High Water Stages Research Articles

Anomaly detection in hydrological network time series via multiresolution analysis

The territorial extension of Brazil imposes logistic challenges on hydrologic monitoring and increases the chances of systematic observational errors, gauge displacements, downsampling during observation, and low density of streamflow samples on high water stage. Consequently, time series would exhibit artifacts such as gaps, high-frequency anomalies, inhomogeneity, and trends. An innovative anomaly detection system based on multiresolution analysis (MADE) was developed and used to detect synthetic anomalies in raw water stage time series. MADE uses both time and frequency as contextual attributes to identify anomalies. The balance between temporal and frequency resolution allows for capturing low-frequency coarse information and high-frequency details. On MADE, Generalized Extreme Studentized Deviate (GESD) detected short time anomalies on water stage wavelet faster modes (2-, 4-, and 8-days periods). For periods greater than 16 days, Wavelet Coherence and Multiple Wavelet Coherence detected similar water stage time series anomalies. MADE outperformed a Long Short-Term Memory model, a time regression neural network k-Nearest Neighbor model and an Empirical Data Analytics model coupled with clustering techniques on detecting both fast and slow time-scales synthetic anomalies introduced in a São Francisco River water stage time series, using time and frequency domain to pursuit point, collective and contextual anomalies.

Differentiating the Effects of Streamflow and Topographic Changes on the Water Level of Dongting Lake, China, Using the LSTM Network and Scenario Analysis

Dongting Lake is the second largest freshwater lake in China and an internationally critical habitat for migratory birds. However, after 2004, the multiyear mean water levels of West Dongting Lake (WDL), South Dongting Lake (SDL), and East Dongting Lake (EDL) in the high-water stage decreased by 1.05 m, 1.15 m, and 1.32 m, respectively. Different areas of Dongting Lake experienced various degrees of shrinkage. It is necessary to study the dominant driving factors and their contributions to the falling water level. In this study, the water level changes in Dongting Lake were analyzed, and a long short-term memory neural network model was constructed to simulate the water level of Dongting Lake. Moreover, the contribution of changes in streamflow and topographic conditions to the water level changes in different areas of Dongting Lake was estimated with scenario analysis. The research results show that the changes in the streamflow were the main driving factors for the water level decline of WDL, SDL, and EDL in the high-water stage, and their contributions were 0.74 m, 0.97 m, and 1.16 m, respectively. The topographic changes had a great falling effect on the water level of Dongting Lake, and the falling effect on the water levels from October to June of the following year was the strongest in EDL (0.81 m), followed by WDL (0.49 m), and the weakest in SDL (0.3 m). These results can provide a scientific reference for the management of the water resources of Dongting Lake.

Floating rooted hydrophytes and flow and sediment dynamics: Field study in secondary channels of the Paraná River

Worldwide, aquatic vegetation is a key component in many river systems due to its diverse interactions as well as the environmental services it provides. In the Paraná fluvial system, large mats of floating rooted hydrophytes are present in channels with different water conditions whose interaction with flow and sediment dynamics is currently unknown. This work aimed to evaluate the temporal coverage variation of floating rooted hydrophytic mats as well as the alteration of flow dynamic and sediment deposition associated with their presence in natural conditions. Four different secondary channels were analyzed for two different and consecutive water stages: mean and high-water levels. Hydrophytic coverage ranged from 5% to 67% and from about 3% to 14% of the total discharge drained throughout the vegetated areas of the channels, being the lowest values recorded during the high-water stage. The specific discharge distribution and flow velocities at the vegetated cross-sections were altered when compared to non-vegetated sections. Mean velocities and depths were markedly lower inside vegetation mats. Additionally, fine sediments (silt and clay) dominated the bed samples below the hydrophytic mats of the vegetated sections in all the channels and water level stages under study. Nonetheless, the highest wash load was mainly recorded outside the hydrophytic mats during mean waters, while it was registered within the mats during high waters. Grain size of bed material below the hydrophytic mats as well as flow velocities inside them indicated sedimentation promoted by the hydrophytic mats. Understanding how flow and sediment deposition can be altered by hydrophytic mats is of great relevance not only in terms of the role they play in the Paraná fluvial dynamics, but also for their appropriate inclusion in hydraulic field measurements and hydrodynamic models widely used to predict such dynamics.

Modelling and Numerical Simulation Approaches to the Stage–Discharge Relationships of the Lansheng Bridge

In recent years, extreme rainfall events with short delays and heavy rainfall have often occurred due to severe climate change. In 2015, Typhoon Soudelor caused a short-delayed heavy rainfall event in Nanshih River, which caused damage to a section of the Lansheng Bridge discharge station. The section was relocated upstream to rebuild the discharge station in 2019. However, the new discharge station cannot measure high flow due to the bridge structure. The flow observation range of Lansheng Bridge is therefore limited to normal flow, making it impossible to accurately estimate the flow during high-water stages. The purpose of this study is to use the past flow data of Nanshih River to estimate the flow rate under different return periods using frequency analysis. We used a Digital Elevation Model (DEM) to map the river’s topography, and used the 3D hydraulic calculations of the FLOW-3D model to estimate the water stage and discharge of the Lansheng Bridge. We then verified the accuracy of the model with the measured flow and water stage, and finally used the water stage and discharge data obtained from numerical simulation to construct the stage–discharge rating curve of the Lansheng Bridge. In addition to preventing flood disasters, this study approach can provide reliable data for use in water conservation. It may also be utilized to overcome the problem of measuring and estimating high flow during typhoon floods.

Snow drought and monsoon floods—hydrological extremes in the Cedar Valley watershed during water year 2021, southwestern Utah

Water year 2021 was a year of extremes in the Cedar Valley watershed of southern Utah, with snow drought resulting in extremely low snowmelt runoff of Coal Creek and intense monsoon rainfall resulting in several floods in different parts of the valley. Winter snow accumulation was depressed throughout southern Utah, perhaps due to La Nina conditions affecting winter storm trajectories. Coal Creek, the principal stream providing surface water to Cedar Valley, typically receives most of its annual flow from snowmelt runoff, but in 2021 had a peak snowmelt discharge 15% to 25% of that recorded in the previous two years and the third lowest snowmelt runoff on record. Following this extremely low snowmelt runoff period, more than 10 floods of Coal Creek occurred following monsoon storms in July and August that exceeded the 2021 snowmelt peak. Additionally, several thunderstorms produced rainfall rates in exceedance of the 100-year event and induced flooding within Cedar City and the town of Enoch. Flood inundation modeling using HEC-RAS and high-resolution topographic data showed good agreement with field and pubic-survey data on the high-water stage during the Enoch flooding, and demonstrated that the flooding was likely exacerbated by the low topography and limited drainage potential in flooded areas. Whereas the monsoon storms improved soil moisture and helped alleviate drought conditions, they also resulted in urban flooding and did little to replenish the regional water supply.

Modeling of arsenic dynamics in groundwater of а river floodplain contaminated with mine tailings: Ogosta River case, NW Bulgaria

This study aims to reveal the arsenic dynamics in groundwater of а river floodplain contaminated with mine tailings under temperate climate conditions and natural river hydrodynamics. Arsenic concentrations were monitored in the primary morphological units of the floodplain in the upper stretch of the Ogosta River in NW Bulgaria. Iron, lead-silver, and gold mining heavily affected the river valley in the second half of the 20th century. We used groundwater monitoring data from 21 piezometers for the period 2016-2020. Based on the geochemical and geomorphological conditions in the valley, the piezometers were grouped into three clusters. Regression models were developed for each cluster and representative piezometers to predict arsenic concentrations. In the active floodplain, seasonal fluctuations in arsenic concentrations followed the river and groundwater regime. In this part of the valley floor, we determined two periods of elevated arsenic concentrations during the spring and autumn/winter seasons that coincide with high river water stages. Arsenic content in the groundwater of the higher floodplain was less dependent on the water level fluctuations but followed changes in redox potential, electrical conductivity, and water temperature. The obtained results showed the elaborated models as valuable tools for studying arsenic dynamics in alluvial aquifers of contaminated river floodplains. The suggested models could be coupled with groundwater monitoring systems to monitor arsenic concentrations and identify periods of the year with levels below and above threshold values.

Experimental Study on Anti-Scour Property and Erosion Resistance of 3D Mat Materials for Slope Protection in Waterway Engineering

3D mats are environmentally friendly and ecological materials for protecting river and waterway banks. The anti-scour properties of the materials and the erosion resistance of the soil under them can be studied to provide decision support for the selection of slope protection materials and their applicable areas. In this paper, an indoor prototypical scouring experiment with a flume is carried out to study the anti-scour properties of three types of 3D mat materials (vegetation grass mats, Enkamat and reinforced Mike mat) and the erosion resistance of the underlying soil under typical combined conditions of flow rate and water stage. It is concluded that the 3D mats increase the resistance coefficient of the bed surface, and that with the same incoming flow, the average flow velocity is inversely related to the resistance coefficient. There are three scouring modes for 3D mats under the action of water flow: material failure caused by mechanical damage, performance failure caused by serious erosion of the soil mass and non-failure. Of the three mat materials, the reinforced Mike mats are more resistant to scouring than the other two unreinforced materials, and the erosion volume ratios of reinforced Mike mats, vegetation grass mats and Enkamat are 59.24%, 61.81% and 62.17%, respectively, under the same small flow rate and high water stage. The results show that the reinforced Mike mats have the best anti-scour property and soil conservation performance, followed by Enkamat and the vegetation grass mats. In addition, reinforced materials outperform non-reinforced ones in their anti-scour performance and their protection for the underlying soil on the bank slope.

The Impact of Precipitation Characteristics on the Washout of Pollutants Based on the Example of an Urban Catchment in Kielce

This paper reports the results of studies on the concentrations of total suspended solids (TSS) and heavy metals (HMs) (Cu, Zn, Cr, Ni, Cd, Pb) in stormwater. Pollutant loads were calculated for the observed high water stages. Pollutographs showing M/Mc = f(V/Vc) relationships were generated. In the description of the relationships, two functions, namely the exponential and the power functions, were employed. These represented the dynamics of the pollutant washout from the surface of the catchment area. The analyses demonstrated that the exponential function provides a slightly better description of the course of the process compared with the power function. In the former case, correlation coefficients (R) ranged from 0.900 to 0.999, whereas in the latter they ranged from 0.864 to 0.999. The analyses of correlations between the characteristics describing discharge hydrographs and the values of pollutant washout coefficients indicate that the strongest statistical relationships were identified for TSS. It was demonstrated that the value of the washout coefficient for total suspended solids (kTSS) drops with an increase in rain intensity (q). This also depends on the 10-min precipitation (Ptd=10). Regarding the studied heavy metals, a statistically significant impact of the dry period (tbd) on the washout coefficient was observed only for lead (kPb). Taking into account the washout coefficient in the first flush model makes it possible to improve the accuracy of calculations. This is important for understanding the studied phenomenon.

Determining the Regional Geochemical Background for Dissolved Trace Metals and Metalloids in Stream Waters: Protocol, Results and Limitations—The Upper Loire River Basin (France)

To avoid the improper disqualification of a watershed for which the water–rock interaction (WRI) may produce trace element concentrations exceeding established guidelines, it is of the utmost importance to properly establish natural geochemical backgrounds. Using the example of the crystalline Upper Loire River Basin, we are proposing a methodology based on the selection and chemical characterization of water and sediment samples from 10 monolithologic watersheds supposedly lowly impacted by anthropogenic inputs. We collected water samples from each watershed’s spring down to its outlet and measured dissolved major, minor and selected trace elements (Al, As, Ba, Cd, Co, Cr, Cs, Cu, La, Ni, Pb, U, V and Zn) at low- and high-water stages. Results show that the chemical signature of the stream waters is controlled by mineral weatherability rather than by the available rock stock. As a result, the variability in dissolved metal concentrations between the principal lithologies is similar to that observed within each of them. While some elements mostly result from WRI, others clearly identify high inputs from topsoil leaching. Comparison with published data evidences the need to subdivide studied watersheds into distinct sectors, according to the distance from the spring, in order to define reliable natural backgrounds.

Hydrodynamic Model of the New Waterway Through the Vistula Spit

Abstract The decision to build a new waterway (strait) in the Polish part of the Vistula Spit was made in 2017. The new connection between the Gulf of Gdańsk and the Vistula Lagoon is planned as an artificial navigable channel with a lock and a small port. During storm surges and wind tides in the gulf or in the lagoon, sluicing will be required for vessels to tackle the Vistula Spit. This procedure does not require significant water flow through the channel in normal conditions. However, in the case of a lock failure or in the case of controlled opening of the gate to increase water exchange in the lagoon or to reduce flood risk in the Vistula Lagoon, high flow rates may occur in the navigable channel and in the neighboring port basin. In order to inves-tigate the hydraulic conditions in such extraordinary situations, numerical modeling of the hydrodynamics during water damming in the gulf or in the lagoon is performed. To analyze the hydrodynamics of the artificial connection between the sea and the lagoon during periods of high water stages, mathematical modeling is required. This paper presents the shallow water equations (SWE) model adapted to simulate the flow through the port basin and the navigable channel. The calcula-tions allowed the relation between the water head and the capacity of the navigable channel to be found, as well as to analyze circulations which may occur in the port basin.

Temporal and spatial variability of heavy metals in bottom sediments and the aquatic macrophyte Paspalum repens of the Orinoco River floodplain lagoons impacted by industrial activities.

This study investigated the water parameters and the levels of several heavy metals in leaves and roots of the aquatic macrophyte Paspalum repens and in bed sediments of one unpolluted lagoon and two polluted lagoons of the Orinoco River floodplain to know the impact of the alumina refining wastes on these ecosystems. The sampling was performed during four hydrological periods, covering one hydrological year. Chemical parameters in water (pH, conductivity, and total dissolved solids) and the levels of Al, Pb, Cr, and Cu in sediments were the highest in Macanillal (LMaca) lagoon, whereas sediments of Punta Cuchillo (LPC) lagoon also had elevated concentrations of Al and Fe in comparison with Las Aruhacas (LArh) lagoon (unpolluted lagoon). Chemical parameters in waters returned almost to natural values during high water stage because of the huge inundation of the Orinoco River during the high discharge periods. The solid/liquid discharges of industrial effluents over these systems also affected the grain size distribution of sediments in the lagoons. In all the studied lagoons, the distribution of elements in leaves of P. repens was in the order K ≥ Cr > Ca > Mg > Al > Fe > Mn > Cu > Pb, whereas Al was found to be the more abundant element in roots. The high abundance of Cr in P. repens was related with the high Cr accumulation potential shown by aquatic macrophytes. Despite this, the concentration of elements in P. repens did not show differences between the plants collected in the polluted lagoons versus the plants collected in the unpolluted lagoon. This suggests that P. repens is unsuitable for bio-monitoring studies of heavy metals in these aquatic environments impacted by alkaline residues.

Hydrological response to climate change and human activities: A case study of Taihu Basin, China

Climate change and human activities have changed a number of characteristics of river flow in the Taihu Basin. Based on long-term time series of hydrological data from 1986 to 2015, we analyzed variability in precipitation, water stage, water diversion from the Yangtze River, and net inflow into Taihu Lake with the Mann-Kendall test. The non-stationary relationship between precipitation and water stage was first analyzed for the Taihu Basin and the Wuchengxiyu (WCXY) sub-region. The optimized regional and urban regulation schemes were explored to tackle high water stage problems through the hydrodynamic model. The results showed the following: (1) The highest, lowest, and average Taihu Lake water stages of all months had increasing trends. The total net inflow into Taihu Lake from the Huxi (HX) sub-region and the Wangting Sluice increased significantly. (2) The Taihu Lake water stage decreased much more slowly after 2002; it was steadier and higher after 2002. After the construction of Wuxi urban flood control projects, the average water stage of the inner city was 0.16–0.40 m lower than that of suburbs in the flood season, leading to the transfer of flooding in inner cities to suburbs and increasing inflow from HX into Taihu Lake. (3) The regional optimized schemes were more satisfactory in not increasing the inner city flood control burden, thereby decreasing the average water stage by 0.04–0.13 m, and the highest water stage by 0.04–0.09 m for Taihu Lake and the sub-region in the flood season. Future flood control research should set the basin as the basic unit. Decreasing diversion and drainage lines along the Yangtze River can take an active role in flood control.

Magnetic Fingerprinting of Fluvial Suspended Particles in the Context of Soil Erosion: Example of the Canche River Watershed (Northern France)

AbstractIn Northern France, land use is dominated by agriculture. Erosion by runoff results in heavy loss of fertile soil into surface waters. There is a need for cost‐effective tools to trace the sediment flux in catchments. This study highlights the potential of environmental magnetism to provide rapid non‐destructive parameters to characterize the spatiotemporal runoff versus bedload signal in a watershed. Between 2015 and 2017, within the Canche River watershed, several spatiotemporal sampling campaigns of suspended particulate matter (SPM) were undertaken and two distinct “snapshot campaigns” of flood events were conducted at key locations acquiring, in addition, hydrodynamical observations (discharge, turbidity, sediment load, etc.). Agricultural soils and SPM within the watershed have similar values for bulk magnetic concentration (isothermal remanent magnetization, IRM). The magnetic mineral assemblage of the SPM is dominated by soft ferromagnetic (sensu lato) minerals during low water conditions and is enriched in high‐coercivity phases during high water stages associated with rainfall events. Low‐temperature remanence experiments identified goethite and hematite as the high‐coercivity phases. IRM acquisition component analysis of the room temperature results quantify the relative input of high‐ versus low‐coercivity components focused on a given confluence site. Results from snapshot campaigns highlight the link between the enhanced runoff input of high‐coercivity particles during flood events and show that the S ratio parameter is an effective tool to trace erosion of topsoils.

Changes in the Nature of Long-Term Fluctuations of Water Flow in the Subarctic Region of Yakutia: A Global Warming Perspective

Global warming has begun to affect Yakutia, an area recognized as the coldest region of the Northern Hemisphere. Previous research has indicated that the effects of global warming will be long-term. When modeling oncoming climatic changes, researchers often forecast the related water flow changes in various water bodies as well. However, these evaluations frequently differ from the actual water flow data. Thus, the current study identifies and assesses the trends in long-term flow fluctuations in the current context of global warming. This is particularly relevant in the subarctic region of Yakutia, because the local climate is not significantly influenced by anthropogenic factors. The region has an essentially uniform climate, and the river basins within the subarctic zone flow in the same direction. Thus, the study parameters can be adequately compared. Analysis of changes in the water regimen parameters of the rivers in this region is of particular importance. This study demonstrates that the changes in the long-term river regimen in the region, within approximately equivalent climate zones, have been highly and locally variable indifferent areas and time periods. However, we were unable to detect any specific consistency in these changes. The water content of almost all rivers in Yakutia has increased in the last 30 years (approximately), thus confirming general assumptions based on predictive models of climate changes; however, in most cases, such changes were the result of reaching the high-water stage of established long-term cycles. The nature of long-term fluctuations in the water flow of rivers did not change in about half of the Yakutia rivers. One water body showed a further decrease in the water content from the norm, both in terms of duration and water flow rate. Meanwhile, specific water bodies exhibited extreme long-term fluctuations, which are predicted to be a reaction to global warming. Prior to the onset of significant warming in the region, the trends of long-term water discharge fluctuations were stationary. Then, the trends of certain rivers became non-stationary due to the reasons indicated above. On their own, quantitative characteristics are insufficient to evaluate actual changes in water regimens. Moreover, evaluations obtained in the absence of a trend analysis of specific long-term discharge fluctuations, which can only be performed via graphic visualization, are most likely to be inaccurate.

Impact of the Artificial Strait in the Vistula Spit on the Hydrodynamics of the Vistula Lagoon (Baltic Sea)

In the Vistula Lagoon, storm surges are induced by variable sea levels in the Gulf of Gdańsk and wind action. The rising of the water level in the southern part of the basin, exceeding 1.0 m above mean sea level, can be dangerous for the lowland area of Żuławy Elbląskie, causing the inundation of the polders adjacent to the lagoon. One of the potential possibilities to limit the flood risk is to decrease the water level in the lagoon during strong storm surges by opening an artificial canal to join the lagoon with the Gulf of Gdańsk. The decision to build a new strait in the Vistula Spit was made in 2017. In order to analyze the impact of the artificial connection between the sea and the lagoon during periods of high water stages in the southern part the lagoon, mathematical modelling of the hydrodynamics of the Vistula Lagoon is required. This paper presents the shallow water equations (SWEs) model adapted to simulate storm surges driven by the wind and sea tides, and the numerical results obtained for the present (without the new strait) and future (with the new strait) configuration of the Vistula Lagoon.

Variations of Surface and Subsurface Water Storage in the Lower Mekong Basin (Vietnam and Cambodia) from Multisatellite Observations

In this study, we estimate monthly variations of surface-water storage (SWS) and subsurface water storage (SSWS, including groundwater and soil moisture) within the Lower Mekong Basin located in Vietnam and Cambodia during the 2003–2009 period. The approach is based on the combination of multisatellite observations using surface-water extent from MODIS atmospherically corrected land-surface imagery, and water-level variations from 45 virtual stations (VS) derived from ENVISAT altimetry measurements. Surface-water extent ranges from ∼6500 to ∼40,000 km 2 during low and high water stages, respectively. Across the study area, seasonal variations of water stages range from 8 m in the upstream parts to 1 m in the downstream regions. Annual variation of SWS is ∼40 km 3 for the 2003–2009 period that contributes to 40–45% of total water-storage (TWS) variations derived from Gravity Recovery And Climate Experiment (GRACE) data. By removing the variations of SWS from GRACE-derived TWS, we can isolate the monthly variations of SSWS, and estimate its mean annual variations of ∼50 km 3 (55–60% of the TWS). This study highlights the ability to combine multisatellite observations to monitor land-water storage and the variations of its different components at regional scale. The results of this study represent important information to improve the overall quality of regional hydrological models and to assess the impacts of human activities on the hydrological cycles.

Flood Inundation Assessment Considering Hydrologic Conditions and Functionalities of Hydraulic Facilities

This study proposed a two-phase risk analysis scheme for flood management considering flood inundation losses, including: (1) simplified qualitative-based risk analysis incorporating the principles of failure mode and effect analysis (FMEA) to identify all potential failure modes associated with candidate flood control measures, to formulate a remedial action plan aiming for mitigating the inundation risk within an engineering system; and (2) detailed quantitative-based risk analysis to employ numerical models to specify the consequences including flood extent and resulting losses. Conventional qualitative-based risk analysis methods have shown to be time-efficient but without quantitative information for decision making. However, quantitative-based risk analysis methods have shown to be time- and cost- consuming for a full spectrum investigation. The proposed scheme takes the advantages of both qualitative-based and quantitative-based approaches of time-efficient, cost-saving, objective and quantitative features for better flood management in term of expected loss. The proposed scheme was applied to evaluate the Chiang-Yuan Drainage system located on Lin-Bien River in southern Taiwan, as a case study. The remedial action plan given by the proposed scheme has shown to greatly reduce the inundation area in both highlands and lowlands. These measures was investigated to reduce the water volume in the inundation area by 0.2 million cubic meters, even in the scenario that the flood recurrence interval exceeded the normal (10-year) design standard. Our results showed that the high downstream water stage in the downstream boundary may increase the inundation area both in downstream and upstream and along the original drainage channel in the vicinity of the diversion. The selected measures given by the proposed scheme have shown to substantially reduce the flood risk and resulting loss, taking account of various scenarios: short duration precipitation, decreased channel conveyance, pump station failure and so forth.

Retrospective Simulation of an Extreme Flood on the Oka River at the City of Ryazan and Impact Assessment of Urban and Transport Infrastructure

Numerical modeling of flow dynamics of rivers with comprehensive channel patterns and wide floodplains during high water stage is considered to be one of the most effective methods for implementing both research and civil-engineering projects. However, realistic results of simulations can be obtained only if the model has been calibrated and validated against field observations and remote sensing data. This approach is realized for a 2D hydrodynamic model of the Oka River at the city of Ryazan (central European Russia). The Oka has a meandering channel and a wide floodplain with a complicated distributary network. The feasibility of allocating new residential quarters and infrastructure facilities on artificial “islands” on the floodplain was studied using STREAM_2D software package. Because of a significant decrease in the maximum runoff of the Oka in the recent decades, the simulations were made for the extreme spring snowmelt flood of 1970 for various scenarios of floodplain development in the past, present, and future.

Are seasonal variations in river-floodplain sediment exchange in the lower Amazon River basin resolvable through meteoric cosmogenic 10Be to stable 9Be ratios?

The lower Amazon basin contains vast floodplains that exchange sediment with the main river. The exchange of sediment between the floodplain and the channel follows a seasonal cycle that is anticorrelated with the hydrological cycle. At low water stages, sediment that has been stored in the floodplain for potentially several thousands of years is eroded and transferred from the floodplain to the mainstem. During high water stages, most sediment transported in the main channel stems directly from the eroding source with little intermittent storage. We apply the meteoric cosmogenic 10Be to stable 9Be ratio (10Be/9Be) as a denudation and weathering proxy to investigate this seasonality in sediment transport. Single meteoric 10Be concentrations ([10Be]) have previously been shown to record floodplain storage; whereas fractions of mobilized 9Be, a trace metal released during weathering, provide degrees of weathering. The resulting 10Be/9Be ratio provides denudation rates of the sediment sources. We compare 10Be/9Be measured on suspended sediment from river depth profiles at two sites (Óbidos/Macapa) and during two hydrological seasons (high/low water stage in 2013). We show that careful construction of river depth profiles in combination with Rouse modeling is necessary to exclude the grain size dependence that together with hydrodynamic sorting introduces a bias into single [10Be] and [9Be]. In contrast, the 10Be/9Be is largely uniform across grain sizes and is thus unaffected by sorting. Our 10Be/9Be ratios, the denudation rates derived from them, and mobilized 9Be fractions do not show variations outside their uncertainties across seasons or sites. Thus, 10Be/9Be show that upstream sediment sources were well mixed by multiple cycles of storage and remobilization in the floodplain.

Possibilities of fish passage through the block ramp: Model-based estimation of permeability

Block ramps offer an opportunity to combine hydrotechnical structures with fish passages. The primary study objective was to evaluate the effectiveness of a block ramp for upstream fish movement in a mountain stream. Geodetic measurements of the bottom surface and water level were taken for three cross-sections. The description of the geometric and hydrodynamic parameters of the block ramp was supplemented with information on the width and length of crevices between boulders. Measurements of the geometric and hydrodynamic parameters of the block ramp were performed at 76 measurement sites, at three different types of discharge. Ichthyological data were collected in the analyzed stream. Measurements covered among others total length, width, and height of caught fish. Salmonid, cottid, balitorid, and cyprinid fish were studied. The determination of the main effects of the geometric and hydrodynamic parameters of the block ramp on the possibilities of use by target fish species employed generalized linear models (GLMs). The study shows that the block ramp cannot provide longitudinal connectivity and migration of fish occurring in the mountain stream. According to estimates, the block ramp did not meet the permeability expectations. The reason for low usefulness of the ramp for fish is particularly excessively strong water current. The stream concentration constituted an unsurmountable velocity barrier for fish moving upstream for each of the analyzed discharges. The developed model suggests that some crevices in the side zones of the ramp could be parts of the migration corridor, but only for small and medium-sized fish. At medium and high water stages, movement of fish in crevices was difficult due to fast water current, and at low and very low discharges, some crevices lost their permeability, and could become ecological traps for fish. The necessity of estimation of ramp permeability during pre-construction phase was emphasized.