# Problem

What is the difference between using a Conduit versus using a Channel link element?

# Solution

For Conduits

• The cross-sectional area is defined in the conduit properties and is used for the entire length of the conduit (they are always treated as prismatic), and structures are typically used for end nodes (manhole or catch basin, which have a vertical vault).
• A large number of different cross sectional shapes are available
• The Constraint Based Design feature in the GVF-Rational (StormCAD) and GVF-Convex (SewerCAD) solvers can design the size of conduits for most shapes.
• Closed cross section shapes like "Box" can surcharge, whereas open cross sections like "Rectangular Channel" extend their sides vertically (the top is open).
• A large number of additional results are provided for the GVF-Rational solver, under the "System time" section. For example System flow time and system intensity, to help track the Rational flow calculations.

For Channels

• The cross-sectional area is defined at the end nodes (cross section node elements, which do not simulate any vertical vault like you would with a manhole or catch basin).
• When a channel is connecting two cross section nodes, the cross-section of the channel is interpolated between the two cross section nodes. See: Are Channels prismatic or non-prismatic?
• When there is only one cross-section node at either the upstream or downstream end of a channel, then the channel will have a constant cross-section, as defined by that one cross-section node.
• Only Trapezoidal and Irregular cross section shapes are currently available
• The Constraint Based Design feature does not size channels/cross section.
• "System flow" results seen in conduits, are not currently available (as of 10.01.01.04)

Although both elements can simulate a wide array of cross section shapes, the channel is typically used when modeling things like rivers, streams or ditches. The conduit is typically used to model an enclosed pipe or culvert barrel. Constraint Based Design can only be used with conduits.

An example of a model that uses both channels and conduits can be see in the \Samples\Office Project\ folder within the installation folder.