2D Parameters Dialog (SWMM)

Depth

Depth threshold used to determine whether to consider a mesh element wet or dry.

Mesh elements with depth of water below this value will be considered dry and a zero depth will be displayed in the results.

Only mass conservation will be considered in elements with depth below this threshold.

Typical value: 0.001 m

Default value: 0.001 m

Momentum

Depth threshold used to determine whether to consider momentum in a mesh element or not.

Movement of water will not be calculated for mesh elements with depth of water below this value; only mass conservation will be taken into account.

Typical value: 0.001-0.01 m

Default value: 0.001 m

Velocity

Velocity threshold.

Mesh elements with water velocity below this value will have velocity reset to zero in terms of momentum calculations.

Typical value: 0 m/s

Default value: 0 m/s

Timestep Stability Control

This parameter ensures that the internal timestep used by the 2D engine is within the stability bounds given by the CFL condition (Courant Friedrichs Lewy condition).

Valid values: 0 < TSC < 1

Typical value: 0.95

Maximum Velocity

Velocity threshold limiting the velocities that can be achieved in an element in a 2D simulation.

Mesh elements with water velocity above this value will have velocity reset to the maximum specified.

Typical value: 10 m/s

Theta

Weighting factor, θ, for the semi-implicit parameter. Weights the explicit and semi-implicit parts of the numerical scheme used for the time integration of the flow equations.

The higher the value, the more weight given to the implicit part.

Valid values: 0 < θ ≤ 1

Typical value: 0.9

Inundation mapping depth threshold

Depth threshold used to determine Time to first inundation for mesh elements.

Time to first inundation is reported as the time (from the start of the simulation) at which water depth in the mesh element first exceeds this threshold.

Default value 0.01m

The initial state interpolation search radius. Used when calculating initial state values for 2D mesh elements from an Initial State Simulation.

See See Initial State Interpolation for details.

Default value: 100

The initial state interpolation weighting exponent. Used when calculating initial state values for 2D mesh elements from an Initial State Simulation.

See See Initial State Interpolation for details.

Default value: 2

Displayed for on-premise runs

Options for using a graphics card to perform 2D calculations:

• If suitable card is available - Default setting for all new runs.

  Use a GPU card for 2D calculations if a suitable card is available, otherwise default to CPU. A message will be displayed in the log to indicate if suitable GPU card has not been found.

• Never - Do not attempt to use GPU card for 2D calculations.
• Always - Always attempt to use GPU card for 2D calculations. An error will occur if a suitable GPU card is not found.

Displayed for cloud runs

Options for using a GPU instance to perform 2D calculations:

• If optimal for selected network (recommended) - Default setting for all new runs.

  The software determines if a simulation is suitable to run on a GPU instance.

  If suitable, a 2D simulation is submitted to a GPU instance, otherwise it will be submitted to a CPU instance. A message is displayed in the simulation log if a 2D simulation fails to run on a GPU instance.

• Never - Never use a GPU instance for 2D simulations. A 2D simulation is submitted to a CPU instance.
• Always - Always use a GPU instance for 2D simulations. A message is displayed in the simulation log if a 2D simulation fails to run on a GPU instance.