Channel objects can be used to model man made channels or a simplistic representation of a river channel.

(For detailed modelling of river channels, a River Reach object should be used. Channel objects can be automatically converted to river reach objects; see Converting Channels to River Reaches for details.)

The cross section of a channel is defined as a Channel Shape object. You can create new channel shapes or re-use an existing channel shape by selecting it from the Shape ID list in the Channel Properties Window.

Hydraulic Model Characteristics

Erosion / Deposition model

The erosion/deposition model evaluates friction factors for the sediment bed, lower third of the conduit, and upper two-thirds of the conduit (to match the way we define roughness in conduits).  To minimise changes to this model, we calculate composite roughness values for the lower 1/3 and upper 2/3 sections of each channel inside the simulation engine.

How we do this:

  1. Calculate conveyance at 1/3 channel depth.
  2. Use the Manning equation to determine an assumed constant n value up to 1/3 channel depth.
  3. Calculate conveyance at channel depth.
  4. Use the Manning equation to determine an assumed constant n value up to channel depth.
  5. Use the equivalent roughness concept to determine the n roughness value for the upper 2/3 of the channel.

We use the Manning equation because we can use a simple direct method to determine n.

Base flow

The default base flow depth for both a conduit and a channel is the sediment depth + 5% (Base Flow Factor) of the conduit height minus the sediment depth. This is increased to 10% for conduits of slope greater than 0.01 (Slope Where Base Flow Is Doubled). This is subject to a minimum base flow depth of 0.02m (Minimum Base Flow Depth).  You can change these defaults for a particular network in the Simulation Parameters.

For a channel, defining a base flow of 5% of the channel depth may have an excessive impact on hydraulic results, especially if your cross-section definition includes the flood plain.  So you can set a user-defined value of base flow depth in each channel.

Normally, a depth of a few centimetres should suffice. If your simulation results contain depth spikes, increasing the base flow depth may help.

If you set the user defined base flow depth to zero then InfoWorks ICM will calculate a base flow depth from the simulation parameters (see above).  A non-zero base flow depth will be reset to the minimum base flow depth, if it is lower.

Channel Data Fields

Channel Shape

Channel Shape Data Fields

Converting Channels to River Reaches

Simulation Parameters

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