Reconstruction palaeoflood hydrology using slackwater flow depth method in the Yanhe River valley, middle Yellow River basin, China

Abstract

Water depth above the flood deposits should be taken into account in calculations of the palaeoflood peak stages, which can provide more accurately estimate of palaeoflood stage. Here we present a new method, slackwater flow depth, to assess palaeoflood peak stage and to reduce the underestimation of palaeoflood stage. Palaeoflood slackwater deposits (SWDs) were identified by palaeohydrological criteria in cliff riverbank on the Yanhe River, middle Yellow River basin. Palaeoflood events recorded in four layers of SWD were dated by optical stimulated luminescence to 9.5–8.5ka. The estimation of palaeoflood maximum stage was 778.3m using the slackwater flow depth method and the palaeoflood peak discharge is 15,000m3/s using the step-backwater method. Palaeoflood results greatly extend the current flood data series in the Yanhe River basin. The regional flood history including gauged flood, historical and palaeoflood data was compiled and evaluated for the major tributaries of the middle Yellow River. The relationship between palaeoflood peak discharges and drainage areas in this region fit well with the global maximum curves. The results of site-specific and regional palaeoflood evaluations demonstrate that the approach estimates the true palaeoflood peak stage and discharges and improves the flood frequency analysis of extreme and rare floods for a particular basin. Meanwhile, the advantages and uncertainties of this method need ongoing discussion in palaeoflood investigations.