Box Culvert Connection is a closed connection with a rectangular cross section. However, increasing the Corner Splay value from “0” (default) gives the Box Culvert an increasingly octagonal shape. A Corner Splay can be introduced for pipe strengthening purposes. The flow routing through a Box Culvert Connection is described in Analysis of Junctions and Connections.
As illustrated in the image above, the addition of a Corner Splay reduces the Diameter / Base Width and Height of the connection to an extent, affecting its Capacity and Flow Velocity.
Parameters to specify:
Length, Slope, either Manning's n or Colebrook-White Roughness, Diameter/Base Width, Height, Corner Splay, see Connections Inputs.
Upstream (US) Cover Level, Upstream Invert Level, Downstream (DS) Cover Level and Downstream Invert Level.
Entering a value for Manning's n or Colebrook-White Roughness will clear the value of the other. Manning's n is used by default.
If the Slope or Downstream Invert Level are changed by the user, the other variable will be updated to match.
If the Height or Upstream Invert Level are changed by the user, the other variable will be updated to match.
Automatic Setting of Levels
Where possible connection levels are automatically set from Surface Data data, existing Stormwater Controls - SWC and existing Junctions. This is done following the rules below but can be overruled by the user. Where levels have been overruled by the user or by the Pipe Sizing procedure the values will be shown in red to indicate they are no longer following the rules below and will not be automatically updated.
US Cover Level
- If the US coordinate is on a surface then set the US Cover Level to be the surface level at the US coordinate (in the case of a Stormwater Control this may be at the location of an Inlet or Outlet).
- If the US coordinate is not on a surface (either a surface is not loaded or the US coordinate is not on a surface) then set the US Cover Level to the Cover Level of the upstream Manhole or the Exceedence Level of the upstream Stormwater Control.
DS Cover Level
- If the DS coordinate is on a surface then set the DS Cover Level to be the surface level value at the DS coordinate (in the case of a Stormwater Control this may be at the location of an Inlet or Outlet).
- If the DS coordinate is not on a surface (either a surface is not loaded or the DS coordinate is not on a surface) then set the DSCL to the Cover Level to the Cover Level of the downstream Manhole or the Exceedence Level of the downstream Stormwater Control.
- The Invert Level is set from the Height parameter, if already specified, i.e. from a Template.
- If the Height is not specified then the Height is first set from the US item variables. For Simple Junctions, this is 0. For Manholes, this is the Cover Level - Invert Level. For Stormwater Controls this is Exceedence Level - Base Level.