For some preliminary analyses there may be very little information on the characteristics of a catchment. For cases like this when an estimate is needed for the Time of Concentration, a probabilistic method can be used with only a catchment area.
For obvious reasons these formula should be used as a preliminary estimate and only where no further information is available.
Australian Methods
The below method is used in Australia to estimate Time of Concentration for catchments up to 250km².
US Methods
A number of similar methods have been derived from US studies. Details for some are given below.
Related Spreadsheets from CivilWeb;
Runoff Calculator Spreadsheet
This spreadsheet calculates the design runoff flow for a site in accordance with the a number of different methods including the Wallingford Procedure.
Attenuation Design Spreadsheet
This spreadsheet calculates the requirements for a attenuation system and assists the user to design a suitable system.
Soakaway Design Spreadsheet
This spreadsheet calculates the requirements for a soakaway system and assists the user to design a suitable system.
Full Drainage Design Suite
Full drainage design suite (50% Discount) including 7 spreadsheets;
- Colebrook White Pipe Design
- Manning Pipe Design
- Manning Open Channel Design
- Linear Drainage Design
- Runoff Calculator
- Attenuation Design
- Soakaway Design