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Evidence for ungauged large freshwater palaeofloods in valley‐confined landscapes frequently includes giant flow‐eddy bars, deposited in alcoves along the floodway margins. Elevations of the bar tops commonly are used to define the minimum water level for computational flood simulations. Field study has shown that giant bar stratigraphy and sedimentology can be distinctive; identifying the alluvial signature of large palaeofloods where the morphological evidence may be less clear. However, whether the shape and stratigraphy of eddy bars provide indicators as to the nature of the floodwaves has not been considered widely. Flood hydrographs might be dam‐break surge waves, gradually varied, or steady flows, for example. Yet, if bar form and stratigraphy vary systematically with the nature of the flood wave, then bars have additional value in defining the style of unrecorded floodwaves for environmental interpretation and flood modelling purposes. An experimental water flume was used to reproduce three styles of scaled floodwave that might be associated with sudden and more protracted releases of water from upstream reservoirs. Discharge was through a channel consisting of a series of contractions and expansions. Eddy bars were deposited within the flow separation zones that formed at each flow expansion. The basic hydraulic characteristics of the floodwaves were recorded and the form of the bars and the stratigraphy were examined. The results indicate that each style of flood deposited a distinctive barform and related stratigraphy. In this manner, we demonstrate that the examination of the form and stratification of giant bars in the natural environment can provide information on the style of the palaeoflood – sudden release or protracted flow – that was responsible for the deposition of the bars. Such information assists with the identification and interpretation of the nature and source of the floodwater as well as informing attempts to model hydrograph shapes. [ABSTRACT FROM AUTHOR]

There are major challenges in dealing with the effects of climate change on flood hazard world-wide. Discharge resulting from extreme rainfalls depend on catchment characteristics and commonly represent a local response that cannot be interpreted entirely from climate models. In practice, this uncertainty makes it difficult to adapt to future risks as mandated by the European Flood Directive (2007/60/EC). In a case study (rambla de la Viuda, Castelló) an analysis of peak discharges (100-year recurrence) has been applied based on extreme precipitation projections (RCP 8.5 scenario) made with regional climate models (Eurocordex), and converted into instantaneous discharge using a distributed hydrological model (TETIS). The analysis shows a high variability in the results, making difficult to determine the goodness of the climate models. On the other hand, long series of floods obtained from historical and sedimentary records (paleofloods) have been analysed, obtaining centennial long records of flood discharges. This information incorporates flood events that have occurred in past periods of relative warming or increased flood activity, considering that extreme events that have occurred in the past may be repeated in the future. These past discharges have been analysed in conjunction with instrumental records, substantially improving the calculation of the flood quantiles required in the Flood Directive hazard maps. Paleoflood extreme data allow validation of climate and hydrological model data for high quantiles. This approach is a win-win action, relatively low-cost, and allows progressing on the adaptation to climate change. Likewise, this information from the past provides "real" evidence of flood events as a direct guide of flood possibilities, such that local people are motivated to deal with their local flood problems increasing the risk culture. [ABSTRACT FROM AUTHOR]

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Extreme rainfall is projected to increase with climate change, but the impact of climate change on floods is uncertain. Infrastructure design based on information available from short gauged time series (typically ~30 – 80 years) may not take account of the full range of possible flood events, or be suitable for identifying non-stationarity. Australian palaeoflood and palaeo-hydroclimate records drawn from a wide variety of natural archives and documentary sources suggest that Australia has been subjected to larger flood events in the past; a pluvial period for eastern Australia in the eighteenth Century is particularly note-worthy. If the current infrastructure is inadequate for past floods, it is unlikely it will adequately mitigate future floods. We discuss how improved awareness, and incorporation, of palaeoflood records in risk estimates could help guide infrastructure planning and design, flood event prediction and inform flood mitigation policy. This is particularly relevant for Australia with its notoriously variable hydroclimate. [ABSTRACT FROM AUTHOR]

Extreme floods are anticipated to become more frequent in a future warmer climate. However, the long-term alterations in flood patterns across different regions of Europe remain unclear. In this study, we present a 15,000-year record of extreme floods in the Duero River, located in the southwestern Atlantic region. We analysed slackwater flood sediments, quantified the discharge and timing of individual flood beds over millennial time scales, and identified their potential climate influences. The composite record includes at least 62 floods grouped into ten flood-rich periods (with an average duration of 230 years). A high-frequency phase of moderate-magnitude floods (>10 events) occurred at ∼11.6–11.5 ka, following a period of reduced flood activity during the Younger Dryas. Similar clusters of Early Holocene floods (10.8–10.3 ka, 9.5 ka) coincided with or preceded meltwater pulses from the North Atlantic. The absence of palaeoflood records with discharges exceeding 6100 m3/s during the Mid-Holocene suggests a decline in winter hydro-meteorological extremes. High flood magnitudes were recorded during transition periods toward cooler and wetter conditions at 4.4, 2.3, 0.5, and 0.11 ka with discharges ranging from 7600 to 10,000 m3/s. These periods were interpreted as indicative of a southward shift in cyclone tracks in Europe driven by negative phases of the North Atlantic Oscillation (NAO). Conversely, flood magnitudes decreased during past warmer climate conditions (1.7 ka, 0.9 ka, and the present), although flood frequency remained high. The current decline in flood frequency reflects an increase in flood regulation due to dams, but it is also consistent with the prevailing positive trend in the NAO observed over the last 40 years. • 15-ka record of extreme floods in one of the largest river catchments in S Europe. • Early Holocene flood-rich periods overlap frequencies of meltwater pulses. • Floods decrease during Mid-Holocene indicating a positive mode of NAO-like circulation. • Late Holocene flood clusters are associated with negative NAO and strong Siberian High. • Flood magnitude declined during past warm periods including the present time. [ABSTRACT FROM AUTHOR]

The surface of the lowland deltaic plain around Taihu (Lake Tai), south of the Yangtze river mouth in eastern China, lies near sea level and until recent drainage and development by human societies was mostly covered by wetlands of various types. It was created by regular overbank flooding, mainly from the Yangtze, and the deposition of mostly mineral sediments over the several millennia since sea level regained its current altitude in the early mid-Holocene and progradation of the Yangtze delta began. Fluvial activity has therefore been the dominant influence on sedimentation in the Taihu lowlands, and in the lower Yangtze valley generally, and has determined the character of the mainly inorganic sediment sequences that have accumulated there, with autochthonous deposition of organic sediments within the local wetland plant communities playing a minor role. The presence of both clastic flood horizons and peat layers within the deposits of the Taihu plain attests to great variability in the magnitude of fluvial input from the Yangtze, with repeated extreme floods occurring at some periods, but with periods when the growth of peat layers shows low water tables, little exogenic sediment input and so little fluvial influence. We have examined the published evidence for these different depositional environments in the lower Yangtze and the Taihu plain during the Holocene, comparing the flood history with the middle and upper reaches of the Yangtze catchment. Discrete phases of high or low flooding influence are recognised, and these correspond with large-scale Holocene climate history. Intensified human land use in recent millennia has complicated this relationship, amplifying the flooding signal. Our palynological research shows that algal microfossil type and abundance is a useful proxy for changing water depth and quality in the aquatic environments of the Holocene Taihu wetlands, and can recognise flooding events that are not registered in the floodplain lithological sequences.

A detailed field study was conducted on the palaeoflood deposit profile in the Baoji–Tianshui Gorge in the upper Weihe River. The sequence of palaeoflood events was established through field observation and grain size analysis with chronological supports from Optical stimulated luminescence (OSL) dates and from archaeologically-constrained age frameworks. The paleoflood peak water level and peak discharge were reconstructed using the "pinch-out elevation method" and the "thickness-sediment content relationship." The results show that three large-scale paleoflood events occurred during a period of 3200–3000 yr BP in the Baoji–Tianshui Gorge, upper Weihe River. The peak water levels varied between 660.48 and 661.40 m and the peak discharge varied between 23,200 and 25,200 m3/s among the three large-scale paleoflood events. The same methodology was used to calculate the modern flood peak discharges that yielded a deviation of only 3.6% between the reconstructed and measured peak discharges, further verifying the acceptance of this method for the reconstruction of paleoflood peak discharges. This studyexpanded the database of the palaeoflood hydrology research in the Weihe River and the expanded database may be useful in providing important information for projects such as water conservancy, hydropower, engineering construction, flood control, and disaster mitigation. [ABSTRACT FROM AUTHOR]

Climate change implies changes in the frequency and magnitude of flood events. The influence of climate variability on flooding was evaluated by an analysis of sedimentary (palaeofloods) and documentary archives. A 500-year palaeoflood record at Montlleó River (657 km2 in catchment area), eastern Spain, revealed up to 31 palaeofloods with a range of discharges of 20–950 m3 s−1, and with at least five floods exceeding 740–950 m3 s−1. This information contrasts with the available gauged flood registers (since year 1971) with an annual maximum daily discharge of 129 m3 s−1. Our palaeoflood dataset indicates flood cluster episodes at (1) 1570–1620, (2) 1775–1795, (3) 1850–1890, and (4) 1920–1969. Flood rich periods 1 and 3 corresponded to cooler than usual (about 0.3 °C and 0.2 °C) climate oscillations, whereas 2 and 4 were characterised by higher inter-annual climatic variability (floods and droughts). This high inter-annual rainfall variability increased over the last 150 years, leading to a reduction of annual maximum flow. Flood quantiles (>50 years) calculated from palaeoflood+gauged data showed 30%–40% higher peak discharges than those using only instrumental records, whereas when increasing the catchment area (1500 km2) the discharge estimation variance decreased to ~15%. The results reflect the higher sensitivity of small catchments to changes on flood magnitude and frequency due to climate variability whereas a larger catchment buffers the response due to the limited extent of convective storms. Our findings show that extended flood records provide robust knowledge about hazardous flooding that can assist in the prioritization of low-regret actions for flood-risk adaptation to climate change.

Luminescence chronologies for two new slackwater flood deposit (SWD) sites (Broken River northeast Queensland and Ord River northwestern Western Australia) are presented and these along with other SWD chronologies from the same regions are compared with recently developed high resolution, isotope tropical cyclones (TC) records. Heightened TC activity occurred between 1400 and 1850 CE in Queensland and between 1500 and 1850 CE in Western Australia. A distinct clustering of flood events in northwest Western Australia during the period of enhanced TC activity suggests the two may be related. The SWD records in northeast Queensland do not cluster specifically during the period of heightened TC activity however several major floods do occur during this time suggesting that TCs may have been involved. [ABSTRACT FROM AUTHOR]

This paper provides a new methodological approach to analyse secular patterns of flooding (magnitude and frequency) from sedimentary evidence (palaeofloods), taking into account changes in channel geometry, and their links to historical environmental changes and the inherent social and demographic evolution within the catchment. A case study analysis was focused in Rambla de la Viuda (drainage area of 1500 km 2 ) whose stream flow is related to extreme rainfalls. A 500 years sedimentary archive was reconstructed from eight stratigraphic profiles comprising continuous sequences of slackwater flood deposits interbedded with episodic colluvial and edaphic horizons. Discharge estimates associated to sedimentary flood evidences were obtained from one-dimensional hydraulic modelling. The stratigraphic units were sampled to characterise their geochemical and paleobotanical (phytoliths) contents. Palaeoflood chronology was obtained from radiocarbon and luminescence (OSL) dating, supported by documentary data (written historical documents). A high frequency and high magnitude palaeoflood period took place during the 15 th -middle 16th century, which seem to correlate in time with general wetter conditions. Three short-term environment stability conditions (land use and climatic) also made possible the development of three paleosols. The lowest flood magnitude and discharges in the sedimentary record was found between the mid-17th to mid-18th centuries, under prevailing drier environmental conditions. Episodic high magnitude flooding took place at late 18th century, correlating in time with palaeovegetation and geochemical evidences of important changes on land use (deforestation and grazing). Poorer developed soils were found at upper stratigraphic sequences (19th century) characterised by thick units of colluvium deposits, usually culminating sequences of short-lived continuous slackwater flood units. Despite of the potential human influence (land-use) on soil hydrology, the long-term behaviour of high magnitude floods (>1000 m 3 s -1 ) has been stationary over the last 500 years. [ABSTRACT FROM AUTHOR]

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]

Palaeo–hydrological and sedimentary investigations were carried out in the Longmenxia Gorge of the middle Yihe River. Five bedsets of flood slackwater deposits (SWD) were found interbedded into Holocene aeolian loess–soil profiles in the river bank at the Longmenxia site. They were identified as the deposits of the suspended sediment load during the extreme flood events of the Holocene. The minimum flood peak discharges were estimated to be 12, 300–15, 300 m 3 /s using the slope–area method. These are about twice the largest gauged record (7180 m 3 /s) that has occurred since 1937. These flood events occurred at 3100–3000 a B.P., 1800–1700 a B.P., 700–550 a B.P. and 350–250 a B.P., as dated by optically stimulated luminescence (OSL) in combination with stratigraphic correlation, to which may be added the recorded events of the 223 and 1761 CE floods. These were associated with Holocene monsoonal shifts and abrupt climatic events. This research not only provides palaeoflood discharge estimates on the middle Yihe River, but also provides important data for understanding interactions between regional hydro–climatic systems and global climate change in humid and semi–humid monsoonal regions, such as China. [ABSTRACT FROM AUTHOR]

Palaeofloods and drainage palaeostage can be approached from sedimentological, stratigraphical, geomorphological, geodetic, and geophysical information. This allows us to supply pre-instrumental and historical data and to assess a particular flood-prone area. It has been proved that the study of Late Holocene fluvial sediments is valuable source to estimate 1 × 102-1x103yr. scale occurrence and long-term recurrence of maximum events. The geological evidence of palaeofloods in lowlands in Central Argentina may reveal higher discharges likely occurred in the near past. In this work, we attempt to identify sedimentological evidence of past floods in Late Holocene sediments from the northern Salado River (NSR), an important tributary of the lower Paraná River basin (Chaco-Pampean plain region). In the yr. 2003, the lower reaches of the NSR recorded an extreme flood event that provoked a disaster in Santa Fe, a city of 500,000 inhabitants located at the river mouth. Considering the importance of this event, we developed a geomorphometry methodology for discriminating different levels of fluvial terraces and flood indicators in a representative area of the NSR, using multi-scale resolution Digital Elevation Model (DEM) data. Descriptions of flood-associated fluvial landforms and sedimentological stratigraphic attributes were performed in the field. High-resolution geodetic information and digital optical images were obtained from UAV photogrammetry. Ground Penetrating Radar (GPR) cross-sections were achieved and addressed to detect extreme flood evidence. A geomorphometric routine was applied to simulate the extreme flood scenarios, based on the data obtained from the field. The map resulting from the simulation was compared to satellite images recorded in the yr. 2003 extreme flood. A series of slackwater deposits and other palaeostage indicators (SWD-PSI) showed elevations higher than those reached over the yr. 2003 extraordinary flood (instrumentally recorded) and in the yr. 1914 historic flood event. The geomorphometric simulation of a flood event, calibrated from these diagnostic landforms, allowed us to extend the flood-prone area beyond the boundaries of the current active floodplain and channel. The integrative methodology enabled the mapping of areas potentially prone to flooding. The estimations of the discharges associated to the inferred palaeofloods could be 50–80% larger than the maximum events historically documented and instrumentally measured. • Combined geological and geodetic record enable reconstruction of extreme palaeofloods. • Palaeoflood indicators are more realistic tracks for flooding hazard assessment. • Geomorphometric routines calibrated in the field enable mapping maximum flood areas. • Sequence fluvial stratigraphy is a good approach for palaeoflood succession studies. [ABSTRACT FROM AUTHOR]

Mediterranean fluvial hydrology is characterised by decadal-to-multi-centennial length wet and dry episodes with abrupt transitions related to changes in atmospheric circulation. Since the mid-1990s site-based flood chronologies from slackwater deposits in bedrock rivers and regionally aggregated flood histories from alluvial deposits have developed increasingly higher resolution chronological frameworks, although regional coverage is still uneven. This paper analyses the spatial and temporal distribution of extreme Holocene hydrological events recorded in fluvial stratigraphy in the Iberian Peninsula (Spain and Portugal), southern France, southern Italy, Northern Africa (Morocco and Tunisia) and eastern Mediterranean (Greece, Crete, Turkey, Cyprus and Israel). This study constitutes the most comprehensive investigation of Holocene river flooding ever undertaken in the Mediterranean and is based on the analysis of 515 14 C and 53 OSL dates. It reveals that flood periods in different regions cluster into distinct time intervals, although region-wide flooding episodes can be identified at 7400–7150, 4800–4600, 4100–3700, 3300–3200, 2850–2750, 2300–2100, 1700–1600, 1500–1400, 950–800, ca. 300, 200–100 cal. BP. Periods with more frequent floods in the western Iberian region coincide with transitions to cool and wetter conditions and persistent negative NAO mode. In Northern Africa increased flood frequency coincides with periods of generally drier climate, while in the eastern Mediterranean there is a higher incidence of extreme flood events under wetter conditions. Our meta-data analysis identifies an out-of-phase pattern of extreme events across the Mediterranean over multi-centennial timescales, which is particularly evident between the western Iberian and eastern Mediterranean regions. This centennial-to-multi-centennial see-saw pattern in flooding indicates that bipolar hydroclimatic conditions existed in the Mediterranean during the Holocene. [ABSTRACT FROM AUTHOR]

Results of OSL dating and sedimentary studies from the profile of the low alluvial terrace of the middle Warta River are presented. The samples were dated using the single-aliquot regenera-tive method. Dating was used to establish a timing of the Weichselian Late Glacial events in the river valley environment. Stable conditions on the floodplain are expressed by the deposition of organic-rich series radiocarbon dated at 12 900-12 600 cal BP and 11 600-10 770 cal BP. Samples for OSL dating were collected from the mineral material deposited during the intensification of flood events during the Weichselian decline. The results obtained for the alluvia range from 12.78 ± 0.62 ka b2k to 14.33 ± 0.74 ka b2k. Sedimentological criteria allowed to distinguish between particular flood events. Overestimation of OSL ages is probably a result of rapidity of environmental changes in that time. [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]

We report the occurrence of large floods in the Sabarmati River Basin during cal AD 1400-1440. Slackwater palaeoflood deposits have been preserved in the highly dissected ravines along the middle reaches of the river, wherein 5-6 discrete flood events have been identified. The minimum discharge that emplaced the highest deposit has been estimated as ~15,680 m³s-1 and is higher than that recorded (3050 m³s-1) during the recent 2006 flood. The timing of these high-magnitude flood events in the Sabarmati and adjacent river basins suggests that extreme hydrological events have occurred in response to excess monsoon periods and are largely controlled by the regional climatic conditions. Moreover, these flood events are seen to be broadly synchronous in the alluvial river basins of Gujarat across climatic zones, but are at variance in pattern from the records of the bedrock peninsular rivers. [ABSTRACT FROM AUTHOR]

South Asia is drained by some of the most flood-prone rivers in the world. Flooding during the monsoon season is the most recurring, widespread and disastrous natural hazard in South Asia that results in enormous social, economic and environment consequences every year. Several massive floods have occurred in the recent decades causing huge economic losses and human suffering. On average, the total damage is close to USD 1 billion annually. To answer the question whether flooding in South Asia is getting worse and more frequent, all available data were considered: the annual peak discharge data for major rivers, post-1985 information on floods from the global archive of large floods and palaeoflood records from nine Indian rivers. According to the global archive data, 372 large and 55 extreme flood events have occurred since 1985. Although there is no significant trend, all types of data point to clustering of large floods. Palaeoflood records show that modern floods (post-1950) have higher flood levels than the late Holocene floods. Notwithstanding the limitations of data, there is enough evidence to conclude that (1) incidences of flood-generating extreme rainfall event are rising and (2) human interventions have made the recent floods more destructive. [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: Two stages of depositional high-discharge fluvial environments are recorded in the infilling of a rock shelter in a canyon of the Segura River, namely: (1) First stage: aggradational alluvial gravels in the lower part, interpreted as braided channel bars (Seventh millennium to 2030calBC), and (2) Second stage: slackwater flood deposits in the upper part (between 2030calBC and after 900AD) during a stage of main channel incision. Reconstructed flood discharges for the second stage were a minimum of 700m3/s. Extreme palaeofloods that inundated the cave from the canyon inlet were successively higher and are correlated to quick-rising flash floods. The characteristics of cultural remains preserved by flood deposits reveal long periods of human cave occupation (and passage through the canyon) without extreme floods occurring. These long periods of low-discharge fluvial flow punctuated by catastrophic flash floods are linked to a torrential fluvial regime. The torrential regime is the current hydrologic and climatic scenario in the streams of semi-arid southeastern Spain. It is discusses the climatic versus anthropogenic factors affecting the fluvial development. We conclude that the archaeo-fluvial record of the Pozo Rock Shelter indicates that the present-day semi-arid conditions of the southeastern Spain drylands extend back to circa 4000yr BP. Methodologically, the combination of fluvial palaeohydrology and geoarchaeology appears to be a robust tool to reconstruct long-term Holocene climate changes. [Copyright &y& Elsevier]

ABSTRACT The largest Kuiseb River floods initiate at the basin's semi-arid headwater. Downstream, along the hyperarid Namib Desert, these floodwaters are feeding shallow alluvial aquifers, the only available water for human activity and for the natural ecology. Here, we characterize the largest floods and their changing frequency and magnitudes using palaeohydrological methods. Along 120 km of the rivers canyon 35 palaeoflood deposit sites were identified. At five of these sites we conducted stratigraphic and geochronological analyses and flood discharge estimations. The upper bound of the largest flood over the late Holocene is ∼1475 m3 s−1. Over the last 1300 years more than ten floods have exceeded 1250 m3 s−1. An additional 33 floods exceeded 400 m3 s−1. The last millennium was characterized by one large flood every 30-40 years during the periods 1250-1335, 1355-1565 and 1715 AD to the present. A slight increase in flood frequency (not magnitude) occurred during 1565-1715 AD (one large flood in ∼20 years) and during two short episodes, 1185-1205 and 1335-1355 AD (seven and four floods in 20 years, respectively). These episodes of increased flood frequency are associated with other proxy records of higher water availability in the Namib. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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]

This paper provides a synoptic view of extreme monsoon floods on all the nine large rivers of South Asia and their association with the excess (above-normal) monsoon rainfall periods. Annual maximum flood series for 18 gauging stations spread over four countries (India, Pakistan, Bangladesh and Nepal) and long-term monsoon rainfall data were analyzed to ascertain whether the extreme floods were clustered in time and whether they coincided with multi-decade excess monsoon rainfall epochs at the basin level. Simple techniques, such as the Cramer's t-test, regression and Mann-Kendall (MK) tests and Hurst method were used to evaluate the trends and patterns of the flood and rainfall series. MK test reveals absence of any long-term tendency in all the series. However, the Cramer's t test and Hurst-Mandelbrot rescaled range statistic provide evidence that both rainfall and flood time series are persistent. Using the Cramer's t-test the excess monsoon epochs for each basin were identified. The excess monsoon periods for different basins were found to be highly asynchronous with respect to duration as well as the beginning and end. Three main conclusions readily emerge from the analyses. Extreme floods (>90th percentile) in South Asia show a tendency to cluster in time. About three-fourth of the extreme floods have occurred during the excess monsoon periods between ~1840 and 2000 AD, implying a noteworthy link between the two. The frequency of large floods was higher during the post-1940 period in general and during three decades (1940s, 1950s and 1980s) in particular. [ABSTRACT FROM AUTHOR]

A new methodology, based on Bayesian age modelling, is presented for the analysis of palaeoflood geochronologies and palaeodischarge data. Bayesian age models were developed, using the Oxcal radiocarbon calibration software, for the geochronologies of three palaeoflood sites in Spain, namely the Gaudalentín, Tagus and Llobregat rivers in SE, Central and NE Spain, respectively. The age–depth plots resulting from the applied Sequence models enabled the construction of flood magnitude-frequency plots through substitution of the original stratigraphic depth data with the associated minimum discharge quantified by hydraulic modelling. The age models presented demonstrate that a Bayesian approach for analyzing Holocene flood magnitude and frequency prevents the loss of geomorphic and hydrologic information inherent in radiocarbon frequency methods previously used in the analysis of palaeoflood data sets. Frequency approaches do not allow proper consideration of flood magnitude information and only incorporate those geomorphic units specifically dated. The Bayesian age models calculate modeled ages for undated units as well, so that all the individual flood events identified in the field can be incorporated and visualized in the data output. The palaeoflood age models therefore illustrate: (1) the age range for clusters of palaeoflood events; (2) the number of events within each flood cluster, with an age estimate and palaeodischarge value for each event; and (3) the potential impact of discharge censoring on the record, for example the role of accommodation space infilling on the quantification of palaeodischarge. The methodology and results are briefly discussed within the wider context of fluvial palaeohydrology, in particular: (1) the role of Bayesian modelling in future fluvial palaeohydrology research; and (2) the value of bedrock gorge sites for investigating past flood–climate relationships, given the problems of deciphering allogenic and autogenic drivers in alluvial sedimentary records. [ABSTRACT FROM AUTHOR]

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]

Abstract: A long-term flood record from the Buffels River, the largest ephemeral river of NW South Africa (9250 km2), was reconstructed based on interpretation of palaeoflood, documentary and instrumental rainfall data. Palaeoflood data were obtained at three study reaches, with preserved sedimentary evidence indicating at least 25 large floods during the last 700yr. Geochronological control for the palaeoflood record was provided by radiocarbon and optically stimulated luminescence (OSL) dating. Annual resolution was obtained since the 19th century using the overlapping documentary and instrumental records. Large floods coincided in the past within three main hydroclimatic settings: (1) periods of regular large flood occurrence (1 large flood/~30yr) under wetter and cooler prevailing climatic conditions (AD 1600–1800), (2) decreasing occurrence of large floods (1 large flood/~100yr) during warmer conditions (e.g., AD 1425–1600 and after 1925), and (3) periods of high frequency of large floods (~4–5 large floods in 20–30yr) coinciding with wetter conditions of decadal duration, namely at AD 1390–1425, 1800–1825 and 1915–1925. These decadal-scale periods of the highest flood frequency seem to correspond in time with changes in atmospheric circulation patterns, as inferred when comparing their onset and distribution with temperature proxies in southern Africa. [Copyright &y& Elsevier]

Abstract: Channelized, surface, liquid flow occurs on Earth, Mars, and Titan. In this paper, such fluvial flow is constrained to involve volatiles that can undergo phase transitions under surface conditions and can be stable as liquids over geologically significant periods of time. Evidence for channelized, surface, liquid flood flow has been observed on Earth and Mars and hypothesized for Titan. The mechanisms for generating flood flow vary for each body. On Earth, the mechanism that generated the largest flooding is widespread glaciation (e.g. the catastrophic release of water from glacial lakes), which requires an atmospheric cycle of a volatile that can assume the solid phase. Volcanism is also a prevalent cause for terrestrial megaflooding, with other mechanisms producing smaller, though more frequent, floods. On Mars, the mechanism for flood generation has changed over the history of the planet. Surface storage of floodwater early in the history of that planet gave way to subsurface storage as the climate cooled. As on Earth, flooding on Mars is an effect of the ability of the operative volatile to assume the solid phase, although on Mars, this solid phase occurred in the subsurface. According to this paradigm, conditions on Titan preclude extensive megaflooding because the operative volatile, which is methane, cannot as easily assume the solid phase under current conditions. Mechanisms that produce smaller but more frequent floods on Earth, namely extreme precipitation events, are likely to be the most important flood generators on Titan in the recent past. [Copyright &y& Elsevier]

Palaeoflood records are of great significance in revealing the magnitude and frequency of large floods and thus the past monsoon conditions. The Mahi River, one of the major west-flowing rivers of India controlled by the southwest monsoon has preserved deposits of past floods dating back to 5 ka. A flood deposit emplaced by a mega flood event with discharge ~7300 m3s-1 has been found at Diapattan in the upper reaches of the Mahi River basin. Based on the pottery available at the site, the event can be said to belong to late-medieval time. The timing of this mega flood event recorded at Diapattan in the Mahi River basin and records of the adjacent river basins suggest that this event represents the strengthened monsoon during the Medieval Warm Period (900-1400 AD). There exists a correlation between the extreme hydrological events in the Mahi, Narmada and Tapi river basins and this can be attributed to a regional monsoon domain. [ABSTRACT FROM AUTHOR]

Abstract: Palaeoflood chronologies from seven Spanish river basins and floodplain aggradation chronologies from thirteen rivers are analysed. These fluvial records were divided in to two sub-sets, namely Atlantic (10 ka record) and Mediterranean (3 ka record) river basins, which represent distinct modern hydroclimatic conditions. In Atlantic basins floods result from intense, widespread rainfalls associated with Atlantic frontal systems transported by westerly airflow. Mediterranean river flooding is related to heavy rainfall induced by mesoscale convective systems (MCSs) during autumn months. Evidence from radiocarbon dates in slackwater flood deposits shows six periods of flood clusters at 10,750–10,240; 9550–9130; 4820–4440; 2865–2350; 960–790; and 520–290 cal BP. Despite the different flood-producing weather conditions in Atlantic and Mediterranean rivers, the radiocarbon sample clusters overlap and indicate changes in large-scale atmospheric circulation and climatic conditions in the Iberian Peninsula. Comparison with proxy records of mean temperature for the Northern Hemisphere demonstrates a relationship between the period of slackwater flood deposition and cold climatic phases (e.g. the 2650 yr BP climatic event or AD 1590–1650 period of the Little Ice Age). Radiocarbon dates from aggraded floodplain sediments were clustered at 2710–2320, 2000–1830, and 910–500 cal BP. The first cluster period is in phase with the timing of slackwater deposition, whereas the third (910–500 cal BP) occurs in between two periods of increased flood frequency as indicated by the palaeoflood and documentary flood records. It is argued that the 910–500 cal BP floodplain aggradation period reflects the first post-Roman evidence of environmental change related to generalised land-use changes at the catchment scale, which produced high sediment load transported to overbank areas during high flows. [Copyright &y& Elsevier]

Abstract: Flooding of rivers in India is linked with the peak monsoons. Investigating the linkage between monsoonal patterns and flood history of various rivers is therefore of fundamental importance in the Indian context. In the present study, the slackwater deposits in the alluvial reaches of the Mahi river basin, western India have been documented. These occur in the ravines incised during the early Holocene on an alluvial surface comprising sediments of Late Pleistocene age. The slackwater deposits occur at elevations up to 20 m from the present river level and extend to about 500 m inland. The carbonate rich sediments forming the ravine cliffs have provided bank stability and the dissections in the ravines have helped in the accumulation of slackwater deposits due to backflooding of the floodwater from the main channel. Recent gullies have incised the sediments and exposed deposits related to major flood events. The best exposures of slackwater deposits have been observed at Dodka. The sediment succession of the slackwater deposits is dominated by bedsets and laminasets of silt and sand separated by colluvial sediments. Four events of flood deposition occurred during the mid to late Holocene. Two units of slackwater deposits, SWD 2 and 4 have been dated by IRSL at 4.6±1 ka and 1.7±0.5 ka. The stratigraphy of these deposits indicates that the first two slackwater units (SWD1 and SWD2) have resulted due to flooding in a regime of intense monsoon. The other two units, however, represent extreme high magnitude floods in a period of low average precipitation. [Copyright &y& Elsevier]

The catastrophic floods recently occurring in Europe warn of the critical need forhydrologic data on floods over long-time scales. Palaeoflood techniques provideinformation on hydrologic variability and extreme floods over long-time intervals(100 to 10,000 yr) and may be used in combination with historical flood data (last1,000 yr) and the gauge record (last 30–50 yr). In this paper, advantages anduncertainties related to the reconstruction of palaeofloods in different geomorphologicalsettings and historical floods using different documentary sources are described.Systematic and non-systematic data can be combined in the flood frequency analysisusing different methods for the adjustment of distribution functions. Technical toolsintegrating multidisciplinary approaches (geologic, historical, hydraulic and statistical)on extreme flood risk assessment are discussed. A discussion on the potential theoreticalbases for solving the problem of dealing with non-systematic and non-stationary data ispresented. This methodology is being developed using new methodological approachesapplied to European countries as a part of a European Commission funded project (SPHERE). [ABSTRACT FROM AUTHOR]

Palaeoflood records for the Red River in southern Manitoba, Canada, were derived from anatomical tree-ring signatures in Quercus macrocarpa (Michx) collected at 16 living-tree sites, several historical buildings and archaeological sites, and subfossil logs buried in river alluvium. Prolonged inundation of trees during spring and early summer induces the development of anatomical anomalies (flood rings) that provide a proxy record of extreme floods. Flood-signature records for the Lower Red River basin (LRB) extend from AD 1999 to 1648 and suggest that the Red River flood of 1826 was the largest during the last 352 years. The tree-ring record identifies five of the largest seven floods in the LRB during the last 200 years and documents extreme floods in 1747, 1762, 1826, 1852, 1950, 1979 and 1997. The Upper Red River basin tree-ring flood record extends from AD 1997 to 1448 and contains flood rings for 1510, 1538, 1658, 1682, 1726, 1727, 1741, 1747 and 1762. Factors influencing the formation of flood rings, and hence efficacy of flood-ring records, include flood timing, age and availability of trees, and variations in response along the stem. Evidence from the LRB indicates intervals of increased flood frequency during the mid-1700s, the mid-1800s, and the second half of the twentieth century, and intervals without extreme flooding in 1648-1746, 1763-1825 and 1862-1949. The tree-ring evidence supports the premise that high Red River flows are non-stationary and that past climatic and landscape changes may have influenced local flood risks. [ABSTRACT FROM AUTHOR]

As a contribution to the estimation of extreme floods and rainfall, palaeofloods in the East Alligator River in tropical Australia were examined to derive estimates of palaeodischarges and their frequency. Nine extreme floods have occurred over 8400 years in a non-stationary series, the youngest five of which are stationary, and the youngest three of which occurred during wet periods produced by variations of the Southern Oscillation Index (SOI) modulated by the Pacific Decadal Oscillation (PDO). The magnitudes of these floods are similar, with one possible exception (in 2007 CE). The extreme floods in the region lie close to, or above, the Australian flood envelope curve showing that floods larger than the expected are possible. Their magnitudes also approximate the Probable Maximum Flood (PMF) but with a much higher frequency than expected. The annual exceedance probability (AEP) of the palaeofloods is 0.3%, which may also be the AEP for the rainfall. These results will be used as input to the design of an artificial landform at the Ranger uranium mine, within the East Alligator catchment, that has to last for 10,000 years. The 2007 CE flood was probably the most extreme flood (and associated rainfall) likely to occur in the vicinity of Ranger under the current climate and will occur in the future along with climate change. Because of the uncertainties associated with projections of future extremes the best design rainfall AEP for the Ranger landform is 0.3%. • Longest palaeoflood record in northern Australia of 8ka in the East Alligator River. • Eight of nine palaeofloods magnitudes above the Australian Flood Envelope Curve. • The large floods occur when La Niñas are frequent. • AEP for peak rainfall-generating floods of 0.3% is the same for PMF and PMP. • Design for 10ka uranium mine tailings can be based on this AEP. [ABSTRACT FROM AUTHOR]

Climate change implies changes in the frequency and magnitude of flood events. The influence of climate variability on flooding was evaluated by an analysis of sedimentary (palaeofloods) and documentary archives. A 500-year palaeoflood record at Montlleó River (657 km2 in catchment area), eastern Spain, revealed up to 31 palaeofloods with a range of discharges of 20–950 m3 s−1, and with at least five floods exceeding 740–950 m3 s−1. This information contrasts with the available gauged flood registers (since year 1971) with an annual maximum daily discharge of 129 m3 s−1. Our palaeoflood dataset indicates flood cluster episodes at (1) 1570–1620, (2) 1775–1795, (3) 1850–1890, and (4) 1920–1969. Flood rich periods 1 and 3 corresponded to cooler than usual (about 0.3 °C and 0.2 °C) climate oscillations, whereas 2 and 4 were characterised by higher inter-annual climatic variability (floods and droughts). This high inter-annual rainfall variability increased over the last 150 years, leading to a reduction of annual maximum flow. Flood quantiles (>50 years) calculated from palaeoflood+gauged data showed 30%–40% higher peak discharges than those using only instrumental records, whereas when increasing the catchment area (1500 km2) the discharge estimation variance decreased to ~15%. The results reflect the higher sensitivity of small catchments to changes on flood magnitude and frequency due to climate variability whereas a larger catchment buffers the response due to the limited extent of convective storms. Our findings show that extended flood records provide robust knowledge about hazardous flooding that can assist in the prioritization of low-regret actions for flood-risk adaptation to climate change. [ABSTRACT FROM AUTHOR]

Long-term data on flooding events are necessary for understanding the flood frequency and magnitude variations, but the available instrumental records span only a few decades. Recently, lake sediment sequences have emerged as a relatively untapped archive for high-magnitude floods over longer timescales. In the present study, multi-proxy data from a lacustrine sequence at Timbi in the Dhadhar river basin were analysed to determine high magnitude floods in this semi-arid region of western India in response to southwest monsoon variability. The results indicate the occurrence of discreet high magnitude flood events and depositional phases corresponding to different climatic conditions during the mid to late Holocene. Three large flash floods between 4830 and 2730 cal yr B.P. (Phase-I) have been identified as coeval with flood events from fluvial archives and correlated to the widespread period of aridity and weak monsoon recorded in the lakes of north western India. A shift in the depositional environment from fluvial to lacustrine occurred around 2730 cal yr B.P. as inferred from an abrupt change in the sediment character and palynofacies caused by high intensity flash floods and high sediment influx. Phase II (2730–1730 cal yr B.P.) was marked by periodic erosion and deposition in the catchment and sediment influx during pulses of higher precipitation as evident in the dominance of Glomus sp. and Alternaria sp., and relatively low values in concentration-related magnetic parameters and S-Ratio. A high magnitude flood event occurred at 1770 cal yr B.P. towards the end of phase II. During phase III (1730–880 cal yr B.P.) the monsoon was enhanced and climate was warmer as suggested by low χfd%, SIRM/χ, S-Ratio, higher Ba/Sr ratio and presence of aquatic palynomorphs. A high percentage of structured Organic Matter (OM), low fungal remains and increased Ba/Sr ratios between 880 and 360 cal yr B.P. indicate higher lake waters and better monsoon condition during phase IV. The phase V (360–0 cal yr B.P.) corresponds to lake level lowering, soil formation and eutrophication. The Timbi lake sediments demonstrate the potential for lakes in semi-arid alluvial plains of western India to preserve proxy flood records providing additional archives for generating long-term datasets. The flood record generated substantiates palaeoflood data from the fluvial archive suggestive of regional-scale southwest monsoon variability. Low frequency-high magnitude floods occurred during arid periods and low magnitude-high frequency events during relatively strengthened monsoon and thus have implication for linking the palaeoflood events to the southwest monsoon intensity in the semi-arid continental regions. • Lacustrine lithostratigraphy records palaeofloods in semi-arid alluvial plains. • High magnitude flood events during prolonged aridity around 4800 cal yr B.P. • Low magnitude-high frequency flood events between 2700 and 1700 cal yr B.P. • Signatures of wetter period during MWP but no indicators for major flood events • The deposition phases are in response to SW monsoon variability. [ABSTRACT FROM AUTHOR]