Search Results (19)

Large-scale river degradation constitutes a global challenge, rendering the ecological restoration of impaired rivers ever more crucial. While ecological restoration projects have enhanced the quality of river habitats, given the dynamic nature and complexity of river and lake ecosystems, the achievement of sustainable restoration of fish habitats and the assurance of its effectiveness continue to face numerous challenges. Consequently, this study proposes an improved approach to determine the ecological flow requirements of fish habitats in impaired rivers. In relation to the screening of key species, a bespoke evaluation index system has been developed specifically for impaired rivers lacking rare and endemic fish species. Primary data were collected via field surveys, ecological monitoring, and a review of the literature, while the analytic hierarchy process (AHP) was utilized to quantitatively identify key species. In the development of the assessment framework, three core indicators were integrated: habitat-weighted usable area (WUA), habitat connectivity index (HCI), and microhabitat heterogeneity index (RMH). Incorporating the ecological requirements of key fish species across different life stages, a systematic analysis was undertaken to explore the ecological response effects of different indicator combinations under varying flow regimes. The results revealed that a flow rate of 160 m³/s gives rise to an inflection point in the RMH diversity index at 1.618, whereas a flow rate of 240 m³/s results in a significant inflection point in the HCI at 0.652. At a flow rate of 260 m³/s, the WUA attains 2,007,928 m². The optimal ecological flow range was determined to be 160–240 m³/s for the breeding period (March–June), 240–260 m³/s for the foraging period (July–October), and 120 m³/s for the winter period. These findings provide a theoretical framework for the restoration of target fish populations in similarly degraded rivers. Full article

Coreius guichenoti, once widely distributed in the upper reaches of the Jinsha River, has become a nationally protected species in China due to the profound impacts of cascade reservoirs. To assess the influence of substrate on the suitability of spawning habitat for C. guichenoti, this study develops a substrate-inclusive habitat model using fuzzy logic based on expert knowledge. Taking the Pingdi Town section of the lower Jinsha River—a historical spawning site for C. guichenoti—as a case study from March to July 2020, we simulated changes in the spawning habitat suitability index (HSI) and compared the results with those from traditional models that exclude substrate factors. The results showed that in the first and second halves of May, Weighted Usable Area (WUA) and Overall Suitability Index (OSI) increased by 42.31% and 38.73%, respectively, while MSP exhibited dramatic increases of 236.04% and 614.56%. These improvements were primarily observed along the riverbanks, where HSI increased by approximately 0.25. From a management perspective, the HSI results provide a scientific basis for optimizing ecological flow regulation. Incorporating substrate factors into spawning habitat models offers a more objective and comprehensive assessment of habitat quality. Habitat restoration measures, such as targeted substrate improvement in key riverbank areas, may further increase habitat suitability, providing additional opportunities for conservation planning in regulated rivers. Full article

In light of Switzerland’s 2050 energy goals, the nation aims to boost its domestic hydroelectric output, notably focusing on small-scale hydroelectric power plants. Concurrently, there is an effort to renovate hydroelectric plants to make them more environmentally friendly, emphasizing ecological flow regulation to improve river conditions. This study explores the application of a non-proportional flow allocation method to better assess both ecological and economic outcomes. Unlike traditional fixed or proportional flow methods, this approach allows for a more dynamic balance between hydropower generation and riverine ecosystem health. This study focuses on two key species, brown trout and grayling. In particular, this work highlighted that trout are better suited for low-flow conditions (Weighted Usable Area, WUA, peaks below 1 m³/s), while grayling require significantly higher flows (WUA peaks over 4.5 m³/s). This disparity in habitat preferences raises concerns about the current reliance on single-species models, emphasizing the need for multi-species ecological assessment in future studies. When applied to a small hydropower plant in the Swiss Jura, the non-proportional flow method resulted in an improvement of ecological conditions of at least 37.7%, which consequently led to a reduction of the hydroelectric production of at least 10%. Through strategic upgrades to the facility (e.g., by minimizing hydraulic losses, implementing more efficient turbines, or incorporating photovoltaic panels over water channels), it is possible to simultaneously enhance both energy output and environmental sustainability. These findings suggest that non-proportional flow allocation holds significant potential for broader use in sustainable hydropower management, providing a pathway toward meeting both energy production and ecological conservation goals. Full article

As rivers face growing environmental challenges due to climate change and the construction of artificial structures, it is essential that we improve river ecosystems to maintain their ecological functions and preserve the health of aquatic habitats. The aim of this study was to assess the aquatic ecosystem health of the lower reaches of the Tan River. We employed the Physical Habitat Simulation System and Hydrologic Engineering Center’s River Analysis System to calculate the ecological flow rate based on the weighted usable area (WUA) of Zacco platypus, which is a representative fish species in the Tan River, and the flow rate relationship curves. By analyzing the flow rates in the Tan River across different seasons from 2012 to 2021, we determined that the seasonal optimal ecological flow rate was 10.21–10.27 m³/s. Meanwhile, the WUAs for spring, summer, and autumn and winter were 90–100%, 95–100%, and 75–100%, respectively. Despite meeting the ecological flow criteria for summer, fall, and winter over 50% of the time, spring fell short at 41%; hence, the Tan River flow rates should be secured particularly in spring. This study highlights the urgency of addressing seasonal variations to ensure the overall health of the Tan River ecosystem. Full article

Hydropower operations significantly alter the natural hydrological conditions of rivers, exerting adverse effects on riverine ecosystems. Accurate identification of fish habitats under hydropower operation and maintaining suitable ecological flow are crucial for riverine ecological conservation and water resource management. Coreius guichenoti was selected as the target species and the Yibin reach of the downstream Jinsha River was selected as the studied river reach. Subsequently, Weighted Usable Area (WUA) and Habitat Connectivity Index (HCI) were employed to comparatively analyze the habitat quantity and quality before and after the construction and operation of the Xiangjiaba hydropower station, namely the natural period (1991–2005), construction period (2006–2014), and operation period (2015–2020). Finally, correlations between WUA, HCI, and flow were established to determine the optimal ecological flow corresponding to optimal fish habitats. The results indicate that the average WUA and HCI during the construction period are similar to the natural period. In comparison to the natural period, the average WUA decreases by 9.2%, and the average HCI decreases by 0.05 during the operation period. It is determined that the habitat conditions are optimal when the flow is between 3000 and 5000 m³/s. After further refining the flow scenarios, the suitable ecological flow is determined to be 3500 m³/s. This study can provide a scientific basis for the water resources management in the Jinsha River and contribute to the field of riverine ecological conservation and restoration. Full article

To reveal the evolution of habitat distribution for multiple fish species in the lower reaches of the Gongzui Hydropower Station, this study conducted a catch survey to determine the target species of the reach. Based on their suitability curves, a combined suitability assessment model for multiple fish species was constructed. The reliability of the model was verified by combining acoustic observations of flow fields and fish distribution in specific flow conditions. A two-dimensional hydrodynamic model was coupled to quantitatively analyze the distribution characteristics of fish habitat patches under different flow conditions. The results indicate that the correlation coefficient between the multi-species comprehensive suitability index and the number of fish is 0.676, which indicates that the model can better evaluate the distribution of multiple fish habitats in the study river reach; the weighted usable area (WUA) decreased as the discharge increased; from low flow condition (<800 m³/s) to high flow condition (>2000 m³/s), the patch area of suitable habitat decreased from 11,424 m² to 1268 m², and the connectivity between patches also showed a downward trend; and the habitat shifted to the near-shore area of the downstream wider and shallower section, which was highly correlated with the migration process of low-depth and low-velocity areas. The model proposed in this study can establish a rapid response between the suitable habitat distribution of multiple fish species and discharge conditions, which can provide a research method for quantitative evaluation of multi-species habitats in river, and make a significant contribution to the sustainable development of riverine fisheries resources and river water ecology. Full article

Weirs are often constructed on mountainous rivers because of their low construction costs and their ability to provide irrigation and facilitate landscaping, yet there is little research on how fish habitat quality in mountainous rivers responds to weir distribution. This study categorized the distribution characteristics of weirs on typical reaches according to their sinuosity and calculated the corresponding habitat suitability index (HSI) and weighted usable area (WUA) under various discharge conditions using a coupled MIKE21 and habitat suitability model. Then, the relationship between the distribution characteristics of weirs and the quality of fish habitats under different discharge conditions was analyzed. The results show that weirs in mountainous rivers can affect the habitat suitability of the rivers, but this effect is closely related to discharge conditions and layout mainly because the key hydraulic factors that determine habitat quality for different sinuous reaches vary under different discharge conditions. This study found that in high-sinuosity rivers with high discharge conditions, water depth is the key factor determining the quality of fish habitats, so weirs can improve habitat quality by improving the suitability of downstream water depth. However, in other conditions, velocity is the key factor determining habitat quality, in which case weirs cannot improve habitat quality and can even degrade it. Therefore, other methods of improving velocity are needed to enhance habitat quality. The results of this study provide a reference for the protection of fish habitats in mountainous river channels and the determination of suitable locations for weir construction. Full article

Dam removal is considered an effective measure to solve the adverse ecological effects caused by dam construction and has started to be considered in China. The sediment migration and habitat restoration of river ecosystems after dam removal have been extensively studied abroad but are still in the exploratory stage in China. However, there are few studies on the ecological response of fishes at different growth stages. Considering the different habitat preferences of Schizothorax prenanti (S. prenanti) in the spawning and juvenile periods, this study coupled field survey data and a two-dimensional hydrodynamic model to explore the changes in river morphology at different scales and the impact of changes in hydrodynamic conditions on fish habitat suitability in the short term. The results show that after the dam is removed, in the upstream of the dam, the riverbed is eroded and cut down and the riverbed material coarsens. With the increase in flow velocity and the decrease in flow area, the weighted usable area (WUA) in the spawning and juvenile periods decreases by 5.52% and 16.36%, respectively. In the downstream of the dam, the riverbed is markedly silted and the bottom material becomes fine. With the increase in water depth and flow velocity, the WUA increases by 79.91% in the spawning period and decreases by 67.90% in the juvenile period, which is conducive to adult fish spawning but not to juvenile fish growth. The changes in physical habitat structure over a short time period caused by dam removal have different effects on different fish development periods, which are not all positive. The restoration of stream continuity increases adult fish spawning potential while limiting juvenile growth. Thus, although fish can spawn successfully, self-recruitment of fish stocks can still be affected if juvenile fish do not grow successfully. This study provides a research basis for habitat assessment after dam removal and a new perspective for the subsequent adaptive management strategy of the project. Full article

River–lake interaction is important for maintaining biodiversity, yet it is vulnerable to hydrological alteration. The connectivity of the channel connecting Poyang Lake and the Yangtze River not only ensures the regular migration of fish but also makes Poyang Lake a feeding and fattening ground for them. Unfortunately, human activities have dramatically changed the hydrodynamic conditions of Poyang Lake, which is experiencing severe drought due to the obvious decline in the water level in autumn and winter, especially since 2003. However, the possible impacts of the changes in the water level on the habitats of migratory fish remain unclear due to the limitation of traditional techniques in spatiotemporal analysis. Here, we combined a hydrodynamic model and habitat suitability model to simulate variations in the suitable habitat area and their connectivity under different water-level conditions. The conditions for the migration pathway of the target fish were obtained by a hydroacoustic survey using the Simrad EY60 echosounder. The results showed that the change in water level will significantly affect the spatiotemporal change in the suitable habitats and their connectivity. In particular, we found the existence of two thresholds that play a dominant role in illuminating the connectivity of effective suitable habitats (HC). Firstly, the maximum value of the weighted usable area (WUA) and HC can be achieved when the water level is more than 16 m. Secondly, when the water level is between 10 and 16 m, the changes in the HC are sensitive and rapid, and the area flooded at this stage is called the sensitive area. HC is a crucial element in fish migration and habitat conditions. Under the condition of continuous drought in the middle reaches of the Yangtze River, our research contributes to clarifying the influence of water level on key habitats for fish and optimizes the practice of river–lake ecological management. Full article

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. Full article

The attraction efficiency of a by-pass fishway installed at Gangjeong-Goryeong Weir on the Nakdong River in South Korea was evaluated according to flow rate variation of the main channel. Optimal flow rate that achieved the maximum value of attraction efficiency at the fishway entrance was also determined. The weir can adjust the flow rate of the main channel and the fishway by operating sluice gates. The weighted usable area (WUA) calculated on the basis of habitat suitability criteria (HSC) for target species using River2D (a two-dimensional physical habitat model) was regarded as an indicator of attraction efficiency. The simulated velocity field by River2D was validated by virtue of measured data acquired from GPS drifter field experiments. Additionally, monthly fish monitoring data obtained with a fish trap served as supporting data to confirm the validity of the estimated attraction efficiency. The monitoring results revealed that the fishway attraction efficiency was the highest during the spawning season (from April to June). The target fish used the fishway most frequently in April. However, many other fish species used the fishway in June. Simulation results revealed that the flow rate of the main channel at the weir should be maintained at 190 m³/s in order to most effectively attract the target fish species into the fishway entrance. Managing the optimal flow rate by operating the sluice gate is especially important during the spawning season of the target fish to facilitate upstream and downstream migration. Full article

The article aims at assessing the impact of hydraulic characteristics on the habitat quality of mountain and piedmont watercourses. The solution results from the Riverine Habitat Simulation model, where the quality of the aquatic habitat is represented by the weighted usable area (WUA), which is determined using brown trout as the bioindicator. Flow velocity and water depth are basic abiotic characteristics that determine the ratio of suitability of the instream habitat represented by the weighted usable area. The influence of these parameters on the objective evaluation of the habitat quality is the essence of the paper. The measurements were carried out during the summer period at minimum discharges for 17 mountain and piedmont streams in Slovakia. Three methods for assessing the habitat quality were tested, and differences in the results were found to be significant. The evaluation shows the optimum design methods for calculating the weighted usable area. Full article

Water resource regulation is convenient for humans, but also changes river hydrology and affects aquatic ecosystems. This study combined a field investigation and two-dimensional hydrodynamic model (MIKE21) to simulate the hydrodynamic distribution from 1 March to 30 April of 2008–2013 and establish the HDI (habitat depth suitability index) and HVI (habitat velocity suitability index) based on static hydraulic conditions at typical points. Additionally, by using MIKE21 to simulate the hydraulic state in the study area under 20 flow conditions from 530–1060 m³/s, and combining these states with the HCI (habitat cover type suitability index), HDI, and HVI, we simulated the WUA (weighted usable area) and habitat connectivity under different runoff regulation scenarios to study the water requirements of Schizothorax during the spawning period in the Yanni wetland. The results showed the following: (1) the suitable cover type was cobble and rock substrate, with nearby sandy land; furthermore, the suitable water depth was 0.5–1.5 m, and the suitable velocity was 0.1–0.9 m/s. (2) Using the proximity index to analyse the connectivity of suitable habitats, the range of ecological discharge determined by the WUA and connectivity was 424–1060 m/s. (3) Habitat quality was divided into three levels to detail the flow demand further. When the flow was 424–530 m³/s or 848–1060 m³/s, the WUA and connectivity generally met the requirements under natural conditions. When the flow was 530–636 m³/s or 742–848 m³/s, the WUA and connectivity were in a good state. When the flow was 636–742 m³/s, the WUA and connectivity were in the best state. This study complements existing research on the suitability of Schizothorax habitat in Tibet, and introduces the connectivity index to enrich the method for calculating ecological water demand, providing a reference for resource regulation and the protection of aquatic organisms. Full article

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. Full article

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. Full article