Tuflow and estry manual Version 3

Table 4.14 Hydraulic Structure Modelling Approaches

Structure	1D Approach	2D Approach
Box Culvert (For culverts with a steep slope, use a 1D element)	OK	OK
Circular Culvert	OK	N/A
Bridge	OK	OK
Weirs	OK	OK

1D Approach Preferred approach where the total structure width is less than the cell size.

Entry and/or exit losses may need to be reduced where the structure width is significant compared with the cell size (Syme 2001b).

Momentum is not transferred into or out of the 1D element from the 2D domain. “Suppressed” flow patterns in the 2D domain occur at the structure outlet when using 1D elements, especially if the structure width is significant compared with the cell size. The water tends to spread out evenly, rather than jet out as occurs if using a 2D representation. This may be overcome by applying “wing walls” in the 2D domain at the structure outlet by assigning flood free elevations to the ZU and ZV Zpts either side of where the 1D element discharges into the 2D domain.

2D Approach Preferred where the total structure width is greater than the cell size. The flow area must be adequately represented by the 2D Zpts and any adjustments to cell widths. The head drop across the structure during different flow regimes should be validated against other methods and/or literature.

Some additional form losses are normally required to achieve correct head drop (see Syme 2001b). Where the cell size is less than the depth, use the Smagorinsky Viscosity formulation. Care should be exercised using cell sizes less than 2m (Barton 2001).

Momentum is transferred through the structure, providing far more realistic flow patterns than using a 1D element.