Subcatchment Definition

Subcatchment areas are defined in a file stored in the IRIS_OVERLAY directory (typically etc/vaisala/irisrda/overlay).

These are given the suffix .cat and are referred to as catch files.

When IRIS starts, the start-up log shows the processing of the catch files.

In general the files contain the following information for each subcatchment:

• Subcatchment index number (an integer 1, 2, 3, ...) and name.

  The name is used for display.

• The threshold (mm) of accumulation depth for the warning.

• The subcatchment points in LAT/LON coordinates.

  These points must define a closed region and be in sequence about the perimeter of the region. That is, the first point and the last point must be the same.

  Subcatchments that share the same boundary must be entered as complete closed regions, that is, the shared boundary points are the same for adjacent subcatchments.

• The location of an internal point for the labeling.

  This point must be within the bounded region of the catchment.

Each catch file usually has many subcatchment regions. There can be multiple subcatchment files for different applications such as:

• For different radars in a network.
• To specify different warning thresholds to account for different integration times.
• To cover different major watershed areas.

Overlapping subcatchments in a file are permitted. For example, a large watershed region could be input as a single large catchment and the smaller tributary watersheds within it be specified as well. IRIS allows a maximum of 20 different catch files to be created.

For more information, see the Overlay utility in IRIS and RDA Utilities Guide (M212925EN).