2.2 Understanding the 2D Mesh (Zone) in InfoSWMM 2D

The 2D zone, alternatively described as a mesh, consists of a series of contiguous triangles, whose shared boundaries cover the catchment surface. The height of each point on each triangle is derived from a ground model GRID or TIN.

It is significant that the 2D zones are meshed, where the size and orientation of the triangles can be varied, rather than a grid, where the layout is fixed. Meshes allow more detail and complexity in locations only where it is needed.

Triangles are derived using the Shewchuk triangulation method (Shewchuck).

Each 2D zone must include a boundary and the characteristics of the triangles within the zone must be defined. The creation of a 2D zone is described below. A 2D zone can include the following elements:

· Porous Wall Polylines are polylines use to impede or prevent flow through them. A common application of these features are to model fences.

· Porous Polygons are polygons used to impede or prevent flow through them. A common application of these features are to model buildings.

· Break Polylines are lines along which mesh triangle boundaries must be created. These can be used to define the top of a ridge or the low point in a channel.

· Boundary Polylines are optional lines (but must be created coincident to 2D Simulation Polygon boundaries) and are used to alter boundary properties along the line.

· Mesh Polygons are polygons within the 2D Simulation Polygons (2D zones) where the triangles have different maximum triangle area. They are most commonly used to define smaller triangles in areas of greater complexity.

· Initial Conditions (IC) Polygons are polygons within the 2D Simulation Polygons (2D zones) where the area has specific initial depth and velocity conditions.

· Roughness Polygons are polygons within the 2D Simulation Polygons (2D zones) where the area has specific Manning's roughness that differs from the roughness value of the 2D Simulation Polygon.

· 2D Simulation Polygons are polygons that define the outer boundary of a 2D zone. 2D Mesh will only be generated within these boundaries and 2D simulation will also happen only within these boundaries.

Each object can be either created within InfoSWMM 2D, or created in a GIS and then

imported using the provided import tools.

2D zone triangles (2D Mesh) can be created once all the objects and the ground model

have been prepared.

The interaction with the below ground system whereby water floods from the manholes

on to the 2D zone and then possibly back into the manholes is also described below.

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