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Specify FU area Specify FU area

Specify functional unit areas (Step 5)

You must assign areas to every functional unit in each sub-catchment. The functional units that appear depend on those you defined previously. You can assign areas manually (using either the Table or Map tabs), or from a raster such as a land use map. This is synonymous to the menu item Edit » Functional Units » Assign Area....

To assign FU areas manually using the Table tab:

• Choose Manual Area Allocation from the Available Methods drop-down menu;
• For each sub-catchment, enter the area that is allocated to each FU. You can specify this as an absolute value in the Area (ha) column, or as a percentage in the Area (%) column; and
• You may enter the areas individually, or use the Apply-to options to fill multiple cells at once. This is explained in detail in the Using the Apply-to options section. You can also copy values from one cell and paste into other cells. Right-click on the source cell (the one you want to copy) and choose Copy. Then, right-click on the target cell, and choose Paste. The resulting table is shown in Figure 8.

Figure 8. Geographic Wizard, Assigning FU areas

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When assigning FU areas manually using the Map tab, you can view the entire catchment and its outlines. FU areas can be assigned as follows:

• Click on a sub-catchment that you want to assign a model to, or highlight several using the mouse (drag and select). Alternatively, use Ctrl to select several sub-catchments. If you hover the mouse over a selected sub-catchment you will see the its number or name;
• To assign the area covered by each FU to the selected sub-catchments, select a cell in the table you want to assign the area to; and
• Use the Apply-to options to assign the same area to the selected sub-catchment/FU combinations.

If the areal percentages per sub-catchment, do not sum to 100%, the percentage cell turns pale red (to indicate an error) for that sub-catchment. In Figure 9, SC # 1 (Urban FU), the area percentage should be 50, not 5. The error applies only to SC#1, so the cell for SC#2 is not pale red.

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Figure 10 shows the correct areal percentages for SC#1.

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You can assign areas to multiple FUs simultaneously, using the Apply-to options on the right of the screen. This is useful when you have a large number of sub-catchments, each containing several FUs.

• In the Area (ha) or Area (%) column, click in any cell;
• Enter a value or percentage;
• Specify the appropriate values in the Apply selected cell to: options (to the right of the table); and
• Click Apply, and the value will propagate through the specified sub-catchments and/or FUs.

To assign FU areas using a raster:

• Click Load to upload a raster file;
• If the land use map does not include a mapping of grid code to land use, click Assign Mapping;
• In the resulting window, assign a FU to each grid code using the drop-down menu in the FU column (Figure 11); and
• Click OK to close the Match FU Definitions to Raster window.

For each sub-catchment, the FU areas MUST add to 100% (+/- 0.1%). If areas do not sum to 100%, cells in the Area column will be shaded pale red. An exclamation mark will also appear on the left side of the first column.

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Assign catchment models Assign catchment models

Assign catchment models (Step 6)

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