Utilizing the mesh editing objects
Discern which of the 2D mesh enhancing objects you need to use.
In ICM, there are several objects that can help to enhance a 2D mesh:
Roughness zones
Surface can be made up of many different land covers with different associated roughness values.
Within ICM, it is possible to spatially distribute the roughness to account for the variation in land roughness values.
Allows for varying the surface roughness of the 2D elements within a 2D zone. These can be imported as polygons or digitized on the GeoPlan window.
Roughness definitions
Instead of simply representing roughness as a single value, there are also roughness definitions that enable roughness to be defined as a function of depth.
The roughness value in the mesh elements changes dynamically during a simulation, according to the roughness definition.
Voided areas
A void or voided area is one that has no elements generated inside it and that no flow can pass through. Think of them as polygons with infinitely high vertical walls.
Features like storage and boundary polygons are automatically treated as voids when meshed to ensure that these areas are not double counted in both domains.
Can also be added to a model as polygons. These polygons must all have a common name in the Category field. In the Mesh 2D Zones dialog box, this category must be selected under Voids.
Can be used to represent buildings, to exclude areas from the mesh to simulate flow around buildings.
The advantage of this approach is that it can significantly reduce the number of elements in dense areas.
A disadvantage is that the depth outside of the building is assumed to be equal to the depth inside, and this can be difficult to query. Additionally, flow can become trapped against a void, especially if it is U-shaped and the depth can build up unnaturally.
Mesh zones
Can be used to divide a 2D zone into regions of different mesh resolution, allowing the model requirements to be streamlined.
Can be imported or manually digitized.
Can also be used to define zones in which ground level modification is required.
Often used to lower roads to represent this important flood channel where it is not adequately represented by the ground model.
This also ensures that elements lie within the boundary, as it is treated as a break line.
Mesh level zones
Can be used where mesh element elevations are to be modified based on ground level elevations or user-defined values.
Can be used to define specific zones in which ground levels are to be modified in the 2D mesh.
General lines
Can be used to model features that act as break lines or walls in a 2D zone.
When used to represent a break line during the mesh generation process, the line represents a fully permeable feature.
Purpose is to enforce the lines as mesh element edges.
When used to represent a wall during the mesh generation process, the line represents an infinitely high, impermeable wall – it is now recommended to use a Base Linear Structure (2D).
To use a general line or set of general line objects as a break line or wall, it must be assigned a unique category in the Mesh 2D Zones dialog box.
Porous wall objects
Porous wall objects are line objects used as part of the mesh generation process.
Porous polygon objects are polygons representing enclosed walls.
These two sets of objects share parameters with a specified porosity and height that are considered during the 2D simulation process.
For InfoWorks networks, the porous wall functionality has been replaced by the Base Linear Structure (2D), but it is still available for backward compatibility.
It can be common to see buildings represented in areas of detail as a combination of mesh zones and porous polygons. The mesh zone is used to set the flood threshold level of the building. The porous polygon restricts flow into and out of the building without blocking it completely, as would happen due to windows, walls, and air bricks.
Buildings
Polygon objects used to represent rain falling onto a roof and entering the drainage system and/or remaining on the surface.
Also used to define an area where roughness, mesh levels, and porosity are applied within a 2D mesh. This prevents the need to represent these using multiple objects.
Each building will drain to either a single node, link, or 2D point source. Buildings include the ability to limit the discharge into the network and to place the excess flow onto the 2D.
Use the Single element box to choose whether the building is to be represented as a single element in the mesh.
Network results objects
Used to interrogate results in an InfoWorks network.
There are 3 network results objects:
- Network results point (2D): used to interrogate results at a point within a 2D mesh.
- Network results line (2D): used to interrogate results along a line within a 2D mesh.
- Network results polygon (2D): used to interrogate results in an area within a 2D mesh.
These objects require building into the mesh to ensure that the element faces are coincident to the line and polygon objects. That is, they are used as break lines.