Calculating the Time of Concentration
If:
And:
- The Tc Data Collection is set to TR-55 Sheet Flow, TR-55 Shallow Concentrated Flow, or TR-55 Channel Flow, or any combination of these
The Tc Data Collection of the catchment shown above has the following settings:
The Tc Methods can be either be set in the Prototype for the catchment - before the catchment is automatically delineated, or specified in the properties for the catchment - after it has been automatically delineated.
Note that the Hydraulic Length and Slope properties in the picture above are currently zero. The purpose of the Calculate Flow Path command is to calculate these values, for each method.
Clicking the Calculate Flow Path icon reads the overall length of the Flow Path, which is automatically calculated when the catchment is automatically delineated. The Calculate Flow Path dialog is displayed, and by default the overall length of the Flow Path is assigned to the first Tc Method:
To specify a smaller Hydraulic Length for the first Tc Method, select the first row and click the Select Location icon. The Flow Path is displayed graphically, and you can specify a position along it to define the new length:
The remainder of the overall Flow Path length is assigned to the next Tc Method. Alternatively, you can type a new length directly in the dialog.
Having defined the Hydraulic Lengths for each Tc Method, click Accept to update the data for the catchment. The Tc Data Collection is now updated to include the new values for the Hydraulic Length and Slope properties.
The Slope value is calculated using the elevations from the terrain model that was used to automatically delineated the catchment, at the relevant locations along the Flow Path.
Specifying a Time of Concentration (Tc) Method for a Catchment