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Benson Liu

Hi Karl,

The time of concentration and critical duration are different concepts. The time of concentration is the time taken for water from the most remote part of the catchment to travel to the location of interest while the critical duration is the storm duration that results in the highest peak flow from the durations that have been run.

Most time of concentration calculations only take into account physical characteristics of the catchment such as area, reach length and slope while the critical duration also takes into account the rainfall inputs such as rainfall depths and temporal patterns. As they use different inputs and represent different aspects of the catchment it is not surprising that they are different.

Kind regards,