File → Import and File → Export move a network between the SWMM model
and StormSewer's own project format, and write the network out as tables
or GeoJSON. All of the mapping lives in one place
(swmm/src/design.rs) and its assumptions are stated
here.
Makes a new SWMM model from a storm-sewer project —
the nodes, conduits, catchments, and a design storm from the project's
IDF curve. One undo step (import project) over a blank
model, so Ctrl+Z empties it again.
What is written:
FLOW_UNITS CFS. Values are written in U.S. customary units
whatever the project's unit system.[JUNCTIONS] and
[OUTFALLS] with the project's inverts and rims
(MaxDepth = rim − invert), and
[COORDINATES].[CONDUITS] with length, n
and offsets from the project's per-pipe inverts;
[XSECTIONS] with the project's shape (circular, box,
elliptical, arch).%Imperv by the
inverse of the C line (%Imperv = 100 · (C − 0.20) / 0.75,
clamped 0–100), width = area / flow length, and [POLYGONS];
a node's own local area becomes a polygon-less subcatchment
<node>_DA with width √area and 2 % slope, since the
project holds no slope for it.[TIMESERIES] built by the alternating-block
method from the project's design-return-period IDF curve —
5-minute blocks over 2 hours by default. The IDF curve is what the
project has, it is valid over that duration range, and the alternating-
block storm reproduces the curve's intensity at every duration up to the
storm length (§15.7).The status bar reports the import with the first of the mapping's
notes; the full list of assumptions is the one in §12.2 and §15.7. The
older .ssn text network imports the same way.
The reverse: the open SWMM model becomes a storm-sewer project, by
the mapping in §12.2 —
circular/box/elliptical/arch conduits, junctions and outfalls,
subcatchments folded into C·A and inlet times. Objects that do not map
are listed in the status bar
(… 3 object(s) not exported: …) and the count is in the
message. The hydrology (IDF, return period, Min Tc, K) comes from the
storm-sewer workspace's current project, which is the template for the
mapping; the design panel's own basis is not used here. Metric models
are refused.
Two files, <name>-nodes.csv and
<name>-links.csv:
Name,Kind,X,Y,Invert,MaxDepth,Type
Name,Kind,From,To,Length,Roughness,InOffset,OutOffset,Shape,Geom1,Geom2,VerticesKind is Junction / Outfall / Divider / Storage or
Conduit / Pump / Orifice / Weir / Outlet; Type is the
outfall or divider type; Vertices is the count of
the link's interior vertices (the coordinates themselves are in the
GeoJSON). Length, roughness and offsets are filled for conduits only.
Cells with commas or quotes are quoted.
One FeatureCollection: a Point per node and
rain gage, a LineString per link (through its vertices), a
Polygon per subcatchment. Properties carry
name, kind, and the object's row columns.
Coordinates are the model's own map units; no CRS is assumed or written,
and the file says so in a top-level note. Assign the CRS in
your GIS when you load it.
[BACKDROP]; Georeference… can write the world file back (§3.9). File → Load PNG Background… and
DXF Underlay… are drawing aids that import nothing.[TIMESERIES] (and
gages); Export to File… writes a series as SWMM's external file (§8.5)..stm: the storm-sewer
workspace imports it; then §13.1..out and
.rpt are read, never written or converted. CSV of results
is per view (chapter 10).