Time of Concentration
The time of concentration (Tc) is found by summing the time for each individual flow segment within the drainage area. Both single and multiple flow segments are modeled with the Tc calculator.
The General Equation for Tc
The Tc equations provided in Bentley SewerCAD can be categorized into two broad categories:
- Equations that solve for velocity, then use velocity to solve for the travel time through a flow segment
- Equations that directly solve for the travel time through a flow segment--in these cases, the software back solves for velocity and includes it in the output report
Note: Some types of Tc equations can apply to flow segments within a multiple-segment Tc calculation (see preceding diagram). 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.