Porous Polygon Data Fields (SWMM)

Porous Polygon data can be edited on either the Porous Polygon Grid Window of the Polygons Grid or the Porous Polygon Property Sheet.

The following describes all the data which can be used to define a Porous Polygon.

Common Data Fields

Fields that are common to the majority of objects can be found in the Common Fields topic.

Porous Polygon Data

Database Table Name: sw_porous_polygon

Show Columns	Database Names
	Size, Type and Units
	Defaults and Error Limits

Field Name

Help Text

Database Field

Data Type

Size

Units

Precision

Default

Error Lower Limit

Error Upper Limit

Warning Lower Limit

Warning Upper Limit

Porous Polygon

The name used to identify this polygon.

polygon_id

Text

Asset ID

For reference only. Designed as a reference to an asset database, but could be used for anything.

asset_id

Text

Area

Polygon area. Default value calculated from polygon geometry.

area

Single

Porosity

Porosity factor between 0 and 1, where 0 represents impermeable and 1 represents fully permeable.

porosity

Double

0.0

Crest level

Type of wall.

Note that a porous polygon collinear with the boundary of a 2D zone, will override the boundary condition of the 2D zone along the coincident portion of the boundary. The coincident portions of the polygon are considered infinitely high, regardless of any crest level specified.

Database Value	Description	Help Text
Infinite	Infinite	Wall is considered to be an infinitely high barrier.
Height	Height	The height of the wall (above ground level) is specified in the Height field.
Level	Level	The level of the wall (above datum) is specified in the Level

crest_level

Text

Infinite

Height

Enabled if Crest level of type Height is selected.

Height of the top of the wall from ground level.

For each segment of wall, this is the height above the highest of the ground levels of the two computational elements either side of the wall.

height

Double

0.0

Level

Enabled if Crest level of type Level is selected.

Height above datum of the top of the wall.

level

Double

0.0

Remove wall during simulation

Collapse option for wall:

Database Value	Description	Help Text
Never	Never	Wall never collapses.
Fully	Fully	The entire length of the wall collapses when the wall removal threshold is met in any of the mesh elements adjacent to the wall.
Partially	Partially	When the wall removal threshold is met in a mesh element adjacent to the wall, the length of the wall adjacent to the mesh element collapses.

remove_wall

Text

Never

Wall removal trigger

Variable used to determine when wall is collapsed. This trigger variable relates to the 2D results in the mesh elements adjacent to the wall face.

Database Value	Description	Help Text
Depth	Depth	Depth of water in mesh elements adjacent to wall.
Elevation	Elevation	Water surface elevation of mesh elements adjacent to the wall.
Velocity	Velocity	Velocity in mesh elements adjacent to the wall, in the normal direction to the wall.
Unit flow	Unit flow	Flow per unit of length in mesh elements adjacent to wall, in the normal direction to the wall.
Total head	Total head	Total head in the normal direction to the wall, in adjacent elements to the wall multiplied by the Hydrostatic pressure coefficient. Total head is calculated as: V = A x H Where: H = h + u2/(2g) V(m): Corrected head A: Hydrostatic pressure coefficient H(m): total head h(m): depth u(m/s): normal velocity to the wall g(m/s2): gravity
Force per unit length	Force per unit length	Total force per unit length in the normal direction to the wall, in adjacent elements to the wall. Force per unit length is calculated as: F = A x 0.5 x ρgH2 Where: F(kN/m): Force per unit length A: Hydrostatic pressure coefficient H(m): total head ρ(Tm/m3): water density g(m/s2): gravity

wall_removal_trigger

Text

Depth

Use difference across wall

Check this option to determine when the wall collapses by calculating the difference in the Wall removal trigger variable between the two elements on either side of the wall.

If this option is not checked, wall collapse will be determined by value of trigger variable in any of the mesh elements adjacent to the wall.

use_diff_across_wall

Boolean

Depth threshold

Enabled when Wall removal trigger is set to Depth.

When the Use difference across wall option is not selected: the wall is collapsed if the depth of water in any of the mesh elements adjacent to the wall exceeds the Depth threshold.
When the Use difference across wall option is selected: the wall is collapsed when the difference between the water depths of the two elements adjacent to the wall exceeds the Depth threshold.

depth_threshold

Double

0.0

Elevation threshold

Enabled when Wall removal trigger is set to Elevation.

When the Use difference across wall option is not selected: the wall is collapsed if the water surface elevation in any of the mesh elements adjacent to the wall exceeds the Elevation threshold.
When the Use difference across wall option is selected: the wall is collapsed when the difference between the water surface elevation of the two elements adjacent to the wall exceeds the Elevation threshold.

This only applies if at least one of the adjacent elements is wet.

elevation_threshold

Double

0.0

Velocity threshold

Enabled when Wall removal trigger is set to Velocity.

When the Use difference across wall option is not selected: the wall is collapsed if the normal velocity to the wall in any of the mesh elements adjacent to the wall exceeds the Velocity threshold.
When the Use difference across wall option is selected: the wall is collapsed when the difference between the velocity normal to the wall of the two elements adjacent to the wall exceeds the Velocity threshold.

velocity_threshold

Double

0.0

Unit flow threshold

Enabled when Wall removal trigger is set to Unit flow.

When the Use difference across wall option is not selected: the wall is collapsed if the flow per unit length normal to the wall in any of the mesh elements adjacent to the wall exceeds the Unit flow threshold.
When the Use difference across wall option is selected: the wall is collapsed when the difference between the flow per unit length normal to the wall of the two elements adjacent to the wall exceeds the Unit flow threshold.

unit_flow_threshold

Double

0.0

Total head threshold

Enabled when Wall removal trigger is set to Total head.

When the Use difference across wall option is not selected: the wall is collapsed if the corrected total head in the normal direction to the wall in any of the mesh elements adjacent to the wall exceeds the Total head threshold.
When the Use difference across wall option is selected: the wall is collapsed when the difference between the corrected total head normal to the wall of the two elements adjacent to the wall exceeds the Total head threshold.

Corrected total head is calculated by the following equation:

V = A x H

Where:

H = h + u2/(2g)

V(m): Corrected head

A: Hydrostatic pressure coefficient

H(m): total head

h(m): depth

u(m/s): normal velocity to the wall

g(m/s2): gravity

total_head_threshold

Double

0.0

Force threshold

Enabled when Wall removal trigger is set to Force per unit length.

When the Use difference across wall option is not selected: the wall is collapsed if the force per unit length in the normal direction to the wall in any of the mesh elements adjacent to the wall exceeds the Force threshold.
When the Use difference across wall option is selected: the wall is collapsed when the difference between the force per unit length normal to the wall of the two elements adjacent to the wall exceeds the Force threshold.

Force per unit length is calculated as:

F = A x 0.5 x ρgH2

Where:

F(kN/m): Force per unit length

A: Hydrostatic pressure coefficient

H(m): total head

ρ(Tm/m3): water density

g(m/s2): gravity

force_threshold

Double

0.0

Hydrostatic pressure coefficient

Multiplying factor applied when using Total head or Force per unit length as the Wall removal trigger.

hydro_press_coeff

Double

1.0

No rainfall

Used to control whether porous polygon receives any rainfall.

If this option is checked, (when polygon represents a building for example), any rain that falls on the porous polygon will be received by the subcatchment and flow directly into the drainage system. Similarly, the porous polygon will not evaporate any water (because the flood water will be inside the building).

no_rainfall

Boolean