Abstract:

Through the research of the sedimentary profile in the Quyuan river mouth site on the first river terrace in the upper reaches of the Hanjiang River,a major tributary of the Yangtze River，a set of palaeoflood slack water deposits（SWD）were found in the profile.Samples were taken from field and the grain size,magnetic susceptibility and ignition loss amount were analyzed in detail in the laboratory.The results show that the palaeoflood slack water deposits contained in the profile were different from the palaeosoil and the flood slack water deposits recorded a group of palaeoflood events occurred in the upper reaches of the Hanjiang River.Combined with stratigraphic correlation and OSL technique,the age of the palaeoflood events were determined during 5000-5500 a BP.According to the theory of sedimentology and hydrology,using the palaeoflood slack water deposits pinch out method and slack water deposits thick sand content method,we found that the palaeoflood water level elevation recorded by this profile was 169 m and 171 m,respectively.Restored its peak flow by slope method,the flood peak discharges were reconstructed to be 60 577 m3/s and 68 978 m3/s.At the same time,the result was checked by various methods,such as the modern flood event occurred in 2011,which indicated the reconstructed peak discharge was reliable.This study provides important data for engineering construction in the upper reaches of the Hanjiang River,and provides an important reference for the Middle Route Project of South to North Water Diversion Project