# Point connections for coupling 1D-2D models

Describe point coupling as a method of combining 1D and 2D models, and identify relevant build and result checks.

When combining 1D and 2D river models, exchange of flow between 1D and 2D systems can only take place at specific objects.

To accurately represent exchange of flow, select an approach appropriate for mechanism and scale of model.

Point coupling takes place between single element and node object.

Typically used in locations with manholes, gullies, or outfalls.

Link between 2D elements and 1D nodes is made up of point connections.

### Nodes with 2D Flood Types:

2D nodes are used to model exchange of flood water between collection system and 2D meshed area.

Node types defined as 2D nodes:

• Manhole (with flood type set to 2D, Gully 2D, or Inlet 2D)
• Outfall 2D
• Connect 2D

By default, interaction between 1D and 2D nodes is based on depth values.

### Manhole: Gully 2D:

Manhole node with flood type set to Gully 2D allows you to define head-discharge relationship.

Allows flexibility to define flow characteristics you want to represent for any structure, inlet, or outlet.

For example, can be used to minimize flow into sewer system from surface.

### Manhole: Inlet 2D:

Can use additional equations and parameters to represent inlets in an ICM network.

Using Inlet 2D flood type allows you to define a head-discharge curve.

Additionally, can specify simplified equation using A and B parameters.

Define flow efficiency parameters, or specify inlet parameters based on FHWA equations.

### 1D-2D Nodes Build Checks:

Three important questions to ask when converting 1D nodes to 2D nodes:

Is the 1D-2D flow exchange appropriate?

• Consider linkage type selected and system to be used.
• 2D flood type may be appropriate for storm system with inlets not modelled explicitly, but probably is not appropriate for a foul or sanitary network—would let too much unrestricted flow into network.

Are the node locations appropriate?

• Common issue with nodes is processing of ground model.
• Despite correct node location, smoothing or cleaning of ground model may mean that true ground height is not represented at that location.
• May need to adjust node location slightly, within element that reflects true ground level.

Are the 1D-2D ground levels sufficiently aligned?

• Ideally, equivalent.
• At best, should have reasonable alignment within a foot, with higher accuracy in areas of interest.

### 1D-2D Nodes Results Checks:

For 2D nodes, check results for instances of flow limiting—may indicate that representation is not appropriate.

When modelling 2D inlets, flow capping can limit exchange between 2D and 1D network, where inflow at node would exceed volume contained in 2D element at any given timestep.

May occur if inlet node is located in a 2D element that is too small.