SWMM5 globals.h Summary

 Below is a step-by-step explanation of globals.h, which contains global variables shared across EPA SWMM5. These variables store the current state of an SWMM simulation, including file handles, simulation options, time parameters, and large arrays for subcatchments, nodes, links, etc.

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1. Header and Update History

//   globals.h
//   Project: EPA SWMM5
//   ...
//   Global Variables
//   ...

• The header comment explains that this file holds global variables for the SWMM project.
• The update history lines describe changes in different builds of SWMM (like added or modified variables).

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2. Include Guard

#ifndef GLOBALS_H
#define GLOBALS_H
...
#endif //GLOBALS_H

• Prevents multiple inclusion errors if globals.h is included in more than one source file.

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3. Global File Handles (TFile)

EXTERN TFile
  Finp, Fout, Frpt, Fclimate, Frain, Frunoff, Frdii,
  Fhotstart1, Fhotstart2, Finflows, Foutflows;

• Each TFile object references a file used by SWMM:
  1. Finp: The primary input file (the .inp format).
  2. Fout: The binary results file (internal format).
  3. Frpt: The report file (the .rpt text output).
  4. Fclimate: The climate file (daily temperature, evaporation, wind speed, etc.).
  5. Frain: A rainfall interface file (external format).
  6. Frunoff: A runoff interface file (converting subcatchment runoff to routing).
  7. Frdii: The RDII inflow file (rainfall-derived infiltration/inflow).
  8. Fhotstart1 & Fhotstart2: The hotstart files for saving/initializing states.
  9. Finflows & Foutflows: Additional interface files for inflows/outflows.

EXTERN means these variables are declared as external to be defined once in another .c file (usually globals.c).

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4. Simulation Counters and Text Buffers

EXTERN long
  Nperiods, TotalStepCount, ReportStepCount, NonConvergeCount;

EXTERN char
  Msg[MAXMSG+1],
  ErrorMsg[MAXMSG+1],
  Title[MAXTITLE][MAXMSG+1],
  TempDir[MAXFNAME+1],
  InpDir[MAXFNAME+1];

• Nperiods: Number of times the program saves results (reporting periods).
• TotalStepCount, ReportStepCount: Count how many times steps SWMM has performed in routing, and how many of those were at reporting intervals.
• NonConvergeCount: Number of time steps that failed to converge in dynamic wave.
• Msg[] and ErrorMsg[]: Buffers for storing text messages or error messages.
• Title[][]: Up to MAXTITLE lines of project title text.
• TempDir and InpDir: Directories used for temporary files or the input file’s directory.

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5. Reporting Flags and Object Counts

EXTERN TRptFlags RptFlags; // Reporting options

EXTERN int
  Nobjects[MAX_OBJ_TYPES],
  Nnodes[MAX_NODE_TYPES],
  Nlinks[MAX_LINK_TYPES],
  ...

• RptFlags: A structure controlling which data SWMM reports.
• Nobjects[]: how many objects (gages, subcatchments, nodes, links, etc.) appear.
• Nnodes[] and Nlinks[] store how many node or link sub‐types (like outfalls or pumps) exist.

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6. Major Simulation Options / Flags

EXTERN int
  UnitSystem,
  FlowUnits,
  InfilModel,
  RouteModel,
  ForceMainEqn,
  LinkOffsets,
  SurchargeMethod,
  AllowPonding,
  InertDamping,
  NormalFlowLtd,
  SlopeWeighting,
  Compatibility,
  SkipSteadyState,
  IgnoreRainfall,
  IgnoreRDII,
  IgnoreSnowmelt,
  IgnoreGwater,
  IgnoreRouting,
  IgnoreQuality,
  ErrorCode,
  Warnings,
  WetStep,
  DryStep,
  ReportStep,
  RuleStep,
  SweepStart, SweepEnd,
  MaxTrials,
  NumThreads,
  NumEvents;

Each integer configures a major piece of SWMM logic:

• UnitSystem: US or SI.
• FlowUnits: CFS, GPM, CMS, etc.
• InfilModel: infiltration method (Horton, Green-Ampt, etc.).
• RouteModel: routing method (None, Kinematic Wave, Dynamic Wave).
• ForceMainEqn: Hazen-Williams or Darcy-Weisbach for force mains.
• LinkOffsets: depth vs. elevation offset.
• SurchargeMethod: EXTRAN or Preissmann slot.
• AllowPonding: node ponding.
• InertDamping, NormalFlowLtd, SlopeWeighting, Compatibility, SkipSteadyState: advanced dynamic wave or compatibility options.
• IgnoreRainfall, IgnoreRDII, IgnoreSnowmelt, IgnoreGwater, IgnoreRouting, IgnoreQuality: skip certain processes.
• ErrorCode: tracks the last error code.
• Warnings: number of warnings issued so far.
• WetStep, DryStep, ReportStep, RuleStep: time steps (seconds) for runoff and reporting.
• SweepStart, SweepEnd: day of year for street sweeping.
• MaxTrials: max trials in dynamic wave.
• NumThreads: parallel threads for dynamic wave.
• NumEvents: number of detailed routing events.

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7. Time Step Values

EXTERN double
  RouteStep,
  MinRouteStep,
  LengtheningStep,
  StartDryDays,
  CourantFactor,
  MinSurfArea,
  MinSlope,
  RunoffError,
  GwaterError,
  FlowError,
  QualError,
  HeadTol,
  SysFlowTol,
  LatFlowTol,
  CrownCutoff;

• RouteStep: current routing time step in seconds (may be smaller than ReportStep).
• MinRouteStep: lower limit for dynamic wave variable stepping.
• LengtheningStep: an alternative approach to reduce wave speeds.
• StartDryDays: how many dry days before simulation start.
• CourantFactor: factor in dynamic wave stepping.
• MinSurfArea: min. nodal area to avoid continuity issues.
• MinSlope: min. conduit slope.
• *_Error: store continuity errors for runoff, groundwater, flow, or quality.
• HeadTol, SysFlowTol, LatFlowTol: tolerances for dynamic wave or system flow stability.
• CrownCutoff: fraction for partial pipe flow classification.

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8. Simulation Date/Time Variables

EXTERN DateTime
  StartDate, StartTime, StartDateTime,
  EndDate, EndTime, EndDateTime,
  ReportStartDate, ReportStartTime, ReportStart;
  
EXTERN double
  ReportTime, OldRunoffTime, NewRunoffTime,
  OldRoutingTime, NewRoutingTime, TotalDuration, ElapsedTime;

• Dates are stored in DateTime (a double representing days from some reference).
• StartDateTime = StartDate + StartTime.
• EndDateTime = EndDate + EndTime.
• ReportStart = ReportStartDate + ReportStartTime.
• ReportTime: current reporting time in milliseconds.
• OldRunoffTime, NewRunoffTime, OldRoutingTime, NewRoutingTime: track the previous/current times in msec for runoff or routing steps.
• TotalDuration: total sim length in msec.
• ElapsedTime: current elapsed simulation time in days.

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9. Climate & Weather Structures

EXTERN TTemp Temp;
EXTERN TEvap Evap;
EXTERN TWind Wind;
EXTERN TSnow Snow;
EXTERN TAdjust Adjust;

• These structures store temperature data, evaporation settings, wind speed, snow data, and monthly adjustments (like Adjust has monthly multipliers for infiltration or rainfall, etc.).

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10. Dynamic Arrays of Objects

EXTERN TSnowmelt* Snowmelt;
EXTERN TGage*     Gage;
EXTERN TSubcatch* Subcatch;
EXTERN TAquifer*  Aquifer;
EXTERN TUnitHyd*  UnitHyd;
EXTERN TNode*     Node;
EXTERN TOutfall*  Outfall;
EXTERN TDivider*  Divider;
EXTERN TStorage*  Storage;
EXTERN TLink*     Link;
EXTERN TConduit*  Conduit;
EXTERN TPump*     Pump;
EXTERN TOrifice*  Orifice;
EXTERN TWeir*     Weir;
EXTERN TOutlet*   Outlet;
EXTERN TPollut*   Pollut;
EXTERN TLanduse*  Landuse;
EXTERN TPattern*  Pattern;
EXTERN TTable*    Curve;
EXTERN TTable*    Tseries;
EXTERN TTransect* Transect;
EXTERN TStreet*   Street;
EXTERN TShape*    Shape;
EXTERN TEvent*    Event;

• Each pointer references a block of memory allocated at runtime. For example, once SWMM knows Nobjects[GAGE] is 5, it allocates TGage *Gage of length 5.
• Node, Link, Pollut, etc. each reference an array of their respective structures.

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11. Final Observations

• This file does not define these variables; it only declares them with EXTERN.
• Typically, globals.c or similar is where they’re defined.

Hence, globals.h is a single point that gathers all cross‐module global variables, so the entire SWMM codebase can access them consistently.