Combined Catchments

A combined catchment is a catchment made up with a number of sub-catch­ments, which are defined in the Catchment definitions menu.

The runoff from the combined catchment is found by simple addition of the simulated runoff from each of the subcatchments. This type of catchment can especially be used during the calibration process to quickly get the total runoff at a gauge location, based on all upstream sub-catchments.

Combined catchments are not shown on the map, and can only be edited from the Tabular tab. Use the Append ‘+’ or Delete ‘-’ buttons above the over­view table to add or remove a combined catchment.

The various properties specified for a combined catchment are described below.

·         Combined catchment name. The combined catchment can be given any name.

·         Total area. The total area of the catchment is automatically computed, and is equal to the sum of the areas from all its subcatchments.

·         Subcatchments. All subcatchments have to be added in this table using the Append ‘+’ button. They can be deleted using the Delete ‘-’ button. Each subcatchment has to be selected from the drop-down list amongst the catchments defined in the Catchment definitions menu. The area considered for each subcatchment is always its total area.

·         Calibration plot. It is possible to save the calibration plot by enabling ‘Calibration plot’. The calibration plot shows observed and simulated run­off for the catchment.

·         Observed discharge. When the ‘Calibration plot’ is enabled, a time series of observed runoff has to be specified here with the Browse '…' button.