The RTK parameters are a property of each catchment. However, it is not uncommon for many catchments with similar characteristics to share the same RTK parameters. Therefore, the RTK parameters are entered in a named RTK table and that table can be shared among many catchments.

The RTK table is a set of RTK parameters that is available to be assigned to catchments. The following table shows some example ranges of RTK values.

Example RTK Values

In most cases, the RTK hydrograph implicitly accounts for infiltration so when using RTK, you should set this type of infiltration to zero. This can be done by setting the infiltration rate to zero in the fLoss method or setting fc and fo to zero in the Horton (generic) method.

To create a RTK table:

1. Open your model in Drainage and Utilities, then do one of the following:
2. Click the New button to create a new RTK table, then type a new name for the RTK table.
3. Enter RTK values for Rapid Inflow, Moderate Infiltration, and Slow Infiltration. You can use the Tab key to quickly move from one field to the next. If you do not use one of the flow components, set the R value of that component to zero.
4. Drainage and Utilities validates your RTK data as you enter it and displays errors and warnings in the status bar at the bottom of the RTK Tables dialog box. Be sure to check this status bar for any errors or warnings as you enter data.
5. Click Close to close the dialog box and save the RTK table.
6. In the Property Editor for the catchment, select the new RTK table from the drop-down menu in the RTK Table field.

To assign an RTK table to a catchment:

The advantage of using FlexTables to assign RTK tables to catchments is that the hydrograph types can be assigned globally.

1. To assign an RTK table to a catchment using the Property Editor, perform these steps:
2. Double-click a catchment in your model.
3. In the Property Editor, select Unit Hydrograph as the Runoff Method.
4. Select RTK Unit Hydrograph as the Unit Hydrograph Method.
5. In the RTK Table field, select the desired RTK table from the drop-down menu, or select New to create a new RTK table.
6. To assign an RTK table to a catchment using a FlexTable, perform these steps:
7. Open or create a catchment FlexTable.
8. For information on creating FlexTables, see "Creating a New FlexTable"-151. For information on adding columns to an existing FlexTable, see "Editing FlexTables"-153.
9. Add the following columns to the FlexTable:
10. Runoff Method
11. Unit Hydrograph Method
12. RTK Table
13. In the Runoff Method cell in the FlexTable, select Unit Hydrograph.
14. In the Unit Hydrograph Method cell, select RTK Unit Hydrograph.
15. In the RTK Table cell for the catchment, select the appropriate RTK table or click the Ellipses (...) button to create a new table.