River Channel Research Articles

A national-scale high-resolution runoff risk and channel network mapping workflow for diffuse pollution management

Managing diffuse pollution from agricultural land requires a spatially explicit risk assessment that can be applied over large areas. Major components of such assessments are the precise definition of both channel networks that often originate as small channels and streams, and Hydrologically Sensitive Areas (HSAs) of storm runoff that occur on land surfaces. Challenges relate to regions of complex topography and land use patterns, particularly those which have been heavily modified by arterial drainage. In this study, a national scale, transferrable workflow and analysis were developed using a specifically commissioned LiDAR survey. Research on the first half of Northern Ireland (6927 km2) is reported where field-edge drain to major river channels were mapped from 1 m (16 points per metre) digital terrain models, and in-field HSAs were defined across over 400,000 fields with a median field size of 0.86 ha. Manual drainage mapping supplemented with a novel automated drainage channel correction process resulted in an unparalleled high-resolution national drainage network with 37,320 km of channels, increasing mapped channel density from 0.9 km km−2 to 5.5 km km−2. The HSAs were based on a Soil Topographic Index (STI) system using hillslope and contributing area models combined with soil hydraulic characteristics. In all, 249 km2 of runoff risk HSAs were identified by extracting the top 95th percentile of the modelled STI as the areas with the highest propensity to generate in-field runoff. At field and individual farm scale these targeted risk maps of diffuse pollution were delivered to over 13,000 farmers and form part of the nationwide Soil Nutrient Health Scheme programme.

Evolution of riparian vegetation in response to anthropogenic effects: The Taleqan River, Iran

AbstractDuring the last decades, human interventions, such as dam construction and land‐use change, have caused changes in geomorphic patterns and riparian zones in many rivers in Iran. This study aimed to assess the spatio‐temporal evolution of riparian vegetation and the spatial area of biogeomorphic feedback windows (BFWs) located in the riparian Salicaceae vegetation patches and their traits responding to human interventions in the Taleqan River during 1990–2022. The river was divided into five reaches using the geomorphic unit system (GUS) method, and the river sensitivity index (SI), location of BFWs, vegetation typology and main cover typology were investigated in the reaches using aerial photographs and satellite images from 1990 to 2022. For this purpose, the main cover typology was classified into grassland, woody vegetation, bank‐attached bars, islands, vegetated islands, river channels and urban areas. The stem diameter and density, degradation level and longitudinal/latitudinal alluvial bars in each of the BFWs were investigated using the field survey. Based on the findings, the lowest values of the SI (braiding index [BI], channel activity [CA] and channel width [CW]) and the highest expansion of BFWs were observed in the upstream reaches of the Taleqan River. Human disturbances in these reaches were less than in the reaches downstream, allowing the expansion of vegetation habitats. The vegetation patches were unstable and scattered in the midstream and downstream, and the width decrease of the river channel was created by land‐use change and channelization. A significant direct relationship was observed between BFW establishment, stem diameter and density, and vegetation height. The BFWs create an opportunity for engineer vegetation to prevent erosion and expand new habitats by creating biogeomorphic accumulation landforms and trapping alluvial bars on the lee side of engineer woody vegetation. This study highlights the interactions between riparian areas and hydrogeomorphic processes within riparian corridors exposed to human disturbances to help better define a comprehensive plan for river management.

Influences of channel bed morphology on flow structures in continuous curved channels

Introduction: The formation of bars and pools, characterized by concave and convex bed morphology, is a typical feature of curved rivers. The channel bed morphology has a significant influence on the flow structures in curved channels.Methods: Based on data from physical model experiments, this study employs the RNG k-ε model and the VOF (Volume of Fluid) method to perform three-dimensional numerical simulations of flow in continuous curved channels.Results: By comparing the variations in flow structures between channels with a flat bed and channels with bars and pools, the results show that the presence of bars and pools leads to an increase in longitudinal flow velocity on the convex bank side near the entrance of the upstream bend, while in the downstream bend it is opposite. The high-velocity region shifts slower towards the concave bank along the bend. The presence of point bars weakens the circulation near the convex bank in the upstream bend, resulting in a smaller circulation intensity. The decrease in circulation intensity is the largest (−23.91%) at the apex of the bend. In the downstream bend, the remaining circulation from the upstream bend attenuates slower in the pool and has a greater impact distance, increasing the circulation intensity in the downstream bend. The section near the bend entrance shows the largest increase in circulation intensity, with a rate of 128.18%. The unevenness of the bed topography increases the unevenness of the bed shear stress in the downstream bend.Discussion: The findings of this study contribute to a deeper understanding of the complex flow structures and evolution trends in natural curved rivers, providing scientific basis for the management of curved river channels.

First attempt to measure macroplastic fragmentation in rivers

Direct field measurements of macroplastic fragmentation during its transport in rivers are currently unavailable, and there is no established method to perform them. Previous studies have showed that macroplastic fragmentation results in the production of harmful microplastics, and river channels can be hotspots for this process. Therefore, obtaining information about this process is crucial for quantifying the production of secondary microplastics in rivers and assessing the related risks for riverine biota and human health. Here, we propose a simple low-cost methodology for quantifying riverine macroplastic fragmentation by conducting repeated measurements of the mass of tagged macroplastic items before and after their transport in the river. As a proof-of-concept for this method, we conducted a 52–65 day experiment that allowed us to measure a median fragmentation rate of 0.044 ± 0.012 g for 1-liter PET bottles during their transport at low to medium flow in the middle mountain Skawa River in the Polish Carpathians. Using the obtained data (n = 42), we extrapolated that during low to medium flows, the median yearly mass loss of PET bottles in the study section is 0.26 ± 0.012 g/year (0.78 ± 0.036 % of bottle mass), and the median rate of bottle surface degradation is 3.13 ± 0.14 μm/year. These estimates suggest a relatively high fragmentation rate for a PET bottle in a mountain river even under low to medium flow conditions without high-energy transport. We discuss how our simple and relatively low-cost methodology can be flexibly adapted and future optimized to quantify macroplastic fragmentation in various types of rivers and their compartments, informing future mitigation efforts about the rates of formation and dispersion of secondary microplastics.

Structural control on the landscape evolution and avulsive behavior of rivers at mountain exits: The example of the Kosi River in eastern Nepal Himalaya

The Kosi River flows from the eastern Nepal Himalaya into the state of Bihar (India) and has experienced frequent avulsions, causing extensive flood-related damage. Because of this avulsive behavior, the Kosi is called the “Sorrow of Bihar.” The avulsion of 2008 was the most catastrophic avulsion event recorded for the Kosi and has been attributed primarily to hydrological and sedimentological processes that formed a super-elevated river channel and caused avulsion. Detailed topographic analysis of the region near the Kosi exit from the Himalaya, using mean-corrected and resampled 1-arc, Shuttle Radar Topography Mission (SRTM) and Real Time Kinematic Global Positioning System (RTK-GPS) datasets, reveals that the Kosi channel is super-elevated only relative to its eastern floodplain. The western floodplain elevation is similar to or higher than the Kosi channel in the region between the Kosi River exit from the main eastern Nepal Himalaya and the Kosi barrage at the Indo-Nepal border. Structurally, the Kosi exits the Himalaya in the transition zone between the closed Trijuga dun to the west and the Dharan salient to the east. The Trijuga dun is closed by the Main Frontal thrust (MFT)-related frontal topography or the Outer Churia Hills. The eastern slopes of these hills induce west-to-east topographic slope in the channel, such that topographic avulsion indices are highest only in the Outer Churia Hills affected parts of the Kosi Channel and the 2008 avulsion region. Therefore, our preferred model for the primary control on the channel's asymmetric, metastable, super-elevation is the influence of the tectonically controlled MFT-related Outer Churia Hills on the Kosi River channel. Geomorphological processes have operated in the Kosi channel in this backdrop. This study emphasizes that detailed structural and topographic analysis of river exits from mountain belts like the Himalaya can provide better insights into river channel metastability and avulsion worldwide.

Mercury stocks in discontinuous permafrost and their mobilization by river migration in the Yukon River Basin

Abstract Rapid warming in the Arctic threatens to destabilize mercury (Hg) deposits contained within soils in permafrost regions. Yet current estimates of the amount of Hg in permafrost vary by ~4 times. Moreover, how Hg will be released to the environment as permafrost thaws remains poorly known, despite threats to water quality, human health, and the environment. Here we present new measurements of total mercury (THg) contents in discontinuous permafrost in the Yukon River Basin in Alaska. We collected riverbank and floodplain sediments from exposed banks and bars near the villages of Huslia and Beaver. Median THg contents were 49+13/-21 ng THg g sediment−1 and 39 +16 /-18 ng THg g sediment−1 for Huslia and Beaver, respectively (uncertainties as 15th and 85th percentiles). Corresponding THg:organic carbon ratios were 5.4+2 /-2.4 Gg THg Pg C-1 and 4.2+2.4 /-2.9 Gg THg Pg C-1. To constrain floodplain THg stocks, we combined measured THg contents with floodplain stratigraphy. Trends of THg increasing with smaller sediment size and calculated stocks in the upper 1 m and 3 m are similar to those suggested for this region by prior pan-Arctic studies. We combined THg stocks and river migration rates derived from remote sensing to estimate particulate THg erosional and depositional fluxes as river channels migrate across the floodplain. Results show similar fluxes within uncertainty into the river from erosion at both sites (95 +12 /-47 kg THg yr-1 and 26 +154/-13 kg THg yr-1 at Huslia and Beaver, respectively), but very different fluxes out of the river via deposition in aggrading bars (60 +40/-29 kg THg yr-1 and 10+5.3/-1.7 kg THg yr-1). Thus, a significant amount of THg is liberated from permafrost during bank erosion, while a variable but generally lesser portion is subsequently redeposited by migrating rivers.

FORMATION AND EVOLUTION OF SANDBARS IN THE PADMA RIVER, BANGLADESH

Sandbars are natural formations in river channels, typically composed of sand and other sedimentary particles, created by river flow and erosion-deposition The shapes, sizes, and types of these sandbars exhibit diversity depending on factors such as river flow, sediment composition, hydrological conditions, and erosion-deposition processes. These sandbars are an integral part of the river ecosystem and influence the water flow patterns, navigation routes, aquatic habitats and even provide shelter to humans and habitats. In the context of Bangladesh, there is a considerable size of population that dwell in these sandbars. The process of sandbar formation and recession is quite dynamic, and its complexity is further accentuated within the confluence zones. The Ganges, the Brahmaputra, and the Meghna River systems together form the largest delta (GBM Delta) in the world which is characterized by numerous interlaced rivers, canals, and streams. These river systems contain numerous sandbars which contribute to its complex river morphology. These sandbars are home to many people, animals, and wildlife. However, the dynamic nature of sandbars, high monsoon discharge, flooding and erratic erosion-deposition patterns make the sandbar formation and recession process quite unpredictable and puts the lives of people living on it in danger. This paper aims to study the morphological changes in sandbars, the erosion-deposition patterns within these river systems causing the sandbar formations, compare the sandbar formations in the two confluence zones of the Padma River, determine the changes in water-sandbar surface area ratio, visualize the evolution of sandbars, and quantify the movements of sandbars. The study revealed that over the past two decades (1990-2010), the main channel of the river was dominated by sandbar area. In contrast, in the past 7 years (2016-2022), the average surface area of water within the main channel of the Padma River was approximately 73,387 ha while the sandbars covered an area of around 51,274 ha, highlighting the recent dominance of water in the main channel. Conversely, in a similar time frame (2016-2022), at the two confluence zones of the Padma River, the average surface area of sandbar was greater than that of water within a 30km radial distance from each confluence node. At the upstream confluence (Padma-Jamuna-Ganges), the average surface area of sandbars was approximately 40150 ha while water covered an area of around 28531 ha. Similarly, at the downstream confluence (Padma-Meghna), sandbars covered an area of 43696 ha on an average while water covered an area of around 40889 ha. This showed that sandbars have been rapidly accumulating at the two confluence zones. It is also observed that the sandbars are very dynamic as both lateral and longitudinal migrations are observed. It is however evident that the littoral sandbars are more stable compared to the medial sandbars and therefore more suitable for habitation. From visual inspection it is evident that the bankline of the medial sandbar (Amirabad) shifts more rapidly compared to the littoral sandbar (Harirampur within the period from 2016 to 2022. Additionally, the coefficient of variation of area for the littoral sandbar and the medial sandbar are approximately 2.11% and 5.37% respectively. This indicates that the area of the littoral sandbar is more stable over the years compared to the medial sandbar as it has a lower coefficient of variation and therefore is less active. Over the years, the confluence nodes on either side of the Padma River have constantly shifted due to rapid sandbar accumulation. Between 1990 and 2022, the maximum shifting of the upstream and downstream confluences reached approximately 7500 meters and 18000 meters respectively, both in the southeast direction.

Ctenopharyngodon idella’s Movement Behavior in Response to Hydraulics at Fishway Entrance with Different Entrance Angles

The hydrodynamics at the fishway entrance play an important role in attracting fish into a fishway. Adjusting the entrance angle of the fishway to allow suitable water flow patterns at the entrance is an effective measure that can be used to improve the attraction efficiency. In this study, we analyzed the movement behavior of grass carp (Ctenopharyngodon idella) in a river channel at a fishway entrance with different fishway entrance angles (30°, 45°, and 60°) and different replenishment velocities (0.1 m/s, 0.2 m/s, and 0.3 m/s). The flow velocity was 0.32–0.50 m/s when the fish head deflected into the entrance under different entrance angles for grass carp. As the entrance angle of the fishway increased, the fish energy consumption increased. The range of energy consumption for grass carp increased from 1.26–3.59 × 10−3 J to 3.32–7.33 × 10−3 J when the entrance angle was increased from 30° to 60°. There was a negative correlation between the entrance angle of the fishway and the deflection angle of the tested fish’s head. This research presents a reference that combines fish swimming behavior and hydraulics to optimize the design of fishway entrances.

Influence of a Meandering Channel on the Threshold of Sediment

River meanders and channel curvatures play a significant role in sediment motion, making it crucial to predict incipient sediment motion for effective river restoration projects. This study utilized an artificial intelligence method, multiple linear regression (MLR), to investigate the impact of channel curvature on sediment incipient motion at a 180-degree bend. We analyzed 42 velocity profiles for flow depths of 13, 15, and 17 cm in a laboratory flume. The results indicate that the velocity distribution was influenced by the sediment movement threshold conditions due to channel curvature, creating a distinct convex shape based on the bend’s position and flow characteristics. Reynolds stress distribution was concave in the upstream bend and convex in the downstream bend, underscoring the bend’s impact on incipient motion. Bed Reynolds stress was highest in the first half of the bend (0 to 90 degrees) and lowest in the second half (90 to 180 degrees). The critical Shields parameter at the bend was approximately 8–61% lower than the values suggested by the Shields diagram, decreasing from 0.042 at the beginning to 0.016 at the end of the bend. Furthermore, our findings suggest that the MLR method does not significantly enhance the understanding of sediment movement, highlighting the need for a more comprehensive physical rationale and an expanded dataset for studying sediment dynamics in curved channels.

On the transferability of residence time distributions in two 10-km long river sections with similar hydromorphic units

Quantifying hydrologic exchange fluxes (HEFs) at the stream-groundwater interface and their residence time distributions (RTDs) in the subsurface are important for managing the water quality and ecosystem health in dynamic river corridors. However, field measurements and directly simulating high-spatial resolution HEFs and RTDs can be time-consuming, particularly at watershed-scale. Recent research has proposed the potential application of using hydromorphic units (HUs), which cluster the bathymetry and surface water hydrodynamics attributes, to aid in RTD estimation. However, more pioneering studies have demonstrated that underground structure and large-scale river channel geomorphology are the primary factors controlling the HEFs and RTDs. To address this contradiction, this work evaluates the HEFs and resulting HU-RTD relationships for two 10-km long river sections along the Columbia River, leveraging a one-way coupled three-dimensional transient surface–subsurface water transport modeling framework. Applying such a framework at the two river sections with similar HUs allows for quantitative comparisons of HEFs and RTDs using both statistical tests and machine learning classification models. The comparison reveals that the similarity and transferability of the HU-RTD relationship is very low for the two investigated river sections. This suggests that, creating a general algorithm to estimate RTDs in large-scale river reaches based solely on surface water hydrodynamics and short-distance bathymetry topography data may be nearly impossible.

Dynamic Spatiotemporal Evolution and Driving Mechanisms of Vegetation in the Lower Reaches of the Tarim River, China

Analyzing the changes in vegetation under different factors is crucial for ecological protection in arid areas. The spatial-temporal variations of vegetation in the lower reaches of the Tarim River (LRTR) from 2000 to 2020, were analyzed using the Theil-Sen estimator and the Mann-Kendall test. The future trends of NDVI are projected to use the Hurst exponent method. The driving mechanisms of vegetation changes were analyzed using the GeoDetector method and multivariate residual analysis. The NDVI values in the LRTR significantly increased during the study period, indicating good vegetation recovery. The overall vegetation level remains poor and was primarily concentrated around the riverine areas. There is still a risk of vegetation degradation in most areas of the future LRTR. Compared to climate change, vegetation was more affected by human activities. Human activities have helped restore the riparian vegetation and prevented the degradation of vegetation far from the river. Therefore, distance from river channels is the strongest explanatory factor (q = 0.078) for vegetation changes, followed by precipitation, and temperature, while changes in slope have minimal impact on vegetation. Statistics have found that when two factors are combined, their impact on vegetation change is stronger. These findings are beneficial for identifying vegetation evolution patterns in LRTR and providing theoretical support for the government to carry out ecological restoration.

FORMATION OF THE ARCHITECTURAL AND URBAN PLANNING SPACE OF OXBOW LAKES: SCIENTIFIC AND PRACTICAL EXPERIENCE

Problem statement. Following the adoption of Law No. 1641-VIII on October 4, 2016, the Ukrainian legislation introduced the “basin management principle”. This principle entails comprehensive (integrated) management of water resources within the river basin area [1]. In the valleys of lowland rivers with numerous bends, particularly in the Dnipro, Danube, and Vistula rivers, oxbow lakes are formed, representing remnants of old river channels. Oxbow lakes are small lakes that form on floodplains due to erosion and sediment deposition. In large cities, such lakes are important centers of biological diversity, improve microclimate, act as barriers to floods, and have an attractive appearance. However, oxbow lakes are susceptible to drying up, silting, and turning into marshes. Therefore, research on oxbow lakes in the context of urban planning is highly necessary to prevent chaotic development and preserve similar ecosystems. Additionally, the consolidation of experience in the development and rehabilitation of such objects is practically significant for urban planning. Research objective. The purpose is to examine and summarize the scientific and practical experience in forming the architectural and urban planning space along oxbow lakes. Conclusion. Scientific research in the fields of hydraulic engineering, agronomy, and urban planning that can be implemented in urban planning practice to address oxbow lake issues has been identified and systematized. Using satellite imagery and analytical maps, patterns in the organization of oxbow lake spaces in the largest cities of Ukraine have been identified. Similarly, examples of planning and development of lakeside (old riverbed) territories in Europe, America, Asia, and Oceania have been found and analyzed. Successful practical solutions for the use of scientific and technical methods for preserving oxbow lakes have been identified in the aforementioned examples. Patterns and trends in organizing development and street networks around small floodplain lakes and oxbow lakes have been revealed.

A bacteria-based index of biotic integrity assesses aquatic ecosystems effectively in rewetted long-term dry river channel after water replenishment.

Climate-induced droughts exert a significant influence on the connectivity of river systems. It is estimated that about 25% of the world's rivers ran dry before reaching the ocean due to climate change and human activities. Ecological water replenishment is an effective measure for restoring aquatic ecosystems damaged by drought. It is urgently needed to quantitatively assess the aquatic ecosystems in rewetted dry river channels after water replenishment. This study investigated the variations in phytoplankton, zooplankton, benthic macroinvertebrates, and benthic bacterial communities in the rewetted dry river channel of Yongding River after water replenishment. In comparison with the water column communities, the benthic macroinvertebrates were identified as limiting factors for ecological restoration in rewetted dry river channels. In the absence of a certain recovery time for benthic macroinvertebrates, the benthic bacterial-based index of biological integrity, especially calculated based on their intrinsic properties, can properly assess aquatic ecosystems in rewetted dry river channels.

Assessing controls on sedimentation rates and sediment organic carbon accretion in beaver ponds

Beaver dams trap sediment, promote channel-floodplain connectivity, modify biogeochemical cycling and organic carbon (OC) storage, and influence geomorphic form. Beaver-related sediment accumulation has been investigated at longer timescales (e.g., > 1000 years) and shorter timescales (< 10 years), but we lack information on sedimentation and sediment-associated OC accretion rates over multiple decades in relatively persistent beaver ponds (10–100 years old). We coupled field surveys of 45 beaver ponds with historical aerial imagery and radiometric dating with 7Be, 210Pb, and 14C to calculate sedimentation rates, mean sediment depth, and sediment OC content at two study sites in the southern Rocky Mountains, USA. Sedimentation rates in beaver ponds (median = 5.7 cm yr−1, mean = 11.6 cm yr−1) decreased with pond age. Incised, single threaded reaches had greater variability in mean sediment depth compared to less incised reaches. In less incised reaches, mean sediment depth and beaver dam height increased with pond age, indicating more stable dams and depositional environments. Sediment OC content within beaver ponds (median = 0.8 %, mean = 1.7 %) increased with finer sediment grain size distributions. Sediment OC accretion rates in ponds ranged between 0.13 and 23 Mg C ha −1 per year. We used Monte Carlo simulations to estimate it would take ∼100 years or more of uninhibited beaver activity for deposition to laterally reconnect adjacent terraces in the incised study reaches, a common objective within many stream restoration projects. Our findings show that beaver ponds in complex, multi-threaded reaches better retain fine sediment over longer timescales, highlighting the need to incorporate geomorphic context when considering whether beaver can help restore incised river channels and floodplain connectivity, retain fine sediment, and store OC on the landscape.

Prediction of Dynamics of Riverbank Erosion: A Tale of the Riverine Town Chandpur Sadar

River channel migration often occurs inside the floodplain areas of the river. The structural changes occurring in rivers within floodplain zones serve as a significant ecological signal of their tremendous impact on both ecological and human survival. The aim of the research is to assess the spatial and temporal fluctuations of the Meghna River's bankline from 1990 to 2020 (for 30 years), and to predict the future bankline position. The Landsat imageries from USGS were used for this study. The bankline was extracted from satellite imageries (Landsat) using Modified Normalized Difference Water Index (MNDWI) indices. The variations in bankline dynamics were assessed through the application of Net Shoreline Movement (NSM) and End Point Rate (EPR) analyses using the Digital Shoreline Analysis System (DSAS). Predictive modeling was conducted utilizing the Modified EPR Model, with validation performed via the Root Mean Square Error (RMSE) technique. Adjustment of errors was achieved by employing error coefficients tailored to each individual transect. Over the past three decades, the cumulative river erosion in Chandpur Sadar amounted to 18.03 square kilometers, with the highest Net Shoreline Movement (NSM) recorded at −1979.62 m during the study period. The forecasted maximum Net Shoreline Movement (NSM) is anticipated to be −495.79 m, signifying that the transect is associated with erosion, resulting in landward movement. Conversely, the minimum NSM is projected to be −1.01 m. The most significant movement is expected to occur in Puran Bazar, while the least movement is foreseen in Bakharpur. On average, the NSM across all transects is predicted to be −76.25 m. This study presents a cost-effective approach for evaluating the changes in river erosion over time. This technique may be valuable for policymakers in developing effective plans to reduce the negative impacts of erosion-related risks.

Numerical simulation of hydraulic characteristics and pollutant transport in the channels with different ice coverages

ABSTRACT In winter, rivers at high latitudes often freeze and an ice cover emerges at the free surface of the river. According to the coverage degree of the ice cover, rivers can be divided into free-flowing, partially frozen, and completely frozen. The presence of ice cover can greatly alter the hydraulic conditions of rivers, complicating the transport of pollutants in river channels. The distribution of pollutants in rivers with different ice coverages was simulated using the Detached Eddy Simulation (DES) model in this paper. The velocity distribution, the pollutant diffusion coefficient distribution, the turbulent kinetic energy distribution, and the vortex distribution with different ice coverages were analyzed. The velocity in the ice cover zone is at a lower rate than in the open flow zone. With the increase of the ice coverage, the turbulent kinetic energy of the ice cover area in partially frozen conditions gradually increases, which makes the water flow turbulence increase. The diffusion coefficient of pollutants in the ice cover area is greater than that in the open flow area, so pollutants disperse more quickly in the ice cover area. The turbulence energy and the diffusion coefficient have similar distribution characteristics beneath the ice cover. The presence of the ice cover promotes the movement of the vortex from the open flow area to the ice cover area, which may be the reason for the larger turbulence energy and the diffusion coefficient. The simulation results can provide a reference for ice disasters and water quality remediation.

An assessment of maintenance works and their impact on macroinvertebrate communities and long-term recolonization to small lowland watercourses

Due to their small size and high anthropogenic pressure, small watercourses are particularly prone to severe siltation and are densely overgrown with macrophytes. Many of these watercourses are subject to regular maintenance works (RMW), consisting of seasonal desilting and vegetation clearance, in order to ensure unobstructed water flow. The aim of the study was to assess the impact of three types of maintenance works: dredging and mud removal (DMR), river channel vegetation removal (RCVR) and river bank vegetation removal (RBVR) on taxa species richness, macroinvertebrate density and the Shannon-Wiener diversity index, as well as their changes and long-term benthic recolonization one and two years after completion of the works. The study was carried out in 21 habitats on eight rivers in the European Central Plains Ecoregion. A total of 107 zoobenthic taxa were found at all sites, and their species composition was characteristic of highly hydrophytic waters with low hydrological and hydrochemical quality parameters. A significant decrease in macroinvertebrate taxa richness was observed one year after the works, as the average number of taxa had dropped from thirteen to eight, with a further fall to seven taxa two years after the RMW. The same was true for density, which had decreased from an average of 2496 to 786 individuals per square meter one year after the RMW, while, a gradual recolonization was recorded two years after the RMW, with an average density of 1295 individuals per square meter. The Shannon-Wiener index, which had averaged 2.528 before the RMW, also decreased, falling to 1.982 and 1.832 one and two years after. BACI statistical analyses showed that of the three types of maintenance work, desilting and bottom sediment removal had the largest negative impact, significantly reducing taxonomic composition (by an average of 53%), density (by an average of 43%), and ecological index values (by an average of 40%). Over-frequent maintenance can prevent macroinvertebrate populations from recovering, thus depleting the environment of valuable taxa, including those that provide food for fish and other vertebrates.

Lithostructural Control in the Development of Potholes in the Rock Bed of the Carnaúba River, Seridó Geopark, NE Brazil

Granitic forms resulting from turbulent flow, with hydraulic vortices, characterize the rocky bed of the lower course of the Carnaúba River, in a geosite of the Seridó Geopark, in the Seridó Oriental microregion, Northeast Brazil. These forms constitute a variety of types of potholes that individually represent various stages of evolution, in addition to reflecting the variation in the erosive potential of river flow throughout the Quaternary. From a bibliographical review, fieldwork (quantification and measurements of the potholes), high-resolution photogrammetry and morphostructural analysis of the generated cartographic products, it was possible to establish a correlation between the preferential orientation of the potholes and the direction of the planes of weakness, as well as the classification of potholes by morphometric parameters. In this work it was demonstrated that the efficiency of hydraulic vortices is associated with discontinuity structures and the mineralogical composition of granite facies, with abrasive erosion being responsible for sculpting potholes, with different dimensions and geometries. In the rocky bed of the Carnaúba River, the small potholes deepen and their diameter evolves into cylindrical shapes as the turbulent vertical flow increases, eventually becoming sigmoidal. The lateral potholes, located on the walls of the river channel, are deeper than they are wide, and represent a destructive phase of evolution.

Study of flood protection water levels for railway projects in the plains river network area

The Taihu Lake basin is characterised by a developed water system and a longitudinal river network, which is prone to flooding during the flood season. This poses a threat to the construction and operation of river-related railways, bridges, and other infrastructures, and therefore the design value of the water level of the river channel must be provided prior to the construction of roads and bridges in the basin. The Yanyi Railway traverses numerous river systems without the benefit of measured hydrological data. In order to address this deficiency, two methods were constructed using the Taihu Lake basin model: the historical water level frequency analysis method and the typical design storm method of the basin. These methods were employed to calculate the flood protection water level of each river under different design schemes and to analyze the reasons for the differences in the results. The results indicate that the water level results of the historical water level frequency analysis method are also applicable to the construction of the Yanyi Railway, provided that an economic perspective is taken.

Hydrological Regime of Rivers in the Periglacial Zone of the East European Plain in the Late MIS 2

At the end of the Pleniglacial and the first half of the Late Glacial period, approximately between 18 and 14 ka BP, rivers of the central and southern parts of the East European Plain had channels up to 10 times as large as the present day channels of the same rivers. These ancient channels, called large meandering palaeochannels, are widespread in river floodplains and low terraces. The hydrological regime of these large rivers is of great interest in terms of the palaeoclimatology of the late Marine Isotope Stage 2 (MIS 2). In this study, we aimed at quantitative estimation of maximum flood discharges of rivers in the Dnepr, Don and Volga basins in the late MIS 2. To approach this, we used massive measurements of the morphometric characteristics of large palaeochannels on topographic maps and remote sensing data—palaeochannel width, meander wavelength and their relationships with river flow parameters. The runoff depth of the maximum flood, which corresponds to the maximum depth of daily snow thaw during the snowmelt period, was obtained for unit basins with an area of &lt;1000 km2. The mean value for the southern megaslope of the East European Plain was 44.2 mm/day (6 times the modern value), with 46 mm/day for the Volga River (5.5 times), 45 mm/day (6.3 times) for the Don River and 39 mm/day (8 times the modern value) for the Dnepr River basins. In general, the Dnepr basin was drier than the Don and Volga basins, which corresponds well to the modern distribution of humidity. At the same time, the westernmost part of the Dnepr River basin was relatively wet in the past, and the decrease in humidity from the past to the modern situation was greater there than in the eastern and central regions. The obtained results contradict the prevailing ideas, based mainly on climatic modeling and palynological data, that the climate of Europe was cold and dry during MIS 2. The reason is that palaeoclimatic reconstructions were made predominantly for the LGM epoch (23–20 ka BP). On the East European Plain, the interval 18–14 ka BP is rather poorly studied. Our results of paleoclimatological and palaeohydrological reconstructions showed that the Late Pleniglacial and the first half of the Late Glacial period was characterized by a dramatic increase in precipitation and river discharge relative to the present day.