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At the Jinsha site it has been discovered, through field surveys and observations of the geomorphology and sedimentology, that the direction of flow of ancient rivers, obtained through debris fabric measurement, was consistent with the direction in which buried palaeotrees had been broken, indicating that the Jinsha site possibly suffered palaeofloods. By sampling the suspected palaeoflood sediments at the Jinsha site and analysing their grain size distribution and Zr/Rb and Ba/Nb ratios, the paper discovered that the sediments tend to be composed of coarse particles, with a relatively high percentage of traction load components and saltation load components. Various samples had relatively great differences in particle size distribution; the change in the percentage content of coarse sand particles being very obvious, and the sedimentary particles exhibiting upward coarsening within the same layer. The Zr/Rb ratios and Ba/Nb ratios of the sediments reflect the changes in hydrodynamic forces within the sedimentary environment. When the hydrodynamic force was relatively weak, the Zr/Rb ratios are relatively low and the Ba/Nb ratios relatively high; whereas when the hydrodynamic force was strengthened, the Zr/Rb ratios increase and the Ba/Nb ratios decrease. On account of these sedimentological and geochemical characteristics, these sediments are judged to be palaeoflood sediments. The AMS 14 C dating results of the palaeoflood sediments shows that the period when sudden flooding occurred frequently in the Chengdu Plain was 4.0–3.6 ka BP, contemporaneous with an ancient global flooding event. This palaeoflood event probably brought about the extinction of the Baodun Culture. [ABSTRACT FROM AUTHOR]

A set of 121 radiocarbon and OSL dates has been compiled from the Upper Dnieper River and tributary valleys, Western European Russia. Each date was attributed according to geomorphic/sedimentological events and classes of fluvial activity. Summed probability density functions for each class were used to establish phases of increasing and reducing fluvial activity. The oldest detected reduction of fluvial activity was probably due to glacial damming at LGM. Within the Holocene three palaeohydrological epochs of millennial-scale were found: (1) high activity at 12,000-8,000 cal BP marked by large river palaeochannels; (2) low activity at 8,000-3,000 cal BP marked by formation of zonal-type soils on -floodplains; short episodes of high floods occurred between 6,500-4,400 cal BP; (3) contrasting hydrological oscillations since 3,000 cal BP with periods of high floods between 3,000-2,300 (2,000) and 900-100 cal BP separated by long interval of low floods 2,300 (2,000)-900 cal BP when floodplains were not inundated - zonal-type soils were developing and permanent settlements existed on floodplains. In the last millennium, four centennial-scale intervals were found: high flooding intervals are mid-11-mid-15 century and mid-17-mid-20 century. Intervals of flood activity similar to the present-day were: mid-15-mid-17 century and since mid-19 century till present. In the context of palaeohydrological changes, discussed are selected palaeogeographic issues such as: position of the glacial boundary at LGM, role of changing amounts of river runoff in the Black Sea level changes, floodplain occupation by Early Medieval population. [ABSTRACT FROM AUTHOR]

Abstract: We present an annual reconstruction of extreme rainfall events interpreted from detrital layers and turbidites interbedded within a varved sediment record since the 14th century in Montcortés Lake (NE Spain, 1027 m a.s.l.). Clastic microfacies intercalated within the biochemical calcite varves were characterized and their depositional dynamics interpreted using high-resolution geochemical and sedimentological analyses. Annual number of detrital layers was compared against instrumental records of extreme daily rainfalls providing minimum rainfall thresholds and return periods associated to the identified types of clastic microfacies. Non-continuous detrital layers were deposited during rainfall events higher than 80 mm (>2-year return period) while graded detrital layers and turbidites were associated with higher magnitude rainfall events (>90 mm and >4-year return period). The frequency distribution of extreme hydro-meteorological events is not stationary and its pattern coincides with historical floods from the nearby Segre River. High frequency of heavy rainfalls occurred during the periods AD 1347–1400 and AD 1844–1894. A lower frequency of heavy rainfall was found during the periods AD 1441–1508, 1547–1592, 1656–1712, 1765–1822 and 1917–2012. The 20th century stands out as the longest interval within the studied period of very low number of extreme rainfall events. Variability in extreme rainfall events prior to the 20th century is in phase with solar activity, suggesting a mechanistic link in mid-latitude atmospheric circulation patterns that ceased during the 20th century. [Copyright &y& Elsevier]

Abstract: Annually laminated (varved) lake sediments with intercalated detrital layers resulting from sedimentary input by runoff events are ideal archives to establish precisely dated records of past extreme runoff events. In this study, the mid- to late Holocene varved sediments of Lake Mondsee (Upper Austria) were analysed by combining sedimentological, geophysical and geochemical methods. This approach allows to distinguish two types of detrital layers related to different types of extreme runoff events (floods and debris flows) and to detect changes in flood activity during the last 7100 years. In total, 271 flood and 47 debris flow layers, deposited during spring and summer, were identified, which cluster in 18 main flood episodes (FE 1–18) with durations of 30–50 years each. These main flood periods occurred during the Neolithic (7100–7050 vyr BP and 6470–4450 vyr BP), the late Bronze Age and the early Iron Age (3300–3250 and 2800–2750 vyr BP), the late Iron Age (2050–2000 vyr BP), throughout the Dark Ages Cold Period (1500–1200 vyr BP), and at the end of the Medieval Warm Period and the Little Ice Age (810–430 vyr BP). Summer flood episodes in Lake Mondsee are generally more abundant during the last 1500 years, often coinciding with major advances of Alpine glaciers. Prior to 1500 vyr BP, spring/summer floods and debris flows are generally less frequent, indicating a lower number of intense rainfall events that triggered erosion. In comparison with the increase of late Holocene flood activity in western and northwestern (NW) Europe, commencing already as early as 2800 yr BP, the hydro-meteorological shift in the Lake Mondsee region occurred much later. These time lags in the onset of increased hydrological activity might be either due to regional differences in atmospheric circulation pattern or to the sensitivity of the individual flood archives. The Lake Mondsee sediments represent the first precisely dated and several millennia long summer flood record for the northeastern (NE) Alps, a key region at the climatic boundary of Atlantic, Mediterranean and East European air masses, aiding a better understanding of regional and seasonal peculiarities of flood occurrence under changing climate conditions. [Copyright &y& Elsevier]

Abstract: The grain-size distribution (based on cumulative probability curves) in the sediments produced by potential palaeofloods at the Shiniusi archaeological site is similar to that of modern flood sediments from the Wujiang River Drainage in the upper Yangtze River. There is an obvious pattern in the curves, with two segments, and the mean grain size (Mz), standard deviations (σ1), skewness, and kurtosis are all similar. Combined with the AMS14C dating data and the ages judged based on the presence of cultural remains, our data suggests frequent palaeoflood events within the Wujiang River Drainage. We hypothesize the existence of seven high flood possibility layers in the QST4 unit from Shiniusi archaeological site: during the periods of the Ming Dynasty (1368–1644 AD) to the Qing Dynasty (1616–1911 AD), and the end of the Eastern Zhou Dynasty (770 BC–256 BC) to the Shang Dynasty (1600–1100 BC). We also hypothesize ten high flood probability layers in the QST2 unit from Shiniusi archaeological site: during the periods of the Ming Dynasty to the Qing Dynasty, the periods of Song Dynasty (960–1279 AD) to the Yuan Dynasty (1206–1368 AD), as well as during the Han Dynasty (207 BC–220 AD) to the Eastern Zhou Dynasty (770 BC–256 BC). These results are consistent with palaeoflood events inferred from pollen and spore analysis and from historical records in other rivers. [Copyright &y& Elsevier]

Abstract: The cross-referencing of sedimentological, stratigraphic, geoarchaeological and radiocarbon data enables us to establish the geomorphologic evolution of the Late Holocene coastal flood plain of the Turia River. The Holocene marine transgression formed a coastal barrier lagoon environment in the coastal plain. During the Late Holocene, increased sediments supplied to the low reach of the river promoted: (a): the progradation of deltaic coastal sandy ridges on the coastline and (b): the aggradation of the floodplain on top of the sedimentary sequence. Four phases are clearly recognised in the geoarchaeological record of the flood plain. (1): High magnitude flooding events (2800BP to 3rd century BC). (2): Slow riverbed aggradation and progressive levee formation (low energy flood regime) in Roman times (2nd century BC to 5th century AD). (3): Swampy environmental processes (6th to 9th centuries). (4): Second high-magnitude flooding phase (11th century). The navigable channel of the Roman and early Islamic periods became a wide and shallow braided channel in Medieval times. These phases are correlated with others detected by researchers in many areas of the Mediterranean region and with global Holocene climate events. [Copyright &y& Elsevier]