Palaeoflood Events Recorded By Sediments From Daluze Paleolake In The Heibei Plain Since Late Holocene

Hebei plain,located in the east of Taihang Mountain and south of Yanshan Mountain,is one of the significant downstream discharge regions of rainstorm.Then,it was aslo one of the main flood-hit areas because of the effects of frequent floods from Taihang Mountain.Daluze Lake was situated at the south central Hebei plain and the alluvial fan front zone of Fuyang River,Zhang River,Hutuo River,etc.As result of one of the main detention basin of floods derived from Taihang mountain,Daluze Lake is the ideal place of studying palaeoflood.Thereforce,the palaeoflood research in this region will provide some important information and scientific basis for assessment and prevention of flooding damage in the future.Sections Yuying?YY?and Yaozhuang?YZ?that is east of Daluze Paleolake were choosed for studying palaeoflood.Grain size,loss on ignition,reflectance,and pollen were analyzed for the sediments from Sections YY and YZ.In combination with the dating results of AMS ¹⁴C and OSL,the frequency and intensity of the Holocene extreme flood events will be assessed.Four and three periods of large paleoflood events can be identified for sections YY and YZ,respectively.Palaeofloods occurred at 3.49 ka BP,2.94 ka BP,2.44 ka BP,and 1.18 ka BP for section YY.And,three palaeofood events of 2.90 ka BP,2.36 ka BP,and 1.27 ka BP can be recorded by sediments from section YZ.Comparing to the two palaeoflood records,it can be determined that there have been four periods of large flood events of 3.49 ka BP,2.9ka BP,2.4 ka BP,and 1.3 ka BP since the Late Holocene.And then,the flood events identified by the ancient river channel in the North China Plain and Palaeoflood slackwater deposit from rivers in the Taihang Mountain occurred at 3.5 ka BP,2.5 ka BP,2 or 1.5 ka BP,which were consistent with our results from Daluze Lake sediments..Flood was generally transient response to the terrestrial hydrological processes for extreme weather events.Paleoflood usually occurred during the periods of climate transition or large hydrological change.The palaeoflood event of 3.5 ka in the Hebei Plain happened to weaker Asian summer monsoon with decreased rainfall and dry climate.Meanwhile,the deterioration of vegetation caused by less rainfall exacerbates floods.Flood of 1.3 ka?the occurring age of 1059 a BP for sectionYanchi next to section Yuying?coincided with the flood of the Huanghe River during the Daguan reign?AD 1108?of the Northern Song,which may be related to drought in the early Northern Song Dynasty.Thus,it can be determined that floods were usually closely related to a dry climateduring climatic transition which was charactered by increased hydrological variability,the declined vegetation,and the reduced vegetation coverage.Furthermore,the destruction of vegetation caused by human activity in Taihang Mountain was also one of the important reasons of the Late Holocene floods.