Model Parameters Options (SWMM)

To view and edit the parameters that define which options are to be used primarily for modelling a SWMM network, select Model parameters | Options from the Model menu. These options will be displayed in a Property Sheet.

The Object Properties Window for Model Parameters Options contains the following information:

Database Table Name: sw_options

Show Columns

Database Names

Size, Type and Units

Defaults and Error Limits

Field Name

Help Text

Database Field

Data Type

Size

Units

Precision

Default

Error Lower Limit

Error Upper Limit

Warning Lower Limit

Warning Upper Limit
Network flow units

The type of flow units which are to apply to the SWMM network. Options are:

  • CSF (Cubic feet per second) (default)
  • GPM (Gallons per minute)
  • MGD (Million gallons per day)
  • CMS (Cubic meters per second)
  • LPS (Liters per second)
  • MLD (Million liters per day)
units Text 4   0 CFS        
Allow ponding

The check box which indicates whether or not excess water is allowed to collect above nodes and be re-introduced into the system as conditions permit. Unchecked (no ponding) by default.

Note that ponding will only occur at a Junction node if a non-zero value is set for its Ponded area parameter.

 allow_ponding Boolean     0 False        
Infiltration model

Specifies how the infiltration of rainfall into the upper soil zone of a subcatchment is to be modelled. The options are:

Further information about the infiltration models can also be found in the SWMM5 Reference Manual, Volume 1 - Hydrology.

The infiltration model chosen in this field is default for all subcatchments included in a SWMM network. However, it also is possible to set a different infiltration model for individual subcatchments using the Infiltration model parameter in the applicable subcatchment properties.

 infiltration Text 32   0 Horton        
Force main equation

Determines which equation will be used to compute friction losses during pressurised flow for conduits with their Shape set to Force_main. The options are:

  • H-W - Hazen-Williams equation (default)
  • D-W - Darcy-Weisbach equation
 force_main_equation Text 4   0 H-W        
Inertial damping

Determines how the inertial terms in the St. Venant momentum equation is handled. Options are:

  • None (Keep) -maintains the inertial terms at their full value under all conditions
  • Partial (Dampen) - reduces the inertial terms as flow comes closer to being critical and ignores them when flow is supercritical (default)
  • Full (Ignore) - excludes the inertial terms from the momentum equation, essentially producing a Diffusion Wave solution
 inertial_damping Text 8   0 Partial        
Minimum conduit slope The minimum value allowed for a conduit's slope (%). If not set or 0 (default) then no minimum is imposed. min_slope Double   S 5 0 0      
Minimum nodal surface area The minimum surface area used for nodes when computing changes in water depth. If 0 is entered, then the default value of 1.167 m2 (12.56 ft2) is used. min_surfarea Double   NA 3 1.167 0      
Normal flow criterion

Specifies which condition is checked to determine if flow in a conduit is supercritical and should therefore be limited to the normal flow.

The options are:

  • Slope - checks if the water surface slope is greater than the conduit slope
  • Froude (Froude number) - checks that the Froude number is greater than 1.0
  • Both (Slope and Froude) - checks both conditions (default)
 normal_flow_limited Text 6   0 Both        
Head convergence tolerance

When the difference in computed head at each node between successive trials is below the specified value the flow solution for the current time step is assumed to have converged.

 head_tolerance Double   Y 4 0.0015 0      
Maximum trials per timestep Specifies the maximum number of trials that the SWMM engine uses at each time step to reach convergence when updating hydraulic heads at the conveyance system's nodes. The default value is 8. max_trials Long integer     0 8 0      

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