This procedure automates simplification of a SWMM5 model network by removing junctions that connect exactly two conduits where certain criteria are satisfied. The lengths of the conduits on either side of the deleted junction are added, and the properties of the upstream conduit are retained, with the exception of the downstream offset, which is obtained from the most downstream deleted conduit. This procedure must be used with care, as it does not check constraints such as differing Manning's Ns, presence of control rules, etc. An iterative process is used. The program selects a junction at random from among junctions meeting criteria for removal. It merges two pipes and then randomly selects another eligible junction. The process is repeated until no candidate junctions exist. The procedure does not remove any junction with fewer or more than one conduit connection, any storage junction, or any junction connected to a weir, pump, orifice, or multi-barrel conduit.

 

The user may optionally populate and edit the JunctionCodes table in the \NetSTORM\SWMMSimplification.mdb database. The program reads this table during the Identify step. Any junction listed that is not marked InvertVerified will be assigned high priority for merging. High merge priority is also assigned to any junction with invert less than -900.

 

 

Merge Rules

Height tolerance - Conduits with heights differing by more than this ratio will not be merged. Note that the program does not check conduit width or Manning's N. The comparison is strictly based upon the height parameter. E.g. a ratio of 0.4 would allow a 4 ft pipe to be merged with a 3 ft pipe but not with a 6 ft pipe.

Minimum junction depth (ft or m) - Junctions with less clearance between rim and invert will not be merged. This facilitates retention of potential ground flooding locations in the simplified model.

Maximum conduit length (ft or m) - Merged conduits will not exceed this length. 

Preserve all shape changes - checking this box ensures that conduits of different shapes will not be merged. E.g. a 4 foot circular pipe might otherwise be merged with a 4-foot high box culvert.

Preserve catchment inlets - checking this box ensures that subcatchment inlet junctions will not be eliminated. If this box is not  checked, the procedure will re-route deleted inlet loads to the next downstream junction.

 

• Import - data are loaded from a SWMM5 input file into the SWMM5Simplification.mdb database in the NetSTORM software folder.  The user may bypass this step and manually populate the required data tables if the model is being built directly from a database.
• Identify - critical junctions in the model are identified. Critical IDs are assigned as in the table below. Any junction or link with a positive Critical ID is preserved during simplification. The user can manually edit values in the database after the Identify procedure is run.
• Simplify - The junctions and links tables are modified when this procedure is run
• Export - The data tables are exported to a SWMM5-format data file. This step may be run at any point when the database is populated with valid data.

 

 

Critical	Reference Table	Explanation
-99	Junctions / Links	removed during simplification
-1	Junctions	high priority removal candidate (Invert<-900 or unverified)
0	Junctions / Links	removal candidate
1	Junctions	storage junctions and outfalls
1	Links	pumps, weirs, and orifices
2	Junctions	connected to weir, pump, orifice, or multi-barrel conduit
3	Junctions	does not have exactly one upstream and one downstream link
4	Junctions	pipe size changes exceeds user-specified tolerance
5	Junctions	shape transition
6	Junctions	user-specified shallow junctions unless sealed
7	Junctions	catchment inflow location
8	Junctions	connected to long pipe

 

The procedure re-writes the [JUNCTIONS], [CONDUITS], [XSECTIONS], [DWF], [LOSSES], [INFLOWS], and [SUBCATCHMENTS] sections of the input file. Any comments in these sections are lost. 

 

[DWF] loads are consolidated at the next downstream junction. Only one flow pattern is preserved though. 

[SUBCATCHMENT] loads to deleted nodes are shifted the next preserved downstream junction.

[INFLOWS] are consolidated at the next downstream junction. Scale Factors and Baseline values are summed. In some cases this may yield inappropriate results!

[CONTROLS] are not checked.

 

The [LABELS] sections is amended with the deleted junctions.

The [VERTICES] section is replaced with vertices of deleted junctions. Any existing vertices are deleted.

 

The program has received minimal testing on open channel models.