Tuflow and estry manual Version 3

3.13.1Channel Hydraulic Properties (CS) Tables

Each channel requires a hydraulic cross-section properties table to define its conveyance. The properties are defined at a cross section positioned midway along the channel, or as of Build 2005-05-AN, can be derived from cross-sections located at the channel ends for G and S channels. The water level used for calculating the channel properties from the property tables is normally the mean of the water levels at the nodes, except for upstream controlled friction flow conditions and some hydraulic structure flow regimes.

The hydraulic properties are listed in Table 4 .12. To generate the hydraulic properties, a channel requires a hydraulic properties (CS) table or a cross-section from which to calculate the properties. The exceptions are:

• 
  For culverts (C and R) the attribute information supplied (ie. diameter, width, etc) is sufficient to define the hydraulic properties – no cross-section properties table is required.
  
• 
  For weirs (W), if no cross-section or hydraulic properties table is specified, and a Diameter_or_Width attribute value greater than 0.01 is specified, the weir is defined as being a rectangular section 5 meters high based on the invert and width values.
  

Cross-section hydraulic properties tables may come from a number of sources:

• 
  Calculated by ESTRY using a cross-section profile in a .csv or similar formatted file.
  
• 
  A hydraulic properties table in a .csv or similar formatted file.
  
• 
  External sources such as MIKE 11 processed data .txt files or ISIS .pro files.
  
• 
  ESTRY’s traditional fixed field format (CS tables).
  

Cross-section profile and hydraulic properties data are accessed using a 1d_ta layer as described in Section 3.13.3.

External sources are defined using the XS Database and M11 Network commands. Cross-sections are extracted using the channel attributes Branch, Topo_ID and XSect_ID_or_Chainage as described in Table 4 .10. The hydraulic properties table is automatically created from the external source. The conversion from these sources preserves all the hydraulic properties listed in Table 4 .12 including any vertical variation in bed resistance (Manning’s n) values.

Alternatively the hydraulic properties tables can be specified using ESTRY’s standard fixed field formats, the documentation for which is reproduced in Section E.2. These tables can be entered directly into the .ecf file or preferably placed in a separate file and read using the CS Data command.

As of Build 2002-06-AB, it is possible to let the water level at a cross-section to extend above the highest elevation in the hydraulic properties table. The default is to treat any water levels that exceed the top of the table as being an instability (except for culverts and bridges), resulting in a WARNING being issued. See Depth Limit Factor for further details.

As of Build 2005-05-AN, rather than use a cross-section midway, cross-sections can be specified at the ends of G and S channels. This also saves having to enter upstream and downstream invert levels for these channels. See Section 3.13.4 for more details.
Table 4.12 Channel Cross-Section Hydraulic Properties