Transects

Transects are geometric cross section data describing how bottom elevation varies with horizontal distance over the cross section of a natural channel or irregularly-shaped conduit. The figure below displays an example of a transect for a natural channel.

MIKE+ offers a tool for automatically generating or editing transect data from survey points or DEM data. Access the Create and Update Transects tool from the Network Editing Tools toolbox on the CS Network menu ribbon.

 

Figure: Definition of Transect data (Source: EPA SWMM Help Manual)

 

Figure: Access the Create and Update Transects tool from the CS Network menu ribbon

Each transect has a unique ID. When a conduit has an IRREGULAR shape then a user-defined Transect must be set to define the cross-section shape for the conduit.

The SWMM engine converts these data into tables of area, top width, and hydraulic radius versus channel depth. In addition, as shown in the figure above, each Transect can have a left and right overbank section whose Manning roughness can be different from that of the main channel. This feature can provide more realistic estimates of channel conveyance under high flow conditions.

The Transects editor organizes the related input data into the following groups:

• Identification. General identification and description
• Geometric & Hydraulic Properties. Transect geometry and Manning n information

 

Figure: The SWMM Transects editor

 

Figure: Transects Identification groupbox

Edit field	Description	Used or required by simulations	Field name in datastructure
ID	ID of the transect	Yes	MUID
Description	Descriptive information on the transect	No	Description
Transect Geometry
Left Bank Station	Left overbank station	Yes	Xleft
Right Bank Station	Right overbank station	Yes	Xright
Horizontal Shrink/ Expand Factor	Horizontal shrink/expand factor by which the distance between each station is multiplied	Yes	Wfactor
Elevation Offset	Elevation offset	Yes	Eoffset
Meander Ratio	Meander ratio	Yes	LFactor
Manning n
Left Overbank n	Manning n for left overbank	Yes	Nright
Right Overbank n	Manning n for right overbank	Yes	Nleft
Channel n	Manning n for main channel	Yes	Nchannel

Table: Edit fields in the Transects editor (mss_Transect)

 

Figure: Transects geometry groupbox on the Transects editor

Specify station-elevation value pairs describing the transect in the Transects Data secondary table.

Edit field	Description	Used or required by simulations	Field name in datastructure
Station	Distance of cross section station from some fixed reference	Yes	Station
Elevation	Elevation of the channel bottom at a cross section station relative to some fixed relative reference	Yes	Elevation

Table: Edit fields in the Transects Data secondary table