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 Elevation, Upstream Invert Elevation, Downstream (DS) Cover Elevation, Downstream Invert Elevation, Culvert Type and Culvert Entrance.
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 Elevation are changed by the user, the other variable will be updated to match.
If the Height or Upstream Invert Elevation are changed by the user, the other variable will be updated to match.
If the Culvert Type is updated, the available Culvert Entrances are updated to reflect the options available for each culvert type.
Automatic Setting of Elevations
Where possible connection elevations 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 elevations 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 Elevation
- If the US coordinate is on a surface then set the US Cover Elevation to be the surface elevation 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 Elevation to the Cover Elevation of the upstream Manhole or the Exceedance Elevation of the upstream Stormwater Control.
DS Cover Elevation
- If the DS coordinate is on a surface then set the DS Cover Elevation to be the surface elevation 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 Elevation to the Cover Elevation of the downstream Manhole or the Exceedance Elevation of the downstream Stormwater Control.
Invert Elevations
- The Invert Elevation 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 Elevation - Invert Elevation. For Stormwater Controls this is Exceedance Elevation - Base Elevation.
- If the Stormwater Control has an outlet that is not free discharge then the outlet level is used instead.