Probablistic Methods

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