By field investigation in the upper reaches of the Hanjiang River

palaeoflood slack-water deposits (SWD)were found in loess profile on Tuojiazhou terrace land in Yunxian County of Hubei Province.Based on field observation

laboratory analysis

including loss on ignition

magnetic susceptibility

calcium carbonate and the grain-size distribution

four SWDs were identified as the most typical Holocene palaeoflood deposits in the Hanjiang River basin and which recorded four palaeofloods events.By using stratigraphic correlations and OSL dating

these four palaeofloods events were dated to 12 600-12 400aB.P.

4 200-4 000aB.P.

3 200-2 800aB.P.and 1 900-1 800aB.P.in Eastern Han Dynasty

respectively.Then according to the palaeoflood peak stages and reasonable hydraulic parameters

the peak discharges of four palaeofloods were calculated by using the slope-area method.To validate the calculation

the flood peak discharges of extraordinary floods in 1983

2005and 2010were also reconstructed by using the same method and hydraulic parameters in the same cross-section.The error between the reconstructed and gauged discharges was 1.99%~4.21%.This indicated that the reconstructed palaeoflood peak discharges were reliable.And the reconstructed results of palaeoflood discharges were also consistent with the relationship between palaeoflood peak discharge and drainage area.This study prolonged the flood data sequence of Hanjiang River to a time-scale of over 10 000-years.More importantly

it provided significant data for flood control and hazard mitigation in the upper reaches of the Hanjiang River.