Modeling river junctions

Some aspects of modelling can be more of an artform than a science. Modelling river junctions is a great example of this. The goal is to accurately represent the true geometry as much as possible by not excluding or double-counting large areas.

If working with a minor tributary, it is usually best to define a cross section as close to the main riverbank as possible. A break node and cross section are needed at the connection point on the main river. Build the tributary river reach link while ensuring that the cross section for the main river is not included, to avoid double counting that section. The calculations for a river reach are only undertaken between sections, so extending the length of the river reach link beyond the last cross section does not affect the calculations.

Alternatively, the approach of creating a major junction with a central break node can be taken. A small area may be missing from the model, but it can be made as marginal as possible by placing the river ends as close to the junction as feasible. The minor junction approach would be just as applicable to this situation—decide which branch to treat as the main river. Often, the decision comes down to the availability of cross section data close to the junction.

Note that if a large area would be excluded from the model using this approach, a storage area and storage node can be used in combination to explicitly define the otherwise lost area. If the bathymetry is included in an available ground model, the Model > Update from ground model tool can be used to efficiently populate this data.

By default, ICM does not undertake any additional calculations at a junction to account for headlosses, but it is possible to specify additional losses at these points, if necessary, through the river reach headloss properties.