Reconstructing the magnitudes of Holocene extraordinary floods in the upper Huai River, China

Abstract

Palaeoflood natural archives provide vital insights for reconstructing extraordinary flood magnitudes and understanding climate change. Palaeohydrological investigations were conducted in the upper Huai River, North China Plain. A Holocene loess-paleosol sedimentary profile containing six palaeoflood slackwater deposits (SWD, SWD6–SWD1) was identified in the Luzhuang reach of the upper Huai River, where the Maoji River (a tributary of the Huai River) enters the Huai River. Sediment samples were collected for physicochemical analysis and optically stimulated luminescence (OSL) dating, respectively. The results revealed that the sedimentary accumulation consists of modern soil (MS), paleosol (S₀), aeolian loess (L₀), and transitional loess (L_t) sediments were predominantly silt (>50 %), whereas SWDs were mainly sand (>60 %). Geochemically, the elemental composition of SWDs was similar to that of MS, S₀, and L₀ sediments, but distinct from L_t. The MS, L₀, S₀, and L_t sediments demonstrated moderate weathering that was more pronounced than that of SWDs. Using OSL dating and stratigraphic chronological frameworks, six extraordinary palaeoflood events have been identified in the Luzhuang reach of the upper Huai River since approximately 8.5 ka in the Holocene. The palaeoflood magnitudes were reconstructed using the HEC-RAS hydraulic model, with six reconstructed palaeoflood peak discharges ranging from 9260 to 17,810 m³/s. Moreover, the sensitivity of the peak discharge calculated using the HEC-RAS model to the roughness coefficient was low, with a relative error of only −8.7 %–2.9 %. These extraordinary palaeoflood events corresponded to periods of climate change and instability, closely related to the El Niño-Southern Oscillation (ENSO). This study provides valuable insights into the effects of global change on regional hydrological systems.