The Urban Flow-Divider Node
- 23 Sep 2022
- 4 Minutes to read
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The Urban Flow-Divider Node
- Updated on 23 Sep 2022
- 4 Minutes to read
- Print
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Junction nodes represent manholes and drains in your urban system, and connections between pipes. In Kinematic Wave routing, a two outflow pipes cannot be connected to a Junction node, and therefore a Flow-Divider node must be used instead.
The Flow-Divider node is identical to the urban Junction node aside from the specification of diverted flow. In the case of Dynamic Wave routing, Flow-Divider nodes will be treated as Junction nodes.
The lower half of the Divider node Properties Window is shown below.
Rules of Flow-Divider nodes
A Junction node may have multiple inflow Conduit Links connected. Multiple outflow links from a Junction node are also allowed if using Dynamic Wave routing. If using Steady-State or Kinematic Wave routing, only a single outflow link is possible from a Junction node; an Urban Divider Node may be suitable if two outflow links are required.
Divider label/name
The Flow-Divider node name by default will be provided by parameters setup in the Urban Model Defaults menu.
Junction node parameters
Coordinates
The x and y coordinates of the Junction node are shown in these fields. These values are automatically populated based on the node location on the map.
Description
This field allows for an optional text description. The field will be blank by default.
Tag
This field allows for an optional text tag, to allow you to categorise units. The field will be blank by default.
Inflow
Inflows can be specified for a Junction node. These can be external direct, dry weather or RDII inflows. If inflows are not defined, the Junction node will only receive inflow from any Urban Subcatchment Nodes with the Junction node label selected as the subcatchment outlet.
Treatment
Addition of pollutants is not currently available within the software. If your model already contains defined pollutants, these will be unaffected, however you will not be able to access the pollutant editor form.
Invert elevation
The invert elevation of the Junction is provided in this field. By default this value will be provided by parameter setup in the Urban Model Defaults menu.
Maximum depth
The maximum depth of the Junction, from ground surface to invert, is provided in this field. If zero, then the distance from the invert to the top of the highest connecting link will be used. By default this value will be provided by parameter setup in the Urban Model Defaults menu.
Initial depth
This field contains the initial water depth in the Junction at the start of the simulation. By default this value will be 0.
Surcharge depth
This field specified the additional depth of water beyond the maximum depth that is allowed before the Junction floods. This parameter can be used to simulate bolted manhole covers. By default this value will be 0.
Ponded area
A positive ponded area for the Junction node can be provided in this field. This allows water that leaves the Junction node to pond, and subsequently re-enter the Junction node if conditions allow. By default this value will be provided by parameter setup in the Urban Model Defaults menu.
Note that to utilise this parameter, it is also necessary to allow ponding in the Urban Model Settings menu.
The Ponded Area parameter is used differently if working with integrated modelling.
Diverting flow in Divider nodes
It is necessary to specify a Diverted Link. The Flow-Divider node will divide the flow between the two outflow links connected from it. One of these outflow links is specified in this field to determine how this divide occurs. Let's refer to these two outflow links as PipeA and PipeB.
If PipeA should receive all flow until a known value F is reached, at which point PipeB should be start receiving flow, enter the label for PipeB in the Diverted Link field. Leave Type as the default value CUTOFF, and in the Cutoff Flow field, enter the value F.
If PipeA should receive all flow until its capacity is reached, at which point PipeB should be start receiving flow, enter the label for PipeB in the Diverted Link field, and adjust Type to OVERFLOW using the drop-down on the left. No other parameters are needed for this case.
If the diverted flow going to PipeB is dependent on the total flow, enter the label for PipeB in the Diverted Link field, and adjust Type to TABULAR using the drop-down on the left. In the Curve Name field, double-click to open the Curve Editor. This opens in a new window and contains a table to define the relationship between the diverted flow and the total flow. Tips for defining curves are provided below.
Finally, if the diverted flow going to PipeB would be most accurately computed using a weir equation, enter the label for PipeB in the Diverted Link field, and adjust Type to WEIR using the drop-down on the left. The Minimum flow field, Maximum depth field and Coefficient field will all contain zeros by default. To edit these values, click in the field, type a new value, then press the Enter key on your keyboard.
Top Tips to Define Curves
If no curve is defined and the field is shown blank, we recommend double-clicking the field to open the Curve Editor and entering a name for your curve, alongside the data required. It is also possible to name your curve in the field initially before double-clicking on this name, however the name then must be provided a second time in the Curve Editor window.
If you have previously defined a curve (and so a curve name is provided in the field), you can double-click the name to edit the details.
If you would like to define a new curve whilst retaining the previous curve, click in the field and use the Backspace key to delete the name so the field is blank. Then double-click to enter the Curve Editor, and enter your curve details (with a new name!) When you return to the Divider node properties, you will now notice your previous curve and new curve are both available from the drop-down.
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