Variable Depth Channel

Variable Depth Channel is any channel with varied upstream and downstream cross sections, where along the length of the channel the cross section varies between the two. The flow routing through a Channel Connection is described in Analysis of Junctions and Connections.

Parameters to specify

Length, Slope, either Manning's n or Colebrook-White Roughness, Upstream Height, Downstream Height, Upstream Base Width, Downstream Base Width, Upstream Left Side Slope, Downstream Left Side Slope, Upstream Right Side Slope, and Downstream Right Side Slope, see Connections Inputs.

Upstream (US) Cover Elevation, Upstream Invert Elevation, Downstream (DS) Cover Elevation and Downstream Invert Elevation.

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 Upstream Height or Upstream Invert Elevation are changed by the user, the other variable will be updated to match.

If the Downstream Height or Downstream Invert Elevation are changed by the user, the other variable will be updated to match.

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 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.

For Variable Depth Channels the upstream and downstream heights are independent, so the rules above are applied separately at each end — the upstream Height from the upstream node's depth and the downstream Height from the downstream node's depth — and either end can be overruled by the user without affecting the automation at the other end.

Automatic Cross Sections

When a new Variable Depth Channel is added downstream of a junction that already has one or more Variable Depth Channels immediately upstream, the new channel's upstream cross section is set to match the downstream cross section of whichever upstream Variable Depth Channel has the largest downstream cross sectional area.