flow width + Downstream flow width) / 2) x Reach length

    Wetted Area

    The wetted area represents the cross-sectional area and applies only to a river section or conduit unit.

    Wetted Perimeter

    The wetted perimeter is an available output from the river section or conduit unit only. An array of depths and corresponding wetted perimeters is calculated for each river section at the beginning of a simulation. During a simulation the wetted perimeter is then calculated by linear interpolation of this relationship at the current depth.

    2D Flow

    The flow (in cubic meters per second) output between two adjacent river nodes is assigned to the upstream of the two (i.e. the earlier in the data file). A positive value indicates that the direction of flow is into the 1D domain

    Pump Data

    When selecting the Pump Data option, two variables are output to the supplementary results file: ‘Pump power’ and ‘Pump efficiency’. The pump efficiency is calculated during the initial derivation of the four-quadrant pump curve using Suter’s method.

    Pump power, P is defined as the torque (Nm) multiplied by the angular velocity (rad s-1)

    Note: the angular velocity is the pump speed (rpm) multiplied by 2π/60.

    The relationship between efficiency and torque is as follows:

    Efficiency = ρ g Q h / (T ω) = ρ g Q h /P

    where ρ is the density, g is acceleration due to gravity, Q is the flow and h is the total head (the difference between the discharge head and the suction head).

    Note: when the pump is not operating (i.e. Stopped or Off), the pump power will be output as zero.

    Stream Power per Unit Width

    This is calculated as 

    Density of water x acceleration due to gravity x current discharge x bed slope in the "downhill direction" / the current top width

    This is given in units of kg s^(-3)

    Stream Power

    This is calculated as 

    Density of water x acceleration due to gravity x current discharge x bed slope in the "downhill direction"

    This is given in units of kg m s^(-3)

    Average Shear Stress

    This is calculated as 

    Density of water x acceleration due to gravity x current wetted area x bed slope in the "downhill direction" / current top width

    This is given in units of kg m^(-1) s^(-2)


    Hint: The structure of the .zzx file is identical to the results file produced by an Flood Modeller Quality simulation (*.zzc). By changing the extension of a zzx file to '.zzc' (taking care not to overwrite any results from a Quality simulation), the user may view the results graphically from the user interface.

    System volume

    • Output approximate system volume - Outputs the approximate storage volumes in channels, reservoirs, and cumulative inflows and outflows to a comma separated (CSV ) file (extension .ivl ).

    • Volume output interval - The interval (in seconds) at which approximate system volumes are written to the *.ivl file (if the previous option is selected). If left at zero, output will be written for the first and last timesteps . The default value is zero.


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