Understanding the flooding simulation engine

Step-by-step:

In InfoDrainage, the 1D - 2D Analysis uses a 1D simulation engine to calculate the flows in the pipes, manholes, and other structures below the ground in combination with a 2D simulation engine to predict flood flows across the catchment surface. This enables the program to represent the overflow from the sewer or channel network; the movement of the flooded water on the surface; and the re-entrance of the flooded water back into the sewer or channel network.

The 1D - 2D Analysis uses, in combination:

• A 1D simulation engine to calculate the flows in the pipes, manholes, and other structures below the ground.
• A 2D simulation engine to predict flood flows across the catchment surface.

Three areas in which the exchange between the two engines can happen:

• at manholes
• along the banks of open channels
• along the outline of stormwater controls

There are no limits on how many locations the water can be exchanged, or how many times the water is exchanged.

Note that in this example, the open channel, the pond, and the manhole do not need to be connected by the same 1D network; they can be connected to different outfalls.

The computation of the exchange between the 1D network and the 2D surface accounts for the respective heads at the location of the possible exchange. The flow exchanged is calculated using an orifice equation for the manholes, and a weir equation for the channel banks and pond outline.

The 1D - 2D Analysis is more computationally intensive than the 1D-only Analysis, due to the extra effort of running the 2D engine and the overhead of the exchange between the two engines.

Increase in analysis time depends on factors like:

• amount of water in the 2D domain.
• percentage of the 2D domain that is wet.
• how many locations the water is exchanged between the two engines.