River Management Research Articles

Development of AI-based hybrid soft computing models for prediction of critical river water quality indicators.

Prediction of river water quality indicators (RWQIs) using artificial intelligence (AI)-based hybrid soft computing modeling techniques could provide essential predictions required for efficient river health planning and management. The study described the development of a novel AI-based relative weighted ensemble (AIRWE) hybrid model for predicting critical RWQIs, i.e., biochemical oxygen demand (BOD) and total coliform (TC). The study involved comprehensive water quality (WQ) monitoring from 30 locations along the Damodar River to establish the baseline data and delineate the WQ. The representative input features showing a strong association with BOD and TC were identified using Spearman's rank-coupled orthogonal linear transformation (SOT). The relative weighted ensemble (RWE) method was applied to determine the relative weights for base learners in the AIRWE model. The statistical analysis of the developed model revealed that it was most efficient and accurate for predicting BOD (R2, 0.97; RMSE, 0.06; MAE, 0.04) and TC (R2, 0.98; RMSE, 0.06; MAE, 0.05) over the traditional techniques. The tstat (BOD 0.02 and TC 0.47) was lesser than tcrit (1.672), confirming its unbiased predictions. The SOT technique removed the data noise and multicollinearity, whereas RWE curtailed the individual model's limitations and predicted more reliable results. The model resulted 97% accuracy with high precision (96%) in classifying the river water quality for various end uses. The study describes a novel approach for researchers, scientists, and decision-makers for modeling and predicting various environmental attributes.

Two-stage channels can enhance local biodiversity in agricultural landscapes

Field drainage causes habitat loss, alters natural flow regimes, and impairs water quality. Still, drainage ditches often are last remnants of aquatic and wetland habitats in agricultural landscapes and as such, can be important for local biodiversity. Two-stage channels are considered as a greener choice for conventional ditches, as they are constructed to mimic the structure of natural lowland streams providing a channel for drainage water and mechanisms to decrease diffuse loading. Two-stage channels could also benefit local biodiversity and ecosystem functions, but existing information on their ecological benefits is scarce and incomplete. We collected environmental and biological data from six agricultural stream systems in Finland each with consequent sections of a conventional ditch and a two-stage channel to study the potential of two-stage channels to enhance aquatic and riparian biodiversity and ecological functions. Biological data included samples of stream invertebrates, diatoms and plants and riparian beetles and plants. Overall, both section types were highly dominated by few core taxa for most of the studied organism groups. Riparian plant and invertebrate communities seemed to benefit from the two-stage channel structure with adjacent floodplains and drier ditch banks. In addition, two-stage channel sections had higher aquatic plant diversity, algal productivity, and decomposition rate, but lower stream invertebrate and diatom diversity. Two-stage channel construction did not diversify the structure of stream channels which is likely one explanation for the lack of positive effects on benthic diversity. However, both section types harbored unique taxa found only in one of the two types in all studied organism groups resulting in higher local gamma diversity. Thus, two-stage channels enhanced local biodiversity in agricultural landscapes. Improvements especially in aquatic biodiversity might be achieved by increasing the heterogeneity of in-stream habitat structure and with further efforts to decrease nutrient and sediment loads.

Noncontact Automatic Water-Level Assessment and Prediction in an Urban Water Stream Channel of a Volcanic Island Using Deep Learning

Traditional methods for water-level measurement usually employ permanent structures, such as a scale built into the water system, which is costly and laborious and can wash away with water. This research proposes a low-cost, automatic water-level estimator that can appraise the level without disturbing water flow or affecting the environment. The estimator was developed for urban areas of a volcanic island water channel, using machine learning to evaluate images captured by a low-cost remote monitoring system. For this purpose, images from over one year were collected. For better performance, captured images were processed by converting them to a proposed color space, named HLE, composed of hue, lightness, and edge. Multiple residual neural network architectures were examined. The best-performing model was ResNeXt, which achieved a mean absolute error of 1.14 cm using squeeze and excitation and data augmentation. An explainability analysis was carried out for transparency and a visual explanation. In addition, models were developed to predict water levels. Three models successfully forecasted the subsequent water levels for 10, 60, and 120 min, with mean absolute errors of 1.76 cm, 2.09 cm, and 2.34 cm, respectively. The models could follow slow and fast transitions, leading to a potential flooding risk-assessment mechanism.

Delta Blue(green)s: The Impact of Drought and Drought Management Actions on Microcystis in the Sacramento–San Joaquin Delta

Cyanobacterial phytoplankton blooms are more prevalent in the freshwater Sacramento-San Joaquin Delta (Delta) since the late 1990s, including blooms driven by overgrowths of potentially toxigenic organisms of the genus Microcystis. Data from 2014 to 2021 were used to show how flow dynamics, water temperature, and water clarity drive occurrence of Microcystis. We used a Microcystis bloom in the central Delta from 2021 as a case study for how novel monitoring tools can track blooms in real-time and be used post hoc to evaluate the effects of management actions. Microcystis was detected throughout the Delta in all but the highest-flow years, and bloom incidence and severity increased during drier years. In the South Delta, Franks Tract, lower San Joaquin River, and Old River regions, where blooms are most prevalent, higher water temperatures and clarities combined with lower exports from state and federal water projects were the best explanatory factors for the occurrence of Microcystis blooms. Nutrient concentrations were lower in summer than in winter, but only became limiting at high phytoplankton concentrations. We used satellite data and in situ continuous monitoring of flow, phytoplankton communities, and water quality to track hydro-biogeochemical conditions during the 2021 case study Microcystis bloom in the Central Delta. We did not find evidence that changes to Delta outflow regulatory standards contributed to this bloom, but changes in flow caused by a salinity barrier placed in west False River may have exacerbated the bloom. The frequency and severity of droughts are expected to increase in the future as a result of climate change, and our study demonstrates how continued monitoring of cyanotoxins, water quality, and phytoplankton communities could help improve management of cyanobacterial blooms in the Delta and other estuaries.

Fingerprint Finder: Identifying Genomic Fingerprint Sites in Cotton Cohorts for Genetic Analysis and Breeding Advancement.

Genomic data in Gossypium provide numerous data resources for the cotton genomics community. However, to fill the gap between genomic analysis and breeding field work, detecting the featured genomic items of a subset cohort is essential for geneticists. We developed FPFinder v1.0 software to identify a subset of the cohort's fingerprint genomic sites. The FPFinder was developed based on the term frequency-inverse document frequency algorithm. With the short-read sequencing of an elite cotton pedigree, we identified 453 pedigree fingerprint genomic sites and found that these pedigree-featured sites had a role in cotton development. In addition, we applied FPFinder to evaluate the geographical bias of fiber-length-related genomic sites from a modern cotton cohort consisting of 410 accessions. Enriching elite sites in cultivars from the Yangtze River region resulted in the longer fiber length of Yangze River-sourced accessions. Apart from characterizing functional sites, we also identified 12,536 region-specific genomic sites. Combining the transcriptome data of multiple tissues and samples under various abiotic stresses, we found that several region-specific sites contributed to environmental adaptation. In this research, FPFinder revealed the role of the cotton pedigree fingerprint and region-specific sites in cotton development and environmental adaptation, respectively. The FPFinder can be applied broadly in other crops and contribute to genetic breeding in the future.

Characterizing seasonal, environmental and human-induced factors influencing the dynamics of Rispana River's water quality: Implications for sustainable river management

This study will comprehensively evaluate the Rispana River's aquatic environment from February to June 2021, integrating physicochemical, biological, and hydrological data. Key objectives include identifying pollution sources, assessing climate change impacts, and evaluating health effects on humans and aquatic life. Analysis of 50 water samples reveals significant pH variations across five sampling sites influenced by natural and human factors. Fluctuating water temperatures (16.41 °C–20.81 °C) impact various parameters, including dissolved oxygen (DO), total dissolved solids (TDS), and biochemical oxygen demand (BOD). Microbiological assessment detects coliforms, indicating contamination with potential health risks. The study highlights the degradation of the Rispana River due to pollution and climate change. Urgent action is needed to mitigate impacts and safeguard human and aquatic health. Sustained monitoring and strategic management approaches are crucial for the river's sustainability. Collaborative efforts are necessary to address pollution sources and restore the river's health, emphasizing the importance of protecting this vital resource for current and future generations.

Climate change is poised to alter mountain stream ecosystem processes via organismal phenological shifts

Climate change is affecting the phenology of organisms and ecosystem processes across a wide range of environments. However, the links between organismal and ecosystem process change in complex communities remain uncertain. In snow-dominated watersheds, snowmelt in the spring and early summer, followed by a long low-flow period, characterizes the natural flow regime of streams and rivers. Here, we examined how earlier snowmelt will alter the phenology of mountain stream organisms and ecosystem processes via an outdoor mesocosm experiment in stream channels in the Eastern Sierra Nevada, California. The low-flow treatment, simulating a 3- to 6-wk earlier return to summer baseflow conditions projected under climate change scenarios in the region, increased water temperature and reduced biofilm production to respiration ratios by 32%. Additionally, most of the invertebrate species explaining community change (56% and 67% of the benthic and emergent taxa, respectively), changed in phenology as a consequence of the low-flow treatment. Further, emergent flux pulses of the dominant insect group (Chironomidae) almost doubled in magnitude, benefitting a generalist riparian predator. Changes in both invertebrate community structure (composition) and functioning (production) were mostly fine-scale, and response diversity at the community level stabilized seasonally aggregated responses. Our study illustrates how climate change in vulnerable mountain streams at the rain-to-snow transition is poised to alter the dynamics of stream food webs via fine-scale changes in phenology-leading to novel predator-prey "matches" or "mismatches" even when community structure and ecosystem processes appear stable at the annual scale.

Biogeomorphological response to river restoration of a suburban river with large wood: Creating a restoration vision and cost‐effectively monitoring the response trajectory using the citizen science MoRPh survey

AbstractBiogeomorphological responses to river restoration are rarely reported. Despite a transition in the emphasis and priorities of river management over the last 40 years from controlling river channel forms and processes to restoring and supporting natural processes, forms and functions, remarkably little information is available on project outcomes. Here, using the example of Beverley Brook within Wimbledon Common, Greater London, UK, we illustrate how standardised detailed monitoring information can be assembled at a very low cost using the citizen science MoRPh survey and we demonstrate the importance of having a pre‐project vision of likely outcomes that can be tracked by the monitoring programme. We show how a pre‐project and five post‐project surveys undertaken over 4 years according to a before‐after‐control‐impact (BACI) design provides scientifically robust data. Analysis of the survey data quantifies the nature, abundance and spatial distribution of restoration interventions, the immediate responses to those interventions, and the ensuing trajectory of biogeomorphological adjustments. Changes in the persistence, size, position, abundance and evolution of habitats reveal the degree to which the restoration achieved the pre‐project biogeomorphological vision and why the recovery trajectory progressed at the observed rate and to the observed end point over 4 years. Our approach has enormous potential for monitoring the outcomes of river interventions. Whilst our project was limited in its spatial scale and focus on physical habitats, we suggest how these limitations could be overcome whilst still containing costs.

Conservation planning for Gangetic dolphin (Platanista gangetica) in smaller rivers of the Ganga River Basin, India

The complex and dynamic networks of river system, vital for the maintenance of biodiversity and ecosystem services, are under pressure due to human-induced water stress disrupting ecological processes. Recognition of the importance of rivers as source of life though has led to efforts towards protecting large rivers, nevertheless the conservation and management of smaller rivers remained mostly neglected, creating significant gaps in ecological restoration initiatives. In the present study, we assess the distribution and population status of Gangetic dolphin (Platanista gangetica) in the small rivers in the Ganga River Basin for integrating it into the basin wide river conservation strategy. We observed that the Gangetic dolphin inhabited most tributaries and sub-tributaries of the Ganga River, with a naïve occupancy rate of Ψ̂ = 0.68 ± 0.04 (mean ± SE) having 606 ± 142.77 (mean ± SE) individuals and accounts for 15% of the total Gangetic dolphin population in the Basin. The results of N-mixture and MaxEnt models demonstrate that channel depth, presence of meanders and water discharge were key predictors of distribution in these rivers, and the proximity to confluences were identified as a critical predictor. About 54% (620 km) of 1150 km of the surveyed river stretches exhibited suitability for dolphins in the Basin, indicated by a probability distribution score of ≥0.50. Combining this data with the available information, we delineated a total of 2850 km stretch covering entire Ganga River System suitable for Gangetic dolphins within the Basin. Notably, the 620 km of suitable stretches identified in smaller rivers represent 22% of the overall suitable stretches across the entire basin. These stretches were translated to conservation priority stretches for systematic conservation planning involving various stakeholders for improved river conservation in the Basin.

Analyzing natural bed‐level dynamics to mitigate the morphological impact of river interventions

AbstractLocal river interventions, such as channel narrowing or side channels, are often necessary to maintain safety, ecology, or navigation. Such interventions have different effects on the river's bed morphology during periods of high‐ and low‐discharge events. Mapping the bed‐level variations for different discharge levels and understanding these effects can provide new opportunities for the design of interventions in multifunctional rivers. At any moment, the local bed level in a river is composed of bed‐level changes that occur at various spatial and temporal scales. These changes consist of bed aggradation/degradation trends on a large scale, on an intermediate scale bed‐level variations as a result of discharge fluctuations, and on small‐scale moving river bed forms like dunes. Using the river Waal in the Netherlands as a case study, we analyze the intermediate‐term bed‐level changes resulting from discharge fluctuations (dynamic component) and propose adaptations to the design of floodplain interventions such that possible negative impact on the local bed‐level changes is minimized. Time series of bed levels along two 10 km stretches of the case study are considered for a period of 16 years (2005–2020). Using a wavelet transform, we isolate bed‐level variations resulting from discharge events. These bed‐level variations are presented based on the magnitude of the discharge event and are compiled in an interactive atlas of river morphodynamics, allowing us to mitigate the impact of interventions. This will help river managers in the design of interventions and lead to improved management, operation, and maintenance of multifunctional rivers.

Morphology of the bronze objects from the Pinchuga-6 burial ground

The article is concerned with bronze objects of the end of the Early Iron Age from the fully excavated burial ground of Pinchuga-6 in the Lower Angara River region. The cemetery is dated to the 3rd–4th centuries BC. All burials were made following the rite of burial on the side. Three categories of copper alloy products have been distinguished: belt set parts, jewelry, and cult castings. The components of the belt sets include flat openwork buckles, hoops and bird-shaped overlays. Flat openwork buck-les have no analogues in the neighbouring territories. They appeared on the basis of the circle of post-Hunnic cultures of South-ern Siberia and were used in the Angara taiga until the mid-1st millennium AD. One belt hoop with volutes and an openwork patch is of a typical Tashtyk Culture appearance. At the end of the Early Iron Age, bird-headed belt plates were used across a vast territory that stretched from the Ural Mountains in the west to the banks of the Yenisei and Angara Rivers in the east. The jewelry includes tubular cast and spiral beads, stripes and pendants. The majority of items are multi-functional — they could be worn different ways. All of them were widespread in the first half of the 1st millennium AD, and they do not have a clear cultural and chronological reference. At Pinchuga-6, various objects of cult casting were found, including ornitho-, zoo- and ichthyomor-phic images, and disks with a circular ornament. These items have similarities among the Ishim and Kholmogory collections, materials from the Aidashinskaya cave, and Tomsk and Ust-Abinsk burial grounds. Pinchuga-6 is currently the farthest north-eastern site where such objects have been found. The grave goods of the cemetery contain items of different cultural attribution made of copper-based alloys. In this single complex in the Angara River region, objects from Western Siberia, Khakass-Minusinsk depression, and, possibly, of local origin have been found. XRF analysis of the items has been carried out. Lead-tin and tin bronze prevail, although being in approximately equal quantities, individual objects are made of copper, a small amount of arsenic is traced in two buckles, one ornithomorphic image is cast from an alloy with a significant amount of silver. The clo-sest in this feature, as well as in the amount of tin and lead in the alloys, are the products of the Tomsk burial ground.

Metallographic study of non-ferrous metal products from the Maray 1 site of the Baitovo Cul-ture in the Lower Ishim River region

The article examines non-ferrous metal products from the Baitovo Culture materials of the Early Iron Age hillfort of Marai 1. This settlement is located in the forest-steppe of the Ishim River region of Western Siberia. The upper building hori-zon marks the settlement of the Baitovo Culture dating to the 4th–2nd centuries BC. Metallographic analysis of 28 items was carried out using the Axio Observer D1m microscope (Zeiss). As a result, eight technological schemes characteristic for the metalworking activities of the Baitovo population have been identified. The study shows that prevailing were smithing tech-nologies in different temperature regimes for the production of non-ferrous metal objects (16 specimens, 57.2 %). The pref-erence was given to hot forging in the red-heat regime at 600–800°C (7 specimens, 25 %), cold forging with annealing (5 specimens, 17.8 %), as well as incomplete hot forging at 300–500°C (3 specimens, 10.7 %). Casting without further refine-ment was recorded in the microstructures of arrowheads, ingots and splashes (9 specimens, 14.2 %). Casting, followed by a slight degree of deformation (20–30 %), was noted in three cases. This scheme correlates with the metalworking traditions of the Itkul and Krasnoozerskaya Cultures, and it was dominant on the territory of the Tobol-Ishim region during the Early Iron Age. Such a low percentage of items related to it could be explained by the absence in Marai 1 of large items cast in moulds needing further refinement (knives, celts, etc.). A microstructural study confirmed the use of pure oxidized copper by the craftsmen of the Baitovo Culture, with characteristic inclusions of Cu–Cu2O eutectic, associated with the Ural production centres. Arrowheads and an ingot made of pure oxidized copper were probably a direct import from the territory of the Itkul Culture. Low-alloy tin and arsenic bronzes, coming from the metal production centres of Kazakhstan and Altai, were also used to the same extent for production of some tools and jewellery. The correlation between the type of product, composition of raw materials and technology of its manufacture has been revealed, which is most clearly manifested in arrowheads and awls. The use of high temperatures and significant degrees of compression (80–90 %) has been recorded in a number of cases, resulting in the appearance of rejects. Cracks of hot brittleness, as well as of cold brittleness, occurred in the process of technological cycle, carried out with an excess of the tensile strength of the metal.

Marriage and Memories of the Slave Trade Among the Ejaghams of Cameroon's Cross River Region

Using interview data collected from communities in Cameroon's Cross River region, this study examines the experiences of “slave descendants” in their marriages/attempted marriages with “freemen.” Using theories from Mary Douglas and Erving Goffman to analyse their stories, I demonstrate that while “slave descendants” are legally permitted to marry members of “freeman” origin, in practice, some cultural privileges are stripped from those who choose to intermarry, especially impacting those of “freeman” origins. Among “freeman” individuals, beliefs exist that marrying a “slave descendant” can limit their social and cultural potential. For example, they believe such marriages will contaminate the purity of their bloodline. Correspondingly, I discovered that many “slave descendants” aspire to unions with “freemen,” despite discrimination and rejection, to give their children a “half-pure” blood identity. They believe that giving their children this “half-pure” blood identity helps improve their future prospects.

Prediction of movable bed resistance in open channels with dune forms incorporating the effects of flow separation and water temperature

Flow separation behind the dune forms may have reduced the contact area between the flows and the bed surface, in addition to producing form drag in open channels. In this study, a novel predictor is developed based on the underlying mechanism of movable bed resistance across a dune-dominated bed. The mechanism is derived to a new formula based on the energy loss division approach to generalize the relationships among the grain drag, form drag and flow separation. The flow separation length is expressed to quantify the flow separation effect with a modified empirical method. Additionally, the water temperature effect is incorporated into the novel predictor due to the inclusion of fluid viscosity in both the roughness function and suspension number. A global database with a wide spectrum of measurements from the available literature was created to test the novel predictor. Approximately 83.3 % of flume data fall within a range of ± 30 % error, and ∼ 80.0 % of field data plot within this range. The optimized predictor has a better accuracy than the other four previously developed models in all five evaluation indicators. Furthermore, this predictor effectively reflects the impacts of water temperature on flow resistance to reproduce four variation modes. The diverse modes are jointly determined by suspension number and roughness Reynolds number. In actual river management, this predictor is used to interpret the effects of lower water temperature on sediment carrying capacity and flood routing. Seasonal variations in water temperature and the underlying effects of water temperature occur in rivers worldwide, which implies the need to pay more attention to this aspect in river management strategies.

Riparian habitat connectivity restoration in an anthropized landscape: A multi-species approach based on landscape graph and soil bioengineering structures.

In urbanized areas, rivers and riparian ecosystems are often the only ecological corridors available for wildlife movement. There, riverbanks are often stabilised by civil engineering structures (dykes, riprap). This can lead to habitat degradation and loss of landscape connectivity. Fascines (willow bundles tied together) could be an alternative to riprap, since they maintain the quality of the natural ecosystems by using native vegetal species instead of rocks, but their potential positive impact needs to be assessed. We proposed a landscape-scale decision-making method for river managers who want to restore banks by transforming riprap into fascines to improve landscape connectivity. We applied our methodology to a case study involving a 25 km-stretch of the Arve River, France. We selected four target vertebrate species based on biological traits to cover a wide range of dispersal capacities. For each species, we used landscape graphs to assess habitat connectivity under different contrasted riverbank scenarios. Scenarios included replacing all-natural banks with ripraps or replacing all ripraps with fascines. In addition, we systematically tested the effect of replacing individual 100 or 500 m sections of ripraps by fascines, to locate where riverbank restoration would maximize connectivity gain. The four species selected responded very differently to the scenarios (up to +14% and +46% change in Probability of Connectivity for common toads and Eurasian beavers, respectively, 0% for common sandpipers and barred grass snakes). The restoration of specific riverbank sections could result in important gains in PC (up to +33% for one single section for one species) but no section maximized connectivity gain for all the target species.

Human interventions alter morphodynamics of meandering channels: Insights from decadal to pre-industrial observations in the Yangtze River

Human activities, such as reservoir construction and bank revetment, significantly alter downstream flow and sediment regimes and river channel changes, impacting river ecosystem services. However, our understanding of how intense human activities affect morphodynamics of meandering channels in big river systems remains incomplete due to the lack of high-resolution in-situ data. Here, we use comprehensive data encompassing hydrology and sediment, historical channel maps, and high-resolution river bathymetry to investigate the evolution of meandering bends in the Middle Yangtze River (MYR) across three distinct phases: the natural period (1490–1975), the bank revetment period (1975–2002), and the post-dam period (2003–2018). The study revealed that, in the absence of human intervention, the meandering channels of the MYR naturally experienced inner bank deposition and outer bank erosion, largely governed by curvature-induced secondary flow patterns in flow and sediment transport mode. In 1975–2002, outer-bank revetments reduced erodibility, stabilizing outer banks, while inner banks continued to experience lateral and vertical deposition, causing a narrower and deeper channel hydraulic geometry. Conversely, meandering bends had exhibited an unusual pattern of ‘outer bank deposition and inner bank erosion’ in 2003–2018. Channel morphological changes characterized by channel incision and widening were driven by changes from erodible bank boundaries to solidified bank boundaries, substantial reduction in suspended sediment concentration, and an altered and extended effective flow range (10,000–25,000 m3/s). Our findings highlight that human interventions such as damming and bank revetments can alter the conventional erosion–deposition morphodynamics of meandering bends in large river systems, carrying vital implications for sustainable river management in the Anthropocene.

Evaluation of the high-energy flood of mid-July 2021 as a morphologic driver in the anthropogenically developed Ahr Valley, Germany, in interaction with infrastructures

BackgroundThis study explores morphologic changes in the Ahr River, Germany, caused by the high-energy flood in mid-July 2021. This study aims to assess the flood's significance as a morphological driver using the Lateral Mobility Index (LMI), as well as the impact of infrastructure on morphodynamics in terms of the formation of mud deposits and stagnant water pools, considering three focus areas of about 1 to 5 km river length. The three focus areas cover differences in the valley morphology as well as near natural and anthropogenically affected sections.ResultsThe LMI is derived from orthophotos from 1998 to 2022, and based on the surface area of the old and the new channel. It describes the sum of new and abandoned channel area in relation to the previous channel area. For the 2021 high-energy event, an increased LMI suggests an increasing change in river course and morphology. Post-flood, the LMI in focus areas 1 (furthest upstream, LMI of 1.5) and 3 (at the Rhine confluence, LMI of 3.2) surpasses the historic LMI by a factor of about 3. Focus area 3 exhibits the highest activity, while focus area 2 (LMI between 0.25 and 0.70) the lowest. The area of mud deposits and stagnant water pools increased immediately after the flood, especially in focus area 3. Over the following months, initial post-flood mud deposits not only washed away but also rebuilt to some degree later on.ConclusionsThe LMI enabled to quantitatively identify a rare and significant morphological disruption in the Ahr River’s lateral development in three focus areas, and thus, serves as additional proof that the flood of mid-July 2021 was a high-energy event impacting the local river geomorphology. Infrastructure impacted the formation of mud deposits and stagnant water zones during and after the flood, with additional influence from factors such as driftwood and valley width. The data suggested a phase of resuspension of sediments after the flood, likely due to cleanup and ad hoc river management, highlighting the need for continued river monitoring.

Holocene Thermal Maximum paleofloods improve flood frequency analyses in the lower Tennessee River Basin (USA)

Extreme floods are underrepresented in instrumented flow records. Consequently, flood frequency model estimates of extreme floods contain large uncertainty. The lower Tennessee River (LTR) Basin is located within the southeastern United States and is a large, regulated, and socio-economically significant North American river. The flood-of-record for the LTR occurred in 1867 CE. The 1867 flood-of-record is a design flow for the dams built and managed by the Tennessee Valley Authority. Here we develop and apply an extreme paleoflood chronology and use it to improve flood frequency model estimates of large, rare floods. We created an extreme paleoflood chronology that contained paleodischarge estimates for six extreme paleofloods, dating back to 5900 years before present, for a ∼2 km segment of the LTR. We obtained paleoflood hydrologic data from two sources. These included field sampling and analysis of slackwater deposits found in a rock shelter located on a limestone bluff and published extreme paleoflood data from a terrace located within the study segment.Placed within the context of the extreme paleoflood chronology, the 1867 flood-of-record was the largest flood to occur within the last 2000 years and coincided with the conclusion of the cooler, wetter Little Ice Age. The three highest magnitude extreme floods, however, occurred during a peak in Holocene temperatures 6000 to 5000 years ago, during the mid-Holocene Thermal Maximum. Paleodischarge estimates for the three mid-Holocene extreme floods were three times larger than the estimated discharge of the 1867 CE flood-of-record. Different iterations of a Bayesian flood frequency model showed removing the three most extreme, mid-Holocene paleofloods resulted in a rarer annual exceedance probability for the 1867 CE flood-of-record, changing it from an 0.002 AEP (500-year event) to an 0.0007 AEP (1300-year event) and underestimation of annual exceedance probabilities for design flows commonly used in river management and infrastructure design, including the 100-yr, 500-yr, 1000-yr, and 10,000-yr floods. These results suggest that flood frequency models may underestimate design flows if historic-floods-of-record are assumed to be the most extreme floods within these analyses. This finding has implications for regulated rivers worldwide, which now includes most large rivers. The previously unknown, extreme mid-Holocene paleofloods, which were found to be larger than all known modern or paleofloods, significantly altered the estimates of the final flood frequency model. This finding makes a compelling case for seeking out more extreme flood paleodischarge estimates from the mid-Holocene in rivers of the Northern Hemisphere, where the mid-Holocene Thermal Maximum's occurrence is well substantiated. Flood data from the mid-Holocene Thermal Maximum may help improve flood frequency model-based estimates of extreme floods by minimizing risk associated with flood “unknown unknowns.”

Design of Non-Structural Practices for Sustainable Water Quality Improvement in an Urban River: A Case Study of South Korea

Urban rivers exhibit characteristics of low flow and significant water quality fluctuations, making them susceptible to pollution from various sources such as untreated sewage, non-point pollution within the urban area, and unknown inflows. To address water quality management in urban rivers, precise investigations into background water quality, pollution levels, and the characteristics of pollution sources are essential. Following the identification of pollution sources, sustainable river management strategies, incorporating both structural and non-structural measures, are crucial. This study aims to develop continuous and long-term river management strategies, considering the characteristics of urban river basins, through citizen participation governance and non-structural approaches. Citizen networks were formed for each target urban river, and activities for water quality improvement were proposed and implemented. This study provides phased approaches to citizen participation governance, and activities include citizen-led water quality monitoring, the purification and monitoring of riverbank pollution sources, and water-related education. It emphasizes the importance of local residents’ interest in urban river water quality improvement and underscores the need for sustained activities through local citizen networks. Additionally, active participation and investments from the local government, government agencies, and various experts are deemed essential.

Erosion mechanism of point bar retreat under the protection of a flexible mattress

Channel retreat can be responsible for the significant loss of banks, farmland, and wetlands, leading to drastic changes in fluvial sediment and local river regimes. Although current studies focus on the erosion process of natural river channels, the mechanism by which revetments, such as the flexible mattress, influence bank evolution is still unclear. Hence, by conducting a generalized model experiment, this study investigates the point bar failure process under the mattress protection, i.e., the episodic event when the soil reaches the static equilibrium state. Specifically, a scour hole develops at the junction between the soft and hard materials, causing mattress suspension on the bank toe’s side wall and resulting in a reduction coefficient for transverse scouring rate ranging from 0.08 to 0.15. Based on the theories of soil mechanics and river dynamics, the critical conditions for point bar instability were deduced, and a mechanical model describing its erosion process under the mattress protection was established. Furthermore, our model calculated the bank morphology and total erosion volume at different periods in the flume experiment, demonstrating a good agreement with the measured data. Additionally, variations in stability coefficient and forces exerted on soil (including shear strength, gravity, and fluid pressure) of the typical sections during point bar retreat were analyzed. Sensitivity analysis of the bank toe stability emphasized the controlling effect of soil mechanical properties and the negative feedback of mattress weight. The results reveal the interaction mechanism between the mattress protection and point bar failure, theoretically guiding the bank erosion strengthening and river management planning.