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Multicomponent assessment of the impact of hydropower cascade on fish metrics
... CumRcapacity typically emerges as the most predominant factor influencing both species extinction and introduction processes, playing a relatively more crucial role in determining species extinctions. The cumulative impacts of impoundment, habitat fragmentation, and flow-regime modification on hydraulic and habitat conditions over space and time can ultimately lead to the local extinction of specialised species, including rheophilic species, gravel-spawning river fish, migratory fish, and feeding specialists (He et al. 2024;Akstinas et al. 2024), such as Leuciscus chuanchicus, G. pachycheilus, and C. labiosa in the upper Yellow River. Furthermore, the expansion of aquaculture and lentic habitats following cascade dam construction increases the likelihood of non-native species introductions in the upper Yellow River (Jia et al. 2020). ...
Freshwater biodiversity is increasingly imperilled by human activities, with dam construction posing significant threats to fish communities. Species composition changes through introductions and extinctions have been widely reported, yet the long-term consequences of cascade dam construction on multiple facets of biodiversity remain poorly understood. Moreover, the compensatory effects of species introductions on extinction have received limited attention. This study presents a comprehensive evaluation of the impact of extinction-introduction successions, triggered by cascade dam construction, on the taxonomic, phylogenetic, and functional diversity of fish assemblages in the upper Yellow River over five decades. Our results reveal that shifts in species composition significantly increased phylogenetic and functional diversity but not taxonomic diversity, suggesting a greater sensitivity of the former to cascade dam construction. However, introduced species only partially compensate for approximately 50% of phylogenetic and functional diversity losses caused by extinctions. Furthermore, the timing of significant increases in phyloge-netic and functional diversity is not synchronised, with all measures gradually stabilising post-dam construction. Cumulative reservoir capacity, reservoir age, and individual reservoir capacity were identified as key determinants of multifaceted diversity change after dam construction, with cumulative reservoir capacity and reservoir age generally having positive effects, while individual reservoir capacity tended to have a negative impact. These findings stress the urgent need to reassess the compensatory effects of introductions on extinctions under global change, emphasise caution in interpreting short-term data due to non-linear diversity patterns, and highlight the importance of using long-term monitoring and multifaceted diversity metrics in biodiversity conservation actions.
... Comparative studies 29,69,208 Field surveys 18,42,53,57,111,141,190 Use of UAVs GIS integration 215 High-resolution data collection 72,195 Real-time monitoring 25 access areas. Unmanned Aerial Vehicles are equipped with advanced sensors capable of capturing detailed imagery and environmental data, enabling researchers to monitor key water quality parameters such as turbidity, chlorophyll, and surface temperature with exceptional precision. ...
The rapid advancement of drone technology and digital twin systems has significantly transformed environmental monitoring, particularly in the field of water quality assessment. This paper systematically reviews the current state of research on the application of drones, digital twins, and their integration for water quality monitoring and management. It highlights key themes, insights, research trends, commonly used methodologies, and future directions from existing studies, aiming to provide a foundational reference for further research to harness the promising potential of these technologies for effective, scalable solutions in water resource management, addressing both immediate and long‐term environmental challenges. The systematic review followed PRISMA guidelines, rigorously analysing hundreds of relevant papers. Key findings emphasise the effectiveness of drones in capturing real‐time, high‐resolution spatial and temporal data, as well as the value of digital twins for predictive and simulation‐based analysis. Most importantly, the review demonstrates the potential of integrating these technologies to enhance sustainable water management practices. However, it also identifies a significant research gap in fully integrating drones with digital twins for comprehensive water quality management. In response, the review outlines future research directions, including improvements in data integration techniques, predictive models, and interdisciplinary collaboration.
... One of the most common methodologies for estimating hydrological alterations in stream reaches is the indicators of hydrologic alteration (IHA) metrics (Richter et al., 1996). The IHA method has been widely applied in several studies to assess the impacts of anthropogenic activities and climate change on river flow regimes at watershed scales (Zhou et al., 2020;Pardo-Loaiza et al., 2021;Maskey et al., 2022;Akstinas et al., 2023). In addition, knowledge of these IHA metrics and their relationships with climate, land use and other geospatial characteristics can provide vital information for management of water resources, building and evaluating hydrologic models, and assessing instream habitats (Poff et al., 2010;Hrachowitz et al., 2014;McMillan, 2021). ...
Poly(butanediol sebacate‐butanediol terephthalate) (PBSeT) has emerged as a promising biodegradable material, attributed to its excellent tensile strength and water vapor barrier properties. However, certain challenges persist, including susceptibility to puncture and tearing. To solve these problems, the researchers developed a composite material consisting of PBSeT and zinc gluconate (ZG) to improve the performance of PBSeT through the synergistic effect of ionic and hydrogen bonds. Notably, the tearing strength of the PBSeT/ZG‐3 composite exhibits a remarkable increase of 48.7% relative to PBSeT alone, while the puncture load is enhanced by 25.3%. Furthermore, XRD and TG analyses indicate that the incorporation of ZG has a negligible impact on the crystallinity and thermal stability of the composites. Interestingly, the enzymatic degradation properties are significantly improved with increasing ZG content, and the enhanced hydrophilicity imparted by ZG results in a reduction in the water contact angle of the composite materials. In conclusion, the integration of ZG significantly enhances the puncture resistance, tear strength, and biodegradability of PBSeT. These advancements are critical for the development and implementation of novel applications, particularly in the fields of food packaging, films, and medical materials.
In recent years, climate change and catchment degradation have negatively affected stage patterns in rivers which in turn have affected the availability of enough water for various ecosystems. To realize and quantify the effects of climate change and catchment degradation on rivers, water level monitoring is essential. Various effective infrastructures for river water level monitoring that have been developed and deployed in developing countries over the years, are often bulky, complex and expensive to build and maintain. Additionally, most are not equipped with communication hardware components which can enable wireless data transmission. This paper presents a river water level data acquisition system that improves on the effectiveness, size, deployment design and data transmission capabilities of systems being utilized. The main component of the system is a river water level sensor node. The node is based on the MultiTech mDot - an ARM-Mbed programmable, low power RF module - interfaced with an ultrasonic sensor for data acquisition. The data is transmitted via LoRaWAN and stored on servers. The quality of the stored raw data is controlled using various outlier detection and prediction machine learning models. Simplified firmware and easy to connect hardware make the sensor node design easy to develop. The developed sensor nodes were deployed along River Muringato in Nyeri, Kenya for a period of 18 months for continuous data collection. The results obtained showed that the developed system can practically and accurately obtain data that can be useful for analysis of river catchment areas.
The Balkan region has some of the best conserved rivers in Europe, but is also the location of ~3000 planned hydropower dams that are expected to help decarbonise energy production. A conflict between policies that promote renewable hydropower and those that prioritise river conservation has ensued, which can only be resolved with the help of reliable information. Using ground-truthed barrier data, we analysed the extent of current longitudinal river fragmentation in the Balkan region and simulated nine dam construction scenarios that varied depending on the number, location and size of the planned dams. Balkan rivers are currently fragmented by 83,017 barriers and have an average barrier density of 0.33 barriers/km after correcting for barrier underreporting; this is 2.2 times lower than the mean barrier density found across Europe and serves to highlight the relatively unfragmented nature of these rivers. However, our analysis shows that all simulated dam construction scenarios would result in a significant loss of connectivity compared to existing conditions. The largest loss of connectivity (-47 %), measured as reduction in barrier-free length, would occur if all planned dams were built, 20 % of which would impact on protected areas. The smallest loss of connectivity (-8 %) would result if only large dams (>10 MW) were built. In contrast, building only small dams (<10 MW) would cause a 45 % loss of connectivity while only contributing 32 % to future hydropower capacity. Hence, the construction of many small hydropower plants will cause a disproportionately large increase in fragmentation that will not be accompanied by a corresponding increase in hydropower. At present, hydropower development in the Balkan rivers does not require Strategic Environmental Assessment, and does not consider cumulative impacts. We encourage planners and policy makers to explicitly consider trade-offs between gains in hydropower and losses in river connectivity at the river basin scale.
Freshwater aquatic ecosystems are highly sensitive to flow regime alteration caused by anthropogenic activities, including river regulation and atmospheric warming-induced climate change. Either climate change or reservoir operations are among the main drivers of changes in the flow regime of rivers globally. Using modeled unregulated and simulated regulated streamflow under historical and future climate scenarios, this study evaluated potential changes to the flow regime due to climate change and reservoir operations for the major tributaries of the San Joaquin River Basin, California United States. We selected a set of Indicators of Hydrologic Alteration (IHA) to evaluate historical and projected future trends of streamflow dynamics: rise and fall rates, durations and counts of low and high pulses, and the magnitude of extremes. Results show that most indicators have pronounced departures from baseline conditions under anticipated future climate conditions given existing reservoir operations. For example, the high pulse count decreases during regulated flow conditions compared to increased frequency under unregulated flow conditions. Finally, we observed a higher degree of flow regime alteration due to reservoir operations than climate change. The degree of alteration ranges from 1.0 to 9.0% across the basin among all future climate scenarios, while reservoir operations alter the flow regime with a degree of alteration from 8.0 to 25%. This study extends multi-dimensional hydrologic alteration analysis to inform climate adaptation strategies in managed river systems.
China is rich in hydropower resources, and mountain rivers have abundant water resources and huge development potential, which have a profound impact on the pattern of water resources allocation in China. As the main way of water resources and hydropower development, the construction of cascade hydropower stations, while meeting the requirements of water resources utilization for social development, has also brought adverse effects on river ecosystems. Therefore, the impact of the construction of cascade hydropower stations on mountainous river ecosystems, where the minimum ecological flow of rivers must be ensured and reviewed. In addition, this paper proposed the deficiencies and outlooks for cascade hydropower stations based on previous research results.
Mitigating the adverse ecological impacts on stream ecosystems caused by hydropower expansion is a major challenge. To prevent fish from turbine entrainment and to reduce injury and mortality risk, physical barriers such as fine screens with horizontally or vertically oriented bars are frequently installed at turbine inlets. In this study, the species-and size-dependent protection from turbine entrainment of different types of fish protection screens (FPSs) were investigated at five hydropower sites by a net-based monitoring of downstream moving wild fish and hatchery-reared test fish during different seasons (15,223 individuals from 40 species). Across different screen types and fish species, considerably larger individuals were able to pass the FPSs than what would have been expected from common models estimating the physical passability of these mechanical barriers. The examined FPSs with 15 mm and 20 mm bar spacing could be passed by adult barbel (Barbus barbus L.), brown trout (Salmo trutta L.) and European perch (Perca fluviatilis L.) up to a total length (TL) of 32 cm (15 mm FPSs) and 34 cm (20 mm FPSs), respectively. In addition, the 20 mm FPSs could be passed by Danube salmon (Hucho hucho L.) up to 39 cm TL. Consequently, thresholds from modelling and rules of thumb for estimating maximum TLs capable of passing 15 mm and 20 mm FPSs were exceeded by up to 135% for these species. The results of this study suggest that fish species other than eel can also squeeze through physical barriers narrower than body dimensions. No physical fish protection was realised by the investigated 15 mm and 20 mm FPSs for many small-bodied species such as bullhead (Cottus gobio L.), gudgeon (Gobio gobio L.) and spirlin (Alburnoides bipunctatus Bloch) with maximum TLs smaller than 20 cm. This also holds true for juveniles and sub-adults of larger species, which can pass these physical barriers. Since a large part of the downstream moving fish generally consists of small species or small individuals, these fish sizes must be given greater consideration in physical fish protection concepts at hydropower plants.
River barriers reduce river connectivity and lead to fragmentation of fish habitats, which can result in decline or even extinction of aquatic biota, including fish populations. In the Mekong basin, previous studies have mainly focused on the impacts of large dams but ignored the impacts of small-scale barriers, or drew conclusions from incomplete barrier databases, potentially leading to research biases. To test the completeness of existing databases and to evaluate the catchment-scale fragmentation level, a detailed investigation of river barriers for the whole Upper Mekong (Lancang catchment) was performed, by conducting visual interpretation of high-resolution remotely sensed images. Then, a complete catchment-scale barrier database was created for the first time. By comparing our barrier database with existing databases, this study indicates that 93.7% of river barriers were absent from the existing database, including 75% of dams and 99.5% of small barriers. Barrier density and dendritic connectivity index (DCID and DCIP) were used to measure channel fragmentation within the catchment. Overall, 50.5% of sub-catchments contained river barriers. The Middle region is the most fragmented area within the Lancang catchment, with a median [quartiles] barrier density of 5.34 [0.70-9.67] per 100 km, DCIP value of 49.50 [21.50-90.00] and DCID value of 38.50 [9.00-92.25]. Furthermore, since 2010, distribution ranges of two representative fish species Schizothorax lissolabiatus (a rheophilic cyprinid) and Bagarius yarrelli (a large catfish) have reduced by 19.2% and 32.8% respectively, probably due in part to the construction of river barriers. Our findings indicate that small-scale barriers, in particular weirs and also small dams are the main reason for habitat fragmentation in the Lancang and must be considered alongside large dams in water management and biodiversity conservation within the Mekong.
Rivers of Europe, Second Edition, presents the latest update on the only primary source of complete and comparative baseline data on the biological and hydrological characteristics of more than 180 of the highest profile rivers in Europe. With even more full-color photographs and maps, the book includes conservation information on current patterns of river use and the extent to which human society has exploited and impacted them. Each chapter includes up to 10 featured rivers, with detailed information on their physiography, hydrology, ecology/biodiversity and human impacts. Rivers selected for specific coverage include the largest, the most natural, and those most affected by humans.
This book provides the most comprehensive information ecologists and conservation managers need to better assess their management and meet the EU legislative good governance targets.
The proliferation of hydropower development to meet obligations under the Renewable Energy Directive has also seen the emergence of conflict between the hydropower developers and the fisheries and conservation sectors. To address this trade-off between hydroelectricity supply and its environmental costs, this chapter introduces a series of tools and guidance to assess environmental hazards of hydropower in particular on fishes, to enhance assessing cumulative effects from several hydropower schemes and to enable informed decisions on planning, development and mitigation of new and refurbished hydropower schemes. The newly developed European Fish Hazard Index is introduced as objective, comparable, and standardized screening tool for assessing the impacts on fishes at existing and planned hydropower schemes, while explicitly considering the ecological status and consecration value of the ambient fish assemblage. In addition, guidance is provided on assessing the environmental impacts of consecutive hydropower schemes in a river system. This guidance separates between cumulative impacts on habitats and species and thus, considers cumulative length of all impoundments in a river system, total fragmentation by barriers (barrier density), but also different migratory life history traits of species and their encounter probability with hydropower schemes and sensitivity to mortality. Finally, a decision support scheme is provided to balance the environmental risk with appropriate, site-specific mitigation planning and implementation at new and existing hydropower schemes.
Resolving the controversy about hydropower is only possible based on reliable data on its ecological effects, particularly fish welfare.
Herein, we propose a comprehensive assessment of conventional and innovative hydropower using a dataset of 52,250 fish.
The effects of hydropower on fish were most harmful at sites with Kaplan turbines, showing ≤83% mortality. Innovative hydropower, often termed ‘fish‐friendly’, caused ≤64% mortality.
Our findings suggested that the runner peripheral speed, number of turbine blades and turbulence at turbine outlets were the most important factors.
Synthesis and applications. To reduce the impact of hydropower on fish, site‐specific characteristics such as head drop, bypass options and river‐specific species composition need to be more intensively considered in optimal turbine technologies and operation modes.
Aquatic ecosystems are particularly vulnerable to anthropogenic activity and climate change. The changes in flow regimes in Lithuanian lowland rivers due to the operation of hydropower plants (HPPs) and the impact of altered flow on some fish species have already been studied. The impact of climate change on future natural river runoff and the structure of fish assemblages was also investigated. However, it is still unknown how the combined effect of climate change and flow regulation related to hydropower generation may affect fish assemblages in the downstream river reaches below the Lithuanian HPPs. In this study, the physical habitat modelling system MesoHABSIM was used to simulate spatial and temporal changes in aquatic habitats availability for different fish species under the influence of HPP at different climate change scenarios. Changes in the available habitat were assessed for common fish species in four HPP-affected rivers representing different hydrological regions of Lithuania. The modelling results showed that the operation of HPP under climate change conditions in most rivers could be beneficial for small benthic fish species such as gudgeon Gobio gobio and stone loach Barbatula barbatula. Meanwhile, for larger fish species (e.g., chub Squalius cephalus and vimba Vimba vimba) the alteration in the temporal availability of suitable habitat was relatively higher.
Useful and important information for the spatial, ecological, and many other changes in the living environment may be obtained using the analysis of historical aerial photography, with comparison to contemporary imagery. This method provides the ability to determine the state of elements of the space over a long period, encompassing the time when it was not possible to acquire the data from satellite imagery or some other contemporary sources. Aerial images are suitable for mapping spatial phenomena with relatively limited spatial distribution because they possess a high level of details and low spatial coverage. With a comparative analysis of aerial imagery from the past, contemporary aerial imagery, and other sources of aerial imagery, we can obtain information about the nature and trends of the observed phenomena as well as directions of future actions, considering changes detected in the environment, whether they are preventive or corrective in nature. This paper gives the methodological framework for the appliance of the existing knowledge from various fields, intending to use historical aerial photography for monitoring of environmental changes of the Bovan Lake in Eastern Serbia.
Assessing the health of hydrological systems is vital for the conservation of river ecosystems. The indicators of hydrologic alteration are among the most widely used parameters. They have been traditionally assessed at the scale of river reaches. However, the use of such indicators at the basin scale is relevant for water resource management since there is an urgent need to meet environmental objectives to mitigate the effects of present and future climatic conditions. This work proposes a methodology to estimate the indicators of hydrological alteration at the basin scale in regulated systems based on simulations with a water allocation model. The methodology is illustrated through a case study in the Iberian Peninsula (the Duero River basin), where different minimum flow scenarios were defined, assessing their effects on both the hydrological alteration and the demand guarantees. The results indicate that it is possible to improve the hydrological status of some subsystems of the basin without affecting the water demand supplies. Thus, the methodology presented in this work will help decision makers to optimize water management while improving the hydrological status of the river basins.
Hydropower remains the most important and largest source of renewable energy. However, besides many additional benefits, such as dams for water supply, irrigation, flood control, recreation, navigation, etc., hydropower generation has a negative impact on the environment. This study aimed to investigate the hydrologic changes in Lithuanian lowland rivers caused by small hydropower plants (HPPs). Thirty-two indicators of hydrologic alteration (IHA) were studied in 11 rivers downstream of hydropower plants in the post-impact and pre-impact periods. The findings showed that HPPs and reservoirs considerably disturbed the primary flow of river ecosystems downstream. The largest changes in mean IHA values were found for low and high pulse characteristics (up to 57%) and the number of reversals (up to 44%). Only small or no deviations of the timing of annual extreme flows were found. The number of reversals, a low pulse count, and a fall rate were the flow characteristics that fell outside their historical ranges of variability most often. Six (out of 11) hydropower plants were identified that provoked hydrologic alterations of a moderate degree.
Hydropower is considered as a clean energy. However, compared to other renewable sources (like wind and solar), its adverse impacts on society and nature are substantial, and it exists during the construction and operational phase as well. Therefore, there is a need to green the overall hydropower sector minimizing its impact. This paper focuses on greening the small hydropower. It reviews the concept of green hydropower, its history, needs, various frameworks, and categories that are dominant or have shaped the field. Specifically, we have considered concepts from pioneer countries and institutes like the USA (LIHI), Switzerland (EAWAG), U.K. (IHA), and some Nordic countries. With this background, this study has reviewed the Chinese history, their updated progress in greening the system, measurement methods, and key criteria with some leading examples and present a detailed green certification case study. Finally, this paper recommends further improvements that can be made in the field.
Despite growing interest in using lightweight unmanned aerial systems (UASs) for ecological research and conservation, review of the operational aspects of these evolving technologies is limited in the scientific literature. To derive an objective framework for choosing among technologies we calculated efficiency measures and conducted a data envelopment productivity frontier analysis (DEA) to compare the efficacy of using manned aircraft (Cessna with Aviatrix triggered image capture using a 50 mm lens) and UAS (Mavic Pro 2) for photogrammetric monitoring of restoration efforts in dynamic braided rivers in Southern New Zealand. Efficacy assessment was based on the technological, logistical, administrative, and economic requirements of pre (planning), peri (image acquiring) and post (image processing) phases. The results reveal that the technological and logistic aspects of UASs were more efficient than manned aircraft flights. Administratively, the first deployment of UASs is less efficient but was very flexible for subsequent deployment. Manned aircraft flights were more productive in terms of the number of acquired images, but the ground resolution of those images was lower compared with those from UASs. Frontier analysis confirmed that UASs would be economical for regular monitoring of habitats—and even more so if research personnel are trained to fly the UASs.
Hydrological models have traditionally been used for the prediction in ungauged basins despite the related challenge of model parameterization. Short measurement campaigns could be a way to obtain some basic information that is needed to support model calibration in these catchments. This study explores the potential of such field campaigns by i) testing the relative value of continuous water-level time series and point discharge observations for model calibration, and by ii) evaluating the value of point discharge observations collected using expert knowledge and active learning to guide when to measure streamflow. The study was based on 100 gauged catchments across the contiguous United States for which we pretended to have only limited hydrological observations, i.e., continuous daily water levels and ten daily point discharge observations from different hypothetical field trips conducted within one hydrological year. Water level data were used as a single source of information, as well as in addition to point discharge observations, for calibrating the HBV model. Calibration against point discharge observations was conducted iteratively by continually adding new observations from one of the ten field measurements. Our results suggested that the information contained in point discharge observations was especially valuable for constraining the annual water balance and streamflow response at the event scale, improving predictions based solely on water levels by up to 50% after ten field observations. In contrast, water levels were valuable to increase the accuracy of simulated daily streamflow dynamics. Informative discharge sampling dates were similar when selected with either active learning or expert knowledge and typically clustered during seasons with high streamflow.
Hydroelectric facilities often release water at variable rates over the day to match electricity demand, resulting in short-term variability in downstream discharge and water levels. This sub-daily variability, known as hydropeaking, has mostly been studied at large facilities. The ongoing global proliferation of small hydropower (SHP) facilities, which in Brazil are defined as having installed capacities between 5 and 30 MW, raises the question of how these facilities may alter downstream flow regimes by hydropeaking. This study examines the individual and cumulative effects of hydropower facilities on tributaries in the upland watershed of the Pantanal, a vast floodplain wetland system located on the upper Paraguay River, mostly in Brazil. Simultaneous hourly discharge measurements from publicly available reference and downstream gage stations were analyzed for 11 reaches containing 24 hydropower facilities. Most of the facilities are SHPs and half are run-of-river designs, often with diversion channels (headraces). Comparison of daily data over an annual period, summarized by indicators of hydrological alteration (HA) that describe the magnitude, frequency, rate of change, and duration of flows, revealed differences at sub-daily scales attributable to hydropeaking by the hydropower facilities. Results showed statistically significant sub-daily HA in all 11 reaches containing hydropower facilities in all months. Discharge indicators that showed the highest percentage of days with increased variability were the mean rates of rise and fall, amplitude, duration of high pulses, maximum discharge, and number of reversals. Those that showed higher percentages of decreased variability included minimum discharge, number of high pulses, duration of stability, and number of low pulses. There was no correlation between HA values and physical characteristics of rivers or hydropower facilities (including installed capacity), and reaches with multiple facilities did not differ in HA from those with single facilities. This study demonstrates that SHPs as well as larger hydropower facilities cause hydrological alterations attributable to hydropeaking. Considering the rapid expansion of SHPs in tropical river systems, there is an urgent need to understand whether the ecological impacts of hydropeaking documented in temperate biomes also apply to these systems.
The general perception of small run-of-river hydropower plants as renewable energy sources with little or no environmental impacts has led to a global proliferation of this hydropower technology. However, such hydropower schemes may alter the natural flow regime and impair the fluvial ecosystem at different trophic levels. This paper presents a global-scale analysis of the major ecological impacts of three main small run-of-river hydropower types: dam-toe, diversion weir, and pondage schemes. This review's main objective is to provide an extensive overview of how changing the natural flow regime due to hydropower operation may affect various aspects of the fluvial ecosystem. Ultimately, it will inform decision-makers in water resources and ecosystem conservation for better planning and management. This review analyses data on ecological impacts from 33 countries in five regions, considering the last forty years' most relevant publications, a total of 146 peer-reviewed publications. The analysis was focused on impacts in biota, water quality, hydrologic alteration, and geomorphology. The results show, notably, the diversion weir and the pondage hydropower schemes are less eco-friendly; the opposite was concluded for the dam-toe hydropower scheme. Although there was conflicting information from different countries and sources, the most common impacts are: water depletion downstream of the diversion, water quality deterioration, loss of longitudinal connectivity, habitat degradation, and simplification of the biota community composition. A set of potential non-structural and structural mitigation measures was recommended to mitigate several ecological impacts such as connectivity loss, fish injuries, and aquatic habitat degradation. Among mitigation measures, environmental flows are fundamental for fluvial ecosystem conservation. The main research gaps and some of the pressing future research needs were highlighted, as well. Finally, interdisciplinary research progress involving different stakeholders is crucial to harmonize conflicting interests and enable the sustainable development of small run-of-river hydropower plants.
Tropical river basins have experienced dramatically increased hydropower development over the last 20 years. These alterations have the potential to cause changes in hydrologic and ecologic systems. One heavily impacted system is the Upper Paraguay River Basin, which feeds the Pantanal wetland. The Pantanal is a Ramsar Heritage site and is one of the world's largest freshwater wetlands. Over the past 20 years, the number of hydropower facilities in the Upper Paraguay River Basin has more than doubled. This paper uses the Indicators of Hydrologic Alteration (IHA) method to assess the impact of 24 of these dams on the hydrologic regime over 20 years (10 years before and 10 years after dam installation) and proposes a method to disentangle the effects of dams from other drivers of hydrologic change using undammed “control” rivers. While most of these dams are small, run-of-the-river systems, each dam significantly altered at least one of the 33 hydrologic indicators assessed. Across all studied dams, 88 of the 256 calculated indicators changed significantly, causing changes of 5–40%, compared to undammed reaches. These changes were most common in indicators that quantify the frequency and duration of high and low pulses, along with those for the rate and frequency of hydrologic changes. Importantly, the flow regime in several undammed reaches also showed significant alterations, likely due to climate and land-use changes, supporting the need for measurements in representative control systems when attributing causes to observed change. Basin-wide hydrologic changes (in both dammed and undammed rivers) have the potential to fundamentally alter the hydrology, sediment patterns, and ecosystem of the Pantanal wetland. The proposed refinement of the IHA methods reveals crucial differences between dam-induced alteration and those assigned to other drivers of change; these need to be better understood for more efficient management of current hydropower plants or the implementation of future dams.
Maintenance and restoration activities alter the river morphology and hydrology, and in consequence, alter fish habitats. The aim of this research was to investigate the change of habitat availability for fish guilds after carrying out maintenance works, commonly used river restoration measures and a restoration derived from fish habitat requirements. The selected study site is located at a close to natural condition section of Swider River in central Poland. The MesoHABSIM model was used to assess the area of suitable habitats in this site and predict habitat distribution at all planning scenarios. The affinity index which is a measure of similarity of two distributions showed that the likely distribution of habitats for fish resulting from simulated maintenance is 76.5% similar to that under measured conditions. The distribution of habitats caused by river restoration is also similar to that of the baseline in 73.2%. The resemblance between the restoration scenario focusing on fish habitat requirements and the reference conditions is 93.1%. It is beneficial to define the river restoration measures based on habitat availability for fish community. Modelling is a useful tool to simulate the changes and predict which guilds there is abundance of suitable habitats, and for which there are too few. It allows for more effective use of resources according to quantitative target states.
The meso-scale habitat simulation model MesoHABSIM was applied in three Lithuanian lowland rivers to study the effect of low-head hydropower plants (HPPs) on the fish habitats. Stream flow time series on a daily scale for the period 1970–2015 were used to describe flow regime downstream of HPPs for periods before and after their installation. Conditional habitat suitability criteria were developed for 4 species of cyprinid fish, schneider (Alburnoides bipunctatus), dace (Leuciscus leuciscus), roach (Rutilus rutilus) and vimba (Vimba vimba) to simulate their available habitat at different water discharges. Modelling results showed that HPPs have a significant impact on habitat availability in the low flow period in dry years below HPPs due to insufficient released flow. The environmental flow, as prescribed by the Lithuanian national law, is estimated between 80 and 95% exceedance probability of the mean minimum discharge of 30 days. This flow leads to a significant reduction in frequency and duration of available suitable habitats for vimba and schneider during low flow period. The roach habitat is the least affected. The results of habitat modelling are in line with the actual data on the occurrence and relative abundance of considered fish species in the studied river stretches. A general comparison of the relative abundance of modelled fish species in 42 natural river stretches and 20 stretches below the HPPs also showed that the relative abundance of roach is significantly higher, and that of schneider is significantly lower in river sections below the HPPs than the abundance in natural river sections. All results indicate that the current environmental flow does not secure survival of certain fish species. The applicability of the average low flow release during summer could be a plausible alternative to the current environmental flow in order to maintain ecosystem health and services.
Hydroelectricity is critical for decarbonizing global energy production, but hydropower plants affect rivers, disrupt their continuity, and threaten migrating fishes. This puts hydroelectricity production in conflict with efforts to protect threatened species and re-connect fragmented ecosystems. Assessing the impact of hydropower on fishes will support informed decision-making during planning, commissioning, and operation of hydropower facilities. Few methods estimate mortalities of single species passing through hydropower turbines, but no commonly agreed tool assesses hazards of hydropower plants for fish populations. The European Fish Hazard Index bridges this gap. This assessment tool for screening ecological risk considers constellation specific effects of plant design and operation, the sensitivity and mortality of fish species and overarching conservation and environmental development targets for a river. Further, it facilitates impact mitigation of new and existing hydropower plants of various types across Europe.
Hydroelectricity is critical for decarbonizing global energy production, but hydropower plants affect rivers, disrupt their continuity, and threaten migrating fishes. This puts hydroelectricity production in conflict with efforts to protect threatened species and reconnect fragmented ecosystems. Assessing the impact of hydropower on fishes will support informed decision-making during planning, commissioning, and operation of hydropower facilities. Few methods estimate mortalities of single species passing through hydropower turbines, but no commonly agreed tool assesses hazards of hydropower plants for fish populations. The European Fish Hazard Index bridges this gap. This assessment tool for screening ecological risk considers constellation specific effects of plant design and operation, the sensitivity and mortality of fish species and overarching conservation and environmental development targets for a river. Further, it facilitates impact mitigation of new and existing hydropower plants of various types across Europe.
Hydropower is considered a renewable form of energy production, but generating
electricity from rivers is not always environmentally benign. The global demand for
renewables is increasing rapidly as fossil fuels are gradually phased out, so rivers will
continue to be subjected to the pressures imposed by hydropower for decades to come.
Finding ways of operating hydropower plants that limit impacts on downstream river
ecosystems is therefore a pressing global concern. Usually, these plants cause marked and
rapid fluctuations in flow in downstream river reaches, termed ‘hydropeaking’.
Hydropeaks result in a variety of ecological changes in the dynamic mountain rivers they
typically affect; declines in fish and insect populations are evident, especially in reaches
immediately downstream from the plant. While these changes are often acute and readily
apparent, the underlying causal mechanisms remain unclear. We argue here that riverbed
sediments are a critical but neglected causal link between hydropeaking flow regimes and
ecological changes. We outline how a variety of tools from different branches of river
science can now be brought together to understand precisely why hydropeaking alters
sediment dynamics; these tools provide a mechanistic explanation for changes in bed
sedimentary conditions and channel form across multiple scales and, consequently, a
better understanding of ecological changes. By allowing us to simulate the effects of flow
fluctuations on sediment dynamics and channel form, these tools also allow us to develop ways of releasing water from hydropeaking dams that limit impacts on aquatic habitat and species.
The impacts of reservoirs, especially multiple reservoirs, on the flow regimes and ecosystems of rivers have received increasing attention. The most widely used metrics to quantify the characteristics of flow regime alterations are the indicators of hydrologic alteration (IHAs) which include 33 parameters. Due to the difference in the degree of alteration and the intercorrelation among IHA parameters, the conventional method of evaluating IHA parameters that assigns the same weight to each indicator is obviously inadequate. A revised IHA method is proposed by utilizing the projection pursuit (PP) and real-coded accelerated genetic algorithm (RAGA). Data reliability is analyzed by using the length of record (LOR) method. The projection values reflecting the comprehensive characteristics of the evaluation parameters are calculated. Based on these methods, a scientific and reliable evaluation of the cumulative impacts of cascading reservoirs on the flow regime was made by examining the Jinsha River. The results showed that with the increase in the number of reservoirs, the alteration degrees of IHA parameters gradually increased in groups 1, 2, 3 and 4 but decreased in group 5 (each group addresses the magnitude, timing, frequency, duration and rate of change in turn), and the flow duration curves showed a declining trend at the high-flow part and an increasing trend at the low-flow part. The flow regime alteration of the outlet section was more stable than before. This change had a negative impact on downstream fish reproduction and ecological protection. An attempt at ecological regulation was made to simulate the natural rising process of water, and four major Chinese carps have a positive response to the flood peak process caused by manual regulation.
Fish resources in the mid-downstream of the Hanjiang River have showed a serious decline in past decades due to eco-environmental degradation. This study aims to analyze the effects of hydrological alteration on fish population structure and habitat by combining the IHA-RVA method, the FLOWS method and the fish resources survey. Based on the change-points (the years 1990 and 2012) detected in the runoff time-series of the Huangzhuang hydrological station, we divided the study period into three periods: 1956–1989 (Period I), 1990–2011 (Period II), and 2012–2017 (Period III). The percent change in runoff D0 between the different periods (I-II, II-III, I-III) are 42.2%, 69.28%, and 81.68%, respectively. The monthly average flow increased during the dry season but decreased in the wet season. The rise rate of flow showed a 46% and 35% reduction in Period (II) and Period (III), respectively. The average 1-day maximum flow reduced from 12473.6 m³/s to 4466.7 m³/s, while its occurrence time also changed from July and mid-September to mid-August. The average high pulse count in Period (III) had a 38% reduction compared to that in Period (I). The number of species of fish spawning drifting eggs decreased by 6 species, so did the carnivorous fish. In addition, the spawning grounds in the Yicheng-Zhongxiang section was seriously deteriorating. The proportion of omnivorous fish and small fish increased by 16.5% and 24.5% during the past 62 years, respectively. The trend of miniaturization and aging of fish was significant. For Coreius heterodon, the number of suitable fish habitat sections in the study area has decreased from three to zero, while Cyprinus carpio could adapt to changing environment. Our results provide important clues for a better understanding of the changes in fish population structure and habitat under hydrological alteration.
Application of instream habitat models such as the Mesohabitat Simulation Model (MesoHABSIM) is becoming increasingly popular. Such models can predict alteration to a river physical habitat caused by hydropower operation or river training. They are a tool for water management planning, especially in terms of requirements of the Water Framework Directive. Therefore, model verification studies, which investigate the accuracy and reliability of the results generated, are essential. An electrofishing survey was conducted in September 2014 on the Stura di Demonte River located in north-western Italy. One hundred and sixteen bullhead—Cottus gobio L.—were captured in 80 pre-exposed area electrofishing (PAE) grids. Observations of bullhead distribution in various habitats were used to validate MesoHABSIM model predictions created with inductive and deductive habitat suitability indices. The inductive statistical models used electrofishing data obtained from multiple mountainous streams, analyzed with logistic regression. The deductive approach was based on conditional habitat suitability criteria (CHSC) derived from expert knowledge and information gathered from the literature about species behaviour and habitat use. The results of model comparison and validation show that although the inductive models are more precise and reflect site- and species-specific characteristics, the CHSC model provides quite similar results. We propose to use inductive models for detailed planning of measures that could potentially impair riverine ecosystems at a local scale, since the CHSC model provides general information about habitat suitability and use of such models is advised in pre-development or generic scale studies. However, the CHSC model can be further calibrated with localized electrofishing data at a lower cost than development of an inductive model.
The increasing number of water abstractions and water-use conflicts in alpine regions represents a significant threat for these fragile aquatic ecosystems. The use of tools, like multicriteria analysis (MCA), can support related decision-making processes towards sustainable solutions. In this paper, an innovative approach to assess water withdrawals sustainability by integrating the MesoHABSIM (Mesohabitat Simulation Model) into an MCA framework is presented and discussed. The methodology was implemented by replacing, within the MCA assessment, Water Framework Directive biological indicators with the MesoHABSIM based river Habitat Integrity Index, related to watercourse discharge and morphology, which allows quantifying the impacts of withdrawals on river ecosystems and fish communities. The resulting MCA procedure considers four criteria (energy, environment and fishing, landscape, economy) and requires only the use of measurable indicators based on watercourse discharge and its continuous monitoring. It was tested in Aosta Valley region (NW Italy) to both ex ante and ex post scenarios, for different types of water withdrawals and, currently, 20 experimentations, involving 58 hydropower plants and 12 farmer consortia, are ongoing. The proposed MCA process demonstrated its applicability with an increased decision-making quality and involved stakeholders’ satisfaction and is being officially endorsed in the regional River Strategic Plan.
The paper presents an efficient methodology of water body extent estimation based on remotely sensed data collected with UAV (Unmanned Aerial Vehicle). The methodology includes the data collection with selected sensors and processing of remotely sensed data to obtain accurate geospatial products that are finally used to estimate water body extent. Three sensors were investigated: RGB (Red Green Blue) camera, thermal infrared camera, and laser scanner. The platform used to carry each of these sensors was an Aibot X6—a multirotor type of UAV. Test data was collected at 6 sites containing different types of water bodies, including 4 river sections, an old river bed, and a part of a lake shore. The processing of collected data resulted in 2.5-D and 2-D geospatial products that were used subsequently for water body extent estimation. Depending on the type of used sensor, the created geospatial product, and the type of the water body and the land cover, three strategies employing image processing tools were developed to estimate water body range. The obtained results were assessed in terms of classification accuracy (distinguishing the water body from the land) and geometrical planar accuracy of the water body extent. The product identified as the most suitable in water body detection was four bands RGB+TIR (Thermal InfraRed) ortho mosaic. It allowed to achieve the average kappa coefficient of the water body identification above 0.9. The planar accuracy of water body extent varied depending on the type of the sensor, the geospatial product, and the test site conditions, but it was comparable with results obtained in similar studies.
Unmanned Aerial Vehicle (UAV) based Structure-from-Motion (SfM) techniques have renovated 3D topographic monitoring of earth surface, offering low-cost, rapid and reliable data acquisition and processing. Multi-temporal models of the river environment can be produced by autonomous operation in order to determine erosion, subsidence, landslide, soil transport and surface deformation in the riverbeds. Herein, the acquisition of repeated topographic surveys helps us to characterize the flow regime and to monitor the sediment dynamics. This study presents the hydromorphological changes of the meandering structures by using UAV-generated point clouds and Digital Surface Models (DSMs) produced by SfM at different times in the Büyük Menderes Basin located in the western part of Turkey. The processing of the data obtained with the flights were made in January and June 2018 at selected three meander locations with the highest visible changes according to the long-term satellite imageries. Especially, riverbank erosion along the river was determined by digitizing the edges and volumetric calculations of the eroded/deposited sediments derived from UAV-based measurements. In addition to the periodic volumetric differences of the meander structures, the differences in volumetric comparison methods for the same meander structures have been evaluated. Ultimately, the sediment profiles were extracted along the river banks at the selected part of the meanders and the amount of deposited sediments were determined to increase in a range between 1.5% and 3.3% of the total sediment. In conclusion, it is estimated that UAVs will be used instead of conventional photogrammetry aircraft in many future projects, considering the data production times and costs in large areas. Further, various digital cameras and sensors can be mounted on UAVs in order for examining the sediment effect on the health and productivity of plants in agricultural areas around the meanders.
Determination of environmental flows at the regional scale has been complicated by the fine-scale variability of the needs of aquatic organisms. Therefore, most regional methods are based on observation of hydrological patterns and lack evidence of connection to biological responses. In contrast, biologically sound methods are too detailed and resource-consuming for applications on larger scales. The purpose of this pilot project was to develop an approach that would breach this gap and provide biologically sound rules for environmental flow (eflow) estimation for the region of Poland. The concept was developed using seven river sites, which represent the four of six fish-ecological freshwater body types common in Poland. Each of these types was distinguished based on a specific fish community structure, composed of habitat-use guilds. The environmental significance of the flows for these communities was established with help of the habitat simulation model MesoHABSIM computed for each of the seven sites. The established seasonal environmental flow thresholds were standardized to the watershed area and assigned to the corresponding water body type. With these obtained environmental flow coefficients, a standard-setting formula was created, which is compatible with existing standard-setting approaches while maintaining biological significance. The proposed approach is a first attempt to use habitat suitability models to justify a desktop formula for the regional scale eflow criteria.
Construction of small hydropower plants (<10 megawatts) is booming worldwide, exacerbating ongoing habitat fragmentation and degradation, and further fueling biodiversity loss. A systematic approach for selecting hydropower sites within river networks may help to minimize the detrimental effects of small hydropower on biodiversity. In addition, a better understanding of reach‐ and basin‐scale impacts is key for designing planning tools. We synthesize the available information about (1) reach‐scale and (2) basin‐scale impacts of small hydropower plants on biodiversity and ecosystem function, and (3) interactions with other anthropogenic stressors. We then discuss state‐of‐the‐art, spatially explicit planning tools and suggest how improved knowledge of the ecological and evolutionary impacts of hydropower can be incorporated into project development. Such tools can be used to balance the benefits of hydropower production with the maintenance of ecosystem services and biodiversity conservation. Adequate planning tools that consider basin‐scale effects and interactions with other stressors, such as climate change, can maximize long‐term conservation.
Flow is a major driver of processes shaping physical habitat in streams and a major determinant of biotic composition. Flow fluctuations play an important role in the survival and reproductive potential of aquatic organisms as they have evolved life history strategies primarily in direct response to natural flow regimes (Poff et al. 1997; Bunn and Arthington 2002). However, although the organisms are generally adapted to natural dynamics in discharge, naturally caused flow fluctuations may entail negative consequences (e.g., stranding, drift, low productivity), especially if the intensity is exceptionally high or the event timing is unusual (Unfer et al. 2011; Nagrodski et al. 2012). Aside from natural dynamics in discharge, artificial flow fluctuations with harmful impacts on aquatic ecology can be induced by human activities. Hydropeaking—the discontinuous release of turbined water due to peaks of energy demand—causes artificial flow fluctuations downstream of reservoirs. High-head storage power plants usually induce flow fluctuations with very high frequencies and intensities compared to other sources of artificial flow fluctuations (Fig. 5.1). However, run-of-the-river power plants and other human activities may also create artificial hydrographs due to turbine regulation, gate manipulations, and pumping stations.
Since changes in climate and land use operate at broad spatial scales, efficient monitoring of temporal trends in fisheries resources over large geographies is vital to appropriate management. We compared statistical power of single- versus three-pass electrofishing surveys in detecting temporal trends of age 1 and older Brook Trout Salvelinus fontinalis populations in western North Carolina, USA. Empirical estimates of abundance and capture probabilities were obtained from annual three-pass depletion surveys at 14 headwater stream sites between 2012-2017. The coefficients of variation in abundance averaged 26% (SD = 14.2%) across study sites and mean capture probability per pass was 0.72 (Range = 0.57 – 0.84; SD = 0.09). Captures from single-pass sampling and abundance estimates from three-pass removal sampling were highly correlated (r2 = 0.98). Under the range of years sampled (5-25) and annual declines (2.5-7.5%) considered, power to detect temporal trends was similar (∆ power < 0.1) between the two methods when ≥ five sites were monitored. An additional set of simulations with varying capture probabilities demonstrated that differences in power between the two methods increased with lower mean capture probabilities (0.8, 0.5, and 0.2) and larger variation in capture probabilities among samples, suggesting results obtained with Brook Trout populations in North Carolina might not be applicable to other habitat types or species. Variation in fish abundance did not affect the difference in power between the two methods. Single-pass electrofishing surveys can be an efficient survey method to monitor temporal population trend for habitat types and species characterized with high capture probabilities and low variation among samples. However, single-pass data would not typically allow for inferences of capture probabilities and thus abundance. This can be problematic with varying environmental factors and comparisons among data sets collected with different protocols. This trade-off should be carefully considered when designing monitoring programs.
Identifying groundwater (GW)-surface water (SW) interactions in riparian zones is important for assessing the transport pathways of pollutants and all potential biochemical processes, particularly in rivers with artificially controlled water levels. In this study, we constructed two monitoring transects along the nitrogen-polluted Shaying River, China. The GW-SW interactions were qualitatively and quantitatively characterized through an intensive 2-y monitoring program. The monitoring indices included water level, hydrochemical parameters, isotopes (δ18O, δD, and 222Rn) and microbial community structures. The results showed that the sluice altered the GW-SW interactions in the riparian zone. A decrease in river level occurs during the flood season owing to sluice regulation, resulting in discharge of riparian GW into the river. The water level, hydrochemistry, isotopes, and microbial community structures in near-river wells were similar to those in the river, indicating mixing of the river water with the riparian GW. As the distance from the river increased, the percentage of river water in the riparian GW decreased, whereas the GW residence time increased. We found that nitrogen may be easily transported through the GW-SW interactions, acting as a sluice regulator. Nitrogen stored in river water may be removed or diluted by mixing GW and rainwater during the flood season. As the residence time of the infiltrated river in the riparian aquifer increased, nitrate removal increased. Identifying the GW-SW interactions is crucial for water resource regulation and for further tracing the transport of contaminants such as nitrogen in the historically polluted Shaying River.
Hydropower production is a key electricity generation technology in many parts of the world which can play a significant role in the transition towards a green and clean energy system. Hydropower can mobilize flexible energy on demand (hydropeaking) to balance out intermittent electricity from wind and photovoltaics. Adoption of hydropower as a peaking power source could lead to increased frequency of flow ramping in rivers downstream hydropower tailraces, which is one of the main stressors for riverine biota in alpine rivers. Both planned and accidental shutdowns of hydropower turbines need ecological mitigation. Our survey revealed that >3000 km of rivers downstream ca 800 hydropower plants in Norway may be ecologically impacted by non-natural flow fluctuations, and few have appropriate mitigation thresholds. A considerable eco-friendly peaking service may come from the Norwegian hydropower portfolio of over 19 GW installed capacity, with outlets into fjords, reservoirs or other large water bodies which normally dampen the ecological impacts of flow ramping. Intensive flow ramping occurs with irregular intervals from most types of hydropower. Although the highest frequency of stops were revealed in hydropower turbines not impacting river flow from storage hydropower, a significant number of turbine flow stops lasting over half a day in most types and categories of diversion hydropower.
We suggest that further emerging ecosystem-based mitigations need to be adapted in hydropower licenses. This includes operational thresholds for both up and down ramping, constructional measures like by-pass valves, retention basins and increased base-flow or flow cap to ensure sustainability for hydropower operations.
Our data reveal some of the most intensive hydropeaking operations from hydropower impacting longer rivers. Hence, our data underpins the potential for restoring downstream modified flow by ecosystem based measures related to both up and down ramping events in many regulated rivers.
With small cascade hydropower projects (SCHPs) increasingly employed in small and medium rivers, methods to assess changes in health status within the stream system have become essential to river ecological environment management. In this study, we used a cloud based fuzzy evaluation method to synthetically diagnose the health status of a stream, both as a whole and its parts (hydrological regime, riparian landscape, aquatic community, water quality, and social demand), under the impacts of SCHPs. The results indicated that: (1) average maximum and minimum flows decreased by 20% and 10% respectively, since SCHPs were implemented. Furthermore, the 38% increase in low flow frequency indicated that SCHPs might amplify droughts, the opposite of large hydropower projects which have been shown to alleviate drought; (2) implementation of SCHPs enhanced heterogeneity and fragmentation in riparian landscapes and decreased diversity of riparian vegetation, and dominant species were more likely to emerge on the upstream side of dam; (3) diversity of phytoplankton, zooplankton, and benthic animals decreased by 14%, 4%, and 16%, respectively, during high-impact period (HIP); and fish species decreased by 26% with a shift from rapid flow adapted to lentic and slow flow adapted species; and (4) the stream still exhibited a healthy state during HIP, but the degree of certainty belonging to “healthy” decreased from 0.279 to 0.192, indicating that the stream health was nearing a deteriorated state. This evaluation model clarified imperceptible and fuzzy changes in stream health which will be helpful in follow-up management decisions.
Implementing environmental flow (e-flow) is a key measure for restoring and managing river ecosystems. However, illegal competition for water resources or alterations of the natural flow regimes can result in the shortage of e-flow and degradation of river ecosystems. Monitoring and managing e-flow is increasingly critical and necessary in some regions. In this study, a monitoring method and guarantee rate evaluation system for e-flow was developed using remote sensing and hydrological data of the Jiulongjiang and Taizi rivers, China. The results indicated that the monthly e-flow varied with the water demand, ranging from 12.60 m³/s to 189.50 m³/s and 3.50 m³/s to 57.70 m³/s at Punan station, Jiulongjiang River and Tangmazhai station, Taizi River, respectively. Moreover, e-flow accounted for 24% of the average annual runoff for both rivers, which indicated that the ecological environment was in a fair or degrading state. Moreover, the guarantee rate of e-flow at Tangmazhai station is 100%, which indicates that the e-flow meets the requirements and is consistent with the results of the e-flow guarantee rate calculated by the actual measured flow. The guarantee rate of e-flow at Punan station is 0%, and exhibits a certain error with the actual measurement results; this is because a rectangular section exists between the maximum and minimum ecological water levels, which corresponds to a small change in the ecological water surface width of 0.9 m. The low-resolution remote sensing used in this study cannot capture this change, thus causing a large error in the measured result; however, this issue can be addressed by improving the remote sensing technique. The results showed that the monitoring method and guarantee rate evaluation of e-flow can be adopted for several basins, including larger scale river basins, and can improve e-flow management for mitigating the degradation of river ecosystems.
Runoff prediction in ungauged and scarcely gauged catchments is a key research field in surface water hydrology. There have been numerous studies before and since the launch of the predictions in ungauged basins (PUB) initiative by the International Association of Hydrological Sciences in 2003. This study critically reviews and assesses the decadal progress in the regionalization of hydrological modeling, which is the major tool for PUB, from 2000 to 2019. This paper found that the journal publications have noticeably increased in terms of PUB in the past 7 years, and research countries have been expanded dramatically since 2013. The regionalization methods are grouped into three categories including similarity‐based, regression‐based, and hydrological signature‐based. There are more detailed researches focusing on the interdisciplinary and profound improvement of each regionalization method. Namely, tremendous efforts have been made and lots of improvements have been carried out in the parameterization domain for the post‐PUB period. However, there is still plenty of room to improve the prediction capability in data‐sparse regions (e.g., further verification and proof of multi‐modeling adaptation and uncertainties description). This paper also discusses possible research directions in the future, including PUB in a changing environment and better utilization of multi‐source remote‐sensing information.
This article is categorized under:
• Science of Water > Science of Water
Abstract
The concept map of hydrological regionalization methods for runoff prediction in ungauged catchments
River monitoring is a critical issue for hydrological modelling that strongly relies on the use of Flow Rating Curves (FRCs). In most of the cases, FRCs are approximated by least-squares fitting, whose performance may be influenced by measurements variability, which is often limited in high values. In this context, a new formulation has been recently introduced to exploit available knowledge on cross-sectional geometry for a more robust derivation of FRCs. This method combines the wetted-area/stage and the cross-sectionally averaged velocity/stage functions in the FRCs derivation limiting, at least partially, the uncertainty in the extrapolation of higher discharge values. The methodology is tested on four gauged cross-sections of the Tiber River basin, where a relatively high number of measurements are available. This dataset is used to test the reliability of the new approach with respect to the classic method in relatively stable river cross-sections. A jackknifing approach is used to understand the role played by the number of gaugings and range of observations on the applicability of the new formulation highlighting its advantages in data-scarce environments. In particular, we observed that the new approach becomes advantageous when the observations are limited both in terms of the range of observations or in terms of sample size (i.e., <10 samples).
The runoff volume altered by the construction of hydropower plants affects eco‐hydrological processes in catchments. Although the impacts of large hydropower plants have been well‐documented in the literature, few studies have been conducted on the impacts of small cascaded hydropower plants (SCHPs). To evaluate the impacts of SCHPs on river flow, we chose a representative basin affected by hydropower projects and, to a lesser degree, by other human activities, i.e., the Qiuxiang River basin in Southern China. The observed river discharge and climate data during the period of 1958–2016 were investigated. The datasets were divided into a low‐impact period (LIP) and a high‐impact period (HIP) based on the number of SCHPs and the capacities of the reservoirs. The daily river discharge alteration was assessed by applying the Indicators of Hydrologic Alteration (IHA). To separate the impact of the SCHPs on the local river discharge from that of climate‐related precipitation, the back‐propagation neural network (BPNN) was used to simulate the monthly average river discharge process. An abnormal result was found: unlike large reservoirs in large watersheds, the SCHPs regulated the flows during the flood season but were not able to mitigate the droughts during the dry season due to their limited storage and the commonly‐occurring inappropriate inter‐regulations of the SCHPs. The SCHPs also reduced the annual average river discharge in the research basin. The contribution of the SCHPs to the river discharge changes was 85.37%, much higher than the contributions of climate change (13.43%) and other human activities (1.20%). The results demonstrated that the impacts of the SCHPs were different from those of large dams and reservoirs that regulate floods and relieve droughts. It is necessary to raise the awareness of the impacts of these river barriers.
Incorporating limited ecological curves, a novel operation chart optimization method is proposed for the multipurpose hydropower systems, which is capable of improving power generation and overall ecological condition and alleviating ecological degradation under extreme dry or wet conditions. The method mainly includes: (1) determine the optimal ecological discharge using weighted usable area-discharge curve based on the physical habitat simulation model (PHABSIM); and (2) establish the operation chart optimization model aiming to maximizing power generation and overall ecological condition and solve the model with DPSA; then (3) derive the limited ecological curves and incorporate them in the operation chart. A case study is performed with Jasajiang (JS) and Madushan (MDS) reservoirs on the Yuan River in southwestern China. The results show that the optimized operation charts result in a 1.72% and 5.99% increase in hydropower generation and a 0.27% and 1.13% increase in ecological conservation degree for MDS reservoir, respectively. In addition, the frequency of ecological damage is reduced from 6.11% to 1.11% for JS reservoir and from 26.67% to 3.89% for JS and MDS reservoirs, respectively. A further discussion using a time series of random runoff generated by first-order Markov model has confirmed the adaptability of this operation chart. The feasibility and potential applications of this operation chart has been confirmed.
Remote sensing (RS) and geographic information systems (GIS) techniques have become very important these days as they aid planners and decision makers to make effective and correct decisions and designs. Principal component analysis (PCA) involves a mathematical procedure that transforms a number of (possibly) correlated variables into a (smaller) number of uncorrelated variables. It reduces the dimensionality of the data set and identifies a new meaningful underlying variable (Gajbhiye and Sharma 2015a, b; Gajbhiye 2014; Gajbhiye 2015a, b). Morphometric analysis and prioritization of the sub-watersheds of Mohgaon River Catchment, Mandla district in Madhya Pradesh State, India, are carried out using RS and GIS techniques using satellite imageries and topographic maps. In this study, we apply PCA technique for redundancy of morphometric parameters and find the more effective parameters for prioritization of the watershed. The PCA produced more effective parameter form factor (R f), drainage texture (T) and length of overland flow (L o). Finally, the results of PCA reflect a good look on the prioritization of watershed.
Preservation of a good ecological status in riverine habitats emerged as a priority for water management policies in Europe since the negative impact caused by the construction and operation of dams on the ecohydrology and habitat availability became more evident. Ecological flows, as reported in the recently published European guidance, represent a link between water and habitat EU Directives. This study presents the application of a mesohabitat simulation model (MesoHABSIM) to evaluate and quantify ecological flows in a highly regulated Mediterranean watershed (Nestos River, Northern Greece). Data collection was performed through GIS/GPS mapping surveys, hydro-morphological measurements (water depth, flow, substratum type, etc.) and electrofishing samplings at mesohabitat scale under different discharge conditions. In total, 81 hydro-morphological units were surveyed and 7532 fish samples were collected to develop habitat suitability predictions. Ecological flows were calculated in the range 10–15 m³/s as the required discharge which assures the welfare and sustainability of protected fish species populations. In the lower course of the Nestos River habitat time-series indicated irrigation abstractions as a major stressor since summer was the period where habitat availability thresholds were mostly violated. Application of a revised water management plan is required for the downstream part of the Nestos River in order to maintain high ecological standards in the Natura 2000 sites of the Delta.
The Yangtze River is one of the largest and most important rivers in the world. Over the past several decades, the flow regime of the Yangtze River has been altered by human activities, particularly dam construction. Hydrological regimes will be further influenced due to more dams that have been planned and are being built in the upper reach of the Yangtze River (URYR). In this context, to assess the impacts of cascade dam development on the natural flows, four different scenarios of the reservoirs' combination are simulated with a hydrological model (the Soil and Water Assessment Tool) in the URYR. Flow regime changes were investigated using the eco-flow metrics and minimum/optimal ecological flow with the simulated daily river flows. The results indicate that eco-surplus in low flows and eco-deficit in high flows greatly increases due to reservoir operations when more reservoirs are put into service. The minimum ecological flow and the optimal ecological flow cannot be guaranteed from September to November, which is a crucial time for fish spawning. To maintain the natural regime while meeting the requirements for the river ecosystem, we propose that the lower and satisfactory operation limits are 11,680 m³/s and 7235 m³/s and 16,300 m³/s and 9130 m³/s, respectively. Optimizing cascade reservoir operational rules is needed to achieve a better balance between ecological and socio-economic demands in the Yangtze River Basin.