Abstract: In hydrological studies of river and estuary, high/medium/low flow year is generally classified according to annual average runoff. In response to the need of runoff classification in dry season, especially during saltwater intrusion in the Yangtze River Estuary, we examined the differences in classification results of high/medium/low flow year according to annual average runoff, flood-season average runoff, dry-season average runoff, and monthly average runoff in dry season. The classification results according to flood-season average runoff and annual average runoff coincide to a degree reaching 74%, while the results according to dry-season average runoff and annual average runoff coincide with only 38%, and the mean coincidence degree between monthly average runoff in dry season and annual average is 33%. The results suggest that multiple runoff indicators are indispensible for the classification of high/medium/low flow year in various researches on the Yangtze River Estuary.

Key words: runoff, Yangtze River, Datong station, high/medium/low flow year, classification indicators