Sedimentary records of large Holocene floods from the middle reaches of the Yellow River, China

Slackwater deposits have been used as evidence for the magnitude and frequency of palaeofloods which occurred prior to gauged and historical data sets, e.g., Holocene extreme flood reconstruction in North America and Australia. The slackwater deposits from Xiaolangdi Reach of the Yellow River have been identified and related to floods according to both eyewitness accounts and the analysis of sediments. The technique successfully delineated the peak flood level and estimated a discharge of the 1994 AD flood in the Yellow River. The discrepancy of the estimated discharge was less than 5% compared with the instrumental records. When we applied the technique to palaeoflood analysis, the highest slackwater deposits and flood indicators from the tributary mouths, the low river terraces, and the loess platforms and loess alcoves, together with radiocarbon dating, provided evidence of at least six floods with peak discharges greater than 27,300 m(3) s(-1) at Xiaolangdi Section over the last 8500 yr. The largest flood in ca. 7362 yr B.P. had an estimated discharge of 42,900 m(3) s(-1), which is the maximum flood event known in the Yellow River. The results provide a basis for (a) determining the floods which were comparable to the most cataclysmic flood during the last 2360 yr in 1843 AD and (b) estimating the flood magnitude for a 10,000 yr time-scale relevant for building Xiaolangdi Dam, one of the largest dams under construction in the world. The reconstruction of palaeofloods also provides evidence for a phase between ca. 6000-8000 yr B.P., which was much wetter than today, as a result of increased summer precipitation and enhanced Pacific monsoon conditions in eastern China. (C) 2000 Elsevier Science B.V. All rights reserved.