Creation of section and description of cross sections

There are several ways to access the edit window of a reach:

  • Right-click on a reach in the tree or in the graph and choose "Description of the reach XXX"
  • Double clicking on a reach in the tree or in the graph if the "Select" tool is enabled (click or press [Esc])

Reach description

The description of the reach allows entry of:

  • Name of the reach
  • Calculation step that defines the maximum space between each calculation section that will be generated in this reach by TALWEG. This notion is explained in the theoretical documentation. This space step can be defined at 3 levels: at the level of the complete network (Network Properties), at the level of the reach (screen above, on the top left), at the level of the sections (screen above at the bottom, in this case the space step will be applied between this section and the next one). If a level has a value of zero, the value of the upper level is used. If all values ​​are null, a default value (100 m) will be used. A message will be written in the .log file as well as in the message window.
  • Sinuosity coefficient (coefficient, between 0 and 1 which is used to change the volume of the medium bed (if any) to reflect the sinuosity of flow channel inside the medium bed). If 0 or 1 is entered, the volume is not changed, considering that the minor bed and the medium bed are aligned. For example, if we put 0.5 as the sinuosity coefficient, we assume that the curvilinear abscissa in the medium bed is half that in the minor bed (the minor bed meanders in the medium bed).
  • Homothety factors Y and Z for cross sections of the reach (which will override for this reach those defined in Network Properties)
  • Geolocation of the middle point of the reach (preemption point) can be visualized and modified. This geolocation is given in decimal degrees or in metric variables depending on the chosen option.
  • Cross sections can also be imported within the current reach at different format (text, Mascaret)
  • New sections by clicking the button "New" or "Insert"
  • Order of sections by clicking on the two arrows at the left of the listing sections table

We will create sections in the following locations:

  • At the beginning and end of each reach. The abscissas of these two sections will determine the length of the reach. Understand that these sections are physically present at the location of the node at the ends of the reach.
  • Every time change of profile geometry of the section (change in slope ...).
  • At each location of a cross structure formed by one or more devices (weir, gate...) and immediately downstream (same abscissa) of these structures.

Coordinate values ​​between different reaches have no special meaning for the software: they can be continuous or discontinuous between the reaches, increasing or decreasing within the reaches.

Sections description

For each selected section in the table section, we will have:

  • The abscissa in meters (in a reach, the abscissas must be monotonically increasing or decreasing).
  • The bed mode (Minor, Minor-Medium or Major)
  • The type of profile
  • The singularity (a singular section is a section in which a cross structure can be defined)
  • The elevation of separation between the minor and medium bed if the minor-medium bed mode has been activated
  • Factors Y and Z scale factor for the cross sections of the section (which will overwrite for the selected section those defined for the network and the reach selected)
  • the space step DX between this section and the following, until new definition of this DX, for the possible interpolation of new calculation sections. This DX space step can be defined at the level of the complete network, at the level of the reach (see above), and here at the level of this section. If a value is at 0 Talweg will take the value of the higher level
  • the width of the Preissmann slot if this section is closed at the top

Singular sections are the only sections where we can add, in hydraulic mode, a cross structure with one or more devices. It is advisable to create a section downstream at the same abscissa of each singular section for ease of reading in graphics results.

The tab "Profile Section"

Different types of section profiles are available:

  • Predefined
  • Width / Elevation
  • Offset / Elevation
  • Circle
  • Culvert
  • Power function
  • Rectangular
  • Trapezoidal

Predefined profiles enable you to not have to reenter profile that is repeated throughout the network (see Preset profiles : managing a library of cross sections).

The tab "Section description and picture"

Click on the picture to set the picture associated with the section.You can also add free text to indicate and store information if necessary.

For more details on image management, see the dedicated chapter.

The tab "Analysis"

This tab makes it possible to analyze the hydraulic characteristics of the section, and in particular to calculate the critical and uniform flow rates. The "calculator" tool works the same way as in the Q(Z) offtake or boundary condition mode (except the option to select the upstream reach, since here we already are in a given reach).

The tab "Geolocation"

This tab is used to define and visualize the geolocation variables of the section. If the geometry has been imported globally from a .CSV file (HEC-RAS style) or inside reaches from TXT files with geolocation data, this information will appear here. Ditto if the "Automatic construction" mode was used to fill in these data automatically from the graphical layout of the node and midpoint objects on the screen.

For a section, which actually has a spatial extent, assumed in a vertical plane, the geolocation variables are given for a point of the section with various options (midpoint of the section, right bank, left bank, lower point, etc.), as well as an angle of the section with respect to a reference. Currently this reference is the geographical North. In the future other options can be managed (example other fixed orientation, orientation of the central line of the reach, orientation of the drawing line on the screen of the reach, etc.). Geolocation of the chosen point is given in decimal degrees, or in metric variables depending on the chosen option.

Control input

The reaches shown in fuchsia on the network diagram have an incomplete entry. Those considered valid are drawn in blue.

To verify that the input geometry is consistent, use the tools: