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Marios Kyriakou edited this page Sep 27, 2015 · 1 revision


Defines various simulation options.


UNITS                        CFS/GPM/MGD/IMGD/AFD/
HEADLOSS                   H-W/D-W/C-M
HYDRAULICS               USE/SAVE filename
QUALITY                     NONE/CHEMICAL/AGE/TRACE id
VISCOSITY                 value
DIFFUSIVITY              value
TRIALS                       value
ACCURACY                   value
PATTERN                     id
TOLERANCE                  value
MAP                             filename


UNITS sets the units in which flow rates are expressed where:
    CFS     =     cubic feet per second
    GPM     =     gallons per minute
    MGD     =     million gallons per day
    IMGD    =     Imperial MGD
    AFD      =     acre-feet per day
    LPS      =     liters per second
    LPM      =     liters per minute
    MLD      =     million liters per day
    CMH      =     cubic meters per hour
    CMD      =     cubic meters per day

For CFS, GPM, MGD, IMGD, and AFD other input quantities are expressed in US Customary Units. If flow units are in liters or cubic meters then Metric Units must be used for all other input quantities as well. (See Units of Measurement). The default flow units are GPM.

HEADLOSS selects a formula to use for computing head loss for flow through a pipe. The choices are the Hazen-Williams (H-W), Darcy-Weisbach (D-W), or Chezy-Manning (C-M) formulas. The default is H-W.

The HYDRAULICS option allows you to either SAVE the current hydraulics solution to a file or USE a previously saved hydraulics solution. This is useful when studying factors that only affect water quality behavior.

QUALITY selects the type of water quality analysis to perform. The choices are NONE, CHEMICAL, AGE, and TRACE. In place of CHEMICAL the actual name of the chemical can be used followed by its concentration units (e.g., CHLORINE mg/L). If TRACE is selected it must be followed by the ID label of the node being traced. The default selection is NONE (no water quality analysis).

VISCOSITY is the kinematic viscosity of the fluid being modeled relative to that of water at 20 deg. C (1.0 centistoke). The default value is 1.0.

DIFFUSIVITY is the molecular diffusivity of the chemical being analyzed relative to that of chlorine in water. The default value is 1.0. Diffusivity is only used when mass transfer limitations are considered in pipe wall reactions. A value of 0 will cause EPANET to ignore mass transfer limitations.

SPECIFIC GRAVITY is the ratio of the density of the fluid being modeled to that of water at 4 deg. C (unitless).

TRIALS are the maximum number of trials used to solve network hydraulics at each hydraulic time step of a simulation. The default is 40.

ACCURACY prescribes the convergence criterion that determines when a hydraulic solution has been reached. The trials end when the sum of all flow changes from the previous solution divided by the total flow in all links is less than this number. The default is 0.001.

UNBALANCED determines what happens if a hydraulic solution cannot be reached within the prescribed number of TRIALS at some hydraulic time step into the simulation. STOP will halt the entire analysis at that point. CONTINUE will continue the analysis with a warning message issued. CONTINUE n will continue the search for a solution for another n trials with the status of all links held fixed at their current settings. The simulation will be continued at this point with a message issued about whether convergence was achieved or not. The default choice is STOP.

PATTERN provides the ID label of a default demand pattern to be applied to all junctions where no demand pattern was specified. If no such pattern exists in the [PATTERNS] section then by default the pattern consists of a single multiplier equal to 1.0. If this option is not used, then the global default demand pattern has a label of "1".

The DEMAND MULTIPLIER is used to adjust the values of baseline demands for all junctions and all demand categories. For example, a value of 2 doubles all baseline demands, while a value of 0.5 would halve them. The default value is 1.0.

EMITTER EXPONENT specifies the power to which the pressure at a junction is raised when computing the flow issuing from an emitter. The default is 0.5.

MAP is used to supply the name of a file containing coordinates of the network's nodes so that a map of the network can be drawn. It is not used for any hydraulic or water quality computations.

TOLERANCE is the difference in water quality level below which one can say that one parcel of water is essentially the same as another. The default is 0.01 for all types of quality analyses (chemical, age (measured in hours), or source tracing (measured in percent)).


  1. All options assume their default values if not explicitly specified in this section.
  2. Items offset by slashes (/) indicate allowable choices.


UNITS       CFS 
QUALITY     TRACE  Tank23 
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