Functional units (FUs) refer to areas of particular hydrological response. In Source, Functional Unit classes are initially defined in the Geographic Wizard (Specify functional units). This page explains how to manipulate FU areas outside the Geographic Wizard.

Note: Although the user now can edit FUs even though FUs have been assigned in the Geographic Wizard, the user needs to be careful to process the modification as it may result in the loss of any model definition linked to other models (e.g., calibration model, water quality models), and change of the results.

Specify functional unit areas

You can assign areas to every functional unit in each sub-catchment in one of two ways:

Manually using Edit » Functional Units » Assign Area Manually (Figure 1); or
From a raster such as a land use map (Figure 2).

Areas can also be imported into the Functional Unit table from a .csv file.

Note: Areal percentages per sub-catchment must sum to 100%. An error message is shown if Functional Unit areas do not add up to 100%:

A 'Normalize Area Ratios' Button has been introduced in versions of Source after version 4.2.6. This button can be used to manage small errors resulting from decimal rounding. It will automatically fixed the sum of FU areas to equal the sub-catchment area.

This is especially useful when areas are calculated from a shapefile or raster, where resolution differences between sub-catchments and FUs can result in small area differences.

Manual assignment

Manual assignment of functional units is done in the Function unit area configuration dialog (Figure 1). This table lists all combinations of FUs and sub-catchments. For each sub-catchment, enter the area that is allocated to each FU. You can specify this as an absolute value in the Area column, or as a percentage in the Area Ratio column. Values can be entered into individual cells, or in multiple cells as follows:

Use the contextual menu to assign a single value to all cells in the selected column;
Use the panel below the table to re-allocate a percentage of land cover from one pre-defined FU to another. For example, if you have already specified that 50% of each sub-catchment is of FU type "Forest", and 50% is of type "Urban", you could model increases in urban encroachment (by say 5%) as follows:
- Specify the Auto change by field to 5%;
- Specify the From Functional Unit and To Functional Unit fields to Forest and Urban respectively; and
- Click the Auto-increase button (Figure 1).

Figure 1. Assigning FU areas manually

Note: Using filters in the Functional Unit Area Configuraiton dialog is similar to using them in the Feature Table (see Working with filters in the Feature Table). However, there is also a subcatchment filter to help you find subcatchments either by name or by using the subcatchment map, see Subcatchment filter.

Using a raster

Choose Edit » Functional Units » Assign Area Via Raster to open the FU raster dialog (Figure 2);
Click Load to upload a raster file;
Selecting the Save spatial FU data option will save the loaded Raster in the Source project file. This can be useful if you are wanting to keep a copy of the original data, but, since raster files are often very large, be aware that this can have an unwanted impact on the size of the Source project file.
If the loaded land use layer does not include a mapping of grid code to land use, click Assign Mapping. Multiple grid codes can be assigned to a single FU class;
In the resulting dialog (Figure 3), assign a FU to each grid code using the drop-down menu in the FU column. Hover over the map to view the grid code which corresponds to the raster cells; and
Click OK to close the window.

Figure 2. Assigning FU areas using a land use raster

Figure 3. Assigning FU areas using a land use raster, assign mapping

Modify Functional Units

Functional Unit names now can be modified even though they have been assigned in the Geographic Wizard. The functions for FU modification include add, delete, and rename using the Edit » Functional Units » List menu item, which will display the UI of Name Functional Units (Figure 4).

Figure 4. Modify FUs

Add FUs

The user can put the new FU name in Name Textbox (1 in Figure 4), then click on Add button (2 in Figure 4), the new FU will be added to the list of FUs (3 in Figure 4). Click OK button to save the modification.

Delete FUs

The user can click on the unwanted FU name from Functional Units list (3 in Figure 4), then selected FU Name will be displayed in the textbox (4 in Figure 4). Clicking on Delete button (5 in Figure 4) will remove /delete the unwanted FU name from FUs list. Click OK button to save the modification.

Rename FUs

The user can click on the FU name, which needs to be renamed, from Functional Units list (3 in Figure 4) first, then selected FU name will be displayed in the textbox (4 in Figure 4) under Functional Units list. The user can then rename this FU in the textbox and the Delete button (5 in Figure 4) will be changed to Rename button. Clicking on Rename button will rename the selected FU (3 in Figure 4) by modified FU name in the textbox (4 in Figure 4). Click OK button to save the modification.

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