You can add Time of Concentration (Tc) Methods to a catchment in your model. CivilStorm supports 20 different methods, which are listed below. You define the TC Method in the TC Data Collection dialog box. You can define both single and multiple flow segments for a catchment.

Some types of Tc equations can apply to flow segments within a multiple-segment Tc calculation. Other Tc methods are equations intended to model the entire average subarea flow distance and slope in one single flow segment. When combining multiple flow segments to compute Tc, it is up to you to only combine Tc methods that can be modeled in combination with multiple flow segments.

To define the Tc Method for a catchment:

1. Click a catchment in your model to display the Property Editor, or right-click a catchment and select Properties from the shortcut menu.
2. In the Runoff section of the Property Editor, select Modified Rational Method in the Runoff Method field. The Tc (hours) field becomes available.
3. Click the Ellipses (...) button next to the Tc (hours) field. The Tc Data Collection dialog box appears.
4. Click New, then select a Tc Method from the submenu.
5. Different fields become available depending on which Tc Method you select. For each Tc Method, type values in the appropriate fields.
6. Click OK to close the dialog box and save your Tc Collection data (time of concentration in hours) in the Property Editor.

Tc Data Collection Dialog Box

This dialog box allows you to define the Time of Concentration method. Both single and multiple flow segments can be modeled in this dialog box.

The dialog box contains the Tc Method display pane, which lists all of the methods currently assigned to the catchment, a control section that allows you to edit the attributes associated with the method currently highlighted in the table, and the following buttons:

CivilStorm supports the following 13 methods, which are listed along with the required input data for each:

• User Defined Tc—The user-defined time of concentration (Tc) is a method that allows the direct input of the Tc rather than using an equation to calculate it. This method would be used when the Tc needs to be calculated using a methodology that is not supported by CivilStorm , or when a quick estimate of Tc is sufficient for the analysis.
  • User Defined Tc—Lets you explicitly define the Tc, rather than have it calculated for you using one of the other methods.
• Carter—This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
• Eagleson—This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Manning’s n—The Manning’s roughness value of the catchment section.
  • Hydraulic Radius—Lets you define the hydraulic radius of the catchment section.
• Espey/Winslow—This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Channel Factor—Lets you define the Espey channelization factor of the catchment section.
  • Impervious—Lets you define the percentage of impervious area of the catchment section.
• FAA—This method requires the following input data:
  • Overland Flow Length—Lets you define the length of the overland pipe flow of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Runoff Coefficient—Lets you define the rational C coefficient of the catchment section.
• Kerby/Hathaway—This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Manning’s n—The Manning’s roughness value of the catchment section.
• Kirpich (PA)—This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Tc Multiplier—Lets you define the time-of-concentration adjustment multiplier.
• Kirpich (TN)—This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Tc Multiplier—Lets you define the time-of-concentration adjustment multiplier.
• Length and Velocity—This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Velocity—Lets you define the velocity of flow in the catchment section.
• SCS Lag—This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section of the catchment section.
  • CN—Lets you define the SCS runoff curve number of the catchment section.
• TR-55 Sheet Flow—This number represents the sheet flow time computed for each column of sheet flow data. This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Manning’s n—The Manning’s roughness value of the catchment section.
  • 2 yr. 24 hr. Depth—Depth of 2 year 24 hour storm.
• TR-55 Shallow Concentrated Flow—This number represents the sheet flow time computed for each column of shallow concentrated flow data. This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Is Paved—Lets you specify whether the catchment section is paved or unpaved.
• TR-55 Channel Flow—This number represents the channel flow time computed for each column of channel flow data. This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Manning’s n—The Manning’s roughness value of the catchment section.
  • Flow Area—Lets you define the flow area of the catchment section.
  • Wetted Perimeter—Lets you define the wetted perimeter of the catchment section.
• Friend's Equation—This method requires the following input data:
  • Overland Flow Length—Lets you define the overland flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Horton's Roughness—The Horton’s roughness value of the catchment section.
• Kinematic Wave—This method requires the following input data:
  • Overland Flow Length—Lets you define the overland flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Manning's n—The Manning’s roughness value of the catchment section.
• Bransby-Williams Equation—This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
• HEC-22 Sheet Flow—This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Manning's n—The Manning’s roughness value of the catchment section.
• HEC-22 Shallow Concentrated Flow—This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Intercept Coefficient—Intercept coefficient (from HEC-22 Table 3-3).
• HEC-22 Open Channel and Pipe Flow—This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.
  • Manning's n—The Manning’s roughness value of the catchment section.
  • Flow Area—Lets you define the flow area of the catchment section.
  • Wetted Perimeter—Lets you define the wetted perimeter of the catchment section.
• Wallingford (UK)—This method requires the following input data:
  • Hydraulic Length—Lets you define the flow length of the catchment section.
  • Slope—Lets you define the slope of the catchment section.