Time of concentration is a frequently overlooked parameter in urban drainage design. It is often calculated using one of several common equations that are selected based on user familiarity rather than on the characteristics of the drainage basin. Time of concentration can also be calculated incorrectly when the emphasis is placed on finding the longest flow path, which often is not appropriate when used to determine peak flows. This webinar will cover the Kirby-Hathaway Equation; the Kirpich Equation; the FAA Equation; the SCS Method for computing time of concentration; as well as a solution using the physical concepts of sheet flow, shallow concentrated flow, and open channel flow. The webinar will include examples of the different equations and a discussion on when the use of each equation is appropriate. It will also include a discussion on requirements for time of concentration calculations in stormwater design manuals.

Primary Discussion Topics

• Basic concepts of time of concentration, including sheet flow, shallow concentrated flow and open channel flow
• Kirby-Hathaway, Kirpich, and FAA equations
• The SCS method
• Physical Concepts solution
• Appropriate selection of longest flow path

Learning Outcomes

• Know the basic tools needed to select an appropriate method to compute time of concentration
• Become familiar with five different methods that can be used to compute time of concentration
• Understand which method should be used for which type of drainage basin
• Learn how selection of the wrong flow path can impact the calculation of time of concentration and peak flow
• Understand examples of several methods that can be used to compute time of concentration and when each method is appropriate

Webinar Benefits

• Become familiar with five different methods that can be used to compute time of concentration
• Understand which method should be used for which type of drainage basin
• Learn how selection of the wrong flow path can impact the calculation of time of concentration and peak flow

Intended Audience

Civil engineers involved in designing stormwater facilities or regulatory agency personnel responsible for reviewing stormwater facilities or preparing stormwater design manuals.

Webinar Outline

• Basic concepts of time of concentration, including sheet flow, shallow concentrated flow and open channel flow
• Kirby-Hathaway equation, including basin types
• Kirpich equation, including basin types
• FAA equation, including basin types
• SCS Method
• Physical Concepts solution
• Appropriate selection of longest flow path