SWMM - Curves - Transects

Describes the Irregular cross-section of channels in SWMM

It is assigned to a SWMM conduit, when it has a typical section like Irregular assigned by Constructor

An Transect curve has the following properties:

• Identification
  • Description - Use a friendly description when the item name is not enough
  • Name - name of the item
    Avoid names that are too long, or that contain the following characters: '*', '>', '<', '/', '\', '"', ':', ';', '|', '=', '`', '#', ',', '?'
  • Priority - Information about the current state of the item. It might be:
    • Neutral: no problem
    • Critical: Some issue that prevents the item from being calculated or used
• Margins - The distance values that appear on the Station/Elevation grid that mark the end of the left margin and the beginning of the right margin. Use 0 to denote the absence of a margin
  • Left Margin
  • Right Margin
• Modifiers
  • Meander - Ratio between the length of a sinuous main channel and the length of the margin area surrounding it.
    This modifier is applied to all conduits that use this specific transect for their cross section.
    It assumes that the length given for these conduits is that of the longest main channel.
    SWMM will use the shorter bank length in its calculations while increasing the main channel roughness to compensate for its longer length.
    Modifier is ignored if left blank or set to 0
  • Station - A factor by which the distance between each station will be multiplied when transect data is processed by SWMM
    Use a value of 0 if no factor is needed
  • Elevation - A constant value that will be added to each elevation value
• Roughness - Manning roughness values
  Margin roughness values can be zero if they do not exist
  • Main channel
  • Left Margin
  • Right Margin
  
  Excavated or dredged

  Channel type	Manning n
  Aligned channels
  - Asphalt	0.013 - 0.017
  - Brick	0.012 - 0.018
  - Concrete	0.011 - 0.020
  - Debris or riprap	0.020 - 0.035
  - Vegetable	0.030 - 0.40
  - Earth, straight and even	0.020 - 0.030
  - Earth, winding, fairly even	0.025 - 0.040
  - Stone	0.030 - 0.045
  - Not maintained	0.050 - 0.140
  Natural channels (smaller creeks, upper width at flood stage < 100 feet)
  -reasonably regular section	0.030 - 0.070
  -ragged section with pools	0.040 - 0.100

  
  Source: ASCE (1982). Gravity Sanitary Sewer Design and Construction, ASCE Manual of Practice No. 60, New York, NY

The data is populated in the table and plotted on the graph for better visualization:

Elevations must be in ascending order and not repeating and cannot be negative, otherwise the Priority property will be Critical