Occurrence and magnitude of low flows for Canadian rivers: an ecozone approach

Low-flow occurrence and magnitude have been documented for Canada using the National Ecological Framework. The low flow database is composed of the 7-day low flow with 2-year return period (7Q2) values for 453 natural flow hydrometric stations with record lengths of at least 30 years; drainage areas ranged from 10 to 30 000 km2. Occurrence zones corresponding to predominant season for annual low flows are associated with ecozones. The ecozone scale was found to be suitable for regional analysis for several ecozones. For some ecozones there were insufficient data for regional analysis and for others finer resolution is required. Regional regression equations were developed for estimating 7Q2 in terms of area for ecozones containing at least 20 stations. The results of this work will help practitioners to identify the season of low flow occurrence and the appropriate method of analysis, and provide a means of estimating 7Q2 for ungauged sites for some ecozones.