Flooding Time Research Articles

Impacts of Flood on Water Quality of Periyar River and Remediation Using Natural Fibers

ABSTRACT Kerala witnessed a major flood in August 2018, which brought severe effects on the environment and ecosystem, especially affecting the quality of rivers. This study aims in analyzing the impact of the flood on water quality of the Periyar River. The samplings for the study is taken from ten points along the banks of the river Periyar and were tested for its physical and chemical properties. The present water quality of the river was compared with that of the previous year and also with water quality at the time of flood to analyze the impact of flood. The tested samples were found to be polluted, and this study suggests the application of natural fibers for treating the turbid water for safe drinking and household purposes. The fibers are added to the polluted water in proportion of 1 mg/L with a settling time of 30 minutes. In this study, the remediation using natural fibers such as rice husk ash and coir was done, and the results indicate that the application of these fibers improves the water quality parameters such as pH and turbidity.

Experimental study on pore fluid characteristics of fractured sandstone based on nuclear magnetic resonance technology

The groundwater seepage in the fractured rock mass affects the stability of the surrounding rock of the roadway. To understand the fluid seepage characteristics and the change law of the microscopic pore structure of the fractured rock mass under different loading conditions, the low-field nuclear magnetic resonance technology (LF-NMR) was used to conduct a visual experimental study. The T2 spectrum distribution curve tested by nuclear magnetic resonance indicated that the pore structure of the fractured sandstone sample had three peaks (namely micropores, mesopores, and macropores) with medium and large pores distributed from 0.63 μm to 100 μm. Quantitative analysis of nuclear magnetic resonance imaging signals during water flooding of fractured sandstones revealed the characteristics of fluid migration and distribution at different times and locations at different flow rates in the core. The height of the fractured core at 23 mm had small water content and low porosity. The water content at the position of 25–40 mm was higher, and the porosity was large. Under the effect of flow velocity, there were obvious differences in the state of fractured core displacement. That is, the greater the flow velocity, the shorter the water flooding time and the more concentrated the fluid sweep area. The dominant channel for seepage was formed quickly. The research results can provide a reference for preventing the erosion of roadway surrounding rock caused by groundwater fluid.

High resolution detectors for whole-body PET scanners by using dual-ended readout

BackgroundMost current whole-body positron emission tomography (PET) scanners use detectors with high timing resolution to measure the time-of-flight of two 511 keV photons, improving the signal-to-noise ratio of PET images. However, almost all current whole-body PET scanners use detectors without depth-encoding capability; therefore, their spatial resolution can be affected by the parallax effect.MethodsIn this work, four depth-encoding detectors consisting of LYSO arrays with crystals of 2.98 × 2.98 × 20 mm3, 2.98 × 2.98 × 30 mm3, 1.95 × 1.95 × 20 mm3, and 1.95 × 1.95 × 30 mm3, respectively, were read at both ends, with 6 × 6 mm2 silicon photomultiplier (SiPM) pixels in a 4 × 4 array being used. The timing signals of the detectors were processed individually using an ultrafast NINO application-specific integrated circuit (ASIC) to obtain good timing resolution. The 16 energy signals of the SiPM array were read using a row and column summing circuit to obtain four position-encoding energy signals.ResultsThe four PET detectors provided good flood histograms in which all crystals could be clearly resolved, the crystal energy resolutions measured being 10.2, 12.1, 11.4 and 11.7% full width at half maximum (FWHM), at an average crystal depth of interaction (DOI) resolution of 3.5, 3.9, 2.7, and 3.0 mm, respectively. The depth dependence of the timing of each SiPM was measured and corrected, the timing of the two SiPMs being used as the timing of the dual-ended readout detector. The four detectors provided coincidence time resolutions of 180, 214, 239, and 263 ps, respectively.ConclusionsThe timing resolution of the dual-ended readout PET detector was approximately 20% better than that of the single-ended readout detector using the same LYSO array, SiPM array, and readout electronics. The detectors developed in this work used long crystals with small cross-sections and provided good flood histograms, DOI, energy, and timing resolutions, suggesting that they could be used to develop whole-body PET scanners with high sensitivity, uniform high spatial resolution, and high timing resolution.

Peak Spring Flood Discharge Magnitude and Timing in Natural Rivers across Northern Finland: Long-Term Variability, Trends, and Links to Climate Teleconnections

In northern regions, like Finland, peak river discharge is principally controlled by maximum snowmelt runoff during spring (March–May). Global warming and climate change extensively influence both the quantity and temporal characteristics of peak discharge in northern rivers by altering snowpack accumulation and melt processes. This study analyzed peak spring flood discharge (PSFD) magnitude (PSFDM) and timing (PSFDT) in four natural rivers (Simojoki, Kuivajoki, Kiiminkijoki, and Temmesjoki) across northern Finland, in terms of long-term (1967–2011) variability, trends, and links to large-scale climate teleconnections. The PSFDM significantly (p < 0.05) declined in the Simojoki, Kuivajoki, and Kiiminkijoki rivers over time. Both the Simojoki and Kuivajoki rivers also experienced significant decreasing trends of about −0.33 and −0.3 (days year−1), respectively, in the PSFDT during 1967–2011. In these two rivers, the less and earlier PSFDs were principally attributable to the warmer spring seasons positively correlated with the North Atlantic Oscillation (NAO) in recent decades. Moreover, daily precipitation time series corresponding to the PSFD events showed no considerable effects on PSFDM and PSFDT changes in all the natural rivers studied. This suggests that less and earlier historical PSFDs in natural rivers at higher latitudes in northern Finland were primarily induced by warmer springtime temperatures influencing snowpack dynamics.

A simplified method for water depth mapping over crops during flood based on Copernicus and DTM open data

After an extreme rainy event agricultural fields can be submerged by water. Stagnant water can be generated by river’ flooding or by soil saturation causing different damage level to crops. In this work, the flood event occurred on 3rd October 2020 in NW Italy along the Sesia river was assessed with special concern about damages affecting rice crop fields. A method was proposed aimed at detecting flooded areas and giving an estimate of water depth (WD) based on free available Copernicus data (Sentinel-1 and Sentinel-2) and digital terrain model (DTM). In particular, Sentinel-1 pre- and post-event images were compared by differencing (ΔVV). ΔVV was processed at pixel level to detect submerged areas through the thresholding Otsu’s method. A simplified morphological analysis was then performed by DTM tessellation to map WD. A further step aimed at classifying submerged areas was achieved based on DTM and a proximity analysis, making possible to separate areas where water was related to soil saturation from areas where water was coming from the river. Corine Land Cover 2018 level-3 and NDVI from a Sentinel-2 pre-event image were used to map crops that were still to be harvested at the time of flood. These were the ones that were considered while estimating the potential economic loss. A total of 255 ha of rice that still to be harvested were submerged but only 211 ha were affected by river overflow. Using local rice yield and price the resulting economic loss was about 2,200,000 €.

Numerical simulation of dam-breach flood waves

Dam breach due to the earthquake, Land sliding inside the dam reservoir, dam overtopping as a result of intense precipitation in a watershed are examples of dangerous risks which flood caused by any of them should be predicted by suitable hydraulic or numerical models in the framework of a risk management plan. In the present research, 2DHec-Ras model has been applied in order to flood modeling of Sattarkhan dam. This dam is in the North West of Iran, located 15 km from the west of Ahar city, in the East Azerbaijan province, Iran. The downstream part of the dam to Ahar city has been studied considering the population and infrastructures in this district according to two different scenarios of dam failure. The first scenario includes piping of flow and dam failure profile with steep side walls while the second scenario consists of inclined sidewalls in the dam breach profile and overtopping of flow as the main cause of breaching. The population centers have been selected in the downstream area of dam according to the field facts. The maximum flood depth reaches up to 9.1 m for the first scenario and 7.1 m for the second scenario at the Islamic Azad University and Tabriz-Ahar road, respectively. The results show the notable risk for some of the population centers in the downstream of the dam. Furthermore, the arrival time of flood, recession time, and maximum velocities in the targeted areas for preparing emergency action plans has been calculated.

Application of Sentinel-2 Data for Extraction of Flood Inundation along Ganga River, Bihar

Abstract: Remote Sensing techniques played a significant role in the extraction of the flood inundation. The study is based on delineating the flood water of 2019 that affected the Bihar region along the Ganga River using Sentinel 2 satellite imageries. For this purpose the spectral water index methods: NDWI and MNDWI was used. And to differentiate water from the non-water areas certain threshold values were used. The selection of optimum threshold values was an essential task as it helped to precisely detect the inundated areas. The optimum threshold was lower for MNDWIs for the pre-flood time while for the during flood time NDWI the values were lower. For the pre-flood moment NDWI gave the highest Kappa of 0.93 and for the during flood moment, MNDWI 1 produced the highest Kappa of 0.95 and Overall Accuracy (OA) of 0.91. Overall in this experiment, MNDWI 1 estimated better accuracy in determining the water bodies and flooded region. Due to the highest rainfall in the districts of Patna, Khagaria, Begusrai, and Bhagalpur throughout, the areas were adversely affected by floods in 2019. Keywords: Water Index, NDWI, MNDWI, Flood Inundation, Sentinel-2, natural disasters, Accuracy Assessment

Effects of exogenous organic acids and flooding on root exudates, rhizosphere bacterial community structure, and iron plaque formation in Kandelia obovata seedlings

The rhizosphere of coastal wetland plants is the active interface of iron (Fe) redox transformation. However, coupling mechanism between organic acids (OAs) exuded by plant roots and Fe speciation transformation participated by Fe redox cycling bacteria in the rhizosphere is still unclear. Effects of four common OAs (citric acid, malic acid, tartaric acid, and oxalic acid) on root exudation, rhizosphere bacterial community structure, root Fe plaque, and Fe redox cycling bacterial communities of Kandelia obovata were investigated in this study. Long-term flooding (10 h) was conducive to K. obovata seedlings exuding additional dissolved organic carbon (DOC) and nitrogen and phosphorus organic matter (NH4+–N, NO3−–N, and dissolved inorganic phosphorus [DIP]) under each OA level. DOC, NH4+–N, NO3−–N, and DIP in root exudates increased significantly with the increase of exogenous OA level. Notably, long flooding time corresponds to an evidently increasing trend. Exogenous OAs also significantly increased contents of formic and oxalic acids in root exudates. Exogenous OAs and flooding enhanced the rhizosphere effect of K. obovata and significantly enhanced bacterial diversity of the rhizosphere and relative abundance of dominant bacteria in rhizoplane. Bacterial diversity in the rhizosphere of K. obovata seedlings was significantly higher than that in the rhizoplane under the same level of OAs and flooding. Fe plaque content of K. obovata root decreased significantly and the relative abundance of typical Fe-oxidizing bacteria, such as Gallionella, unclassified_f__Gallionellaceae, and Sideroxydans, decreased significantly in the rhizosphere but increased significantly in the rhizoplane with the increase of the treatment level of exogenous OAs. This finding is likely due to the Fe3+ reduction caused by acidification of rhizosphere environment after exogenous OA treatment rather than the result of chemotactic colonization of Fe redox cycling bacteria in the rhizoplane.

Rapid prediction of flood inundation by interpolation between flood library maps for real-time applications

It is important that real-time flood forecasting provides information on inundation extents and depths to emergency responders for flood mitigation planning, warning and rescue operations. Conventional hydrodynamic flood inundation modelling is generally not suited for real-time operations because of its large computational demand. The most widely adopted industry practice is to link a pre-canned library of flood maps with river levels and use an interpolation approach to derive flood surfaces and depths based on selected model inputs. However, there is surprisingly scant information in the literature on the procedures and performance of the library interpolation approach. In this study, we describe the library interpolation approach, introduce univariate and multivariate interpolation schemes, and investigate their performance through a case study of a river in Port Fairy, Australia. The MIKE 11/21 hydrodynamic model was used to construct a pre-canned flood inundation library of design events. The hydrodynamic model was also used to generate outputs for four test cases to evaluate the performance of the library interpolation approach. It is found that the accuracy of the library interpolation approach relies heavily on how the map library was constructed, selection of flood drivers, and shape and timing of hydrographs. The widely deployed univariate interpolation scheme based on a single primary flood driver yields results of varied accuracy, depending on the validity of assumptions, often made implicitly, about the inputs of the non-primary drivers. A newly developed multivariate interpolation scheme overcomes this problem. Overall, it is found that the results obtained using the map library interpolation schemes are generally satisfactory, achieving a hit rate of 0.85-0.99 and a critical success index of 0.85-0.99. However, a major limitation of the library interpolation approach is that the shape and timing of the input hydrographs need to be similar to that used in constructing the map library. Further research is needed to mitigate this limitation.

Simulation of the flood wave caused by hypothetical failure of the Haditha Dam

In this research, the flood wave resulting from the hypothetical overtopping failure of the Haditha Dam on the Euphrates River, Iraq, was simulated, utilizing the ArcMap 10.2 and HEC-RAS 5.0.7 software and the observed field data from the Iraqi Ministry of Water Resources. Flooding parameters were calculated, for the study reach from the Haditha Dam to Heet city and major cities in between. The Manning coefficient of the study reach was calibrated to 0.035 and 0.07 for the main river and the floodplain, respectively. The results showed the flood wave propagation along the study reach, the flood hydrograph and time to the peak discharge/time to the maximum water surface elevation, maximum velocity, and width of the inundated area at the selected cities. The analysis outputs and the inundation maps can be used to provide an emergency action plan for the flooded regions.

Process Controls on Flood Seasonality in Brazil

AbstractA coincidence in the timing of floods and their drivers can be used as a proxy for the causality of flood generation. Here, we investigate the relationship between the seasonality of floods, maximum annual rainfall, and maximum annual soil moisture data of 886 basins in Brazil for 1980–2015 to shed light on process controls of flood generation. Floods tend to occur at the same time of year as soil moisture peaks and lag behind rainfall peaks by 3 weeks. In Amazonia, central and northern Brazil, flood timing is more correlated with the timing of soil moisture peaks than with that of rainfall peaks, which is interpreted as resulting from high subsurface water storage capacities. In southern and southeastern Brazil, on the other hand, flood timing is highly correlated with both soil moisture and rainfall because of low subsurface water storage capacities. These findings can support flood forecasting and climate impact studies.

Cyclic sediment deposition by orbital forcing in the Miocene wetland of western Amazonia? New insights from a multidisciplinary approach

In the Miocene, a large wetland system extended from the Andean foothills into western Amazonia. This system has no modern analogue and the driving mechanisms are not yet fully understood. Dynamic topography and Andean uplift are thought to have controlled deposition, with allocyclic base level changes driven by eustasy and orbital forcing also playing a role. In this study we investigate the presumed orbital cyclicity that controlled sediment deposition, while also assessing sediment source and biomes in the Miocene wetland. We do this by integrating lithological, palynological, malacological and geochemical data from the Los Chorros site (Amazon River, Colombia), and by placing our data in a sequence stratigraphic framework. In this sequence biostratigraphic evaluation, the Los Chorros succession is visualized to be composed of a series of flood-fill packages, with a rapid initial flood, marine-influenced conditions at the time of maximum flood, followed by a longer regressive infill phase. Based on the palynology we could differentiate local vegetation, such as palm swamps, from regional origin such as terra firme vegetation (non-flooded Amazonian forest) and Andean montane forest, while from sediment geochemistry we could separate local and regional sediment sources. At the times of flooding, oligotrophic and eutrophic aquatic conditions alternatively characterized the wetland, as is shown by the presence of algae, floating ferns, and mollusc assemblages, while intervening subaquatic debris points to proximal submerged lowlands. In the lower 20 m of the section, marine influences are intermittently evident and shown by short-lived maxima of mangrove pollen, foraminiferal test linings, dinoflagellate cysts, coastal mollusc species, and an episodic decline in terrestrial biomarkers. The upper 5 m of the section is characterized by floodplain forest taxa with a diversity in tropical rain forest taxa and relatively few lacustrine indicators. These marine, mangrove, and lacustrine indicators suggest that the outcrops at Los Chorros represent predominant marine-influenced lacustrine conditions during periods of sea level highstand. The sequence biostratigraphic evaluation further points to eight 41 kyr obliquity-driven depositional cycles, with rapid phases of transgression. Mangrove elements would have colonised within the timeframe of each sea level rise. Based on this relative age constraint and comparison to regional records, deposition likely took place prior to the 13.8 Myr global sea level fall, and most likely during the period just after 14.5 Ma, between Middle Miocene Climatic Optimum (MMCO; 17–14 Ma) and Middle Miocene Climate Transition (MMCT; 14.7–13.8 Ma). Palynological evidence further suggests that to the west, surface elevation ranged from ~1000 up to ~3500 m and hosted protoparamo vegetation, the oldest yet reported and in agreement with predictions from molecular studies. In contrast, contemporaneous sites to the northeast of the wetland consisted of fluvial and cratonic formations, as shown by their Nd and Sr isotopic sediment signature. In summary, our data lead to an improved understanding of how geological and astronomical mechanisms controlled the floral and faunal distribution and controlled sediment deposition in western Amazonia during the middle Miocene. As Miocene conditions strongly contrast with modern western Amazonia, our data provide an important context for the deep time history and evolution of the modern western Amazon rainforest. • We used a sequence biostratigraphic approach to evaluate cyclic deposition in the Miocene wetland of Western Amazonia. • Repeated flood-fill packages were deposited just after 14.5 Ma, during the Middle Miocene Climatic Optimum. • Local vegetation was formed of mangroves, palm and fern swamps, and terra firme lowland. • Molluscs and algae reflect changing salinity, nutrient levels, and water depths. • Sediments and sporomorphs point at the Andes as principal sediment source, with the Amazon craton as additional supplier. • In the mid-Miocene the Andes already had elevations of up to 3500 m and hosted a protoparamo.

Ferric chloride amendment reduces phosphorus losses from flooded soil monoliths to overlying floodwater

The accumulation of phosphorus (P) in agricultural soils and subsequent losses to waterways contribute to eutrophication in surface water bodies. In agricultural lands prone to prolonged flooding during spring snowmelt, P may be released to overlying floodwater and transported to lakes downstream. Ferric chloride (FeCl3) is a potential soil amendment to mitigate P losses, but its effectiveness for flooded soils with snowmelt is not well documented. Thirty-six intact soil monoliths taken from four agricultural fields in Manitoba's Red River Valley region were surface-amended with FeCl3 at three rates (0, 2.5, and 5 Mg ha–1) to evaluate the effectiveness of FeCl3 in minimizing P losses to porewater and floodwater. Over 8 weeks of simulated snowmelt flooding, porewater, and floodwater samples taken weekly were analyzed for concentrations of dissolved reactive P (DRP), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), and pH. Change in the redox potential was also measured weekly. With time of flooding, redox potential decreased in all soil monoliths. At early stages of flooding, the porewater pH values were significantly lower in FeCl3-amended monoliths but increased with flooding time. Porewater and floodwater DRP concentrations increased in all soils when flooded, but the magnitudes varied. Amendment of FeCl3 decreased the DRP concentrations from 17% to 97% in porewater and 26% to 99% in floodwater, with the effectiveness varying depending on the soil, FeCl3 rate, and flooding time. Amendment of FeCl3 increased porewater concentrations of Ca, Mg, Fe, and Mn. Soil amendment with FeCl3 at both rates shows promise in mitigating redox-induced P losses from flooded soils.

Devising a procedure to calculate and analyze parameters for passing the flood and breakthrough wave taking into consideration the topographical and hydraulic riverbed irregularities

It has been established that the most likely period of breakthrough wave occurrence is the time of spring flooding or heavy rain when water-head facilities are subjected to significant loads that lead to the collapse of their individual elements or the entire structure. In addition, the possibility of man-made accidents that can occur at any time cannot be ruled out. It has been proven that breakthrough wave formation depends on the nature of the destruction or the overflow through a water-head facility. For the study reported in this paper, a model of the kinematics of riverbed and breakthrough flows was used, which is based on the equations of flow, washout, and transport of sediments that are averaged for the depths of the stream. The differential equations describing the nonstationary flow averaged for depth are solved using the numerical grid system FST2DH (2D Depth-averaged Flow and Sediment Transport Model), which implements a finite-element method on the plan of a riverbed's topographic region. These tools are publicly available, which allows their wide application to specific loads and boundary conditions of mathematical models. The construction of an estimation grid involving the setting of boundary conditions and the use of geoinformation system tools makes it possible to simulate the destruction of a culvert of the pressure circuit and obtain results for a specific case of an actual riverbed and a water-head facility. It has been established that there is a decrease in the speed of wave propagation along the profile, from 3 m/s to 1 m/s. The impact of bottom irregularities, the effect of floodplains, and the variety of bottom roughness have also been assessed, compared to the results of their calculation based on one-dimensional models given in the regulatory documents. Hydraulic calculations were carried out taking into consideration the related properties of the main layer of the floodplain, which consists of peat accumulations, and the heterogeneity of the depths and roughness of floodplain surfaces of soils. It has been established that there is almost no erosion of supports in the floodplain zone in this case. It was found that as the distance between the flow and breakthrough intersection increases, there is a decrease in the height of the head from 2.1 m to 1.25 m.

Alum and Gypsum Amendments Decrease Phosphorus Losses from Soil Monoliths to Overlying Floodwater under Simulated Snowmelt Flooding

Phosphorus (P) loss from soils poses a threat of eutrophication to downstream waterbodies. Alum (Al2(SO4)3·18H2O) and gypsum (CaSO4·2H2O) are effective in reducing P loss from soils; however, knowledge on their effectiveness under cold temperatures is limited. This study examined the reduction of P loss from soils with alum and gypsum amendment under simulated snowmelt flooding. Intact soil monoliths (15 cm depth) collected from eight agricultural fields in flood-prone areas of Manitoba, Canada, were surface amended with alum or gypsum, pre-incubated for 2 weeks, then flooded and incubated at 4 °C for 8 weeks. Porewater and floodwater samples collected weekly were analyzed for dissolved reactive P (DRP), dominant cations and anions. An enhanced P release with flooding time was observed in all soils whether amended or unamended; however, alum/gypsum amendment reduced DRP concentrations in porewater and floodwater in general, with alum showing a more consistent effect across soils. The reduction in floodwater DRP concentrations (maximum DRP concentration during flooding) with alum and gypsum ranged from 34–90% and 1–66%, respectively. Based on Visual MINTEQ thermodynamic model predictions, precipitation of P and formation of P-sorbing mineral species with alum and gypsum amendment reduced DRP concentrations at latter stages of flooding.

The role of personality features and wisdom in helping behaviors at the time of flooding

The role of personality features and wisdom in helping behaviors at the time of flooding

Changes in Mechanisms and Characteristics of Western U.S. Floods Over the Last Sixty Years

AbstractClimate change is linked to changing precipitation, yet uncertainty remains as to whether and how hydroclimatic changes will influence flood frequency, magnitude, and timing. Part of this uncertainty is because few regional‐scale studies have analyzed changes in floods produced by different mechanisms. We identify six flood generating mechanisms (FGMs) based on prominent meteorological processes and moisture supply to the soil column in the Western U.S.; these include large‐scale frontal storms (atmospheric and non‐atmospheric rivers), monsoons, convective storms, snowmelt, and rain‐on‐snow. We assess trends in the frequency, magnitude, and timing of floods produced by different FGMs across 119 basins during 1960–2018. Overall, we find decreased frequency and magnitude of rain‐on‐snow‐driven floods, increased frequency and magnitude of convective‐storm‐driven floods, and a temporal shift to earlier in the year for snowmelt‐driven floods. The flood characteristics are generally stable for floods produced by other FGMs.

USING SPACE SURVEY MATERIALS FOR MODELING HYDRODYNAMIC ACCIDENTS AT MINING ENTERPRISES IN KAZAKHSTAN

Abstract. The timeliness of using modern computer programs for modelling flood zones, the consequences of hydraulic accidents, dam breakthroughs, flood and flood forecasting in a complex system of rivers and channels for the prevention of hydro meteorological emergencies is beyond doubt. The use of BIM technologies will make it possible to move from point-based flood risk assessments to areal ones, which will significantly improve the reliability of planned measures to prevent natural and anthropogenic emergencies.The purpose - to perform works on modelling of hydrodynamic accident and forecast of its development by the example of tailings dumps in concentration plant in East Kazakhstan. As the initial data - digital model for the area of work, technical reports on engineering-hydrographical survey, topographic-geodetic works, engineering-geological survey, high-resolution satellite images in a panchromatic survey mode. On the basis of geoinformation modelling methods with use of initial and remote sensing data, final digital terrain model was built in Digital software. The method based on direct hydrodynamic modelling of area flooding was used to calculate hydrodynamic accidents, to model the dynamics of area flooding because of tailings dam break in several levels. The practical result is numerical hydrodynamic modelling of dynamics flooding area because of partial destruction, erosion of embankment dam of tailings concentrator, total area and extent of flooding, as well as the area and depth of partially flooded buildings of residential development was estimated, thematic maps of flooded area were created, as well as maps of water passage with flow velocities during the hydrodynamic accident.Thus, the application of advanced space imagery, GIS technologies in full measure allow for simulating the occurrence, development of hydrodynamic accidents in structures, to determine area, time of flooding.

Channel responses to flooding of Ganga River, Bihar India, 2019 using SAR and optical remote sensing

Indo Gangetic flood plains are subjected to recurring floods due to large low-lying land areas adjacent to major Himalayan Rivers. Recent floods in the Ganga River during the late withdrawal phase of Indian summer monsoon rains in 2019 had reportedly caused death of ∼200–500 people and damaged major infrastructures in different parts of Bihar state, India. This paper presents a detailed analysis of the spatial extent and temporal pattern of flood inundation areas in Patna district of Bihar using Sentinel-1 Synthetic Aperture Radar (SAR) data. The results obtained using K-means classification show that about 1268 km 2 (20% of the studied portion) of the land area were inundated during the peak flooding conditions on 9th October 2019. The peak flooding lasts for more than 20 days, with a maximum water depth of 18 m in the main river. Owing to the continually changing nature of river morphology by recurring floods, we also analyzed the channel morphology and bar characteristics before, during, and after the floods. Geomorphic change assessment indicates that the total bar occupied area was decreased from 661 km 2 for pre-flood time to 446 km 2 in peak flood time, whereas it retains its original shape in post-flood images.

Investigating the interaction of waves and river discharge during compound flooding at Breede Estuary, South Africa

Abstract. Recent studies have drawn special attention to the significant dependencies between flood drivers and the occurrence of compound flood events in coastal areas. This study investigates compound flooding from tides, river discharge (Q), and specifically waves using a hydrodynamic model at the Breede Estuary, South Africa. We quantify vertical and horizontal differences in flood characteristics caused by driver interaction and assess the contribution of waves. Therefore, we compare flood characteristics resulting from compound flood scenarios to those in which single drivers are omitted. We find that flood characteristics are more sensitive to Q than to waves, particularly when the latter only coincides with high spring tides. When interacting with Q, however, the contribution of waves is high, causing 10 %–12 % larger flood extents and 45–85 cm higher water depths, as waves caused backwater effects and raised water levels inside the lower reaches of the estuary. With higher wave intensity, the first flooding began up to 12 h earlier. Our findings provide insights on compound flooding in terms of flood magnitude and timing at a South African estuary and demonstrate the need to account for the effects of compound events, including waves, in future flood impact assessments of open South African estuaries.