Using Spatial Rainfall in Simulations

When running a simulation, InfoWorks ICM checks whether a rainfall event contains rain gauge boundary information. If boundary information is found, InfoWorks ICM automatically uses the linked rainfall profile for all subcatchments that fall within the rain gauge boundary. Therefore it is not necessary to edit the network each time a different rainfall event is used in order to enter the correct rainfall profile for each subcatchment.

Boundary information overrides the profile number entered in the Rainfall Profile field of the Subcatchment in the following way:

Evaporation profiles are applied to rain gauge regions as follows:

By default (subcatchment's Use area-averaged rain option unchecked), for a particular subcatchment, InfoWorks ICM assigns the rainfall profile whose rain gauge region contains the subcatchment. It decides which region contains the subcatchment in the following way:

  1. If the subcatchment has x and y coordinates, InfoWorks ICM uses these to calculate which region contains the subcatchment. If the subcatchment was imported and values updated using the #G flag, the x and y values represent the centroid of the subcatchment calculated from the boundary data.
  2. If the subcatchment has no coordinates, InfoWorks ICM uses the coordinates of its drainage node to calculate the region.
  3. If the drainage node has no coordinates, InfoWorks ICM assumes coordinates of 0,0.

If the x, y point falls exactly on more than one boundary, or falls within overlapping regions, the region with the lower profile number is used.

If rain gauge boundary data is associated with a rainfall event, a InfoWorks ICM simulation will fail under the following circumstances:

Area-averaged rainfall

For very large subcatchments, where the subcatchment overlaps multiple rain gauge regions, using only the rain gauge region that contains the centroid can mean that the simulated subcatchment rainfall is not representative of the rainfall over the subcatchment as a whole.

Check the subcatchment's Use area-averaged rainfall field to calculate the rainfall for the subcatchments as the area-average of the rainfall from all rain gauge regions that overlap the subcatchment. Any areal reduction/calibration factors set for the rain gauge regions are incorporated in the calculation of the area-averaged rainfall. If the subcatchment falls wholly or partly outside any rain gauge region, the simulation will fail with an error during pre-processing. If the subcatchment does not have a boundary, the option is ignored.

The following variables are not area-averaged:

Instead, the values used are those that would apply if using only the rainfall polygon that covers the greatest area of the subcatchment.

Note that the recommended way to set runoff initial conditions for a subcatchment is via the Subcatchment or Surface tabs on the Rainfall Event Editor.

Applying spatially varying rainfall to 2D mesh elements

Spatially varying rainfall and evaporation can also be applied to 2D mesh elements when carrying out 2D Simulations.

For rainfall to be applied to a 2D mesh element, the Apply rainfall etc directly to mesh elements option of the 2D Zone in which the mesh is generated must be selected.

For each mesh element, InfoWorks ICM checks in which rain gauge region (if any) the centroid of the element is located and applies the rainfall profile accordingly.

Spatially Varying Rainfall

Rain Gauge Boundaries