Estimation of the time of concentration of small watersheds located in Northeastern North America

The time of concentration is an important concept in hydrology. It provides a characteristic hydrologicalresponse time (CHRT) useful in many applications. Estimation of the time of concentration is challengingbecause small watersheds (<100 km²) with sub-daily flow and precipitation records are uncommon. Manypractitioners therefore use empirical equations developed from watersheds exposed to differentclimates and with different attributes. The main objective of this study is to develop an approach toestimate the CHRT from physiographic characteristics for small watersheds located in Ontario, Québecand the northeastern USA. Regression trees are used to identify the physiographic characteristicsassociated with CHRT. The fraction of lakes and wetlands was identified as the most significant attributerelated to CHRT, followed by the ratio between the main watercourse length and the square root of themain watercourse slope. Uncertainties on estimated CHRT values based on regression tree are alsoprovided.