Paleofloods recorded by slackwater deposits in the upper reaches of the Hanjiang River valley, middle Yangtze River basin, China

A paleo-hydrological study was carried out along the upper-reach gorges of the Hanjiang River that drains from the Qinling and Dabashan Mountains. Two bedsets of paleoflood slackwater deposits were found embedded in Holocene loess soil sequences within riverbank cliffs. All of these were studied by field observations and laboratory analyses, including magnetic susceptibility, particle size distribution and optically stimulated luminescence (OSL) dating. These analyses provided a complete catalog of Holocene flood events on a watershed scale that is important for understanding the regional hydrological responses to monsoonal climatic change. The results show that these hydro-climatic events were dated to 9000-8500 and 3200-2800 a B.P. The paleoflood peak discharges were estimated to be 44,35049,860 m(3)/s by using the HEC-RAS model and were verified by different approaches. These results have extended the flood data sequence of the Hanjiang River to a 10,000-year time-scale. The additional data allowed us to refine the flood frequency-peak discharge curve and potentially increase its accuracy. These results will play an important role in mitigating flood hazards and will be useful for hydraulic engineering and the development of water resources in the Hanjiang River basin. (C) 2014 Elsevier B.V. All rights reserved.