Tuflow and estry manual Version 3

3.14.4.3Culverts

Culvert channels can be either rectangular or circular culverts. A range of different flow regimes is simulated with flow in either direction. Adverse slopes are accounted for and flow may be subcritical or supercritical. Figure 4 .8, Figure 4 .9 and Table 4 .16 present the different flow regimes modelled. The regimes are output to the .eof file next to the velocity and flow output values.

The culvert type (“C” for circular, or “R” for rectangular), dimensions, length, upstream and downstream inverts, Manning’s n, bend loss (as of Build 2005-05-AN), entrance and exit losses and number of barrels are entered using the GIS 1d_nwk attributes (see Table 4 .10).

The four coefficients are as follows:

• 
  The height contraction coefficient for box culverts, and is usually 0.6 for square edged entrances to 0.8 for rounded edges. This factor is not used for circular culverts.
  
• 
  The width contraction coefficient for box culverts, with values from 0.9 for sharp edges to 1.0 for rounded edges. This factor is normally set to 1.0 for circular culverts.
  
• 
  The general entry loss coefficient as specified by the manufacturer. The recommended value is 0.5.
  
• 
  The exit loss coefficient, normally recommended as 1.0. (Note: This value when entered in fixed field formats in earlier versions of ESTRY is an exit recovery coefficient. To convert the exit recovery coefficient to an exit loss coefficient, multiply it by –1 and add 1, ie. 0 becomes 1 and 1 becomes 0. Its recommended value was zero.)
  

The calculations of culvert flow and losses are carried out using techniques from “Hydraulic Charts for the Selection of Highway Culverts” and “Capacity Charts for the Hydraulic Design of Highway Culverts”, together with additional information provided in Henderson 1966. The calculations have been compared and shown to be consistent with manufacturer's data provided by both “Rocla” and “Armco”.

Further improvements for calculating culvert flows were incorporated during the 2002-07/08 and 2002-12 builds. The improvements extend the original code to include two new regimes (K and L), regime B for circular culverts, smoother transitioning between flow regimes, better stability and correction of mass errors in rare flow situations. This approach is referred to as Method B, whilst the original approach is Method A. The method is set using Culvert Flow. As of Build 2002-08-AD, the default method is Method B. Prior to this build the default method was Method A. Note: Method B may still be subject to further enhancements.

Table 4.16 1D Culvert Flow Regimes