Background Over the last 200 years, the courses of most European rivers have experienced significant irreversible changes. These changes are connected to different kinds of anthropogenic river use and exploitation, which have varied from running water mills and rafting to large-scale hydroelectric power plants, industrial water withdrawal and flood protection measures. Today, in most developed countries, water quality and ecological river development are important factors in water management. The aim of this study is to evaluate the specific impacts of different time periods during the last 200 years on river courses and their effects on current river management using the example of the 165-km-long German Rur River (North Rhine-Westphalia). The Rur River is a typical central European upland-to-lowland river whose catchment has been affected by various phases of industrial development. Methods In this study, a range of morphological changes over the last 200 years are determined based on historic maps and up-to-date orthophotos. River length, sinuosity, oxbow structures, sidearms and the number of islands are used to investigate human impact. The results are correlated with historic time periods. Results This analysis shows that river straightening increases, especially during the Industrial Revolution, even without direct hydraulic channelization. The period and grade of river straightening have a direct morphodynamic impact on today’s river restorations. Since the Rur River is a typical upland-to-lowland river, the results show an additional impact by geofactors, such as landform configurations. Conclusions Morphodynamic development is correlated with five historic periods of industrial development between 1801 and 2019 up to the introduction of the EU—Water Framework Directive (EU-WFD). Each period shows a different influence on the watercourse, which is connected with human intervention. Even if worldwide comparisons show that the five historical phases differ slightly in their timing between regions, they are applicable to other study areas.
Background Because of global climate change, extreme flood events are expected to increase in quantity and intensity in the upcoming decades. In catchments affected by ore mining, flooding leads to the deposition of fine sediments enriched in trace metal(loid)s. Depending on their concentration, trace metal(loid)s can be a health hazard. Therefore, exposure of the local population to flood sediments, either by ingestion (covering direct ingestion and consuming food grown on these sediments) or via inhalation of dried sediments contributing to atmospheric particulate matter, is of concern. Results The extreme flood of July 2021 deposited large amounts of sediment across the town of Eschweiler (western Germany), with the inundation area exceeding previously mapped extreme flood limits (HQextreme). These sediments are rich in fine material (with the < 63 µm fraction making up 32% to 96%), which either can stick to the skin and be ingested or inhaled. They are moderately to heavily enriched in Zn > Cu > Pb > Cd > Sn compared to local background concentrations. The concentrations of Zn, Pb, Cd, Cu, and As in flood sediments exceed international trigger action values. A simple assessment of inhalation and ingestion by humans reveals that the tolerable daily intake is exceeded for Pb. Despite the enrichment of other trace elements like Zn, Cu, Cd, and Sn, they presumably do not pose a risk to human well-being. However, exposure to high dust concentrations may be a health risk. Conclusions In conclusion, flood sediments, especially in catchments impacted by mining, may pose a risk to the affected public. Hence, we propose to (I) improve the flood mapping by incorporating potential pollution sources; (II) extend warning messages to incorporate specific guidance; (III) use appropriate clean-up strategies in the aftermath of such flooding events; (IV) provide medical support, and (V) clue the public and medical professionals in on this topic accordingly. Graphical Abstract
Background Because of global climate change, extreme flood events will increase in quantity and intensity in the upcoming decades. In catchments affected by ore mining, flooding leads to the deposition of fine sediments enriched in trace metal(loid)s. Depending on their concentration, trace metal(loid)s can be a health hazard. Therefore, the exposure of the local population to flood sediments, either by ingestion (covering direct ingestion and consuming food grown on these sediments) or via inhalation of dried sediments contributing to atmospheric particulate matter, is of concern. Results The extreme flood of July 2021 deposited enormous amounts of sediment across the town of Eschweiler (western Germany), with the inundation area exceeding previously mapped extreme flood limits (HQextreme). These sediments are rich in fine material (with the < 63 µm fraction making up 32% to 96%), which either can stick to the skin and be ingested or be inhaled. They are moderately to heavily enriched in Zn>Cu>Pb>Cd>Sn compared to local background concentrations. The concentrations of Zn, Pb, Cd, Cu, and As in flood sediments exceed international trigger action values. A simple assessment of uptake reveals that the tolerable daily intake is exceeded for Pb. Despite the enrichment of other trace elements like Zn, Cu, Cd, and Sn, they presumably do not pose a risk to human well-being. However, exposure to high dust concentrations may be a health risk. Conclusions In conclusion, flood sediments, especially in catchments impacted by mining, may pose a risk to the affected public. Hence, we propose to (I) improve the flood mapping by incorporating potential pollution sources, (II) extend warning messages to incorporate specific guidance, (III) use appropriate clean-up strategies in the aftermath of such flooding events, (IV) provide medical support, and (V) clue the public and medical professionals in on this topic accordingly.
Many river systems are regulated by dams, which causes an altered flow regime and sediment deficit in the downstream reach. The Rur dam (North Rhine-Westphalia, Germany), constructed from 1900 to 1959, serves as a model example of the impact of a large dam in a European low mountain area on downstream morphology. Today, a new equilibrium incorporates flow regulations, a deficit in suspended sediment supply, and an increased mean sediment diameter downstream of the dam. A hybrid examination of field measurements and numerical modelling shows that the sediment deficit and increased mean sediment diameters downstream of the Rur dam are superimposed by the lithostratigraphy and the sediment supply of tributaries. However, the discharge regulations lead to floodplain decoupling downstream of the dam. Furthermore, the Rur dam functions as a pollutant trap. Overall, more studies on the impact of damming on downstream reaches are needed to classify the impact depending on the river type for sustainable water management.
<p>The narrow valley parts of the Ahr river are located in a low mountain region on the edge of the Volcanic Eifel. In July 2021, a flash flood formed, and energetic water masses with high flow velocities drove significant morphodynamic change and sediment displacements along the Ahr river. The riverbed and the banks experienced erosion, and floodplains showed slope erosion by surface runoff. In other locations, we observed floodplain sedimentation and riverbed infill. Large sediment lenses formed on floodplains, and gravel bank deposits, partly high in organic content, changed the local morphology of the Ahr river. Sorting of the grain size of deposited sediments from coarse to fine was observed providing clues to the complex flow conditions. The change of the river-course was overall limited due to the high urban development and man-made riverbank constraints by infrastructure. In this context, the prediction of future morphological changes in the Ahr river is essential for sustainable water resource management, especially in the context of reaching the goals set by the European Water Framework Directive (EU-WFD). If not properly accounted for, future maintenance and engineering measures affecting the river-course may not only be costly but also introduce new hazards. This study investigates morphological changes in different sections of the Ahr river as a result of the July 2021 mega-event at different spatial scales. Those changes were evaluated in a historic context to compare the observations to theoretical morphological developments of the river unaffected by anthropogenic development. The Lateral Mobility Index (LMI) is used to evaluate stream bed changes. In the upper reaches of the Ahr river, confining bedrock limits morphological riverbed changes as a natural geological boundary. Thus, most morphological changes in the Ahr river occurred in the lower reaches. The LMI caused by the mega-event in the 2.7 km long lower river reach up to the Rhine confluence is 1.2, which indicates severe changes in the river course. However, the LMI between the early 19<sup>th</sup> century and the mid-19<sup>th</sup> century is 2.2, which could result from an increase of confining anthropogenic boundaries within the last 200 years, which further caused reduced river structures and a reduced alluvial corridor. Anastomosis structures with a total channel width of up to 250 meters in the early 19<sup>th</sup> century are non-existent anymore, and the total channel width was reduced to 20 meters on average before the flood event. Although the total channel widened up to 90 meters after the flood event, the structural diversity only slightly increased. Concluding, morphological changes by the flood event in mid-July 2021 did not generally develop towards near-natural river structure, likely resulting from the anthropogenic hard boundaries constraining flow. River engineering actions in the course of rehabilitation after the flood event need to be evaluated on different spatial scales to assess sustainable water resource management for the future.</p>
Land use and water resource management influence the suspended sediment concentration (SSC) in rivers. Fine sediments are an important driver for river development, even in coarse-material-rich rivers. In this study, the sediment rating curve approach is modified to predict SSC several river-km downstream of a sampling site. Further, the prediction is improved by adding sediment input, storage, and dilution effects through relevant anthropogenic measures through a model identification approach. Thus, the impact of the most severe anthropogenic measures, damming and changes in the length of a channel section for the Rur River, could be identified. Further, the impact of describing parameter changes for those measures on the SSC can be computed and considered in future water resource management. In this approach, particle swarm optimization was used to fit parameters in permutable test- and training data sets to identify linear extensions to the sediment rating curve. The input data consists of (1) SSC, which was obtained by sampling along the river section four times a year over approximately two years, (2) discharge data from river gauges supplemented by rainfall-runoff modeling between stations, (3) rainfall data from meteorological stations, and (4) sub-catchment characteristics like river section length and erosivity obtained with GIS. Via incorporating the river section length and sediment deposition in response to damming, we reduced the RMSE (root mean squared error) from 152.27 to 131.83% with a p-value of 0.073 in the Wilcoxon Signed Rank Test. Further integration of sub-catchment parameters like erosivity led to overfitting and decreased prediction accuracy. A catchment-wide prediction was achieved, but sub-catchments operate on different spatial scales with different connectivity behavior, which restricts the transferability of the equation. SSC-Q hystereses provide the first indications of characteristic sediment sources and were used to discuss connectivity behavior within the study area. They are recommended as part of a (sub-) catchment characterization for further studies.
Background Over the last 200 years, the courses of most European rivers have experienced significant irreversible changes. These changes are connected to different kinds of anthropogenic river use and exploitation, which have varied from running water mills and rafting to large-scale hydroelectric power plants, industrial water withdrawal and flood protection measures. Today, in most developed countries, water quality and ecological river development are important factors in water management. The aim of this study is to evaluate the specific impacts of different time periods during the last 200 years on river courses and their effects on current river management using the example of the 165 km-long German Rur River (North Rhine-Westphalia). The Rur River is a typical central European upland to lowland river whose catchment has been affected by various phases of industrial development.MethodsIn this study, a range of morphological changes over the last 200 years are determined based on historic maps and up-to-date orthophotos. River length, sinuosity, oxbow structures, sidearms and the number of islands are used to investigate human impact. The results are correlated with historic time periods.ResultsThis analysis shows that river straightening increases, especially during the Industrial Revolution, even without direct hydraulic channelization. The period and grade of river straightening have a direct morphodynamic impact on today’s river restorations. Since the Rur River is a typical upland to lowland river, the results show an additional impact by geofactors, such as landform configurations.ConclusionsMorphodynamic development is correlated with five historic periods of industrial development between 1801 and 2019 up to the introduction of the EU - Water Framework Directive (EU-WFD). Each period shows a different influence on the watercourse, which is connected with human intervention. Even if worldwide comparisons show that the five historical phases differ slightly in their timing between regions, they are applicable to other study areas.
Background Over the last 200 years, most European river courses experienced significant irreversible changes. These changes were connected with different kinds of anthropogenic river use and exploitation, which varied from running water mills and rafting to large-scale hydroelectric power plants, industrial water withdrawal and measures for flood protection. Today, in most of the developed countries water quality and ecological river development are stakeholders in water management. The aim of the following study is to evaluate the specific impact of different time periods during the last 200 years on river courses, and its effects on the current river management using the example of the 165 km long German Rur River (North Rhine-Westphalia). The Rur River is a representative central European upland to lowland river, whose catchment has been affected by various phases of industrial development.MethodsIn this study, large-scale morphological changes over the last 200 years are determined based on historic maps and up-to-date orthophotos. The indicators river length, sinuosity, oxbow structures, sidearms and the number of islands are used to investigate human impact. The results are correlated with historic time periods.ResultsThis analysis shows that river straightening does increase especially during the industrial revolution, even without direct hydraulic channelization, which applies not only to the study area but also to further examples worldwide. The period and grade of river straightening has a direct morphodynamic impact on today’s river restorations. Since the Rur River is a typical upland to lowland river, the results show additional impact of geo-factors, like landform configurations.ConclusionsThe morphodynamic development is correlated with five historic periods between 1801 and 2019 of industrial development up to the introduction of the EU - Water Framework Directive (EU-WFD). Each period shows different influence on the watercourse which is connected with human intervention. Even if worldwide comparisons show that the five historical phases differ slightly in time between regions, they are applicable to other study areas.
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