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Abstract Background The flood in July 2021 is considered one of the largest flood disasters in Western Europe in decades, with massive socio-economic consequences. The potential emission and remobilization of anthropogenic pollutants can lead to additional environmental consequences, which need to be addressed in long-term mitigation strategies. The Inde River and its tributary, the Vichtbach River, form a catchment located at the transition from the low mountain ranges of the Eifel to the lowlands of the Lower Rhine Embayment in Germany. The area has been an industrial and mining hotspot for centuries, making it a high-risk area for flood sediment pollution. The present study provides an ecotoxicological screening of flood sediments of the Vicht–Inde catchment to gain an impression of the degree of contamination by organic pollutants by means of in vitro effect-based method. Sediment samples were collected within days after the flood and fractionated prior to biotesting, and supportive instrumental geochemical analysis was performed. Results Flood sediments did not reveal estrogenic potential, which was included in the testing strategy as a relevant endpoint for industrial chemicals and untreated wastewater. In contrast, moderate-to-high dioxin-like activity was observed in 70% of the sediment samples with a peak dioxin-like potential at the restored section of the Inde. Overall, four hotspot samples were identified as at risk, which aligned mostly with the high concentration of organic pollutants including PAHs and PCBs. The fractionation allowed the identification of PAHs and their derivates as the most likely toxicity drivers for dioxin-like activity in the sediments of the Vicht–Inde catchment. Conclusion The results provide first information on the prioritization of hotspot locations at risk for a detailed ecotoxicological profiling and a post-flood monitoring of organic contamination. The identified sinks of contamination in the floodplain areas can be considered a source for remobilization of pollution in future flood events, which is highly relevant for the receiving Rur River.

Background: The flood in July 2021 is considered one of the largest flood disasters in Western Europe in decades, with massive socio-economic consequences. The potential emission and remobilization of anthropogenic pollutants can lead to additional environmental consequences, which need to be addressed in long-term mitigation strategies. The Inde River and its tributary, the Vichtbach River, form a catchment located at the transition from the low mountain ranges of the Eifel to the lowlands of the Lower Rhine Embayment in Germany. The area has been an industrial and mining hotspot for centuries, making it a high-risk area for flood sediment pollution. The present study provides an ecotoxicological screening of flood sediments of the Vicht–Inde catchment to gain an impression of the degree of contamination by organic pollutants by means of in vitro effect-based method. Sediment samples were collected within days after the flood and fractionated prior to biotesting, and supportive instrumental geochemical analysis was performed. Results: Flood sediments did not reveal estrogenic potential, which was included in the testing strategy as a relevant endpoint for industrial chemicals and untreated wastewater. In contrast, moderate-to-high dioxin-like activity was observed in 70% of the sediment samples with a peak dioxin-like potential at the restored section of the Inde. Overall, four hotspot samples were identified as at risk, which aligned mostly with the high concentration of organic pollutants including PAHs and PCBs. The fractionation allowed the identification of PAHs and their derivates as the most likely toxicity drivers for dioxin-like activity in the sediments of the Vicht–Inde catchment. Conclusion: The results provide first information on the prioritization of hotspot locations at risk for a detailed ecotoxicological profiling and a post-flood monitoring of organic contamination. The identified sinks of contamination in the floodplain areas can be considered a source for remobilization of pollution in future flood events, which is highly relevant for the receiving Rur River. [ABSTRACT FROM AUTHOR]

The complex and varied climatic conditions, short duration and high intensity of rainfall, and complex subsurface properties of semi-humid and semi-arid watersheds pose challenges for sub-daily flood forecasting. Previous studies have revealed that lumped models are insufficient because they do not effectively account for the spatial variability in hydrological processes. Extending the lumped model to a distributed modeling framework is a reliable approach for runoff simulation purposes. However, existing distributed models do not adequately characterize the high spatiotemporal variability in sub-daily hydrological processes. To address the above concerns, a distributed modeling framework was proposed that is extended from a lumped model and accounts for the effects of time-varying rainfall intensity and reservoir regulation on hydrological processes. The results indicated that the proposed distributed model could simulate sub-daily flood events with mean values of the NSE, BIAS, RPE, and PTE evaluation metrics of 0.80, 9.2%, 13.0%, and 1.05, respectively, which are superior to those of the lumped model. Furthermore, to evaluate the difference between the proposed and existing distributed models, the proposed distributed model was compared with the variable infiltration capacity (VIC) model at various time steps. The proposed distributed model could better capture the flooding processes at shorter time steps, especially at 3 h. Therefore, it could be considered a practical tool for sub-daily flood forecasting in semi-humid and semi-arid watersheds. [ABSTRACT FROM AUTHOR]

With the increasing frequency of floods, in-depth flood event analyses are essential for effective disaster relief and prevention. Satellite-based flood event datasets have become the primary data source for flood event analyses instead of limited disaster maps due to their enhanced availability. Nevertheless, despite the vast amount of available remote sensing images, existing flood event datasets continue to pose significant challenges in flood event analyses due to the uneven geographical distribution of data, the scarcity of time series data, and the limited availability of flood-related semantic information. There has been a surge in acceptance of deep learning models for flood event analyses, but some existing flood datasets do not align well with model training, and distinguishing flooded areas has proven difficult with limited data modalities and semantic information. Moreover, efficient retrieval and pre-screening of flood-related imagery from vast satellite data impose notable obstacles, particularly within large-scale analyses. To address these issues, we propose a Multimodal Flood Event Dataset (MFED) for deep-learning-based flood event analyses and data retrieval. It consists of 18 years of multi-source remote sensing imagery and heterogeneous textual information covering flood-prone areas worldwide. Incorporating optical and radar imagery can exploit the correlation and complementarity between distinct image modalities to capture the pixel features in flood imagery. It is worth noting that text modality data, including auxiliary hydrological information extracted from the Global Flood Database and text information refined from online news records, can also offer a semantic supplement to the images for flood event retrieval and analysis. To verify the applicability of the MFED in deep learning models, we carried out experiments with different models using a single modality and different combinations of modalities, which fully verified the effectiveness of the dataset. Furthermore, we also verify the efficiency of the MFED in comparative experiments with existing multimodal datasets and diverse neural network structures.

Recent flood events (FE) in Germany have shown that the extent and impact of extreme flood events cannot be estimated solely based on numerical models. For analyzing the development of such an event and to develop and implement safety measures more efficiently, additional data must be collected during the event. Within the scope of this research, the possibilities of near real-time recording using an unmanned aerial vehicle (UAV) and data processing with the Structure from Motion (SfM) method were tested in a case study. Different recording parameter combinations were tested in the Laufer Muehle area on the Aisch river in Germany. The focus of the investigations was the identification of a parameter combination that allows a short recording interval for aerial imagery. Based on these findings, the identification of changes in the study area by comparing multitemporal photography (flood prevention), as well as the recording of flooded areas during a FE should be possible. The accuracy analysis of the different parameter combinations between two point clouds as well as the process of change detection was done by a Multiscale Model to Model Cloud Comparison (M3C2) and including ground control points. As a result, a parameter combination was identified which led to the desired results in the study area. The processes were transformed into fully automated and scripted workflows. The results serve as a basis for establishing a workflow for near real-time analyses in future studies. [ABSTRACT FROM AUTHOR]

Study region: The Changzhou Plain, the Taihu Lake Basin, Eastern China. Study focus: This study introduces an event-based approach for assessing the impact of river changes on flood regulation capacity in urbanized plain river network regions for the first time. The Changzhou Plain, river length decreasing by 7.55 %, was taken as an example to assess the effects of river changes on its flood regulation capacity from the 1980s to the 2020 s. New hydrological insights for the region: Two key indices, flood storage capacity (FSC) and remaining flood storage capacity (RFSC), were developed and calculated using a coupled flood model. Both the coefficient of determination (R2) and the Nash–Sutcliffe efficiency (NSE) exceeded 0.90 during model calibration and validation. The Changzhou Plain experienced river degradation from the 1980s to the 2020 s, with 11.14 % reduction in tributary river length and 3.05 % increase in main river length, leading to decreased water surface area and enhanced connectivity among main rivers. Regional FSC and RFSC increased by 8.42 % and 1.97 %, respectively, due to improved connectivity of main rivers from the 1980s to the 2020 s. The reduction in tributary rivers had minimal effects on FSC (increase of 1.62 %) and RFSC (decrease of 1.74 %), while improved connectivity of main rivers contributed to significant increases in both FSC (6.70 %) and RFSC (3.74 %). These findings underscore the effectiveness of enhancing river connectivity as a strategy to bolster flood prevention in the Taihu Plain, offering valuable insights for flood management and river planning.

Flood events, whose number and intensity are predicted to increase in the Mediterranean region, are difficult to monitor. This causes the number of observations of suspended sediment and total phosphorus concentration (|SS| and |TP|, respectively) during their occurrence to be still scarce. Non-perennial or temporary water bodies, which react more promptly to rainfall events, represent ideal natural observatories. In this study, observations of streamflow, |SS| and |TP|, carried out during some flood events, in the Celone river basin, a temporary river located in south-eastern Italy, are presented. The research examined the correlations between flows, concentrations and loads of sediment and phosphorus and investigated factors that influence sediment and phosphorous dynamics in the river basin. The results show no relationship between the time of the year and the precipitation quantity of each event. The high coefficient of determination of the |SS|–|TP| correlations (R2 = 0.67 on average) proves the importance of soil erosive processes in the delivery of phosphorus to the river. More than 73% of the total suspended sediment load and 83% of total phosphorus load in the period 2010–2011 were transported during the 11 monitored events. In addition to the discharge, |SS| and |TP| also depend on numerous other factors related to land management, such as soil cover and fertilizations. The study, thanks to the improved understanding of the mechanisms governing sediment and phosphorus losses, represents a useful contribution for river basin authorities who have to draw up management plans aimed at preventing eutrophication phenomena and soil fertility reduction. [ABSTRACT FROM AUTHOR]

[Objective] The aim of this study is to explore the changes of runoff-sediment relationship at flood event scale in typical watersheds of the Loess Plateau, to discuss the regulation of runoff-sediment relationship by comprehensive management of soil and water conservation, and to provide reference for future ecological restoration and comprehensive management of soil and water conservation in the Loess Plateau. [Methods] We selected the Gushanchuan, Jialuhe and Xichuanhe watershed to explore the changes of runoff-sediment relationship at flood event scale in three watersheds. Based on their flood event data of 1974—1989 and 2007—2019, a linear model was used to analyze the changes of runoff-sediment relationship in different periods of three watersheds, the Pearson correlation coefficient method was used to investigate the correlation of runoff and sediment-related variables, and the driving factors of runoff-sediment relationship change in each watershed were identified. [Results] The runoff depths and sediment yields of flood events in 2007—2019 of each watershed significantly reduced（p＜0.05） compared with 1974—1989, and the greatest changes were observed in the Gushanchuan watershed, with a decrease of 56.48% and 95.03%, respectively. The change in the amount of sediment yield in the Jialuhe watershed was not obvious and the increase in runoff depth was mainly due to the low degree of vegetation restoration in the watershed, the relatively low impact of soil and water conservation measures, and the increase of rainfall in recent years. [Conclusion] After the implementation of soil and water conservation measures, the runoff-sediment relationship of each watershed had changed significantly, and the linear relationship between runoff depth and sediment yield had weakened, which was due to the implementation of soil and water conservation measures on the Loess Plateau, especially the large-scale vegetation restoration, which had reduced the sediment production and transportation capacity of the unit runoff depth in the watersheds, and resulting in the reduction of sediment into the Yellow River. [ABSTRACT FROM AUTHOR]

Studying the characteristics of runoff and sediment processes and revealing the sources of sediment provide key guidance for the scientific formulation of relevant soil erosion protection measures and water conservancy development plans. In the current study, the flow and sediment data of five hydrological stations on the main stream of the Fu River Basin (FRB) from 2007 to 2018 were selected to identify flood events, explore the variation of sediment transport along the FRB, and clarify the sediment sources. The results found that the Jiangyou–Fujiangqiao section is the main source of sediment in the FRB during the flood season. The runoff volume and sediment load during flood events in the Jiangyou–Fujiangqiao section accounted for 35% and 145% respectively of that of Xiaoheba station. These results combined with the change of the sediment load before and after the 2008 Wenchuan Earthquake (May 12) show that the sediment in this section mainly comes from the Fu River tributary–the Tongkou River watershed. The calculation results for the sediment carrying capacity of the Fu River show that the main stream was in a state of erosion in theory. However, according to the calculation results for the interval sediment yield during flood events, the sediment load at the Xiaoheba station was smaller than that at the Shehong station upstream. The analysis indicates that this was not because of sediment deposition in the river channel, but because of sand mining in the river channel and sediment interception by water conservancy projects. If heavy rainfall occurs in the FRB, the sediment accumulated upstream will move downstream with the resulting flood, and the sediment yield in the FRB may further increase. These research conclusions can provide reference information for improving the prediction and management ability of soil and water loss in the FRB and scientific regulation of the Three Gorges Reservoir. [ABSTRACT FROM AUTHOR]

Effective management of reservoir sedimentation necessitates the characterization of flood events, especially in relation to the propagation of the flow peak (Qpeak) and the suspended sediment concentration peak (SSCpeak). This study, based on a one‐dimensional river network hydro‐sediment model together with field data, presents an exploration of the flood events in the Three Gorges Reservoir (TGR) with focus on the propagating characteristics of Qpeak and SSCpeak. The findings reveal that the main flood season (from July to September) contributed over 80% of the annual sediment load into the TGR, with the mainstream Yangtze and its tributary, the Jialing River, being the primary sediment sources. After the impoundment of the TGR, the propagation time of Qpeak decreases with the raise of the water level in front of dam (WLdam). The increases in Qpeak discharge extends the range of river reach dominated by kinematic wave, resulting in an increase trend in Qpeak propagation time. The propagating speed of SSCpeak is closely related to the ratio of sediment concentration to flow discharge and WLdam. Finally, the propagating durations of Qpeak and SSCpeak in the TGR are compared, and empirical formulas are proposed for quantifying their difference. [ABSTRACT FROM AUTHOR]

Sediment accumulation is severe in the Lower Yellow River. Improving sediment-transport efficiency is an important way to save water resources. In this study, we analyzed the sediment-transport efficiency at different sediment concentrations and discharge levels using data from 306 non-overbank floods in the lower reaches of the Yellow River from 1960 to 2016. When the sediment concentrations were below 20 kg/m3, 60 kg/m3, and greater than 100 kg/m3, the clear water volumes for transporting sediment were above 50 m3/t, approximately 16 m3/t, and less than 10 m3/t, respectively. Given current scheduling, the Xiaolangdi Reservoir can lower its water level and increase non-overbank large water flows with an outflow discharge of >3,000 m3/s when the incoming water flow has a sediment concentration of >60 kg/m3. Mathematical modeling indicates that, for an incoming sediment load of 600 million tons in the Middle Yellow River, the average sediment-transport water volume at the downstream Huayuankou Station decreased by 27%, Optimized scheduling at the Xiaolangdi Reservoir could reduce the sedimentation in the downstream channel by 1.1 billion tons more than current scheduling, and extend the reservoir's sediment-trapping period by ten years. These findings can be applied widely in sandy rivers. HIGHLIGHTS The sediment-transport efficiency and associated sediment-transport clear water volume in the lower reaches of the Yellow River were modeled in this study.; The sediment-transport clear water volume of the river channel decreased with increasing sediment concentration.; Optimizing operation of Xiaolangdi Reservoir can improve the sediment-transport efficiency and reduce sedimentation in the Lower Yellow River.;

Tracking changes in the structure of landscape dynamics as a result of flood activity is a complex process. This study presents a model for determining changes to landscapes caused by flood events by evaluating a specific territory in Eastern Slovakia, which has been affected by repeated large-scale flood events in the past. The area has not been subject to a comprehensive monitoring of changes in the landscape structure. Based on the observation of several sets of data, a combination of statistical methods and GIS spatial analysis tools (visualizing tools for compare categories, mapping, and modelling techniques, spatial analysis models for land use change and flood modelling) were used to identify changes in the landscape structure in the period from 1998 to 2021. The results point to the significance of the year 2010, with the precipitation totals for this year showing a level significantly higher than the rolling average and confirming the occurrence of an extreme flood event. The dynamics of landscape structure changes were evaluated based on changes in the representation of selected types of land cover classes. The results of a spatial evaluation of the Corine Land Cover demonstrate that the most-significant area changes were recorded in 2012 in the pasture class, with a decrease of 31% or approximately 96.5 ha. The identified difference in the frequency of representation of individual values of the normalized differential vegetation index confirms the loss of landscape diversity and the emergence of a more homogeneous type of landscape. An assessment of the state of pastures in the study area shows that this class has completely disappeared from the site near the watercourse. [ABSTRACT FROM AUTHOR]

Spatio-temporal variation of suspended sediment load is a topic of real interest in river geomorphology, especially in the current context of climate change and increasing anthropogenic impacts. In the present study, an attempt was made to argue for these variations based on the correlations between the event efficiency index and the degree of sediment availability in river channel following flood events. Data from four gauging stations along the Trotuș River (Romania) were used to show these types of relationships. The results show that the spatial variations of the event efficiency index are in close correlation with the characteristics of the riverbed in the sectors analysed, and the temporal variations reflect the role of flood events in the modification of river channel and the availability of sediment. Major flood events have caused visible changes in the suspended sediment flux, which is why the analysis of the spatial and temporal variations must necessarily take into account the characteristics of the river channel in terms of sediment sources.

• Flood events entering the Three Gorges Reservoir can be classified into six types. • The flood event types affect the propagation of flood peak and suspended sediment peaks in different ways. • Initial water-sediment asynchrony characteristics most influence delayed suspended sediment transport in the reservoir. • The impoundment of upper cascade reservoirs and reservoir scheduling increase the transport lag of suspended sediment. Different velocities of flood and suspended sediment peaks during flood events result in the delayed transport of suspended sediment, which is exacerbated by reservoir impoundment. The diversity of flood events, the asynchronous pattern of suspended sediment peaks during flood formation and human activities lead to notable differences in the propagation of flood peaks and suspended sediment peaks and subsequently affect the suspended sediment lag, which poses certain problems and challenges for watershed governance, especially reservoir management. In this paper, the Three Gorges Reservoir (TGR) is selected as the research object, and we adopts the analysis of measured data, K-means cluster analysis, 1-D mathematical model and random forest regression. First, the flood process of the TGR from 2003 to 2020 is selected, and then flood event types with nine flood indices are identified. The influences of different flood types on flood and suspended sediment peak propagation are subsequently clarified. We then systematically analyse the factors influencing flood and suspended sediment peak propagation, explore the contributions of different influencing factors to the suspended sediment transport lag, and assess the reasons for the recent changes in the suspended sediment transport lag. The results show that (1) flood events entering the TGR can be approximately classified into six different types, the long-duration and dwarf-fat type (Type 1, 6.59 %), the sharp-thin and early-peak type (Type 2, 20.88 %), the medium-duration and conventional type (Type 3, 27.47 %), the short-duration and sharp-thin type (Type 4, 25.27 %), the long-duration and dramatic-change type (Type 5, 5.49 %), and the medium-duration and multiple-peaks type (Type 6, 14.29 %). (2) Different flood event types result in different effects on the propagation of both the flood and suspended sediment peak. Under the condition of a reservoir flood limit level of 145 m, the flood types for which Q p propagates are as follows from slowest to fastest: Type 1 > Type 5 > Type 2 > Type 3 > Type 6 > Type 4. Moreover, the flood types for which SSC p propagates are as follows from slowest to fastest: Type 4 > Type 2 > Type 3 > Type 6 > Type 1 > Type 5. (3) The initial SSC p asynchronous relationship is the most dominant factor influencing the lagged transport of suspended sediment in the reservoir area, accounting for 32.80 % to 89.40 % of the variation in suspended sediment transport lag, followed by the impacts of differences in flood types (8.2 % to 52.20 %) and reservoir scheduling (2.4 % to 15 %). (4) Human activities, particularly the damming of the cascade reservoirs in the upper reaches of the TGR area and the adjustment of the water level from 145 to 155 m in the TGR due to reservoir scheduling protocols, lead to an increase in the lagged transport time of suspended sediment peak. These findings reveal the asynchronous and differential propagation characteristics and motion mechanisms of flood and suspended sediment peaks in the reservoir area, thereby providing a solid theoretical basis for refining sediment peak discharge scheduling in the TGR. [ABSTRACT FROM AUTHOR]

Various multivariate statistical techniques (MST) can provide valuable insights into water quality variability. Despite numerous studies in which these methods have been used, their potential has not been fully exploited. This paper presents an improved approach to better understand the hydrodynamics of karst systems. The integrated application of hierarchical cluster and principal component analysis in combination with factor analysis allowed the construction of an advanced multivariate chemograph. The analytical procedure was applied in a binary karst aquifer known for its complex hydrodynamics and mixing of water with similar hydrochemical composition. In addition, the study area provides access to an integral groundwater flow system (ponor‐cave‐spring) and offers extensive prior hydrogeological knowledge. The approach allowed reduction and discrimination of the main parameters affecting water quality characteristics. Their identification enabled recognition of three predominant recharge components: (a) stored water impact with Cl and electrical conductivity, (b) sinking stream impact with turbidity and bacteria composition and (c) karst aquifer impact with Ca/Mg ratio as principal parameters. The results supported innovative characterization of the dominant processes and isolation of temporal hydrodynamic phases of individual monitoring points within the aquifer system. On this basis, a spatio‐temporal conceptual model was developed and the hydrodynamic behavior of the main springs was revealed. The applied methodology demonstrated to be useful in ascertaining functioning of a complex karst system under flood event conditions. Plain Language Summary: Karst aquifer systems contain important water resources. The quality of karst springs can deteriorate significantly after rain events, but it is difficult to distinguish how water flows and mixes in the subsurface, especially in large and complex systems. Statistical methods are powerful tools for studying these issues, but most common approaches are inadequate in some cases to reveal the origin of the water and its fate. In this paper, we present an approach in which we combined different statistical methods to explain the dynamics of water flow based on the physicochemical and microbiological properties of water. The application of these methods led to the discrimination of parameters most useful for a reliable interpretation of statistical results, such as turbidity, bacteria, Cl, EC, and Ca/Mg, and to the construction of an advanced diagram that we called a multivariate chemograph. This diagram allowed us to see where the water was coming from at any given time to our monitoring points, which allowed us to construct a detailed explanation of water flow dynamics in space and time. Our contribution is important to better predict the fate of contaminants in karst underground and to develop an early warning system for better water supply management. Key Points: A new approach to study and explain hydrodynamics of karst aquifers was developedIt offers an innovative solution to distinguish influential monitoring parametersMultivariate chemographs allowed spatio‐temporal detection of recharge phases [ABSTRACT FROM AUTHOR]

Through the mobilization of movable objects due to the extreme hydraulic conditions during a flood event, blockages, damage to infrastructure, and endangerment of human lives can occur. To identify potential hazards from aerial imagery and take appropriate precautions, a change detection tool (CDT) was developed and tested using a study area along the Aisch River in Germany. The focus of the CDT development was on near real-time analysis of point cloud data generated by structure from motion from aerial images of temporally separated surveys, enabling rapid and targeted implementation of measures. The differences identified in the study area using distance comparison (M3C2) were segmented into individual components and categorized. Subsequently, the data was compared to existing two-dimensional hydrodynamic numerical calculation results (HQ 100 ). The implementation of the CDT is feasible for a variety of RGB camera-equipped aerial vehicles due to the point cloud-based analysis and postprocessing. By overlaying and visualizing the detected changes with numerical simulation results, a quick assessment of the hazard potential in the event of a possible flood can be made. In the case of the study area along the Aisch River, the localization of construction materials, a steel container with debris pile, and a motor vehicle in the flood hazard zone of a potential HQ 100 event could be confirmed, although no mobilization of the materials was to be expected due to the expected hydraulic conditions of a flood event., Competing Interests: Declarations. Ethics approval: All authors have read, understood, and have complied as applicable with the statement on “Ethical responsibilities of Authors” as found in the Instructions for Authors. Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

Results of bathymetric surveys conducted to examine changes of sand dunes geometry in the Vistula River mouth before, during and after the extreme flood event are presented. A total of 2076 dunes were analysed based on a series of bed elevation profiles obtained along the centreline of about 3.3 km length. Low-steepness dunes characterized by the mean lee-side slopes milder than β10°. Dune height and length are substantially out of phase with progressive changes of water discharge exposing a well-pronounced anti-clockwise hysteresis. Distinct behaviour of dune dimensions reflected in increasing of dune steepness H/λ of about 3-fold and decreasing of about 4-fold were observed during rising and falling discharges, respectively. The bed roughness due to dunes presence showed changes of about 10-fold during the both of limbs and is found to be in range of about kdunes=(1/5÷3/5)Hmean. At the mesoscale region, spectra followed sufficiently by the ‘–3 power law’ for low hydrology, with steeper spectrum slopes close to ‘–4’ during moderate and high water discharges. With the development of the flood, potential of flow separation phenomena was increased of about 9-fold, from 2.2% at the flood beginning phase up to 20% at the flood peak. The obtained results could be used for the improvement of the hydraulic numerical models in sand-bed rivers to predict bedforms evolution, flow resistance and turbulence as well as water levels for proper river system management during flood events.

Research on flood events is one of the most important parts to study runoff and sediment transport in the typical watershed on the Loess Plateau. Based on 101 floods in Period I (PD-I, 1970 to 1990) and Period II (PD-II, 2006 to 2018), and combined with rainfall data, the study indicated the evolution of runoff and sediment transport characteristics during flood events in the Chabagou watershed, and reveal its influencing factors in both periods. Results showed: (1) Sediment yield (SY) increased linearly with runoff amount (RA), and the increasing rate of SY in PD-II was around 20% of PD-I, the relationship between peak flow (PF) and sediment concentration (SC) was the power function, and the SC in PD-II was lower than that in PD-I under the same PF. (2) SY was more sensitive to P (precipitation) of the flood event than rainfall intensity (RI), and the sensitivity of RA and SY to P in PD-II was greater than that in PD-I. The sediment delivery modulus (SDM) with rainfall erosivity (RE) was also linear, and the increasing rate of SDM in PD-II was 27% of PD-I. (3) The better improvement of the underlying surface not only raised the threshold of RA and corresponded with peak SC, but also shortened the duration of high sediment concentration and lowered the sediment transportation capacity by contrasting the flood processes. [ABSTRACT FROM AUTHOR]

Muddy, faecally-contaminated river flood plumes in coastal waters are a hazard to contact recreation and bivalve shellfish consumption but are difficult to study, being episodic and transient. We used a new underway flow-through sampler in a small, fast boat, to map a flood plume within Wellington Harbour, while simultaneously sampling water in the Hutt River inflow. Faecal contamination (indexed by E.coli) correlated with flow, salinity, coloured dissolved organic matter, total suspended solids (TSS) and water clarity (light beam attenuation and visual clarity). The freshwater content of the plume agreed well with time-integrated river discharge. Despite the relatively short time-scale (<12 h) of the event, a 21% loss of TSS (particle flocculation and settling), and 30% loss in E. coli (suggesting some die-off) occurred in the plume compared to river loads. E. coli relative to TSS varied up to two orders of magnitude over a year of river flood sampling. A rapid survey of plumes combined with long-term river observations is expected to augment monitoring and inform the extension of remote sensing and modelling efforts to faecal contamination of New Zealand coastal waters. [ABSTRACT FROM AUTHOR]

Kerala experienced extremely heavy rainfall from 8th to 11th August 2019, which caused a widespread flood throughout the state and disrupted thousands of lives as well as a substantial amount of property. The novel approach of utilising the observed and merged satellite rainfall products along with remotely sensed optical and microwave images was applied to monitor the event. The results indicated vast inundation in Wayanad, Ernakulam, Thrissur, Malappuram, Palakkad, and Alappuzha districts on 10th August. A departure of 217% from normal rainfall for Palakkad and 123% for the whole state in the month of August were observed. The synthetic aperture radar (SAR) and optical datasets were successfully used to generate flood extent maps which can be advantageous for planners and governing bodies to control flood incidents over the region. [ABSTRACT FROM AUTHOR]

Social media is increasingly being used to obtain timely flood information to assist flood disaster management and situational awareness. However, since data in social media are massive, redundant, and unstructured, it is tricky to intuitively and clearly obtain effective information. To automatically obtain clear flood information and deduce flood development processes from social media, the authors of this paper propose an event-based and multi-level modeling approach including a data model and two methods. Through the hierarchical division of events (division into spatial object, phase, and attribute status), the flood information structure (including time, space, topic, emotion, and disaster condition) is defined. We built an entity construction method and a development process deduction method to achieve the automatic transition from cluttered data to orderly flood development processes. Taking the flooding event of the Yangtze and Huai Rivers in 2020 as an example, we successfully obtained true flood information and development process from social media data, which verified the effectiveness of the model and methods. Meanwhile, spatiotemporal pattern mining was carried out by using entities from different levels. The results showed that the flood was from west to east and the damage level was positively correlated with the number of flood-related social media texts, especially emotional texts. In summary, through the model and methods in this paper, clear flood information and dynamic development processes can be quickly and automatically obtained, and the spatiotemporal patterns of flood entities can be examined. It is beneficial to extract timely flood information and public sentiments towards flood events in order to perform better disaster relief and post-disaster management. [ABSTRACT FROM AUTHOR]

River runoff and suspended sediment play a critical role in the chemical, physical, biological processes of Earth's ecosystems. We assessed the temporal changes in runoff and sediment load at both the annual and event scales in the Gushanchuan watershed in the middle reaches of the Yellow River. A total of 330 events, from 1955 to 2018, were selected to evaluate the relationships between rainfall, runoff, and suspended sediment load at the Gaoshiya gauging station. Significant reductions were examined in the maximum runoff peaks, suspended sediment concentration, total runoff, suspended sediment yield, and ratio of event runoff to annual total, whereas the ratio of event sediment yield to annual total remained relatively stable. Hysteresis analysis suggested that the complex loops, anti‐clockwise, and figure‐eight loops accounted for 93.7% of the total events in the watershed. High positive correlations were observed between the flood‐event sediment yield, runoff volume, maximum runoff peaks, and total rainfall amount. The flow‐sediment relationship can be well fitted by the proportional model, and was weaker in 1997–2018 than those in the periods of 1955–1979 and 1980–1996. Runoff during the rising limb of the event significantly contributed to the total runoff and sediment yield. Land use changes and various soil conservation practices were responsible for the decrease in the flood frequency and magnitude. The results of this study provide useful insights into the relationships between rainfall, runoff, and suspended sediment dynamics, and their responses to soil conservation practices. [ABSTRACT FROM AUTHOR]

Tracking changes in the structure of landscape dynamics as a result of flood activity is a complex process. This study presents a model for determining changes to landscapes caused by flood events by evaluating a specific territory in Eastern Slovakia, which has been affected by repeated large-scale flood events in the past. The area has not been subject to a comprehensive monitoring of changes in the landscape structure. Based on the observation of several sets of data, a combination of statistical methods and GIS spatial analysis tools (visualizing tools for compare categories, mapping, and modelling techniques, spatial analysis models for land use change and flood modelling) were used to identify changes in the landscape structure in the period from 1998 to 2021. The results point to the significance of the year 2010, with the precipitation totals for this year showing a level significantly higher than the rolling average and confirming the occurrence of an extreme flood event. The dynamics of landscape structure changes were evaluated based on changes in the representation of selected types of land cover classes. The results of a spatial evaluation of the Corine Land Cover demonstrate that the most-significant area changes were recorded in 2012 in the pasture class, with a decrease of 31% or approximately 96.5 ha. The identified difference in the frequency of representation of individual values of the normalized differential vegetation index confirms the loss of landscape diversity and the emergence of a more homogeneous type of landscape. An assessment of the state of pastures in the study area shows that this class has completely disappeared from the site near the watercourse.

A novel comprehensive assessment system, consisting of a bioassay and chemical analysis, was developed to quickly evaluate the human health risk posed by toxic chemicals discharged due to natural disasters. To analyze samples quickly, a yeast-two-hybrid assay (Y2H) and GC–MS equipped with an automated identification and quantification system (AIQS-GC) were employed for the bioassay and chemical analysis, respectively. Since the analysis of 1000 substances by AIQS could be finished within two days following the Y2H assay for screening, this method would complete the risk assessment within three days. To confirm the applicability of this method in real environmental samples, we examined it using sediments circulated by Typhoon Hagibis. In one sediment sample, a distinctive response was indicated by the Y2H assay, and relatively high DDT concentration was identified by AIQS-GC in the same sediment. Therefore, using the results obtained from this method, a human health risk assessment of DDT was conducted, which indicated that the risk could be ignored. Additionally, the contamination of PAHs and alkanes was suggested as well. In this study, the pollution risk assessment could be completed within three days. Therefore, to our knowledge, this is the first study to demonstrate an assessment system with a rapid combination method for emergencies. Consequently, it is believed that this type of novel system would be needed in the future due to the increasing number of natural disasters predicted worldwide.

For rivers flooded by rain, the annual sediment load is mainly derived from one or several rainstorms in the flood season and is of research significance. Based on the theory of runoff erosion power, the M-K method and the daily measured runoff and sediment data for the Xiaoheba, Luoduxi, Wusheng and Beibei stations in the Jialingjiang River basin, this paper analyzed the sediment transport characteristics during flood events in different periods and regions. The results of this paper are as follows: the runoff and sediment discharge during the flood season mainly came from the main stream of the Jialingjiang River. In general, the runoff discharge of flood events in different regions showed no significant decreasing trend, while the sediment transport modulus (sediment load) showed a significant decreasing trend except at Xiaoheba station in 2013-2020. With the gradual increase in runoff erosion power, the variation ranges of the sediment transport modulus (sediment load) in different periods in the Jialingjiang River basin were correspondingly narrowed. The degrees of influence of human activities on the sediment transport processes were weakened in the order of the Wusheng station in mainstream Jialingjiang River, Luoduxi station in Qujiang River and Xiaoheba station in Fujiang River. Affected by the Wenchuan earthquake and rainstorms, the average sediment loads in flood event of the Xiaoheba and Beibei stations in 2013-2020 were higher than those in 1998-2012, while the rate of increase rate at the Beibei station was less than that of the Xiaoheba station. [ABSTRACT FROM AUTHOR]

Spatio-temporal variation of suspended sediment load is a topic of real interest in river geomorphology, especially in the current context of climate change and increasing anthropogenic impacts. In the present study, an attempt was made to argue for these variations based on the correlations between the event efficiency index and the degree of sediment availability in river channel following flood events. Data from four gauging stations along the Trotu River (Romania) were used to show these types of relationships. The results show that the spatial variations of the event efficiency index are in close correlation with the characteristics of the riverbed in the sectors analysed, and the temporal variations reflect the role of flood events in the modification of river channel and the availability of sediment. Major flood events have caused visible changes in the suspended sediment flux, which is why the analysis of the spatial and temporal variations must necessarily take into account the characteristics of the river channel in terms of sediment sources. [ABSTRACT FROM AUTHOR]

Social media is increasingly being used to obtain timely flood information to assist flood disaster management and situational awareness. However, since data in social media are massive, redundant, and unstructured, it is tricky to intuitively and clearly obtain effective information. To automatically obtain clear flood information and deduce flood development processes from social media, the authors of this paper propose an event-based and multi-level modeling approach including a data model and two methods. Through the hierarchical division of events (division into spatial object, phase, and attribute status), the flood information structure (including time, space, topic, emotion, and disaster condition) is defined. We built an entity construction method and a development process deduction method to achieve the automatic transition from cluttered data to orderly flood development processes. Taking the flooding event of the Yangtze and Huai Rivers in 2020 as an example, we successfully obtained true flood information and development process from social media data, which verified the effectiveness of the model and methods. Meanwhile, spatiotemporal pattern mining was carried out by using entities from different levels. The results showed that the flood was from west to east and the damage level was positively correlated with the number of flood-related social media texts, especially emotional texts. In summary, through the model and methods in this paper, clear flood information and dynamic development processes can be quickly and automatically obtained, and the spatiotemporal patterns of flood entities can be examined. It is beneficial to extract timely flood information and public sentiments towards flood events in order to perform better disaster relief and post-disaster management.

The effect of the interplay between unsteady flow and bedform in a flood event on nitrogen cycling in the hyporheic zone (HZ) remains poorly understood. In this study, a reactive transport groundwater model with different flood hydrographs was proposed to investigate the effect of modified hyporheic flow on nitrate dynamics in the HZ, including nitrate source‐sink function, response to the single‐peak flood event and removal efficiency. The results demonstrate that there exists an optimal range of river channel gradients that could enhance the biogeochemical reactions (respiration, nitrification and denitrification) in a flood event. The HZ acts as a nitrate sink especially after the flood event, and its source‐sink function is independent of the unsteady discharge/stage conditions. The nitrate in the HZ has a hysteretic response to peak stage/discharge, and its removal efficiency is decreased by up to 70% compared to steady flow conditions. These findings not only provide a better understanding of nitrogen dynamics under the effect of unsteady channel flow, but also can be applied for river restoration to efficiently remove nitrate in the HZ by modifying river channel gradients. [ABSTRACT FROM AUTHOR]

The article of Blatnik et al. (2019) “Groundwater dynamics between Planinsko Polje and springs of the Ljubljanica River, Slovenia” published in Acta Carsologica, 48/2 focused on describing the hydrogeological behaviour of the aquifer between Planinsko Polje and the springs of the Ljubljanica River. The authors analysed the effect of different high water events that occurred between January 2015 and May 2018. Interpretations were based on hydrographs obtained by continuous measurements of water level, temperature and specific electric conductivity in selected ponors, springs and water active caves located in the area between Planinsko Polje and the springs of the Ljubljanica River. Through these interpretations, different conceptual hydrological models about the dynamics and directions of the flow in the aquifer have been proposed and tested. A flow connection was proposed between the Hrušica Plateau, estavelles located at the NW border of Planinsko Polje, and caves Gradišnica (W2) and Gašpinova Jama (W3) close to town Logatec. In this supplement, we provide new data recorded during an unusual hydrological event in August 2018. These further support and stress the importance of the connection between the Hrušica Plateau and Logatec region (W2 and W3).

Satellite-based precipitation products provide critical precipitation sources with high resolution for hydrologic forecasting. This study aims to assess the suitability of the near-real-time "Early" run and "Late" run of the Integrated Multi-satellite Retrievals for the Global Precipitation Measurement (IMERG) products (IMERG-E and IMERG-L), and the post-real-time "Final" run IMERG product (IMERG-F) and Tropical Rainfall Measuring Mission Multi-satellite Precipitation Analysis (TMPA) 3B42RT in flood simulation, particularly flood events, at hourly scale over a humid region of China. A statistical assessment of the accuracy of selected satellite-based precipitation products shows IMERG-F outperforms the others, and the performance of TMPA 3B42RT is generally better than that of IMERG-E and IMERG-L. Furthermore, IMERG-F performs the best in hourly streamflow simulation, as well as in flood event simulation, with a mean Nash-Sutcliffe efficiency coefficient of 0.71, while IMERG-E, IMERG-L and TMPA 3B42RT present overall acceptable performance. The simulated peak flows tend to be smaller than the observations, and the simulated time lags of occurrence are changeable. This study finds that IMERG and Tropical Rainfall Measurement Mission (TRMM) are suitable for hydrological simulations at hourly scale, and IMERG-E is an appropriate replacement for TMPA 3B42RT in this case. [ABSTRACT FROM AUTHOR]

Wood is recognized as a key element of river ecosystem for a large number of positive feedbacks with biotic and abiotic components, both when it is present as large wood deposit or as live vegetation on the riparian zone. Despite the positive impacts of wood, when considering the high flow events, the presence of woody riparian vegetation within the channel can increase the potential risk related to local wood accumulation, bridge clogging or damages at hydraulic structures. Both the effects given by the riparian vegetation and in-channel dead wood need to be considered when evaluating the large wood-related hazards in rivers. For these reasons, we need to increase the knowledge on the relative importance of floodplains in recruiting large wood. An analysis was conducted on the base of a post event field survey on the Ombrone Grossetano River (Italy) which helped to identify the main variables controlling the uprooting process of riparian vegetation. The implementation of a conceptual model for plant stability helped to predict the tree uprooting that occurred during that flood event. The proposed approach can be extended to any other gravel-bed rivers, such that the evaluation of the vulnerability of woody riparian vegetation can give practical advices for maintenance strategies about vegetation cutting. [ABSTRACT FROM AUTHOR]

Featured Application: The results of the study can be applied in the part of the public administration of the Slovak Republic, especially for the Slovak Water Management Company in cooperation with municipalities in the processing of flood hazard maps and flood risk maps. The study also provides recommendations for the development of the concept of spatial data collection in the territory of the Slovak Republic according to the INSPIRE Directive. Weather-related disasters represent a major threat to the sustainable development of society. This study focuses directly on the assessment of the state of spatial information quality for the needs of hydrodynamic modeling. Based on the selected procedures and methods designed for the collection and processing of spatial information, the aim of this study was to assess their qualitative level of suitability for 3D flood event modeling in accordance with the Infrastructure for Spatial Information in the European Community (INSPIRE) Directive. In the evaluation process we entered geodetic measurements and the digital relief model 3.5 (DMR 3.5) available for the territory of the Slovak Republic. The result of this study is an assessment of the qualitative analysis on three levels: (i) main channel and surrounding topography data from geodetic measurements; (ii) digital relief model; and (iii) hydrodynamic/hydraulic modeling. The qualitative aspect of the input data shows the sensitivity of a given model to changes in the input data quality condition. The average spatial error in the determination of a point's position was calculated as 0.017 m of all measured points along a watercourse and its slope foot and slope edge. Although the declared accuracy of DMR 3.5 is assumed to be ±2.50 m, in some of the sections in the selected area there were differences in elevation up to 4.79 m. For this reason, we needed a combination of DMR 3.5 and geodetic measurements to refine the input model for the process of hydrodynamic modeling. The quality of the hydrological data for the monitored N annual flow levels was of fourth-class reliability for the selected area. [ABSTRACT FROM AUTHOR]

• Both runoff depth and sediment yield of flood events decreased after treatment. • The slope of the runoff-sediment relationship decreased greatly. • The correlations between runoff and sediment variables generally became worse. River runoff and sediment load are characterized by topography, climate patterns, and vegetation in the watershed. The relationship runoff and sediment load has been greatly altered in many rivers throughout the world, as well as rivers in the Chinese Loess Plateau (LP) due to large-scale ecological restoration and soil conservation measures implementation. This study attempts to identify the changes of runoff-sediment relationship in three watersheds: the Gushanchuan River watershed, Jialu River watershed and Xichuan River watershed by using the flood event data during the periods of 1974–1989 and 2007–2019 in the LP. The results indicated that both runoff depth and sediment yield of flood events during 2007–2019 reduced significantly compared with those during 1974–1989 in all the watersheds. The highest decrease was found in the Gushanchuan River watershed, exhibiting reduction of 56.48% and 95.03% in runoff and sediment yield, respectively. The ratios between sediment yield and runoff depth in all three watersheds showed significant decrease during 2007–2019 when comparing to those in 1974–1989. The correlations between runoff and sediment variables became worse in 2007–2019, compared with those during 1974–1989. The implementation of soil and water conservation (SWC) measures (vegetation restoration, terraces and check dams) accounted for the changes in runoff-sediment relationship in all three watersheds. The result of this study could provide valuable information for the influences of SWC implementation and guide soil erosion control in the LP. [ABSTRACT FROM AUTHOR]

The Hawkesbury-Nepean Valley, Australia’s longest coastal catchment, is spanned by a river system of more than 470 km, that runs from Goulburn to Broken Bay, covering a total area of over 2.2 million hectares. This region has remained prone to flood events, with considerable mortalities, economic impacts and infrastructural losses occurring quite regularly. The topography, naturally variable climatic conditions and the ‘bathtub’ effect in the region are responsible for the frequent flood events. In response, the Government at the national/federal, state and local level has focused on the design of efficient flood risk management strategies with appropriate evacuation plans for vulnerable communities from hospitals, schools, childcare and aged care facilities during a flood event. Despite these overarching plans, specialized response and evacuation plans for aged care facilities are critical to reducing the loss incurred by flood events in the region. This is the focus of this present paper, which reviews the history of flood events and responses to them, before examining the utilization of artificial intelligence (AI) techniques during flood events to overcome the flood risks. An early flood warning system, based on AI/Machine Learning (ML) strategy is being suggested for a timely decision, enhanced disaster prediction, assessment and response necessary to overcome the flood risks associated with aged care facilities within the Hawkesbury-Nepean region. A framework entailing AI/ML methods for identifying the safest route to the destination using UAV and path planning has been proposed for timely disaster response and evacuation of the residents of aged care facilities.

Abstract Protecting our water resources in terms of quality and quantity is considered one of the big challenges of the twenty-first century, which requires global and multidisciplinary solutions. A specific threat to water resources, in particular, is the increased occurrence and frequency of flood events due to climate change which has significant environmental and socioeconomic impacts. In addition to climate change, flooding (or subsequent erosion and run-off) may be exacerbated by, or result from, land use activities, obstruction of waterways, or urbanization of floodplains, as well as mining and other anthropogenic activities that alter natural flow regimes. Climate change and other anthropogenic induced flood events threaten the quantity of water as well as the quality of ecosystems and associated aquatic life. The quality of water can be significantly reduced through the unintentional distribution of pollutants, damage of infrastructure, and distribution of sediments and suspended materials during flood events. To understand and predict how flood events and associated distribution of pollutants may impact ecosystem and human health, as well as infrastructure, large-scale interdisciplinary collaborative efforts are required, which involve ecotoxicologists, hydrologists, chemists, geoscientists, water engineers, and socioeconomists. The research network “project house water” consists of a number of experts from a wide range of disciplines and was established to improve our current understanding of flood events and associated societal and environmental impacts. The concept of project house and similar seed fund and boost fund projects was established by the RWTH Aachen University within the framework of the German excellence initiative with support of the German research foundation (DFG) to promote and fund interdisciplinary research projects and provide a platform for scientists to collaborate on innovative, challenging research. Project house water consists of six proof-of-concept studies in very diverse and interdisciplinary areas of research (ecotoxicology, water, and chemical process engineering, geography, sociology, economy). The goal is to promote and foster high-quality research in the areas of water research and flood-risk assessments that combine and build off-laboratory experiments with modeling, monitoring, and surveys, as well as the use of applied methods and techniques across a variety of disciplines.

This paper describes the experience of using weather radar data to simulate a catastrophic flood caused by intense rains that occurred in the period from August 5 to 8, 2017 in the south of Primorye, Russia. The Amba River (243 km2), where historical discharge peak was measured, was chosen as the test watershed of this study. Weather radar hourly precipitation fields with a spatial resolution of 1 km and a modified version of the kinematic-wave-based geomorphologic IUH model were used to estimate the hydrograph at the watershed outlet. The simulation was performed with an hourly time step; using the precipitation grids obtained from initial radar reflectivity data, and then using bias-correction based on precipitation measurement at the closest meteorological station. In the preliminary tests, the simulated discharge was found underestimated about two times in comparison with the observed discharges. After performing a precipitation bias-correction, the simulated and observed discharges showed good accordance. [ABSTRACT FROM AUTHOR]

Abstract In the Mediterranean region, floods are expected to increase as a result of climate change and knowledge of soil erosion hot spots during exceptional rainfalls is required to support mitigation measures. This study quantifies the main sediment sources during an exceptional rainfall event in 2012 (235 mm) at the outlet of two catchments located in NE Spain. To this purpose, suspended sediments were collected during the flood event, complemented with entrapped sediments in mat taken one year after the event. We used fingerprinting methodology and applied the FingerPro unmixing model to estimate the contribution from main sources. The selected tracers clearly distinguished agricultural, rangeland, subsoil and channel banks as the four potential sources in both catchments. In the Vandunchil catchment, the 8 time-integrated suspended sediment samples revealed changes in source contribution during the 2-h sampling sequence. There were relatively high contributions from rangeland, agriculture and subsoil at the beginning of the sampling, representing 30, 40 and 35% of the total source contributions, respectively. Our records captured the delivery of pulses of eroded surface soil transported by runoff with direct connectivity to the stream. The sequence was followed by a sharp increase in channel bank contribution (up to 90%) in comparison to the other sources, reflecting streambank erosion and landslide occurrence, which manifested during the flood. In contrast, in the La Reina catchment, agricultural soils contributed the most (65%) and, together with subsoils (32%), were the main sources. These results reflect the effect of the higher connectivity and slope gradient of these cultivated fields of the La Reina catchment in comparison with those of the Vandunchil catchment. We discuss the possibility of using different properties, such as radionuclides, geochemistry and magnetic measurements, as tracers to distinguish between potential sources during an exceptional event in upland Mediterranean catchments. Our results support the use of fingerprinting techniques to determine variations in source contribution and sediment provenance during flood events, as extreme rainfalls are main drivers of sediment mobilization and key factors in changing landscapes. This is essential in identifying vulnerable hot spots, in which early-stage interventions are needed, and for helping policy makers with management of soil and water resources. Graphical abstract Image 1074 Highlights • Unique opportunity to capture soil response during an exceptional event of 235 mm. • Suspended sediment properties changed during the flood event. • Source contributions varied in response to the rainstorm in a short period. • Switch from soil sources to channel bank provenance was captured during the flood. • Land use and connectivity determined the suspended sediment provenance. [ABSTRACT FROM AUTHOR]