Welcome to the wonderful world of EPA SWMM modeling. We're glad to have you here! 

EPA SWMM is an incredibly powerful and flexible software for water management modeling (see Advantages of SWMM), and Open SWMM is a passionate, friendly and helpful community of users. This sticky post will help you get going with EPA SWMM5 and the Open SWMM / SWMM-USERs community resources and discussion forum.

Getting Started:
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To get started with SWMM, there is no substitute for reading the manuals and experimenting with SWMM models. We are fortunate to have an excellent and comprehensive collection of reference documentation, as well as a growing number of example models. We strongly recommend that you read the SWMM Reference Manuals cover-to-cover, or at least the sections covering the processes you will be including in your model, as well as work through the SWMM Applications Manual.

Another great way to kickstart (or augment) your theoretical and practical SWMM modeling knowledge is with an online training course. In addition, the open access Journal of Water Management Modeling provides free access to over 600 peer-reviewed papers related to SWMM modeling. 

More advanced users and/or those comfortable with reading code can delve into the numerical methods employed by SWMM with the engineer-friendly SWMM Code Viewer.

Posting Questions:
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When posting questions on this discussion forum, please be cognizant of the Conditions for Subscribing and the Guidelines for Posting. The folks participating here are busy professionals who are happy to help out, provided that you've done your homework first: the answer is often readily available in the reference documentation or by searching past discussions archived in this knowledge base. 

Recommended Reading:
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As this discussion forum isn't intended to teach hydrology or hydraulics, we instead point you to this list of reference books recommended by list contributors.

Parameter References:
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A good starting point for initial parameter estimates is the List of Tables in the three SWMM Reference Manuals (Volumes I - III), however local data is usually preferred when available. 

The following past discussions revolve around the parameterization of SWMM.

• Subcatchment discretization discussions:
  • Subcatchment area limitations
  • Subcatchment size, outlets and conduits flow capacity
     
• Subcatchment width discussions:
  • Subcatchment width sensitivity analysis
  • Estimating width for a subcatchment
  • Flow length of subcatchment
  • Characteristic width of subcatchments
  • Estimating subcatchment width
  • Subcatchment basin width in urban areas
  • Catchment width
  • Subcatchment width
  • Runoff subcatchment width
  • Subcatchment width and extremely high peaks
  • SWMM width and routing channel per subbasin
     
• Groundwater parameter discussions:
  • Aquifer or groundwater parameters
  • Groundwater and aquifer parameters
  • Groundwater data
     
• Water quality discussions:
  • Storm water quality parameters

Frequently Asked Questions:
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These past discussions may help augment the reference documentation and reading list in addressing the following questions. 

• What time step should I use?
  • Considerations for selecting SWMM5 time steps (Blog post)
  • Time step for dry and wet periods
  • Reporting time step vs rainfall time step​
  • Variable time step adjustment factor
     
• Is my continuity error acceptable and/or how can I reduce continuity error?
  • Interpreting continuity error
  • Continuity errors what is acceptable
  • Acceptable continuity error in Extran
  • Reducing flow routing continuity error
  • Questions about continuity and solute-transport
  • Continuity error stability
  • Shortening very long surcharged conduits to reduce continuity error
  • Status report tolerances rules of thumb
     
• How can I reduce model instabilities?
  • Regarding error debugging
  • Instabilities vs real spikes
  • SWMM model instability
  • Instability at a weir
  • Outlet instability for dual drainage modeling
     
• Where do I get started with model calibration?
  • Rules for Responsible Modeling (Handbook)
  • Calibration of SWMM model
  • Model calibration (1997) 
  • Model calibration (2004)
  • Minimum calibration criteria
  • Guidance on model calibration
  • Philosophy of lid calibration
  • To calibrate or not to calibrate
  • Calibration of percent imperviousness of subcatchment
  • Discussion of percent routed parameter
  • Help with calibration
     
• How do I reduce model run time / simulation time?
  • Questions about run-time...
  • Different run times on different computers
     
• How do I create a design storm for SWMM?
  • Time distribution of short duration design storms
     
• Why is there a difference between the peak values reported in the status report and those shown in the graphs/profiles?
  • Reporting time step
  • Results displayed do not match
     
• How does SWMM compare to the rational method?
  • Historical basis of runoff methods
  • Comparing flow quantities with rational method
  • SWMM vs rational method
  • Rational method research
  • SWMM versus rational method for calculating the surface water
  • Modified rational method
  • Continuous simulation using the rational method​
  • Modified rational method
  • Flow quantities
  • Runoff coefficients
  • Capacity reduction analysis: fitting a rational method peak flow to a hydrograph
  • Large difference in Q values from SWMM results and hand calculations
  • Fixed infiltration model
  • Replicating the rational method in SWMM (Example Model)
  • Replicating STORM in SWMM (Example Model)
     
• How can I enter (or calculate) a time of concentration?
  • Time of concentration (2019)
  • Approximate time of concentration at node
  • Time of concentration (2009)
     
• How can I fix Error 173: time series has its data out of sequence
  • Error 173: time series has its data out of sequence (Blog post)
     
• For return period analysis, what plotting position should I use?
  • Standard definition for a storm's return period
  • Informal survey of plotting positions for frequency distributions
  • Storm return period exceedance probability question
  • Extreme return periods
     

That's all I have to contribute to this Getting Started FAQ so far. Let me know if you have suggestions for additional content. Until then, happy swmming!