River Flow Characteristics Research Articles

Quantitative Assessment of Ecological Flow in the Yellow River Under Changing Environments

ABSTRACTStudying the streamflow characteristics of the Yellow River mainstem under changing environmental conditions is crucial for the management and sustainable development of water resources within its basin. This research employs a long short‐term memory (LSTM) model to restore the flow characteristics of the Yellow River's mainstream under natural conditions. Additionally, the range of variation approach (RVA) and nonparametric kernel density estimation (KDE) method are integrated to quantitatively assess the impact of environmental changes on streamflow. The findings indicate that: (1) Hydrological variability in the Yellow River was observed in 1985, with a degree of variability ranging from 26% to 58%, classified as moderate. (2) The annual ecological flow value of the Yellow River is 560–1001 m3/s, and the average annual ecological flow assurance is 43%. (3) Based on LSTM simulation results (NSE > 0.7, R2 > 0.8), it is concluded that the ecological flow assurance under natural conditions in the Yellow River exceeds the measured values, primarily due to human activities, which contribute over 52% to this discrepancy. These results suggest that the river ecosystem of the Yellow River's mainstem is relatively unstable and requires further management.

Diatom assemblages in glacial-fed streams of Italian Western Alps

ABSTRACT The rate of glacier retreat has recently increased, with changes in the glacier discharge, river flow and water characteristics, creating specific environmental conditions for highly specialized organisms. We here investigated diatom communities in glacier-fed rivers of the Valle d’Aosta region (NW-Italy), analyzing data collected between 2010 and 2019 for the WFD monitoring programs. We present a complete checklist of the species inhabiting this region, many of which are classified as endangered in the diatom Red List. We found significant differences between sites with different catchment glacier cover (CGC), in terms of taxonomic composition, ecological guilds and abundance of Red List taxa. In particular, we observed a significant increase in species richness with the decrease in CGC, as well as significant differences in terms of taxonomic composition. We highlighted the role of Achnanthidium lineare as an indicator species for streams with the highest glacial influence, together with Hannaea arcus, Eucocconeis laevis and other oligotrophic low profile species that are well adapted to physical stress induced by glacier runoff. On the other hand, streams with lower glacial influence were characterized by motile species mostly belonging to the genera Navicula and Nitzschia, due to the nutrient increase. Didymosphenia geminata was recorded in streams with marginal glacier cover; recently observed blooms indicate that conditions may become increasingly favorable for the spread of this species in Alpine environments, as glaciers retreat. The abundance of Red List diatoms increased significantly with increasing glacier cover suggesting that glacier-fed rivers are niches for the conservation of diatom biodiversity.

Analysis of Hydraulic Characteristics and Acquisition of Flood Management Data Using D-HSI in Natural Streams

Natural disaster prevention requires the maintenance of the proper function of river flow during droughts and heavy rains caused by abnormal weather as well as the minimization of damage via rapid and accurate predictions. This study analyzed hydraulic characteristics by utilizing D-LiDAR (Drone LiDAR) topographic data and D-HSI (Drone Hyperspectral Image) data to quickly and accurately collect and analyze related data. The HEC-RAS model was used to compare and analyze the results obtained via the D-LiDAR topographic data of this study, the roughness coefficient of the river master plan, and the results of applying parameters by adding NDVI. As a result, in the case of a 100-year frequency flood discharge, the average velocity decreased by an average of 2.23 m/s when applying the resistance coefficient by area, based on NDVI. Moreover, the flood level increased by an average of 0.30 m, and the cross-sectional area of ​​the flow capacity increased by an average of 20.17 m2. These results confirms that vegetation has a significant influence on the flow characteristics of natural streams. Hence, the data construction and analysis method used in this study can provide useful information regarding the rapid measurement and analysis of river flow characteristics during floods as well as and the development of prediction techniques and warning-related systems for drought and flood prevention.

Collateral benefits: River flow normalization for endangered fish enabled riparian rejuvenation

AbstractLike most rivers worldwide, the transboundary North American Kootenay/i River has experienced multiple impacts including watershed developments, river channelization, and floodplain clearing, draining, and diking. Construction of Libby Dam was authorized by the 1964 Columbia River Treaty (CRT) between the United States and Canada, and in 1975 began regulating downstream flows for flood risk management and hydropower generation. Following cumulative impacts, the endemic Kootenai River White Sturgeon population collapsed and was designated as endangered in 1994 (U.S. Endangered Species Act). Subsequent Biological Opinions from the U.S. Fish and Wildlife Service prescribed Libby Dam operations to provide springtime flow pulses for sturgeon spawning. These provided the unanticipated benefit of substantial seedling recruitment of native and introduced riparian cottonwoods and willows. The regulated flow regime was further adaptively managed to provide a more normative (natural) regime, to balance ecological functions with flood risk management and hydropower generation. The broadened ecological considerations would be consistent with the proposed priorities for the modernization of the international CRT. The observed responses revealed that (1) diverse aquatic and riparian organisms are dependent on common river flow characteristics; (2) a normalized flow regime provided substantial ecological benefits; and (3) due to multiple influences, hybrid ecosystems develop along regulated rivers, with a blending of natural and altered processes and communities. For other regulated rivers, we recommend that (1) high springtime flows be allowed, as feasible; (2) followed by the gradual post‐peak recession; and (3) the maintenance of sufficient flows through the warm and dry interval of mid to late summer.

ОЦЕНКА ПРОСТРАНСТВЕННО-ВРЕМЕННОЙ ДИНАМИКИ ЗАГРЯЗНЕНИЯ РЕКИ КРАСНОЙ В КАЛИНИНГРАДСКОЙ ОБЛАСТИ

Today, the Kaliningrad region has considerablr strategic significance for the Russian Federation. Due to the fact thatthe region is separated from the main part of the country, the quality of water resources is considered a substantial factor for its economicwell-being. One of the main tools in this area is hydrochemical and hydrological monitoring of surface watercourses. The purpose ofthe work is to assess the spatio-temporal dynamics of the Krasnaya River pollution for 4 hydrological seasons in 2022-2023. Monitoringwas carried out during the autumn (10/15/22), winter (01/15/23), spring (04/23/23), and summer (07/19/23) hydrological seasons,during which water samples were taken at 4 hydraulic stations, and hydrometric characteristics were measured to calculate water flowrates. Water samples were examined for the relevant chemical indicators, on the basis of which integral indicators of water qualitywere determined. In turn, their spatio-temporal variability was determined and cartographically expressed. As a result of the study, thepaper provides information about the state of the watercourses and the influence of anthropogenic and natural factors on them. Thespecific combinatorial index of water pollution showed that the river is polluted from source to mouth. Intra-annual variability wasstudied using the WPI and has a similar spatial interpretation, water quality decreases from source to mouth with slight deviations.Temporal variability has developed in such a way that autumn is the most polluted season, while the remaining seasons have nearlyequal average water pollution indices. The main pollutants can be divided into systematic (petroleum products, iron, BOD5, COD) andnon-systematic (sulfate phosphates, ammonium, and low dissolved oxygen). A correlation was discovered between chemical pollutionand the quantitative characteristics of river flow, natural cycles of aquatic and shore vegetation, and vehicle washing. The emissionsof iron and petroleum products do not fit into any specific regular system: the sources of the former are groundwater, of the latter –anthropogenic activities. In general, the situation with water quality on the Krasnaya River is rated as satisfactory.

The Effect of Natural and Anthropogenic Climate Changes on River Runoff and Snow Water Equivalent in the Lena River Basin

The hydrological models ECOMAG and HBV were used to calculate the characteristics of river flow and snow Water Equivalent in the Lena River basin. The input data included the meteorological observations and the results of calculations with global climate models with the implementation of scenarios of natural climate conditions, taking into account the anthropogenic effect on climate. The calculations were made for a historical period (1970–1999) and up to the end of the XXI century. Hydrological models for several hydrometric gages in the Lena basin were calibrated and verified. The simulation of the annual and seasonal runoff using the climate model data was evaluated by comparison with observation data. According to the results using numerical experiments over the historical period, the increase in the Lena runoff is mostly due to natural climate variations. Conversely, in the XXI century, the anthropogenic climate changes determine the specific features of the regime of river runoff and snow cover. The warming caused by an increase in greenhouse gas concentrations in the atmosphere leads to an increase in snow water equivalent and transformation of the hydrological regime in the area, in particular, to an earlier beginning of active snow melting (up to two weeks) and higher maximal discharges during spring flood. At the same time, the volume of runoff decreases in the summer and increases in the autumn and winter.

Revisiting Kazakhstan’s Hydraulic Structures: A GIS-Based Approach to Dam Design and Allocation Considering Climate Change and Land Use Scenarios

This article discusses the importance of hydraulic structures, particularly dams, in Kazakhstan’s economy due to water scarcity in many regions. The article highlights the need for a comprehensive approach to the location and design of dams considering climate change and land use scenarios. The article also emphasizes the need to update the design parameters and characteristics of dams to consider changes in land use and climate. The Samarkand reservoir hydrosystem is used as an example to discuss the potential hazards of the new spillway and the need for technical upgrading. The article suggests that the development of an integrated GIS-based approach to survey works, location, and design of dams could improve the quality of design and survey works and lead to the modernization of design and operation of reservoirs. The study proposes the use of modern research methods, including space methods, to provide more flexible and safe management of river flow with consideration of environmental and economic interests. The article concludes that the comprehensive GIS-based methodology for the location and design of dams, considering potential changes in river flow characteristics and the impact of changes in land use and climatic scenarios, can improve efficiency and optimize the work of hydraulic engineers.

Ecological Base Flow Characteristics of Typical Rivers on the North Slope of Kunlun Mountains under Climate Change

Under climate change, river ecological base flow becomes particularly critical for the health and stability of inland river ecosystems in arid regions. Taking three typical seasonal inland rivers, including the Kriya River, the Niya River, and the Qarqan River, all on the northern slope of the Kunlun Mountains, as research objects, meteorological data from 1958 to 2019 and hydrological data from 1978 to 2014 were selected to analyze the characteristics of ecological base flow under climate change. The results show that in the past 60 years, the temperature in the Kriya River, Niya River, and Qarqan River basins has warmed at rates of 0.235 °C•(10a)−1, 0.223 °C•(10a)−1, and 0.177 °C•(10a)−1, respectively, while the precipitation has increased at the rates of 0.88 mm•(10a)−1, 3.90 mm•(10a)−1, and 7.92 mm•(10a)−1. The Tennant method was determined as the best algorithm for ecological base flow of inland rivers in arid regions. The interannual maximum values of ecological base flow all occurred in 2010, with three rivers increasing by 5.098 m3·s−1, 2.416 m3·s−1, and 11.343 m3·s−1 respectively, and the regional average increasing by 6.286 m3·s−1. The maximum ecological base flow within the year is in July, and the minimum value is in January, with a high proportion of the flood season. The monthly ecological base flow of rivers has a strong correlation with the monthly temperature and precipitation, with the strongest correlation in the Qarqan River basin and the correlation coefficients of 0.876 and 0.917. We propose ecological base flow guarantee objectives for the three rivers during the dry season, and clarify that the flood season is the key point of ecological base flow guarantee. The guarantee objectives are 0.974 m3·s−1, 0.154 m3·s−1, and 2.167 m3·s−1, for the three rivers, respectively. Our research results can provide scientific reference for the management and regulation of water resources and ecological protection of the northern slope of the Kunlun Mountains.

Quantification of Floc Growth for Sediment with Mixing Intensity

Pollutants related to water quality often exist in rivers and form clusters. These pollutants adversely affect river environments and ecosystems. In Korea, the public’s interest in water quality has been increasing for decades. Many studies on water quality and pollutants in sewage treatment plants have been conducted; however, studies on the formation of flocs based on the flow characteristics of rivers are insufficient. In general, it is known that floc formation is influenced by hydraulic characteristics, such as velocity and turbulence, and that it combines them with contaminants in the river. However, studies that quantitatively analyze this topic are also insufficient. An analysis of floc formation between sediments must be conducted to understand the formation process of sediments and contaminants. Therefore, in this study, kaolin, which is a cohesive sediment, was used to quantify the floc formation process according to the mixing intensity. Turbidity was analyzed to observe the amount of floc formation, and samples were collected to confirm the concentration. Additionally, the turbidity concentration relationship according to the mixing intensity was quantified using an optical microscope. Regarding the mixing intensity, when the rotation speed was 200 rpm or more, the separation of the flocs was dominant. In contrast, when the rotation speed was 100 rpm or less, turbidity changes due to sedimentation and floc formation were dominant. Analyzing mixing intensities and their association with the flow characteristics of rivers may be useful for the management of contaminants in rivers.

Velocity Vector Estimation of Two-Dimensional Flow Field Based on STIV

As an important part of hydrometry, river discharge monitoring plays an irreplaceable role in the planning and management of water resources and is an essential element and necessary means of river management. Due to its benefits of simplicity, efficiency and safety, Space-Time Image Velocimetry (STIV) has attracted attention from all around the world. The most crucial component of the STIV is the detection of the Main Orientation of Texture (MOT), and the precision of detection directly affects the results of calculations. However, due to the complicated river flow characteristics and the harsh testing environment in the field, a large amount of noise and interfering textures show up in the space-time images, which affects the detection results of the MOT. In response to the shortage of noise and interference texture, a new non-contact image analysis method is developed. Firstly, Multi-scale Retinex (MSR) is proposed to pre-process the images for contrast enhancement; secondly, a fourth-order Gaussian derivative steerable filter is employed to enhance the structure of the texture; next, based on the probability density distribution function and the orientations of the enhanced images, the noise suppression function and the orientation-filtering function are designed to filter out the noise to highlight the texture. Finally, the Fourier Maximum Angle Analysis (FMAA) is used to filter out the noise further and obtain the clear orientations to achieve the measurement of velocity and discharge. The experimental results show that, compared with the widely used image velocimetry measurements, the accuracy of our method in the average velocity and flow discharge is significantly improved, and the real-time performance is excellent.

Debris flow characteristics of the compound channels with vegetated floodplains

Compound cross-sections with vegetated floodplains are a common type of cross-section in debris-flow gullies. Floodplain vegetation participates in large-scale debris flow events and regulates debris-flow discharge. Extensive research has been conducted on the water flow characteristics of compound rivers. However, few studies have investigated the debris flow characteristics of compound channels in mountainous areas, particularly those of debris flow and flash flood inundation areas with vegetation. This study discusses the section characteristics of debris flow gullies with vegetated floodplains, gully evolution processes, and their influence on debris flow. The results show that the compound debris flow gully with a vegetated floodplain is formed in the gully from the mature stage to the old-mature stage. The compound sections are developed in flow areas with a gentle slope, which can be bilateral floodplain, unilateral floodplain, and multi-main gully floodplain types. Owing to the vegetation of the floodplain, the roughness of the channel increases, which makes the beach roughness coefficient much larger than that for the main channel. In the integrated Manning coefficient method, the error in resolving the flow velocity and discharge is large and cannot reflect the difference in velocities of the floodplain and main channel, therefore the sectional splitting method is most applicable. Influencing debris flow movement, limiting channel migration, and retaining debris flow to the main channel were the main contributions of the riparian forest zone.

CHANGE WATER CONTENT OF THE VORSKLA RIVER ACCORDING TO THE DATA OF THE HYDROLOGICAL POST OF THE VILLAGE OF CHERNECHCHYNA IN THE PERIOD FROM 1979 TO 2019

The article is devoted to an important problem of today – the analysis of water content of rivers using the example of the Vorskla River, a left-bank tributary of the Dnieper, which originates outside the Sumy region and flows through the territory of the region for about 122 km (26.3% of the river's length). The Vorskla River is characterized by the processes of overgrowth and silting, the river loses its water content and turns into a low-flow reservoir in places, therefore the outlined problem is extremely important. The purpose of the study: to analyze the water content of the Vorskla River using the important quantitative characteristics of the flow of expenses of water to the data of the hydrological post of the village of Chernechchyna in the period from 1979 to 2019. The article considers the concept of water content and describes the research methodology, analyzes the main quantitative characteristics of river flow: expenses of water (average, maximum and minimum). It was established that the average annual expenses of water of the Vorsklа River is characterized by a steady downward trend, low-water years prevail over high-water ones, and the low-water phase has been ongoing since 1989; the value of the indicator of maximum expenses of water decreases sharply, 73.2% of the data of the sample has a value less than 161,3 m3/s, only in 1980 the highest indicator of 585 m3/s was recorded, which is 1,3 times lower than the maximum multi-year expenses of water; the dynamics of the minimum expenses of water of the Vorskla River shows a wave-like downward dynamics, over the past 10 years, the indicator of the minimum expenses of water has decreased and its average value for the period 2010-2019 is 2,23 m3/s, the lowest minimum expenses of water was recorded for the period 1979-2019 (1,52 m3/s) are 6,4 times higher than the minimum multi-year indicator; the trend that scientists state about the intra-annual redistribution of flow is clearly followed (the hydrological indicators of high water are decreasing, and low water, on the contrary, are increasing); all signs of low water are present: all investigated quantitative indicators of flow are decreasing.

Assessment of Land Use Land Cover and River Dynamics of Himalaya: Seti River Sub-Basin of Nepal


 
 
 In rapidly growing areas, land use land cover (LULC) change is one of the most pre-eminent features of environmental changes produced by human-induced activities. LULC changes are critical issues and challenges for environmentally friendly and sustainable development. Understanding land-use and land-cover (LULC) changing patterns is critical for sustainable environmental management, particularly effective water management. This study was focused on the assessment of LULC and sinuosity of the Seti River sub-Basin over 28 years. Satellite imagery of Landsat series (MS, TM, and OLI) were classified using maximum likelihood classifier to create LULC maps for 1991, 2004 and 2019. The LULC change was assessed using change detection analysis and verified the result by confuse matrix. The results showed that forest cover is regaining its original status with the increasing rate of 1.31%. In the meantime, built-up areas are expanding with the rate of 2.62% while agricultural land has decreased with the rate of -1.89% per year and are more converted to built-up area. Trendofsinuosityindexfoundincreasing and varying in different sections of the river path indicated the complex response of changing characteristics of river flow, river mining and geomorphology of landscape. Based on research findings and descriptions from earlier works, river morphology is affected by both natural (topography, climate, precipitation), and anthropogenic (rapid urbanization, foreign labor migration, abandonment of cultivable land, community forest programs, development activities) factors.
 
 

Morphometric analysis using geographical information system techniques in serpeng and sumurup watersheds

Serpeng and Sumurup are allogeneic rivers in Wonosari’s basin, which derive water to Gunungsewu karst drainage system. The river flow characteristics of their allogeneic system are influenced by the watershed and weather conditions of the area. In addition, quantitative morphometry plays an important role in hydrological processes with remote sensing and geospatial techniques used to carry out a morphometric analysis. SRTM (DEM) was an efficient tool for extracting morphometric parameters. The watershed of the Sumurup river was much wider, and covers a total area of 42.80 km2, with a length of the main river being 21.44 km, while the Serpeng watershed covers an area of 10.58 km2 and length of the main river has 8.85 km. However, morphometry of the drainage density of both of them was classified on a medium category which indicates the basin is moderate permeability and has susceptible to flooding and erosion process. The highest order of Sumurup river has 4th level stream orders with has an elongated shape and Serpeng has 3rd level stream orders with an oval shape. Comparative analysis of watershed in the allogenic system could represent the geomorphological expression on the spatiotemporal variation of hydrology behavior of both rivers.

Variation characteristics of high flows and their responses to climate change in permafrost regions on the Qinghai-Tibet Plateau, China

River flow characteristics in permafrost regions on the Qinghai-Tibet Plateau (QTP) have changed rapidly with the intensification of global warming. However, the specific change characteristics and their responses to changes in influencing factors remain unclear. Based on the multi-year flow data of several typical basins in the QTP permafrost regions, combined with the flow duration curve and percentile flow, this study analyzed the variability of annual peak discharge, Q5, Q10, and Q30 (5%, 10%, and 30% percentile flows in the flow duration curve, respectively) and their response relationships with different climate change factors. In addition, the corresponding relationships between different percentile high flows and annual hydrographs were analyzed. The results indicate that, in the context of global warming, changes in the high flows in permafrost regions are bidirectional, either rising or falling, or both. Moreover, the responses of different percentile high flows to climate change are seasonally distinct. Spring high flows are more sensitive to changes in air temperature and normalized difference vegetation index (NDVI), and summer and autumn high flows are more susceptible to corresponding changes in seasonal average precipitation and rainfall intensity. In addition, different percentile high flows can be used to predetermine the level of annual flood events. Among them, the largest, the larger, and all other general flood events during the annual flood season, can be defined by Q5, Q10, and Q30, respectively. The analysis of different high flows combined with the flow duration curve is essential for the further clarification of the hydrological processes in permafrost regions. The prudent utilization of water resources benefits the sustainable development of human society.

Fish habitat restoration on the basis of water morphology simulation.

The hydrodynamic conditions of rivers affect fish habitats by influencing parameters such as river bottom topography. Ecological restoration projects change the water morphological characteristics of rivers. Here, water flow characteristics of the upper Yangtze River before and after the construction of a restoration project were analyzed using the computational fluid dynamics simulation method. The longitudinal diversion dam could divide the river into two flow velocity zones, and the outer flow is similar to the original river with a flow velocity of 0.75 m/s. However, flow velocity on the inner side of the river was about 0.25 m/s, forming a larger buffer area. The eddy became more diversified and stable, with a high eddy viscosity coefficient and less fluctuations, at 9 Pa·s; this was conducive to fish aggregation and spawning. At different depths, large gradient differences were observed between the inner and outer sides of the longitudinal diversion dam, and the turbulent current and upward flow of the inner side were obvious; this was more favorable to the aggregation of different fish species. The longitudinal dam body was under a pressure of about 200.2 Pa at the same flow rate; this was significantly lower than the pressure on the transverse dam body. The field flow test and fish survey data showed that the error rate of the simulation using the RNG turbulent model was less than 10% compared with actual mapping. After the restoration of fish habitats by the longitudinal diversion dam, the number of fish species in the area increased from 40 to 49; The density of fish in the water increased from 71.40 fish per 1,000 m2 before the project to 315.70 fish per 1,000 m2 after the project. These results can provide a reference for the rapid assessment of water morphology and fish habitat restoration in the future.

Peculiarities of numerical simulation of river flows in analyzing the consequences of ship accidents

The consequence of accidents with ships may be the ingress of cargo and fuel into the riverbed. To predict the consequences of such accidents in some cases (the presence of specially protected areas, the proximity of water intake facilities, etc.), it is necessary to take into account the hydromorphological features of the riverbed. One of the stages of such accounting is numerical modeling of river flow. In this paper, the authors analyzed the features of such modeling. For this purpose, a research scheme was drawn up, a mathematical apparatus was selected, a river section was selected, on the example of which the authors studied the features of the modeling process. In addition, based on a comparison of different approaches to modeling the turbulence process, it is concluded that it is preferable for sites with the presence of backwater tanks, stagnant zones and breakaway flows to model not the dissipation of turbulent energy, but the specific kinetic energy of turbulence. It reproduces the flow structure more correctly, speeds up the calculation process and gives better convergence of solutions. The results obtained in this work can be used to analyze the influence of river flow characteristics on the spread of pollution in ship accidents.

Analysis of seasonal and spatial variability of river flow characteristics in Slovenia

The fluctuations between minimum, mean, and high flows in Slovenia are significant, and in recent decades the influence of climate variability is also evident. Due to the lack of precipitation and its uneven temporal and spatial distribution, drought is a growing problem in Slovenia, while on the other hand, the number of extreme flood events is increasing. In the study, the regional diversity and seasonality of characteristic flows, namely mean low (sQnp), mean (sQs), and peak flows (vQvk) from 50 gauging stations are analyzed for the period 1960–2018, applying both an annual and monthly time scale. The ratios between the characteristic flows are calculated, and the results are evaluated both temporally and spatially. The range of values of the ratio vQvk/sQnp varies from about 20 to 1000, while the range of values of the ratio sQs/sQnp is between 2 and 20. Hierarchical clustering of gauging stations for mean low (sQnp) and mean flows (sQs) gave similar results, i.e. gauging stations were clustered into five equal groups in both cases. In the case of hierarchical clustering of gauging stations according to the values of peak flows (vQvk), four groups were formed. However, we can conclude that individual groups are difficult to define spatially in all cases.

Impact of Hydrologic Alteration on Brazos River Pelagophilic Minnows

AbstractThe lower Brazos River has been profoundly altered since the construction of multiple impoundments. The resulting river regulation poses problems for organisms adapted to a natural flow regime and is thought to play a major role in the imperilment of seven native minnows (Smalleye Shiner Notropis buccula, Sharpnose Shiner N. oxyrhynchus, Shoal Chub Macrhybopsis hyostoma, Plains Minnow Hybognathus placitus, Ghost Shiner N. buchanani, Silverband Shiner N. shumardi, and Chub Shiner N. potteri) that synchronize spawning during high flow pulses. Four of the species are presumably extirpated from the region, but their declines and losses differed across time. To address potential reasons for species' declines, we assessed pre‐ and postimpoundment changes in flow regime from five gauging stations across the lower Brazos River to identify river flow characteristics that depart from the natural preimpoundment flow regime. For the seven minnows, there was a strong relationship between the year they were last documented and their historical percentage occurrence in the lower river. Differences in flow duration curves and flow behavior were generally consistent with position in the drainage such that the greatest changes occurred in the highly fragmented upper reach of the study area. However, extensive hydrologic alteration was apparent at all five localities. The extirpated species in the lower Brazos River may have been more sensitive to altered flow regimes and accompanying geomorphic change or were population sinks dependent on recolonization or drift from upstream populations. The relationships between pelagic‐broadcast‐spawning minnows and the flow regime are complex, and nonflow variables, such as population fragmentation, thermal regimes, geomorphology, and larval habitat dynamics, should be considered in environmental flow assessments to aid our understanding of biodiversity loss in this group of species across the North American plains. Managing flows to support species that depend on natural flow regimes will require not only a better understanding of their reproductive life histories, but also the ecology and physiology of early life history stages.

Numerical simulations of turbulent and flow characteristics of complex river reach in Pakistan

The study included the numerical simulation of a curved open channel flow of Chashma Barrage for different velocities along left & right river banks, and water depths downstream of the river reach. The physical model was constructed in one of the experimental trays at the Irrigation Research Institute. Different trials were carried out at low, medium, and high discharges after the calibration of the physical model. A 2D computational fluid dynamics ANSYS FLUENT software was used to simulate various turbulences and flow properties for various discharges (500,000, 800,000, and 957,289 cusecs) using two different turbulent models: k-epsilon and Reynolds’s stress. The simulation findings were compared to the physical modeling results in terms of velocities and water depths for verification. In both velocity (18−27%) and water depth (18−36%) measurements, the k-model had a lower average percentage error than the RS model. On verification using physical modeling, the total average percentage difference from the k-model for all discharges was less than 25%. Numerical simulations based on computational fluid dynamics can be used to better understand turbulence and flow parameters, as well as to assess and develop barrage engineering.