Dynamic Wave Routing Options in InfoSWMM and InfoSWMM SA for the EPA SWMM 5 Engine
The Dynamic Wave page of the Simulation Options dialog, shown below, sets several parameters that control how the dynamic wave flow routing computations are made. These parameters have no effect for the other flow routing methods.
Contents of this simulation option dialog page are described below:
|Inertial Terms||Indicates how the inertial terms in the St. Venant momentum equation will be handled.
|Variable Time Step||Indicates whether or not a variable time step should be used. The variable step is computed for each time period so as to satisfy the Courant stability criterion for each conduit and to prevent an excessive change in water depth at each node. The Routing Time Step Summary Report is available for checking statistics about how InfoSWMM is altering the timestep.
|Time Step for Conduit Lengthening||This is a time step, in seconds, used to artificially lengthen conduits so that they meet the Courant stability criterion under full-flow conditions (i.e., the travel time of a wave will not be smaller than the specified conduit lengthening time step). As this value is decreased, fewer conduits will require lengthening. A value of 0 means that no conduits will be lengthened. The roughness value of the conduit will also be artificially lowered so that the same velocity and flow are maintained after lengthening. Also note that the conduit slope reported in the output will reflect a numerically smaller slope due to a longer conduit length.
Conduit Lengthening in InfoSWMM H2OMap SWMM InfoSWMM SA
If you use the conduit lengthening option in InfoSWMM H2OMap SWMM InfoSWMM SA then your short conduits will be lengthened based on the CFL or explicit time step criterion. Any conduits in which the Length Factor or the courant time step link length over the original length is greater than 1 will be lengthened and will have its roughness lowered so that the conduit is hydraulically the same at full conduit depth. The full area, full width and full hydraulic radius stay the same in the modified link – only the length, slope and roughness are altered.
|Minimum Surface Area||This is a minimum surface area used at nodes when computing changes in water depth. If 0 is entered, then the default value of 12.566 ft2 (i.e., the area of a 4-ft diameter manhole) is used.|
|Use Normal Flow Limit||Selects which condition is used to make InfoSWMM H2OMap SWMM InfoSWMM SA limit the flow in a conduit to the normal flow computed from the Manning equation:
The effect of these three options is on the value of sigma for the non linear term in the St Venant Equation; a sigma value of 1 means that the whole term is used, a value of 0 means that the non linear term is not used for that time step.
|Force Main Equation||Choose the head loss equation to be used to model force mains|
|Maximum Number of Iterations||Allows you to control the maximum number of iterations in the solution. The number of iterations range from 2 to a possible 20 iterations.
|Stopping Tolerance||Controls the Stopping tolerance (internal units of feet) for node iterations.
Two new parameters and a modified table in the output starting in InfoSWMM 11 and H2OMAP SWMM v10 that does the following:
1. Allows you to control the maximum number of iterations in the solution,
2. Controls the Stopping tolerance (internal units of feet) for node iterations, and
3. Shows not only the percent continuity error at a node but the error in million gallons (Mgal)
If you have a high continuity error or want to reduce your existing continuity error then you can increase the number of iterations or lower the stopping tolerance so that at each time step there is less continuity error.