Catastrophic floods in Kosi catchment during August 2008

A breach in embankment of Kosi barrage was reported on 18 August, 2008 which has changed its course and resulted in a fresh channel around 120 km to the east of its previous channel. At the time of failure of the embankment, gushing out of about 2832 m3/s water with great impact breaking into the Mahendra Rajmarg and then taking a southward route into the old 1892-1921 abandoned course of the river, thus leaving the pre-breach C-loop and following a straight route to the Ganga. In this study meteorological aspect are analysed in details in relation to the catastrophic flood in the Kosi river catchment during August 2008. It seems that this catastrophic flood may not be solely due to rainfall in the catchment of Kosi. The breach is due to incorrect strategies of river management, human negligence and poor maintenance of afflux bund of the barrage (Sinha, 2009).

Tephrostratigraphy, Magnetostratigraphy and Geochronology of Some Early and Middle Pleistocene Deposits in New Zealand

<p>Numerous early Pleistocene silicic tephras are exposed in long sedimentary sequences in the East Coast and Wanganui basin regions in southern North Island of New Zealand, some 150-250 km south of the Taupo Volcanic Zone. They provide time planes that can be correlated between different facies and basins. Individual tephras can often be distinguished on the basis of major and trace element glass chemistry, and Fe-Ti oxide composition. Approximately 51 different eruptive events may be recorded in the interval from ca. 1.7 Ma to 0.5 Ma. Early Pleistocene tephras in deep-sea sediments of the Southern Pacific Ocean at latitudes >60 degrees S were previously considered to have been sourced in the TVZ. However, their alkalic compositions are compatible only with volcanoes of Western Antarctica and the Ross Sea region. Most of the tephras examined here are reworked, and many have been emplaced as catastrophic flood deposits in overbank settings of braid plains in the East Coast region. Their mode of emplacement and the presence of ignimbrites in the sequences indicate early Pleistocene transport routes through the site of the present main Axial Ranges, and suggest substantial tectonic uplift in the last 0.8 Ma. Long sequences spanning the Jaramillo Subchron (0.99-1.07 Ma) and older Matuyama Chron are recognised at Mangatewaiiti and Mangatewainui in the East Coast region, and Rewa Hill in the Rangitikei Valley. Numerical age control is provided by 40Ar/39Ar single crystal laser fusion ages from plagioclase in key tephra horizons. This new chronology indicates the tephras are nearly twice as old as several previous studies have suggested, thus requiring a major revision of the New Zealand Pleistocene stratigraphy. By integrating isotopic, paleomagnetic and geochemical data, 3 widespread tephras can be correlated between basins of the East Coast and Wanganui: Pakihikura Tephra (ca. 1.6 Ma), Potaka Tephra (1.00 Ma), and Kaukatea Tephra (ca. 1 Ma). These tephras and others provide a chronological framework for much of the early Pleistocene in southern North Island. Potaka Tephra is particularly widespread, allowing correlation between marine strata of the Castlecliffian (local early Pleistocene stage) type section at the Wanganui coast, and marine strata elsewhere in the Wanganui basin, as well as with fluvial and lacustrine strata in the East Coast. The tephra occurs as an ignimbrite and as a catastrophic flood deposit in the East Coast and as a fallout ash in North Canterbury, South Island (ca. 600 km from source). Potaka Tephra (normal polarity) and Kaukatea Tephra (reversed polarity) bracket the top of the Jaramillo Subchron and constrain its age to ca. 1 Ma. This is in accord with the astronomical calibration of the Pleistocene geomagnetic time scale, but older than previous determinations using the 'chronogram' method on K-Ar data. The precise source vents for the distal early Pleistocene tephras are uncertain, however their ages indicates they are coeval with dated proximal ignimbrite sheets from the Mangakino Caldera in the SW part of TVZ. The large number of distal tephras would imply a greater frequency of eruptions from this source than previously expected.</p>

Tephrostratigraphy, Magnetostratigraphy and Geochronology of Some Early and Middle Pleistocene Deposits in New Zealand

<p>Numerous early Pleistocene silicic tephras are exposed in long sedimentary sequences in the East Coast and Wanganui basin regions in southern North Island of New Zealand, some 150-250 km south of the Taupo Volcanic Zone. They provide time planes that can be correlated between different facies and basins. Individual tephras can often be distinguished on the basis of major and trace element glass chemistry, and Fe-Ti oxide composition. Approximately 51 different eruptive events may be recorded in the interval from ca. 1.7 Ma to 0.5 Ma. Early Pleistocene tephras in deep-sea sediments of the Southern Pacific Ocean at latitudes >60 degrees S were previously considered to have been sourced in the TVZ. However, their alkalic compositions are compatible only with volcanoes of Western Antarctica and the Ross Sea region. Most of the tephras examined here are reworked, and many have been emplaced as catastrophic flood deposits in overbank settings of braid plains in the East Coast region. Their mode of emplacement and the presence of ignimbrites in the sequences indicate early Pleistocene transport routes through the site of the present main Axial Ranges, and suggest substantial tectonic uplift in the last 0.8 Ma. Long sequences spanning the Jaramillo Subchron (0.99-1.07 Ma) and older Matuyama Chron are recognised at Mangatewaiiti and Mangatewainui in the East Coast region, and Rewa Hill in the Rangitikei Valley. Numerical age control is provided by 40Ar/39Ar single crystal laser fusion ages from plagioclase in key tephra horizons. This new chronology indicates the tephras are nearly twice as old as several previous studies have suggested, thus requiring a major revision of the New Zealand Pleistocene stratigraphy. By integrating isotopic, paleomagnetic and geochemical data, 3 widespread tephras can be correlated between basins of the East Coast and Wanganui: Pakihikura Tephra (ca. 1.6 Ma), Potaka Tephra (1.00 Ma), and Kaukatea Tephra (ca. 1 Ma). These tephras and others provide a chronological framework for much of the early Pleistocene in southern North Island. Potaka Tephra is particularly widespread, allowing correlation between marine strata of the Castlecliffian (local early Pleistocene stage) type section at the Wanganui coast, and marine strata elsewhere in the Wanganui basin, as well as with fluvial and lacustrine strata in the East Coast. The tephra occurs as an ignimbrite and as a catastrophic flood deposit in the East Coast and as a fallout ash in North Canterbury, South Island (ca. 600 km from source). Potaka Tephra (normal polarity) and Kaukatea Tephra (reversed polarity) bracket the top of the Jaramillo Subchron and constrain its age to ca. 1 Ma. This is in accord with the astronomical calibration of the Pleistocene geomagnetic time scale, but older than previous determinations using the 'chronogram' method on K-Ar data. The precise source vents for the distal early Pleistocene tephras are uncertain, however their ages indicates they are coeval with dated proximal ignimbrite sheets from the Mangakino Caldera in the SW part of TVZ. The large number of distal tephras would imply a greater frequency of eruptions from this source than previously expected.</p>

Full Lifecycle Monitoring on Drought-Converted Catastrophic Flood Using Sentinel-1 SAR: A Case Study of Poyang Lake Region during Summer 2020

During summer 2020, the most catastrophic flood in the 21st century attacked the Poyang Lake region, one of the flood-prone areas in China. To explore the occurrence mechanism and evolution patterns of this drought-converted flood better, a full lifecycle model is developed in this article. Employing Sentinel-1 Synthetic Aperture Radar (SAR) images, with the advantages of high spatial–temporal resolution and all-day and all-weather working capacity, a bimodal threshold was applied to efficiently extract flood inundation mapping. Thus, 61 Sentinel-1 SAR images in 2020 were used to establish inundation sequences for full lifecycle monitoring. This flood presented an abrupt transformation from drought, a long duration, and the slow receding of water, and its area exceeded 3000 km2 from July to early October. In addition, inundation models that reflect the lake area and water level relationship were introduced to assist near-real-time monitoring. Through hydrological and meteorological analysis, compared with results of previous years (from 2010 to 2019), this study found that the water level from July to October in 2020 was at least 17% higher than the mean level at the same period in history and water volume had increased about 44.13 billion m3 during the flooding period. Similarly, the average precipitation from June to September was significantly higher than the same period of previous years. It was the abnormal sustained heavy precipitation and sharp rising of the water level that caused this catastrophic flood. In particular, the Standardized Precipitation Index (SPI) increased from −1.02 in April to 1.31 in July, indicating that the flood was abruptly converted from drought. The inundated areas of several land types during different periods of the full lifecycle were calculated for damage assessment. It was found that cropland was the most heavily impaired with a maximum inundated area of 1375.67 km2, while other land types including forest, grassland, wetland, and impervious surface were relatively less damaged. The study results demonstrate that flood full lifecycle monitoring based on SAR data is helpful to explore the patterns of flood evolution, analyze causes, and assess damage. Simultaneously, focusing on drought-converted floods contributes to the understanding of flood patterns, which provides relevant management departments with decision support for disaster prevention and mitigation.

Using the Global Hydrodynamic Model and GRACE Follow-On Data to Access the 2020 Catastrophic Flood in Yangtze River Basin

Flooding is one of the most widespread and frequent weather-related hazards that has devastating impacts on the society and ecosystem. Monitoring flooding is a vital issue for water resources management, socioeconomic sustainable development, and maintaining life safety. By integrating multiple precipitation, evapotranspiration, and GRACE-Follow On (GRAFO) terrestrial water storage anomaly (TWSA) datasets, this study uses the water balance principle coupled with the CaMa-Flood hydrodynamic model to access the spatiotemporal discharge variations in the Yangtze River basin during the 2020 catastrophic flood. The results show that: (1) TWSA bias dominates the overall uncertainty in runoff at the basin scale, which is spatially governed by uncertainty in TWSA and precipitation; (2) spatially, a field significance at the 5% level is discovered for the correlations between GRAFO-based runoff and GLDAS results. The GRAFO-derived discharge series has a high correlation coefficient with either in situ observations and hydrological simulations for the Yangtze River basin, at the 0.01 significance level; (3) the GRAFO-derived discharge observes the flood peaks in July and August and the recession process in October 2020. Our developed approach provides an alternative way of monitoring large-scale extreme hydrological events with the latest GRAFO release and CaMa-Flood model.

The impact of catastrophic flood in 2013 on the flora of the Amur floodplain near Komsomolsk-on-Amur.

Рассмотрены различия в локальной флоре амурской поймы до и после катастрофического наводнения 2013 г. Выявлены изменения в видовом составе, спектрах семейств и эколого-ценотических групп высших растений в высокой и низкой пойме у г. Комсомольск-на-Амуре под влиянием наводнения. Установлено, что после катастрофы растительное сообщество низкой поймы меньше изменило свою таксономическую и экологическую структуру, чем высокой, однако восстановительные процессы в низкой пойме протекали медленнее. The local flora differences of the Amur flood plain after and before the catastrophic flood in 2013 have been considered. The flood impact on the modification of species checklist, family and ecological-coenotic spectra of the higher plants in the high and low flood plain in the vicinity of Komsomolsk-on-Аmur have been revealed. It was claimed that after the catastrophe the low flood plain plant community had changed its taxonomic and ecological structure to a lesser degree than that of the high one. However the renewal process was stated to be slower in the low flood plain.