The Urban Subcatchment Node
  • 23 Oct 2022
  • 2 Minutes to read
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The Urban Subcatchment Node

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Article Summary

Subcatchment nodes route rainfall to an outlet. When this outlet is a Junction node, this flow provides the Urban Inflow entering the subsurface system.

It can be specified how water falling should be routed through the pervious/impervious land types of the subcatchment, and the outlet can be another defined Subcatchment node.


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Rules of Subcatchment nodes

A Subcatchment node must have an Urban Rain Gage Node node assigned to provide the inflow. All Subcatchment nodes within an urban network must have the same infiltration method defined, although different parameters (e.g. representing different land types/uses) can be specified within the method.

Subcatchment label/name

The Subcatchment node name by default will be provided by parameters setup in the Urban Model Defaults menu.


The x and y coordinates of the Subcatchment node are shown in these fields. These values are automatically populated based on the node location on the map. The node icon will be placed in the centre of the subcatchment perimeter drawn.

Optional descriptors


This field allows for an optional text description. The field will be blank by default.


This field allows for an optional text tag, to allow you to categorise units. The field will be blank by default.

Rain Gage/Outlet

Rain Gage

The label of the Rain Gage providing the inflow to the Subcatchment node.


The label of the Junction node or Subcatchment node receiving the calculated runoff.

Area parameters


The area of the subcatchment in acres or hectares. This will be calculated automatically when the subcatchment perimeter is drawn if the default area is set to zero in the Urban Model Defaults menu.


The width of the subcatchment in feet or meters - the overland flow path for sheet flow runoff. 

% Slope

Average slope of the subcatchment, as a percentage.

Impervious parameters

All of these parameters relate to the impervious areas of a subcatchment. A percentage of the land that is impervious can be provided, alongside the Manning's n value and depth of depressive storage for both the pervious and impervious parts.

Routing options

Subarea Routing

Option for internal routing within the subcatchment. Select from:

PERVIOUS - route from impervious areas to pervious areas

IMPERVIOUS - route from pervious areas to impervious areas

OUTLET - route from both impervious and pervious areas directly to subcatchment outlet.

Percent Routed

Percentage of runoff to be routed.

Infiltration methods

The infiltration method to be used. The 3 dots to the right of the field enable access to the Infiltration Parameters window for specifying the infiltration parameters to be used. We refer the user to the EPA Manual for further details.


Specify groundwater details for use within the urban simulation. We refer the user to the EPA Manual for further details.

Unused parameters

These parameters are all unused by Flood Modeller at this time, however any previously defined methods will be unaffected. We refer the user to the EPA Manual for further details. 

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