Functional units

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.

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.

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

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.

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.