The Sanitary Mode Job Control dialog defines data that is global to the whole Sanitary Mode simulation, and controls the simulation process.

The following sections describe the Sanitary mode job control parameters.


The first title line is shared between all SWMM modules. The second title line is reserved for the Sanitary Layer only.

Pollutant List (Sanitary Layer)

This flag and the associated dialog allows the definition of the list of pollutants to be used in the simulation. If this flag is OFF, no pollutant routing is done. If this flag is ON, a list of pollutants is selected from the items defined in the Pollutants Global Database.

The pollutants to be used are chosen from those defined in the 'Pollutants' Global Database. Any number of pollutants may be defined, but a maximum of 20 may be used in any particular simulation. (This is the typical configuration but if errors are encountered the SWMM.PAR file should be checked for the actual maximum number allowed). To add a pollutant to the "Use Pollutants" list, highlight the pollutant required in the Pollutant list (left-hand list), then select the "Add" button. To remove a pollutant from the list select the pollutant from the "Use Pollutants" list (right-hand list) and click "Delete."


The Evaporation flag controls whether evaporation data will be defined. Evaporation data is applied for both Sanitary and Hydraulics mode, and is only required if a Storage/Treatment plant (or BMP) or Storage Node is defined in the network.

Evaporation data is used within detention units in storage/treatment plants (BMP) and by Sanitary storage nodes.

Evaporation can also be computed in Hydraulics mode if the Evaporation is enabled and the configuration parameter HDR_EVAP is used. In this case all nodes have evaporation computed based on node area. Since manholes have a small area negligible evaporation occurs from them and storage nodes such as lakes and ponds have appreciable amounts of evaporation computed. Total evaporation from nodes is reported in the output file in Table E19

Monthly evaporation rates are required to correct for evaporation from storage treatment detention units.

Note that this data is not shared with the Runoff module, and must be re-entered.

If the configuration parameter POLLUTANT_EVAP is used, then all pollutants in the simulation can be lost proportionally through evaporation. Since the 2012 version the pollutants are no longer lost through evaporation and the use of the parameter allows backwards compatibility.

Monthly Pan Evaporation. Pan Evaporation Data is input as average values for each month in./day [mm/day]. This data is only required if there are detention units in any storage/treatment plant or a storage node defined within the network. Values of evaporation only need to be entered for the months during which the simulation occurs; others may be left blank.

Gauged Pollutant List

This flag and the associated dialog allows the definition of the list of pollutants to be used in the Gauged Pollutant List. If this flag is OFF, no gauge pollutants are shown. If this flag is ON, a list of pollutants is selected from the list of gauged pollutants shown in the Pollutants Global Database.

The pollutants to be used are chosen from those defined in the Pollutants Global Database. Any number of pollutants may be defined. To add a pollutant to the "Use Pollutants" list, highlight the pollutant required in the Pollutant List (left-hand list), then select the "Add" button. To remove a pollutant from the list, select the item from the left-hand column, and click the "Delete" button.

The pollutant load and concentrations may be generated in the Hydraulics, Runoff or Sanitary Layer, or read from an interface file.

Sewer Infiltration

This flag controls whether sewer infiltration will be simulated. If this flag is OFF, no wet-weather infiltration of sewer drains will be assumed to occur. If this flag is ON, catchment-wide characteristics are selected from the Sewer Infiltration Global Database. The total catchment sewer infiltration is distributed amongst individual conduits.

Dry Weather Sewer Inflow (Global DWF)

This flag controls whether dry-weather sewage inflow will be generated. If this flag is OFF, no sewage inflow calculation will be performed, although inputs can still be entered directly at nodes. If this flag is ON, associated data requirements at nodes will be required, and computations will be performed to generate dry-weather sewer inflows. Additionally, an overall Dry Weather Flow characteristic must be selected from the Dry Weather Flow Global Database. This database type deals with temporal variations of generated sewer flows and pollutant concentrations, certain land use characteristics, and gauged results to compare against for the total catchment.

Removal Equation Variables

This flag allows the definition of variable names to be used in removal equations for Storage/Treatment plants. This flag needs to be ON if there are any Storage/Treatment plants (or BMP's) in the network, otherwise it may be OFF.

The dialog contains the variable names to be used when constructing removal equations for a Storage/Treatment plant. The variables are completely user-definable, but it is recommended that short mnemonics be used to identify the combination of pollutant name and variable type.

The pollutants that appear in this dialog are those from the Pollutants list. Each variable name must be defined and unique. The variable names may be any combination of ASCII characters, without embedded spaces.

 Pollutant. Contains the list of the Sanitary Layer Pollutants, defined in the 'Use Pollutants' list in Job Control.

Initial Concentration. Contains the user-defined variable names representing Initial Concentrations for each pollutant. It is recommended that the variable name be a short mnemonic, perhaps comprising the prefix "IC" followed by a pollutant mnemonic.

Concentration. Contains the user-defined variable names representing Concentrations for each pollutant. It is recommended that the variable name be a short mnemonic, perhaps comprising the prefix "C" followed by a pollutant mnemonic.

Removal Fraction. Shows the user-defined variable names representing Removal Fractions for each pollutant. It is recommended that the variable name be a short mnemonic, perhaps comprising the prefix "R" followed by a pollutant mnemonic.

DO Cycle Simulation

Time Control

This button, and the related dialog, provides for simulation periods and other flow routing control parameters such as convergence tolerance and iteration limits that must be defined.

If the simulation period is greater than that defined in any input SWMM Interface Files, the simulation ends earlier, controlled by the Interface File. Although there is no limit on the simulation length, output is geared towards single events; daily or monthly totals are not printed and zeroes are not suppressed. Also, the start of simulation may be superseded by that in any input SWMM interface file.

Dry days before Start

The total number of dry days prior to the simulation during which solids were not flushed from the system. This allows an initial settled mass in each conduit to be computed at the start of the simulation for subsequent scour/deposition calculations.

Time Step

Size of the time step for computation in the simulation (seconds). The Sanitary Layer uses a constant time step. The size of the time step does not have to correspond to that of another module, eg. Runoff, or of that defined in input SWMM Interface Files. If the time step is not the same for other modules the input hydrograph and pollutograph ordinates are estimated by linear interpolation of the input series on the Interface File. Interpolation is simplified if the time step is an integer multiple or integer fraction of the Interface File time step. If the Interface File contains a variable time step, the shortest of the variable time steps should be used to compute the integer fraction.

Sensitivity tests show that the Sanitary Layer is fairly insensitive to time step size, except for very small values (10 sec). Between values of 2 minutes and 30 minutes, hydrograph ordinates varied by less than 1%. For very short time steps, the peak flow moved downstream faster and showed some attenuation. Note that continuity errors can occasionally arise if the time step is longer than about twice the travel time through any conduit.

Simulation Start/End 

Enter the Year, Month, Day, Hour, Minute, and Second of the simulation start and end. 

Routing Details

These parameters deal with accuracy and control of the flow routing algorithms employed.

Number of Iterations. This defines the maximum number of iterations allowed in conduit flow routing. This parameter helps to eliminate flow oscillations. Flatter pipe slopes (less than 0.1%) require more iterations in the flow routing simulation to help dampen these oscillations. Four iterations have proven to be sufficient in most cases.

Convergence Tolerance. The allowable error for convergence of iterative methods in the routing procedures (dimensionless). Convergence of the flow routing procedure should not normally be a problem. The default value of 0.0001 will provide sufficient accuracy with marginal extra computational effort. Convergence problems may occur when flow enters a dry conduit, which may occur at the beginning of a storm with little or no baseflow. In this case, warning messages describing the problem will be printed if the ‘Print Error Messages’ flag in the ‘Print Control’ dialog is ON. Continuity errors resulting from this condition are usually very small (a fraction of a percent).

Print Control (Sanitary Layer)

This dialog deals with control of the output sent to the text output file during a Sanitary Layer simulation.


Print Every 'x' Time Steps

This option results in printing input data and results at each element at each specified time step. The value entered is the number of time steps between printouts.

Print Total Loads and Moments Only -

This option results in only the loads and moments for each element being printed. Results during the simulation are not printed.

Include Inflow in Input Hydrograph Printouts

Echo inflow hydrographs in the output file.

Print Error Messages

This flag controls the generation of error messages occurring during the flow routing simulation. Such errors may result from non-convergence conditions, for example. Except in unusual cases, these errors will only indicate that a small continuity error has occurred. These can usually be cured by shortening the time step. If this flag is OFF, messages are suppressed, otherwise they are printed.

Print Conduit Hydraulic Properties

This flag controls the printing of flow routing parameters for any of the conduits that may be simulated. If this flag is OFF, the printout will be suppressed, otherwise about 500 lines of output will be generated. The output comprises normalized hydraulic properties for each conduit type.

Save ALL Results for Review

This flag will save all the results for nodes and conduits from analysis to a special file for later graphical post-processing.


This button and dialog provides for the definition of additional Job Control Options required for the simulation.

Kinematic Viscosity

This flag controls the definition of kinematic viscosity for water. This parameter is used to calculate the settling of particles transported in conduits throughout the sewer system. Kinematic viscosity is only required if any pollutant used in the simulation has a scour/deposition relation, as defined in the Pollutants Global Database. If this flag is OFF, the internal default of 1E-5 ft^2/sec [1E-2 cm^2/sec] will be used. If this flag is ON, the value entered in the adjacent field will be used.  

Total Catchment Area

This flag controls whether a total catchment area, in acres or hectares, is to be entered. Entering a total catchment area is only required if dry-weather flow is being modelled, and an input SWMM Interface File is not used. If a SWMM Interface File is used, this value will be ignored and data from the Interface file is used.

Design Undersized Conduits

This flag controls whether a conduit will be resized automatically by the model if it has insufficient flow carrying capacity. When a surcharge condition is encountered (flow exceeds full flow capacity), the conduit is increased in size in 6-inch [150 mm] increments of diameter (for circular pipes, or width for rectangular conduits), until capacity exists to accept the flow. Conduits that are neither circular nor rectangular will be converted to circular if they need to be resized. A message is printed indicating the resizing, and a table of final conduit dimension is printed at the end of the simulation.

The design operation will effectively eliminate surcharging but will also minimize in-system storage within manholes, etc. The net effect is to increase hydrograph peaks at the downstream end of the system. This can create a conflict between controls aimed at curing in-system hydraulic problems, and controls aimed at pollution abatement procedures at the outfall that make use of in-system storage.

Design parameters include: Percent of Full [conduit] Depth (%), Minimum Freeboard (ft, m), Minimum Cover (ft, m) and Maximum number of Barrels [i.e. duplicate conduits].