Hydraulic Habitat Research Articles

Hydraulic Microhabitats at a Regulated River Confluence Influence Chinook Salmon Migratory Routing During Drought

ABSTRACTSuccessful upstream adult migration of Pacific salmon (Oncorhynchus spp.) from estuary to spawning grounds is critical to population recovery, especially during increasingly extreme droughts that degrade migratory habitat. In regulated systems, river confluences can pose significant navigation impediments given complex operational flow release criteria and other cumulative effects. Differing discharge magnitudes and ratios between tributaries may cause divergent confluence hydraulics and hydraulic microhabitat selectivity, influencing migratory routing. This study asks with respect to confluences: (1) Do magnitudes of discharge in each confluence tributary (and resulting combined discharge) influence availability of preferred hydraulic microhabitats in one river versus the other? (2) Does the ratio of discharge magnitudes influence availability of preferred hydraulic microhabitats in one river versus the other? We used data collected from California Central Valley fall‐run Chinook salmon (Oncorhynchus tshawytscha) at the confluence of the Feather and Yuba Rivers as a model system to investigate. We combined observations of migratory behavioural responses to hydraulic microhabitats from dual‐frequency identification sonars, spatially explicit, meter‐resolution hydrodynamic modelling, and machine learning to generate a hydraulic microhabitat selectivity index and simulate upstream migratory pathways for nine pertinent discharge scenarios with four discharge ratios. Statistically significant (p < 0.01) differences in preferred hydraulic habitat were found among both discharge scenarios and ratios, with the Feather River selected in five out of nine scenarios. Discharge magnitude and ratio act as controls on distribution of preferred hydraulic microhabitats, and under certain conditions relevant to drought operations in this system, they can influence migratory routing and propensity of straying.

Assessment of climate change effect on environmental flows for macroinvertebrates using an integrated hydrological-hydraulic-habitat modelling

Study regionA short reach of the Jeziorka river and its upstream catchment in central Poland Study focusClimate change is expected to have significant impacts on freshwater ecosystems, particularly on temperate region streams resulting often in changes to spatiotemporal distribution of macroinvertebrate species, as well as losses in richness and aquatic biodiversity due to the loss of suitable habitat. This study aimed to evaluate the impact of climate change on the habitat suitability and environmental flow violations for the filter feeder functional group of macroinvertebrate communities in a temperate lowland river in central Poland. To achieve this, we have successfully integrated hydrological (SWAT+), hydraulic (HEC-RAS 1D and SRH-2D), and habitat (CASiMiR) models. We have forced the model cascade with GCM/RCM projections to determine changes in future habitat conditions for a selected reach of the Jeziorka river. New hydrological insights for the regionFuture habitat conditions may deteriorate, as reflected in overwhelmingly negative trends in the hydraulic habitat suitability (HHS) index. According to the projections, there will be fewer days with the necessary environmental flows for filter feeders in the future. The frequency and duration of environmental flow violations, caused by too low or too high flows, depend on the climate model scenarios and timeframes. Our findings will aid water resource planners in achieving sustainable water resource management and meeting environmental flow requirements in the face of a changing climate.

Distribution characteristics of hydraulic habitat indicators for fish in typical compound channels in the upper reaches of the Yangtze River

Compound channels consisting of obvious riverbank beaches and deep grooves are widely found in the upper reaches of the Yangtze River, and the special and complex flow structure of compound channels has an important impact on fish habitats. Currently, there are insufficient studies on how the flow characteristics of compound channels affect the suitability of spawning habitats for fish. In this study, two different spawning types of fishes, namely, the Four major Chinese carps and the Schizothorax prenanti, were taken as representatives, and two different hydrodynamic effects, namely, the characteristic flow and the typical flow pulse process, were considered. Using the 3D hydrodynamic model and physical habitat suitability model, we investigated the spatio-temporal distribution characteristics of the habitat suitability indicator for representative fishes in a compound channel, and analyzed the impact of hydraulic characteristics of the compound channel on the suitability of spawning habitats for representative fish species. The results show that the suitable areas for spawning and habitat of the Four major Chinese carps are concentrated in the middle and upper layers of the flow field, with the distribution characteristics of locating in deep grooves under low flow and locating in riverbank beaches under high flow; the spawning and habitat suitability area for the Schizothorax prenanti is located mainly in the near-bottom flow field of the riverbank beach of the compound channel, and with the increase of the flow, the size of the suitable area in the riverbank beach decreases and migrates to the bank gradually. Under the effect of a high-flow pulse process in a certain flow interval, the ideal weighted usable area (IWUA) of habitat suitability indicator greater than 0.8 (HSI ≥ 0.8) for the Four major Chinese carps and Schizothorax prenanti will increase with the increase of flow, and the connectivity of ideal habitat patches will also be enhanced. The results of this study are of great significance for the conservation of river fish resources and ecological engineering construction, etc.

Eco-friendly dredging methods of changing fluvial landforms for enhancing hydraulic habitat quality and river corridor continuum

Hydraulic habitat connectivity, including the longitudinal continuum respect and lateral flood pulse, is critical for fish survival and organism dispersal. Inappropriate and excessive dredging for prevent flooding may harm river ecosystems. The main objective of this study is to evaluate whether eco-friendly dredging presented by changing local river landforms incorporating the concept of nature-based solutions could grow fish habitat quality for improving river continuity and achieving flood control effects. By combining various mathematical models and empirical formulas and verifying them with the data obtained through field surveys, we explore the interconnections of hydrology, river morphology, and the habitat dynamics of four endemic fishes in an alluvial river. The relationship between habitat structure, flood risk, and river topography, flow discharge was presented as the reference for developing the proper river dredging approaches. The results reveal that the primary habitat defects were lack of high-quality habitat, unsatisfied habitat diversity, deficiency in refugia, and disconnectivity. Longitudinal disconnectivity was induced due to shallow water depth, while lateral disconnectivity is primarily caused by fast flow velocity, suggesting different and specific dredging methods were instructed. We recommend that the corresponding eco-friendly dredging schemes for longitudinal and lateral suitable habitat linkages increase fish habitat quality and river corridor continuity. The win-win strategy for enhancing the connection between suitable habitats sustains a more beneficial aquatic corridor and simultaneously achieves alluvial flood disaster risk reduction.

Habitat persistency analysis with HEM‐PEAK: A novel approach for the assessment of hydropeaking impacts and mitigation measure design

AbstractHydropeaking is one of the most severe pressures of hydropower on aquatic ecosystems. The discharge fluctuations due to turbine operations cause frequent shifts in hydraulic habitat characteristics such as flow velocity and water depth. Those rapid changes on a daily or sub daily basis, however, are beyond the possibilities of evolutionary adaptations of aquatic organisms, especially for fish in their sensitive early life stages. Thus, one central aim in terms of the evaluation of hydropeaking impacts or the design of mitigation measures is the analysis or establishment of hydraulically stable habitat conditions. This study presents a novel habitat assessment tool to quantify hydraulically stable habitat conditions in the form of a persistency of suitable habitats in hydropeaking reaches. The HEM‐PEAK tool determines areas that contain equal ranges of depth‐averaged flow velocity and water depth for both base flow and peak flow in three categories. Those areas also exclude dewatering sites, which have to be seen as ‘residual risk for stranding’. In the present study, the model was used to evaluate the YOY habitats of brown trout and grayling. The model was tested for 14 hydropeaking reaches to evaluate the quantity of habitat persistency for different morphological characteristics, such as straight, winding, alternating gravel bars and bifurcation reaches. The findings reveal that there is no relationship between hydraulically stable habitat conditions with reach scale bed slope or the magnitude of dewatering areas. However, the changes in specific discharge in relation to bankfull width could be negatively related to the magnitude of hydraulically stable habitat conditions independent of the morphological type. This relationship is minor for summer scenarios compared to spring, as the initial habitat quality during the increased base flow conditions is already limiting the availability of suitable habitats which might have persistency during peak flow. In detail, several self‐forming bars like point bars and artificial structures like groins and coarse rip‐rap could be determined, which could be explicitly addressed in terms of mitigation measure design based on the application of the HEM‐PEAK tool.

Hydrodynamic modelling to assess habitat suitability of the Ganga River dolphins

AbstractThe Ganga River hosts a metapopulation of endangered aquatic species. This study uses a hydrodynamic model (HEC‐RAS) to assess the habitat suitability of the Ganga River dolphins (GRDs) in a small reach (7.5 km) of the Ganga River at the upstream of Narora barrage in varying flow. We use Lidar points clouds to generate topography, Acoustic Doppler Current Profiler (ADCP), and differential GPS (DGPS) to measure channel bathymetry and streamwise water surface slope. Further, the water level data from satellite altimeter is used to calibrate the model and discharge measured in field to validate the model output. We found that in the high flow period, the required flow depth for dolphin habitat is available throughout in the study reach. However, in the lean flow, the required flow depth and velocity are available only in some patches. The methodology developed here would be very useful in monitoring hydraulic habitat suitability of aquatic species in ungauged rivers.

Ecological Flow Analysis through an Ecohydraulic-Based Catchment Scale Approach

Ecological flow regime analysis through developing a novel ecohydraulic optimization method is the objective of this study in which three components are linked. Hydrological analysis is the first component in which average monthly flow is assessed in different hydrological conditions by applying a drought index in the selected control points or representative reaches in the river basin. Another component is the ecological model in which field ecological studies are used for selecting the target species, and habitat loss was modelled through the fuzzy method. The outputs of the hydrological analysis and hydraulic habitat simulation were then applied in the structure of the optimization model in which minimizing ecological impacts and water supply loss were defined as the purposes. Different evolutionary algorithms were used in the optimization process. A decision-making system was utilized to finalize ecological flow by selecting the privileged algorithm. According to the outputs, the proposed method can mitigate ecological impacts and water supply losses simultaneously. Either particle swarm optimization or differential evolution algorithm is the best approach for ecological flow in this research work. The outputs of optimization indicated that the reliability of the water supply in dry years is less than 32%, while it is more than 80% in wet years, which means that changing the hydrological condition will increase the portion of ecological flow regime significantly. In other words, the reliability of the water supply can be reduced by more than 50%. Hence, using other water resources such as groundwater is necessary in dry years in the study area.

Intraspecific and Interspecific Variations in Habitat Usage by Hemimyzon formosanus and Sinogastromyzon nantaiensis in Riffle Areas of a Mountain Stream

In this study, we explored the structure of two migratory fish species and their variations along the longitudinal gradient of a stream by examining abiotic factors such as spatial scale elements and environmental factors, and biotic factors such as competition. The studied fish species, i.e., Hemimyzon formosanus and Sinogastromyzon nantaiensis, were sampled from the middle and upper reaches of the Nanzihsian Stream using the electrofishing technique, and data were collected on the physical environment covered by the electric grid. Statistical analyses confirmed that the interspecific and the intraspecific hydraulic habitat environments of the two species were different, i.e., H. formosanus was distributed relatively upstream and S. nantaiensis was distributed relatively downstream. Therefore, the habitat use of the two benthic fish species was different. The Nanzihsian Stream experienced an extreme flood event in 2009. The densities of adult and juvenile H. formosanus and S. nantaiensis are significantly higher than those before the extreme flood event in 2021, so we suggest that the H. formosanus and S. nantaiensis populations have recovered to those of the stages before the extreme flood event. We provide an integrated approach for applying engineering and biology to the context of future projects involving river dredging after extreme floods.

Development of an integrated modelling framework to evaluate impacts of pressures on habitat conditions and riverine biota

AbstractIt is becoming extremely challenging to protect the structural and functional integrity of freshwater ecosystems, as many ecological systems face pressures from climate change, population growth and other environmental impacts. However, existing approaches of assessing impacts of external stressors to habitat conditions often neglect the long‐term hydrological changes. This study aimed to develop an integrated modelling framework to assess impacts of different stressors on reach‐scale habitat conditions for benthic macroinvertebrates in a temperate lowland river in central Poland. We coupled hydrological (SWAT+), hydraulic (HEC‐RAS 1D and SRH‐2D) and habitat (CASiMiR) models to predict the response of habitat suitability for the functional group of filter feeders to changes in the catchment for a 135‐m section of the Jeziorka river. Setting up and calibrating individual models required extensive field data collection (e.g., bathymetry field surveys, gauging water levels, discharge and flow velocity measurements and biological sampling). The performance of individual models in simulating discharge, water levels and depth/flow velocity was assessed as satisfactory according to literature. The modelling chain was then applied to compare the effects of three flow scenarios (average, low and high flows). The results showed an overall high value of hydraulic habitat suitability index for filter feeders, with moderately and severely lower values for low and high flow scenario, respectively. The implemented modelling framework performed well could be applied to examine the impacts of climate change and other anthropogenic stressors on reach‐scale habitat conditions. Its practical implementation could be beneficial towards sustainable water resources and environmental flow regime development.

Environmental flow assessment for benthic macroinvertebrate communities using pseudo‐2D hydraulic habitat modelling at a green small hydropower plant

AbstractThe determination of minimum flow requirements for green small hydropower plants (GSHP) in China primarily relies on hydrological methods such as the Tennant method with no seasonal variation. However, the direct application of hydrological methods without local ecological data for calibration lacks ecological validity, potentially resulting in unsuitable minimum flow recommendations for local aquatic biota. Hydraulic‐habitat modelling (HHM) is assumed to provide more ecologically relevant and reliable environmental flow recommendations (EFRs), but benthic macroinvertebrates (BMs), crucial in the aquatic food web, have rarely been the focus in HHM studies. Moreover, the strong subjectivity in HHM processes hinders the comparison of EFRs across different biota and geographical regions. This study aims to investigate the ecological validity of using the Tennant method to set minimum flow requirements for local BM communities and the impacts of various methods used in HHM on derived EFRs. To achieve this, a pseudo‐2D HHM approach is employed, integrating the 1D hydraulic models HEC‐RAS and CASiMiR with the habitat model HABFUZZ. The EFRs downstream of Jiufeng reservoir, one of China's first GSHPs, are derived for wet (April–June) and dry seasons (July–September). Our findings highlight that setting minimum flow alone is inadequate for preserving BM community integrity downstream of GSHPs. It is crucial to incorporate more diverse environmental flow criteria, including minimum flows and peak flows, into GSHP assessment standards, with recommended flow levels varying across different seasons. Additionally, the development of a standardized HHM methodology is essential to mitigate the inherent subjectivity in HHM and facilitate the comparison of EFRs generated from different studies. This study's innovative modelling framework and findings will enhance the optimization of minimum flow assessment criteria for GSHP in China, deepen understanding of seasonal e‐flow requirements of BM communities, and refine the methodology used in BM HHM for e‐flow recommendation.

Modelling macroinvertebrate hydraulic preferences in alpine streams

AbstractAlpine streams face rapid hydrological changes due to the effects of global warming, glacier melting, and increased water uses such as hydropower production. Defining environmental flows (e‐flow) is crucial to mitigate the ecological impacts of flow alterations. Among e‐flow assessment methods, hydraulic habitat models predict changes in habitat suitability for aquatic species under different flow scenarios. They couple hydraulic models of stream reaches with biological models relating the abundance of taxa to microhabitat hydraulics. However, there is currently no suitable biological models for alpine, often fishless streams. In this study, we develop biological models for dominant macroinvertebrate taxa in alpine streams and compare their responses to hydraulics with those published in lowland streams. Using data collected in 150 microhabitats along a gradient of shear stress within five alpine streams, we performed generalized linear mixed models relating macroinvertebrate abundance to microhabitat hydraulics (shear stress, flow velocity, Froude number and water depth). We developed biological models for 41 taxa, and observed significant microhabitat selection for shear stress (18 taxa), velocity (20), Froude number (21), and depth (11). Most of them presented consistent responses across studied alpine streams, with shear stress and velocity as the main drivers. For common taxa, shapes of macroinvertebrate responses to hydraulics were comparable with those observed in lowland streams. Nevertheless, taxa preferred slightly lower shear stress in alpine streams compared to lowland streams, probably due to high‐fine sediment and oxygen concentrations, especially for taxa feeding on autochthonous organic matter. Many (23%) abundant taxa are rheophilic in alpine streams, thereby threatened by flow reduction, including the glacial stream specialists Diamesinae and Rhithrogena delphinensis, which will be also affected by glacier retreat. Combined with hydraulic models, our biological models will facilitate more robust e‐flow assessments, thereby reducing the impacts of flow alterations on alpine aquatic ecosystems.

Developing environmental flow targets for benthic macroinvertebrates in large rivers using hydraulic habitat associations and taxa thresholds

Holistic environmental flows frameworks are built on our understanding of key flow-ecology relationships that support sensitive taxa and critical ecosystem functions under different flow and water level scenarios. Most research on flow-ecology relationships has typically focused on small systems, with less known about flow associations, indicator taxa, and environmental thresholds of assemblage change along hydraulic gradients of large non-wadeable rivers. We assessed benthic macroinvertebrate assemblage structure and applied Taxa Indicator Threshold ANalysis (TITAN) on biomonitoring data collected during a six-year period in the Wolastoq | Saint John River in Atlantic Canada. Flow velocity was strongly associated with the distribution and relative abundance of benthic macroinvertebrates in the river, and taxon associations reflected functional adaptations to flow. We identified 33 genus-level indicator taxa that were either positively or negatively associated with flow velocity. Weaker taxa responses were shown for the gradient in median substrate particle size where 22 negatively and positively responding taxa were identified. We predicted changes in indicator taxon abundance under different flow scenarios using a hydrodynamic model, and characterised the distribution and availability of suitable hydraulic habitat patches within a 20 km reach downstream of a large hydropower generating station. These observations set the stage for the development of ecologically-based flow targets to support holistic environmental flow management in large rivers.

Catchment‐scale applications of hydraulic habitat models: Climate change effects on fish

AbstractApproaches available for estimating the ecological impacts of climate change on aquatic communities in river networks range from detailed mechanistic models applicable locally to correlative approaches applicable globally. Among them, hydraulic habitat models (HABMs) link hydraulic models of streams with biological models that reflect how organisms select microhabitat hydraulics. Coarser but more general species distribution models (SDMs) predict changes in geographic distributions; they generally involve coarse predictors such as air temperature or distance to source but neglect proximate habitat descriptors such as microhabitat hydraulics. We propose an original application of HABM for predicting the ecological impacts of climate change at large scales, a comparison of their predictions with those of SDM and a linkage of the two modelling approaches. We showcase our approach in a large catchment (Rhône River) where an available distributed hydrological model estimates present and future unregulated daily flows over the whole river network. Despite large local uncertainties, simulations showed that climate change may strongly reduce low flow percentiles (e.g., a median reduction of 38.6% for a pessimistic climate scenario), inducing important alteration of fish hydraulic habitat suitability (e.g., a median loss of 3.9%–18.7% for three modelled fish species with contrasting habitat use: brown trout, barbel and sculpin). The HABM and SDM individually predicted consistent or opposite fish responses to climate change, depending on the species and their habitat requirements. Our results illustrate that accounting for ecological responses to proximate habitat variables such as hydraulics can strongly modify projections related to climate change.

Evaluation of water temperature under changing climate and its effect on river habitat in a regulated Alpine catchment

Habitat quality of alpine river is largely affected by human activity. The exploitation for hydropower, combined with anthropogenic climate change, canalter mountain riverine ecosystems, leading to less suitable hydro-thermal regimes for the fish. Here, we present a new methodology to assess water temperature within a river featuring water exploitation for hydropower purposes, usable to assess future potential deterioration of riverine habit suitability in response to (increasing) water temperature. We then propose an application focusing upon the case study of the Serio River, in Northern Italy, largely exploited by hydropower productions and highly populated by a very sensitive species, brown trout (Salmo trutta). The methodology proposed involves a set of tools, i.e. i) the hydrological modelPoli-Hydro, to evaluate natural hydrological regime, ii) a hydropower plants scheme to assess river water withdrawal, iii) fish density-environment curves to evaluate the hydraulic suitability in terms of trout potential density for adult, young, and fry as a function of hydraulic features, i.e. depth and velocity, and iv) a new, physically based model,Poli-Wat.Temp, to assess changes in river water temperature, and possible outbreaks of temperature dependant lethal conditions, such as proliferative kidney disease, and others. To provide an assessment of river suitability, possibly complementing (improving?) models based upon solely hydraulic indexes, we propose a new synthetic River Stress index, combining i) potential fish density as driven by hydraulic variables, and ii) thermal suitability. Given that utmost unsuitable conditions (thermally, and likely hydrologically) are expected under future climate conditions pending global warming, we then projected water temperature, and stream flows until the end of the century, in response to socio-economic scenariosof AR6 of the IPCC, to explore the potential for future decrease of river quality. Water temperature would be largely susceptible to climate change with increase up to + 6.5C° in the worst scenarios, while no clear trend is observed for fish density. Overall, potential density would decrease in winter for adults, and in summer for juvenile and fry in downstream sections. Therefore, by coupling hydraulic, and thermal suitability, one finds that i) Alpine rivers would likely face longer critical periods, with respect to those predicted based upon a solely hydraulic habitat based assessment, and ii) continuous temperature increase as projected until the end of the century would result into worse conditions in summer months, seriously endangering fish guilds.

Integrating satellite altimeter data and geomorphic in‐stream flow tool to assess reach average hydraulic habitat of the Ganga River dolphin

AbstractThe Ganga River ecosystem is under severe anthropogenic stress. Flow regulations through structural barriers alter the geomorphic and hydraulic geometry of riverine habitats. Determining the ecological health of river habitats under the contemporary modification is detrimental to its restoration and management. This study evaluates reach averaged hydraulic habitat of the endangered Ganga River dolphin (Platanista gangetica) in a stretch between Bijnor and Narora barrages. We consider an optimal minimum flow depth as the determining factor of habitat suitability. Field measurement of the hydraulic geometry and flow characteristics show that the optimal flow depth is available in the study reach during the monsoon period, while in the pre‐monsoon, the minimum depth is present only in the reach upstream to Narora barrage. We use a geomorphic instream flow tool (GIFT) and satellite altimeter water level data to simulate reach averaged hydraulic habitat in varying flow conditions in area upstream of Narora barrage. We observe that to maintain the minimum flow depth which supports the dolphin habitat in the study reach, an optimal discharge of about is essential. Furthermore, we develop a water‐level (altimeter) and discharge (simulated from GIFT) rating curve for the study reach. It can be used to get a first‐order estimate of discharge for a given water level or vice versa. This study indicates that the altimetry datasets are good precursors for estimating averaged hydraulic habitat of rivers in the data‐scarce regions. The application of altimeter data can be a boon in the effective management of river habitat health over a reach scale.

Turbulence signatures of natural river morphology in four dimensions

AbstractTurbulent flow in natural river channels drives geophysical processes and exerts a fundamental influence on aquatic biota. An extensive range of turbulence properties have previously been synthesized into four categories or “dimensions” with ecological relevance: intensity, periodicity, orientation and scale (IPOS). We apply this framework across three rivers with differing morphologies in order to assess the statistical coherence of the four IPOS categories within turbulence field data and their utility in discriminating between fundamental units of river habitat. Intensity, periodicity‐scale and orientation were identified as the key gradients in the turbulence data set using multivariate analysis. These gradients all revealed statistically significant differences between rivers and/or geomorphic units. The intensity gradient accounted for the highest variance and most pronounced inter‐reach differences, but the periodicity‐scale and orientation gradients were also useful in distinguishing between certain combinations of rivers and/or geomorphic units. Different turbulence gradients, or combinations of gradients, were important in characterizing differences between rivers and geomorphic units (riffes, pools, steps). The gradients provided improved prediction of geomorphic units compared to standard hydraulic variables (mean velocity, depth), although the extent of improvement in prediction varied between river morphologies. The analysis reveals the statistical coherence of the four categories or “dimensions” of turbulence in multivariate space, connects the ecologically defined IPOS categories of turbulence properties with river types and fundamental units of river habitat (geomorphic units). Turbulence signatures of natural channel morphology are expressed across all four dimensions of turbulence, providing clear evidence that these four dimensions should be routinely considered in ecohydraulics and hydromorphology research to facilitate a full understanding hydraulic habitat.

Suitability Assessment of Fish Habitat in a Data-Scarce River

Assessing fish habitat suitability in a data-scarce tidal river is often challenging due to the absence of continuous water quantity and quality records. This study is comprised of an intensive field study on a 42 km reach which recorded bathymetry and physical water quality parameters (pH, electroconductivity, dissolved oxygen, and total dissolved solids) testing and corresponding water levels and velocity. Frequent water sampling was carried out on 17 out of 90 locations for laboratory water quality tests. Based on this, an interpolation technique, i.e., Inverse Distance Weighted (IDW), generates a map in a Geographic Information System (GIS) environment using ArcGIS software to determine the river water quality parameters. Additionally, a hydrodynamic model study was conducted to simulate hydraulic parameters using Delft3D software followed by a water quality distribution. During validation, the Delft3D-simulated water quality could reasonably mimic most field data, and GIS featured dissolved oxygen. The overall water quality distribution showed a lower dissolved oxygen level (~3 mg/L) in the industrial zone compared to the other two zones during the study period. On the other hand, these validated hydraulic properties were applied in the Physical Habitat Simulation Model (PHABSIM) set up to conduct the hydraulic habitat suitability for Labeo rohita (Rohu fish). Thus, the validated model could represent the details of habitat suitability in the studied river for future decision support systems, and this study envisaged applying it to other similar rivers.

Impact of the construction of a dam and spur dikes on the hydraulic habitat of Megalobrama terminalis spawning sites: A case study in the Beijiang River (China)

• A 2D hydrodynamic model was coupled with habitat suitability curves to simulate the hydraulic habitat of Megalobrama terminalis spawning sites. • The usable habitat area decreased by 35.5%, and the habitat quality and diversity decreased because of the barrage. • The usable habitat area increased by 13.9%, and the habitat quality and diversity increased because of the spur dikes. • The barrage and spur dikes together resulted more improvement for the hydraulic habitat than the spur dikes alone. Water conservancy projects may result in considerable economic and social benefits, though there is widespread concern about how their impact on aquatic ecosystems. However, there is no study about the combined effects of typical hydraulic structures (a dam and numerous spur dikes) on hydraulic habitat conditions. This is why the impacts of the construction of a dam and spur dikes in a reach of the Beijiang River between the Feilaixia and the Qingyuan on fish hydraulic habitat conditions are assessed. A habitat suitability model was established by coupling a two-dimensional (2-D) hydrodynamic model with habitat suitability curves. The coupled model then was used to simulate the spawning sites of Megalobrama terminalis ( M. terminalis ), calculate the usable habitat area (UHA), identify the spatial distribution of suitable spawning ground in the river reach, and analyze the habitat quality and hydraulic habitat diversity. The results show that the dam alone would negatively impact fish habitat, and cause the UHA to decrease by 35.5 % on average. The high-quality habitat area and the hydraulic habitat diversity decreased because of the dam. The spur dikes had positive effects and increased the UHA by 13.9 % on average. In addition, spur dikes increased the high-quality habitat area and enhanced the hydraulic habitat diversity. The lateral discontinuity resulting from spur dikes (the rate of UHA change, RC = 13.9 %) had less impact on the fish hydraulic habitat than the longitudinal discontinuity impact resulting from the dam construction (RC = − 35.5 %). The spur dikes and a dam (RC = 21.94 %) resulted in a more significant improvement effect on the habitat conditions than the spur dikes without a dam (RC = 5.84 %). The dam and spur dikes in combination resulted in better outcomes regarding hydraulic habitat conditions than spur dikes alone, and the spur dikes reduce the ecological stress caused by the dam. The insight from this study can serve as a reference for engineers and scientists who are considering similar river regulation and ecological restoration initiatives aimed at a steady flow pattern that are advantageous for a specific fish species and lifestage.

A study of the hydraulic parameters and ecological significance of braided rivers under flow variations

AbstractOne‐dimensional numerical simulations based on the actual braided‐channel geometry in the middle reaches of the Yarlung Tsangpo River can be used to calculate the characteristics of braided channels in terms of their branching conditions and hydraulic parameters. Numerical modeling in the study area showed that a higher number of branches at fish‐spawning grounds may provide more suitable habitats for local organisms to survive. During most of the year, the distributions of the flow velocity and water depth in the higher‐branching channels were significantly lower than those in the lower‐branching channels. The hydromorphological index of diversity (HMID) of higher‐branching channels was higher than that of lower‐branching channels during all water periods, which showed the higher habitat heterogeneity of higher‐branching channels. The Froude numbers of higher‐branching channels ranged from 0.1 to 0.3, and the stable flow regime partially explained why higher‐branching channels are important habitats for fish‐spawning and nurseries. The lower flow velocities and water depths in the higher‐branching channels may have met the hydraulic habitat conditions for the survival of juvenile fish. This article analyses the characteristics of the hydraulic parameters and the ecological significance of braided river channels and provides theoretical support for the protection of fish habitats in braided rivers.

Flow amplitude or up‐ramping rate? Quantifying single and combined effects on macroinvertebrate drift during hydropeaking simulations, considering sensitive traits

AbstractThe hydrological regime of many alpine rivers is heavily altered due hydroelectric power generation. Hydropeaking operation produces frequent and irregular discharge fluctuations. Depending on the operational changes of flow amplitude and/or up‐ramping rate as well as on river morphology, hydropeaking can lead to quick and strong variations in hydraulic stress affecting stream invertebrates and causing increased drift. In the present flume experimental study, we analyzed trait‐specific drift reactions to single and combined effects of increased flow amplitude and up‐ramping rate. We analyzed taxa according to their hydraulic habitat preference and flow exposure, as these traits seem to be indicative toward hydropeaking. The results show that the sudden increase in discharge and related flow velocity led to increased macroinvertebrate drift proportions in hydropeaking treatments, which differed significantly to parallel control runs (mean drift proportion in all hydropeaking setups: 13% compared to 5% in controls). Increasing flow amplitudes led to an increase in drift for most taxa and traits. This was particularly significant for taxa associated with lentic areas. The effect of the up‐ramping rate on macroinvertebrate drift was nonsignificant but showed strong interactive effects with the flow amplitude, especially for taxa dwelling on the substrate surface. Our results therefore indicate that discharge‐related parameters, such as flow velocity, primarily affect macroinvertebrate drift and the importance of the up‐ramping rate increases, if certain discharge‐related thresholds are exceeded. Vice versa, a reduction of the up‐ramping rate at hydropeaking events with high flow amplitudes may reduce the effect on macroinvertebrate drift. Flow‐exposed (surface) and flow‐sensitive (lentic) taxa showed distinct drift reactions following hydropeaking treatments, which were significantly higher compared to effects on taxa associated to lotic and interstital habitats. Therefore, we conclude that both traits (hydraulic and vertical habitat preference) have proven as promising for analyzing hydropeaking effects. The trait classifications should be extended to a higher number of taxa and to different life stages as these may show different drift patterns.