Holocene paleofloods related to climatic events in the upper reaches of the Hanjiang River valley, middle Yangtze River basin, China

Holocene slackwater deposits along the river channels were used to study the magnitude and frequency of the paleofloods that occurred prior to gaged and historical data sets all over the world. Paleoflood hydrological investigations were carried out in the upper reaches of the Hanjiang River, China. Four bedsets of paleoflood slackwater deposits were found interbedded in the Holocene loess–soil sequence within the cliff riverbanks. They were studied by field observations and laboratory analysis including magnetic susceptibility, particle size distribution and optically stimulated luminescence (OSL) dating. These provide a complete catalog of Holocene flood events at a watershed scale that is very important in understanding the regional hydrological response to monsoonal climatic change. Four episodes of Holocene overbank flooding have been recorded over the basin. These hydroclimatic events were dated to 8500–8400, 4200–4000, 3200–2800, and 1800–1700 YBP by using the OSL method in combination with pedostratigraphic correlations with the previously studied Holocene pedostratigraphy in the Hanjiang River basin. The peak discharges of these flood episodes vary in a range from 26,610 to 47,900 m3 s− 1 as estimated by using the slope–area method of streamflow measurement. These flood events are therefore considered a regional expression of known climatic events and demonstrate Holocene climatic instability. The study provides a solid reference that magnitudes and recurrence frequencies of floods are highly sensitive to climate change in the monsoonal zone in other parts of the world.