River2D Model Research Articles

Quantifying the Impact of Changes in Sinuosity on River Ecosystems

To quantitatively study the hydrodynamic changes in different river morphologies and clarify the impact of morphological changes on river ecosystems, this study examined a section of the Nansha River near Laoniuwan in the Haidian District, Beijing, and characterized different river morphologies by river sinuosity. The River 2D model was used for simulation and analysis, and the depth and velocity diversity indices were introduced to quantify the distribution of depth and velocity under different sinuosities. Cyprinus carpio was selected as the target fish in this study, and its suitability curve was determined using literature and field surveys. Combined with the simulation results, a weighted usable area curve was established to identify its inflection point and maximum value and determine the ecological flow in the river under different sinuosities, that is, to clarify the relationship between sinuosity and ecological flow. The results showed that the lower the sinuosity, the worse the depth and velocity diversity, but a greater sinuosity did not lead to better depth and velocity diversity. The depth and velocity diversity of a sinuosity of 1.5 were better than those of 1.89 in general, except for low flow conditions (Q = 5 m3/s). For rivers with water use restricted by nature and society and where ecological needs exist, ecological engineering that appropriately changes the planform of rivers can be considered to increase the diversity of river/channel geometry and provide a basis for the ecological restoration of rivers.

APPLYING 2D NUMERICAL MODEL TO CALCULATE THE SCOUR AT THE CUA DAI BRIDGE, QUANG NAM PROVINCE

Abstract: When the Cua Dai bridge is built across the Thu Bon River, it causes a narrowing of the flow leading to scour, which seriously threatens the pier and endangers the structure. In order to limit the influence of scour the bridge, it is necessary to ensure that the scour under the bridge is within the allowable range. At the same time, it is necessary to take measures to limit and overcome the causes of scour. Therefore, the study and prediction of locations that are likely to cause scour are of great significance in choosing effective and versatile prevention solutions for works on this river section. Most of the scour formulas for bridge use the 1D average velocity to calculate; The calculated results are much different from the real distribution of flow velocity in the river. Therefore, the results of scour calculation often have big deviations from reality, especially when the river cross-section has no flats or curved rivers... The article focuses on researching scour at the bridge pier based on the two-dimensional horizontal velocity in front of the pier by using RIVER 2D model, built from the mathematical model of two horizontal flows and solved by the finite element method. The results of the paper show that the scour depth of pier by the one-dimensional (1D) average velocity gives much larger than when applying the two-dimensional horizontal velocity to calculate the scour.

Response of Fish Community to Building Block Methodology Mimicking Natural Flow Regime Patterns in Nakdong River in South Korea

Water regulation and flood control of rivers are changing due to streamflow depletion following industrialization and urbanization, significantly impacting aquatic ecosystems. Therefore, restoration of the ecological environment is necessary to maintain a healthy river ecosystem. For ecosystem restoration, the amount of discharge from dams must be controlled and the appropriate environmental flow must be calculated according to the fish species. The change in the flow through the dam due to hydropeaking directly impacts the fish. This study aimed to construct a building block methodology (BBM) using dam inflows in the Gudam Bridge basin upstream of the Nakdong River, build a River2D model of this area, and calculate the natural flow regime and the weighted usable area (WUA). The analysis of the scenarios for the whole period (2006–2020) and by flow regime showed that WUA decreased in some periods, but improved overall in the scenario reflecting the BBM. For Zacco platypus, a dominant fish species of the Gudam Bridge, WUA decreased by ~11% in some periods (in September) but the habitat improvement effect measured up to 79%. Changing the dam discharge pattern by considering the flow regime seemed more effective in improving the habitat of fish living downstream.

Evaluating Attraction and Passage Efficiencies of Pool-Weir Type Fishways Based on Hydraulic Analysis

In this study, a hydraulic analysis technique is presented for evaluating the efficiency of a pool-weir type fishway. The River-2D model with the fish physical habitat module was used for the analysis of the attraction efficiency, and the weighted usable area proposed as an index of the efficiency. For the analysis of passage efficiency, the three-dimensional model, FLOW-3D, was used as an evaluating tool to describe the fluid behavior on a hydraulic structure with a free surface. The ice-harbor type fishway at Dalseong weir in the Nakdong River of Korea was selected as a test-site, and the efficiency was estimated using the hydraulic analysis. The results of River-2D analysis showed that the location of the fishway near the right bank now was not appropriate for attracting the target fish to the fishway due to the deep water depth. The 3D analysis results presented that the flow velocity field inside the fishway showed a similar plunging flow in each pool, but various flow patterns appeared locally.

Ecological Water Requirement in Upper and Middle Reaches of the Yellow River Based on Flow Components and Hydraulic Index.

Deterioration of the ecological environment in the upper and middle reaches of the Yellow River in China substantially impacts the growth and development of aquatic organisms in the drainage basin. This paper builds a conceptual model by applying flow components and fish ecological requirements relation with a relevant object of main fish in the upper and middle reaches of the Yellow River. The paper utilized the flow restoration method by employing the River2D model (two-dimensional model of river hydrodynamics and fish habitat), and a one-dimensional hydrodynamics HEC-RAS (hydrologic engineering center’s-river analysis system). The calculation result showed that the runoff condition required for Silurus lanzhouensis survival is that the monthly lowest flow in a year is 150 m3·s−1, and the lowest flow for suitable flow from April to October is 150 m3·s−1, and 300 m3·s−1 from November to March. The research result is closer to the actual condition and has more outstanding operability. Meanwhile, the results proposed the coupling method of ecological water requirement for the mainstream of the Yellow River. Moreover, the results portrayed the ecological flow process according to the upper envelope of minimum and maximum ecological water requirements of each fracture surface. It is regarded that the ecological flow process is deemed as the initial value of the reservoir regulation model.

Ecological evaluation of weir removal based on physical habitat simulations for macroinvertebrate community

In Korea, rapid urbanization has changed the land use in rural areas, which has resulted in an increase in the number of weirs that are left untended in streams. Previously, changes in stream morphology and fishes were studied following the removal of such weirs. The present study was conducted to investigate changes in the habitat of the macroinvertebrate community after weir removal using physical habitat simulations (PHSs). The functional group approach was used in the PHSs for the macroinvertebrate community. In the functional group approach, macroinvertebrates are classified based on the traits of their food acquisition (i.e., the functional feeding group) or habitat selection (i.e., the functional habit group). In the present study, macroinvertebrate species were divided into the functional habit groups (FHGs) of swimmers, clingers, burrowers, and sprawlers. Hydraulic simulations and habitat simulations were carried out using the River2D model and habitat suitability curves (HSCs), respectively. The distributions of the composite suitability index (CSI) for the FHGs were obtained over the entire study area, and the changes in the suitability of the habitat for the target FHGs were evaluated. The simulation results indicated that habitat suitability for swimmers, clingers, and sprawlers was improved. However, habitat suitability for burrowers was degraded after the weir was removed. Consequently, the removal of the weir increased the diversity of the macroinvertebrate community, thus improving the health of the aquatic ecosystem.

Change in fish community composition following weir removal, field observations, and physical habitat simulations

AbstractThe number of untended weirs has increased in Korea in recent years due to land use changes. The removal of abandoned weirs in streams has been attempted following an agreement between local government and residents. The Gongneung Weir‐2 was built for irrigation in the 1970s and was removed in 2006. The objective of this study was to investigate the impact of the removal of Gongneung Weir‐2 on the composition of the fish community. The study area was a 900‐m‐long reach in the Gongneung‐cheon River in Korea, and Gongneung Weir‐2 was located in the middle of the reach. Before weir removal, field monitoring revealed that five fish species were dominant and accounted for more than 80% of the entire fish community. The composition of the fish community changed significantly after weir removal. Lotic fish became dominant after weir removal, whereas lentic fish were dominant prior to weir removal. Physical habitat simulations (PHSs) for individual dominant fish species were carried out. For the PHS, the River2D model and the adaptive neuro‐fuzzy inference system method were used for hydraulic and habitat simulations, respectively. The distributions of the highly suitable portion for each fish species were identified before and after weir removal. The PHS successfully predicted changes in the composition of the fish community after weir removal. The PHSs for the entire fish community and for the lotic and lentic guilds were undertaken and the simulated results were compared with each other. The PHSs for the entire fish community could not account for the less dominant fish species in the fish community.

Baseflow Contribution to Streamflow and Aquatic Habitats Using Physical Habitat Simulations

A scientific understanding of the baseflow contribution to streams and watershed processes is critical when dealing with water policy and management issues. However, most previous studies involving physical habitat simulation have been performed without considering the seepage of water from the underground into streams. Motivated by this, herein, we report an investigation of the impact of baseflow using physical habitat simulations for both dominant fish and benthic macroinvertebrate. The study area was located along the reach of the Ungcheon Stream, located 16.50 km downstream and 11.75 km upstream from the Boryeong Dam in the Republic of Korea. For the physical habitat simulation, Zacco platypus and Baetis fuscatus were selected as the target fish and benthic macroinvertebrate, respectively. The HydroGeoSphere (HGS) model (Aquanty Inc., Waterloo, ON, Canada) and the River2D model (Version 0.95a, University of Alberta, Edmonton, AB, Canada) were used for hydrologic and hydraulic simulations, respectively. The Habitat Suitability Index (HSI) model was used for the habitat simulations. Three habitat variables, flow depth, velocity, and substrate, were used. To assess the impact of baseflow, this study performed a physical habitat simulation using each representative discharge, with and without considering baseflow. It was found that the baseflow effects significantly increase the habitat suitability in the study reach. To restore the aquatic habitat, a scenario for modifying dam operations through natural flow patterns is presented using the Building Block Approach (BBA). In the study, the adjusted minimum flow allocation concept was used. It was revealed that the modified dam operations significantly increased the Weighted Usable Area (WUA) by about 48% for both target species. The results indicate that modifying the dam operations through restoration to natural flow regimes but also through inclusion of the baseflow are advantageous to aquatic fish habitats.

Dominant Fish and Macroinvertebrate Response to Flow Changes of the Geum River in Korea

This study presents the impact of natural flow patterns on downstream aquatic species habitats in a reach of the Geum River, Korea. The study reach is a 13.4 km long, located downstream of the Yongdam Dam. To assess such an impact, this study performed physical habitat simulations. The River2D model was used for the computation of the flow field and morphology, and the Habitat Suitability Index (HSI) model for the habitat simulation. Three habitat variables—flow depth, velocity, and substrate were used. The Zacco platypus and Baetis fuscatus were selected as the target fish and benthic macro-invertebrate, respectively. Using the building block approach (BBA), the scenarios for modifying dam operations were constructed in the study reach. Scenario 1, scenario 2, and scenario 3 were proposed by using the magnitude–duration concept, base flow allocation concept, and seasonally adjusted minimum flow allocation concept, respectively. Simulation results indicated that the scenarios’ effects significantly increased by about 14.3% for the weighted usable area (WUA). In addition, the morphology change with the restoration of flood events was investigated. It was revealed that the morphology change in the physical habitat simulations further increased by about 13% for the WUA. The change of dam operations through natural flow patterns is more advantageous to aquatic species.

Ecohydraulic modelling of Nestos River Delta under low flow regimes

The determination of a proper minimum environmental flow in a river basin is one of the most critical components of sustainable water resources management, with hydraulic and habitat modelling being the most advance methods for that analysis. The present study illustrates the ecohydraulic modelling of Nestos River Delta at the deltaic zone of a heavily modified watershed under various low flow scenarios, using the RIVER2D Model. RIVER2D is a two-dimensional, depth averaged hydrodynamic and fish habitat model, widely used in environmental flow assessment studies. A detailed digital model of the river channel and its surrounding area was developed, including all the morphological characteristics of the river channel, as well as its various sandy islets. Field surveys in combination with Digital Elevation Model data were used for the development of the digital terrain used as input to RIVER2D model. Several different steady state hydraulic simulations were conducted under typical low flow conditions, producing water depth and water velocity (direction and magnitude) maps for each discharge scenario, while results were verified with the use of field measurements. In the next step, RIVER2D was used for the fish habitat modelling of the study area, with the application of fish preference curves developed specifically for the study area. Finally, the fish habitat modelling was conducted for four different fish species, divided into two age groups, forced under the same five typical low flow conditions. Results reveal that the ecohydraulic modelling of river basins should be considered as an indispensable component in sustainable water resources management.

Computational optimization in simulating velocities and water-surface elevations for habitat–flow functions in low-slope rivers

ABSTRACTThe impact of varying computational mesh discretization on the accuracy of simulating velocities and water-surface elevations was investigated using the River2D model and data from 10 study reaches in three low-slope (<0.2%) Canadian rivers. A wide range of computational aspects were examined, including node spacing (1.35 to 60 m), number of mesh nodes (1250 to 58,000) and domain widths (60 to 800 m). Computed values for average cross-sectional velocities and water-surface profiles were compared with corresponding field survey data. The statistical mean absolute and root-mean-square errors were used to evaluate the discrepancy between measured and simulated values due to the mesh discretization characteristics. The results showed that mesh design discretization had a pronounced effect on the precision of the velocity and water-surface elevation predictions. Although the ratio of node spacing to river reach width may be site specific, it was found that optimal values should be <0.022 to obtain the highest accuracy. Regression equations of optimal ratios of node spacing to river reach width and the corresponding minimum mesh resolution errors were estimated. An example is provided that illustrates how the choice of computational mesh properties can affect habitat characterization for fish.

Ecohydrological modeling and environmental flow regime in the Formoso River, Minas Gerais State, Brazil.

This paper aimed at determining the environmental flow regime in a 1 km stretch of the Formoso River, MG, using River2D model. To carry out the ecohydrological modeling, the following information was used: bathymetry, physical and hydraulic features, and the Habitat Suitability Index for species of the Hypostomus auroguttatus. In the River2D, the Weighted Usable Areas were determined from the average long-term streamflows with percentage from 10% to 100%. Those streamflows were simulated for the later construction of optimization matrices that maximize the habitat area throughout the year. For H. auroguttatus Juvenile, higher values of Weighted Usable Area were associated with the percentage of 60% and 70% of the average long-term streamflows in October and September, respectively. For H. auroguttatus Adult, the highest value of Weighted Usable Area was associated with the percentage of 100% of the average long-term streamflow in September. The environmental flows found for this stretch of the Formoso River varied over the year. The lowest environmental flow was observed in December (2.85 m3 s-1), while the highest was observed in May (4.13 m3 s-1). This paper shows the importance of ecohydrological studies in forming a basis for water resources management actions.

Hydropower Plant Operation Scenarios to Improve Brown Trout Habitat

In this study, different hydropower plant operation scenarios were proposed to assess the best habitat alternative for juvenile and adult brown trout (Salmo trutta). Habitat preferences were determined based on field data collection and translated into fuzzy sets and rules for both life-stages. The River2D model was applied to a 100-m long stream segment immediately downstream of the tailrace of the Ermida small hydropower plant (SHP) to obtain a 2D hydrodynamic description for different operation scenarios. Habitat modelling was performed using Casimir Fish 2D by combining flow and fuzzy rules. Overall, simulation results for the juveniles indicated its best habitat conditions for discharges between 0.5 and 1.0 m3s−1 and the adults for 5.0 m3s−1. Five main operation scenarios were developed according to the electricity pricing periods for dry, average and wet year. The decrease in energy revenue was calculated for each operation alternative. The results indicate that it was possible to reduce hydropeaking effects in brown trout habitat through changes in the hydropower plant operation especially for dry years. The methodology developed in this research should be seen as a decision-making tool to help water managers adapt hydropeaking regimes to reduce the ecological impact downstream of hydropower dams. Copyright © 2016 John Wiley & Sons, Ltd.

Evaluation of Central Valley Spring-Run Chinook Salmon Passage Through Lower Butte Creek Using Hydraulic Modelling Techniques

River2D was used to develop a hydraulic model of an upstream passage impediment for adult spring-run Chinook salmon (Oncorhynchus tshawytscha) on Butte Creek, Tehama County, California. Topographic data were collected by using a total station, survey-grade real-time kinematic global positioning system, and terrestrial light detection and ranging. Stage-discharge relationships were developed at the upstream and downstream ends of the site to use as boundary conditions and to calibrate the 2D model. A pressure transducer was installed at the downstream boundary of the site to provide a time series of flow and water temperatures. Parameters of the hydraulic model were examined to assess upstream passage including minimum thalweg depth along the least width-limiting pathway, velocity, and water surface elevation above and below a jump, and flow partitioning between a split in the main flow paths through the site. The results of the River2D model were used to identify flow levels that met the minimum depth and width thresholds needed for adult spring-run Chinook salmon (SRCS) to migrate upstream through the study reach. A minimum passage depth criterion of 0.27 m was used for adult SRCS. Site-specific passage width criteria were derived from the literature for the study site and ranged from 0.3 to 0.9 m. Model results indicated that a flow of 3.40 cms met the depth criterion and the lower bound of the width criterion. A flow level of 6.8 cms met the depth criterion and the upper bound of the width criterion. Data from the VAKI Riverwatcher fish passage counting device installed just upstream of the study site were related to the stage/passage limiting width and water temperature monitoring data. The monitoring data and results of the predictive modelling will be used by the California Department of Fish and Wildlife to recommend flow criteria that protect migrating adult SRCS. Copyright © 2016 John Wiley & Sons, Ltd.

전주천 상류부의 서식처 적합도 지수 및 생태유량 산정

In this study, WUA (Weighted Usable Area) based on the Instream Flow Incremental Methodology (IFIM) was calculated to determine ecological flow at JeonJu-Cheon by using River2D model. To calibrate River2D, simulation results for low flow conditions of River2D were compared with calibrated HEC-RAS simulation results and the optimum parameters were determined. The results were RMSE (0.18), NSE (0.71) and coefficient of determination (0.78) for velocity and RMSE (0.02), NSE (0.71), coefficient of determination (0.73) for water depth. The result shows that the model successfully simulates the water flows. A selected target fish species to build the habitat suitability index were composed of Zaccoplatypus and Coreoleuciscus splendidus. These species showed the highest occurrences over the past decade in f ish monitoring. Also, The WUA-Discharge curve was calculated with the suitability index in a medium flow conditions. From the result, WUA is changed according to flowrate. In the flowrate-WUA/A graph, ecological flow can be determined at 1.8~2.0 m/s for Zaccoplatypus 2.0 m/s and Coreoleuciscus splendidus 1.8 m/s at JeonJu-Cheon upstream. When compared with flow-duration analysis, it is demonstrative that simulation results fitted ecological flow considering quantity of available habitat for each fish species.

UNCERTAINTY IN PREDICTING THE FISH‐RESPONSE TO TWO‐DIMENSIONAL HABITAT MODELING USING FIELD DATA

ABSTRACTBoth water managers and researchers have the same goal when it comes to fish conservation, namely, to sustain, to improve or to restore aquatic habitat. To this aim, two‐dimensional (2D) hydrodynamic models have been widely used in aquatic habitat studies because they simulate flow with high accuracy and can predict habitat dynamics. The River2D model is able to integrate the habitat suitability curves for fish life stages with the simulated depth and velocity fields and the riverbed characteristics of substrate and cover, thereby estimating the corresponding weighted usable area, and thus predicting the potential distribution of fish species in the river. However, little is known about the in situ variability associated with such predictions both for hydraulic and biological data, whereas ecological responses are known to be driven by variability. Moreover, when calculating habitat availability, differences can be found by considering in the weighted usable area formulation substrate or cover or even both. To test the level of predictive accuracy of hydraulic and biological simulations, we modelled the habitat use by two fish species, the Iberian barbel Luciobarbus bocagei and the Iberian straight‐mouth nase Pseudochondrostoma polylepis, according to their requirements for depth, velocity, substrate and cover and then compared measured and simulated hydraulic and biological outcomes using the River2D model. Results indicate that 2D simulation depends on data collection, especially the density and location of bed topography points. Substantial differences were found in the biological responses. Results may differ when choosing different habitat availability variables. Similarly, habitat use may also be influenced by other biotic and abiotic interactions occurring in ecosystems, and restoration planning should be aware of such variability. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Applicability of 2-D modeling for forecasting ice jam flood levels in the Hay River Delta, Canada

Ice jam floods can present an annual threat to communities adjacent to rivers, especially those situated at river confluences, island or deltas. The objective of this study was to determine whether 2-D modeling might be used to predict expected ice jam flood elevations for such multi-channel systems. The Hay River delta was selected as the demonstration site for this study, and 2-D modeling was employed to calculate ice jam flood levels expected for varying inflow discharge conditions. The River2D model was calibrated for historical ice jam profiles covering a range of discharges from 268 to 1000 m3/s and a relationship was developed to predict the flow split down the East and West Channels based on the inflow discharge to the delta. Also, ice jam rating curves were developed at 0.5 km intervals along each channel facilitating the development of an ice jam profile prediction tool for use by the Town of Hay River.

Multiplex modeling of physical habitat for endangered freshwater mussels

Quantification of the potential habitat available for endangered freshwater mussels can be a challenging task, as habitat use criteria are very complex and often only low numbers of species observations are available. To address this problem in a riverine environment, we developed a concept of a multivariate, multi-scale, and multi-model (multiplex) habitat simulation through combining multivariate time-series analysis of complex hydraulics (CART and logistic regression), micro-scale (River2D), and meso-scale (MesoHABSIM) habitat models, to develop macro-scale management criteria. This concept has been applied and tested on the Upper Delaware River (USA) for the protection and enhancement of existing populations of Alasmidonta heterodon, an endangered freshwater mussel. The physical habitat conditions of approximately 125km of the Delaware River were described using digital aerial imagery and ground-based surveys. The temporal and spatial variabilities of complex hydraulics simulated by a River2D model at 1547 locations were statistically analyzed to select ranges of attributes that corresponded to mussel presence. We applied these criteria to the river's meso-scale hydromorphological unit mappings to identify suitable mesohabitats, which then served as a calibration data set for the coarser scale model. The final meso-scale model's predictions were hydraulically validated offering encouraging results. The meso-scale habitat suitability criteria defined moderately deep, slow-flowing, and non-turbulent hydromorphologic units as providing good conditions for A. heterodon. All three of the developed suitability models (descriptive statistics, CART and logistic regression model) indicated the species preference for hydraulically stable habitats.

BENCHMARKING RIVER HABITAT IMPROVEMENT

ABSTRACTRiver ecosystems have witnessed a long history of human pressure, particularly the disruption of freshwater fish populations. The awareness of this situation has led to many habitat improvement projects, with a variable degree of success. In natural situations, fish populations co‐inhabit throughout the hydrological cycle with different degrees of adequacy, and the sequence of favourable and unfavourable conditions dictates abiotic constraints and biotic interactions that shape the final biological assemblages. We postulate that a part of unsuccessful restoration results is related to insufficient closeness to the natural habitat conditions of the river type that is to be restored, including the naturally adverse periods. We used the river2d model to predict habitat availability as weighted usable area (WUA) at a degraded site that is to be restored, for two native Mediterranean species and their life stages—the Southwestern nase Iberochondrostoma almacai and the Arade chub Squalius aradensis. We then analysed the yearly evolution of the natural WUA at a nearby reference site. Overall, the reference site exhibited the longest periods during which the WUA was continuously lower than the chosen WUA thresholds for each of the four bioperiods. Considerable divergences from natural habitat availability values can be seen for the spawning, rearing and growth bioperiods. Restoration outcomes can result in appreciable deviations—favourable or unfavourable to fish populations—from the WUA occurring under natural conditions over the course of the year. Restoration should therefore take account of local hydraulic and habitat patterns that govern population dynamics and result in the final fish assemblage. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Changes of river morphology and physical fish habitat following weir removal

Gongneung Weir-2 was built in the 1970s to supply water for irrigation. For a long time, the weir was left untended due to the land-use changes that were made to a nearby area. This weir was removed completely on April 4, 2006. The present study investigated the effect of the resultant flow-regime changes on river morphology and fish habitat. Observed changes in the grain size distribution, bed elevation, and cross-section pre- and post-weir removal are provided and discussed in this paper. Various bed zones such as a sand island and a vegetated marshy zone, which can diversify an aquatic habitat, formed after the removal. In fact, changes in the number of observed fish species post-removal also were investigated. Finally, specific changes to the physical habitat of Zacco platypus were numerically simulated using the River2D model. The results indicated that habitat suitability post-removal was enhanced for all flow discharges. The WUA values increased 32.3–53.4% for all life stages in the flow discharge of 1.5 m 3 s −1. The numerical results also showed that after the removal of the weir, the distribution of the physical habitat changed to reflect continuity near the weir.