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Water infrastructure affects the quantity, quality, and environment of water. During reservoir construction, only the social-economic benefits were considered and the health of the downstream river was neglected. Due to the severe downstream river system, the operators and managers faced the challenge of the downstream ecosystem. Many scholars are concerned with the reservoir’s optimum functioning, which considers social and economic advantages. Numerous significant opinions and research findings are being presented on ecological scheduling at the moment, both in China and overseas, which surely deepen the connotations of ecological scheduling and serve as the research basis and critical reference of this work. The influence of hydropower development on hydrological conditions, the categorization and calculation of environmental runoff, and the building and solution of ecological scheduling models are all discussed and researched in this work. The study examined how the ChiTan hydropower project influenced the Jinxi River’s flow. The total hydrologic alteration calculated using RVA is 50.53%. The component analysis is also utilized to eliminate the statistical redundancy in the hydrologic indicators. The indicators’ monthly flow for July and August’s mean minimum flow for 7 days are relevant indicators for the Jinxi River basin’s hydrologic modification regime. [ABSTRACT FROM AUTHOR]

The study quantitatively assesses the hydrological alterations induced by the Luv Kush Barrage on the Ganga River, India, using the Range of Variability Approach (RVA) to analyze changes in flow conditions before and after the barrage construction. The Ganga River, a crucial water source for millions, has experienced significant hydrological changes due to human interventions, notably the construction of the Luv Kush Barrage. Employing indicators of hydrological alteration (IHAs), we compared pre-impact (1972–1994) and post-impact (2001–2014) flow data to ascertain the barrage's effects on the river's flow regime. Our findings reveal significant alterations in the magnitude of monthly streamflow, especially during the monsoon season, with notable decreases in July, August, and September. Alterations were observed in the annual extreme flow conditions, frequency, and duration of high and low pulses, indicating a comprehensive impact on the river's natural flow patterns. These alterations affect the river's ecological health, affecting aquatic habitats, fishery resources, and community livelihoods dependent on the river. The study underscores the necessity for integrated water resource management practices that consider the ecological and socio-economic implications of hydrological alterations. [ABSTRACT FROM AUTHOR]

The temporal changes in the effect of damming on the hydrological and ecological condition of a river and associated riparian wetland were examined in the present study. Does the degree of hydrologic and ecological alteration decline over time? Hydrological alteration was assessed in reference to the wetland water richness (WWR) modelling in three phases: pre-dam phase (up to 1992), post-dam phase 1 (1993–2012), and phase 2 (2013–2020). Periodicity of river flow at season scale was assessed usingthe wavelet transform model. The degree of ecological alteration was measured using a range of variability approach (RVA) and flow duration curve (FDC). From the analysis, it was revealed that after damming, the monthly flow failure rate increased (70–96%). The eco-deficit in the river was further exacerbated as the temporal distance increased. As a consequence of this, wetland water richness (WWR) maps of different phases exhibited continuous loss in the poor WWR parts. Eco-deficit condition of the wetland became severe in post-dam phase 1 and it was continued but with a lesser rate of increase in the next phase. The findings of this study would have significant implications for ecological flow management in rivers even after damming in order to continue eco-flow in downstream river reach and support riparian wetlands of immense ecosystem values. The study suggests conducting comparable studies with longer post-dam lengths in order to better determine how the effects of damming change over time. [ABSTRACT FROM AUTHOR]

Natural flow regime (instream ecological flow) is a vital element of ecological hydrology, serving a crucial role in the fundamental functions of river ecosystems. Intense human activities, especially reservoir operation, have unavoidably altered the flow regime of the Upper Huai River, leading to further impacts on river ecosystems. It is essential to quantify hydrological alterations in flow regimes and their associated impacts on river ecosystems for effective river water management. Ecological flow indicators, namely ecological deficit and surplus, were analyzed to assess instream ecological flow. The overall degree of alteration (Do) and the Dundee Hydrological Regime Alteration Method (DHRAM) were utilized to evaluate the degree of hydrological alteration. Additionally, the Shannon Index (SI) was employed to estimate the impact of hydrological alterations on ecological diversity in this study. The results reveal that the streamflow series underwent mutation in 1987, leading to a decrease in ecological surplus and an increase in ecological deficit. The overall alteration degree is 32%, with a DHRAM level of 3, signifying low hydrological alteration and moderate ecological risk in the region. Furthermore, the biodiversity of the river has markedly declined due to human activities following the alteration. HIGHLIGHTS Ecological deficit and surplus indicators were studied.; Degree of hydrological alteration was measured.; The impact of hydrological alterations on ecological diversity was studied.; Conservation of riverine ecological systems was studied.;

Researchers have long been trying to identify and estimate the impacts on the hydrological regime of rivers caused due to anthropogenic activities. In the present study, IHA was used to analyse the effect of dams on the flow regime of the upper and middle Narmada River. A total of 33 indicators were analysed to calculate Hydrological alteration due to dams in Narmada River. Average HA Index values of all 33 parameters are relatively higher for middle Narmada at Mandleshwar (0.86) than that of upper Narmada at Burmanghat (0.57). The average extreme water conditions have decreased both in frequency and in duration. Specifically, fewer floods and less low flow events have occurred in the post-dam period. The main purpose of this article is to identify and quantify the variations in the hydrologic regime so that the cumulative impacts of anthropogenic activities on water resources and the aquatic ecosystems may be reduced using proper water resource management strategies. [ABSTRACT FROM AUTHOR]

River hydrology is an important proxy for changes in river runoff and an important factor affecting the ecology of rivers. To quantitatively evaluate the hydrology of the Wuijang River basin, this paper uses various tests to analyze runoff. The IHA-RVA method combined with FDC ecohydrological indicators was used to evaluate the hydrology of the Wuijang River basin and to analyze and calculate the contribution of human activities and climate change to runoff. The results show that (1) the runoff in the Wujiang River basin has shown a decreasing trend over the years, with a sudden change in 2005 and mainly two inter-annual cycles; (2) the overall hydrological change in runoff is 48%, which is a moderate change; (3) The changes in FDC ecological indicators are significantly correlated with rainfall, and the correlation between FDC ecological indicators and IHA hydrological indicators is strong; (4) human activities are the main influencing factors of runoff changes in the Wujiang River. The results of this paper have some reference value for the management of the Wujiang River basin and the improvement and restoration of river ecology. HIGHLIGHTS Analysis of changes and trends in the hydrological situation of the Wujiang River basin over the past 60 years.; Analysis of the degree of change in the overall hydrological situation of the Wujiang River basin.; Comparison of results of hydrological situation analysis under multiple hydrological indicators.; Analysis of the contribution of climate change and human activities to hydrological change in the Wujiang River.;

Elucidating the impact of reservoir operation on hydrological signatures is crucial for the effective management of large rivers under the changing climate. This study first revised the reservoir operation scheme in the Soil and Water Assessment Tool (SWAT) model to improve its description of actual operation laws of reservoirs in the upper Yangtze River basin (UYRB). Then, we identified the reservoir-induced hydrological alteration through a hydrological index method driven by observed and simulated daily streamflow from 1960 to 2017. The results revealed the superiority of the revised reservoir algorithm in the SWAT model in simulating streamflow and floods at Cuntan and Yichang stations with the Nash-Sutcliffe efficiency (NSE) coefficient and the Kling-Gupta efficiency (KGE) coefficient improved from 0.01 to 0.08 and 0.01 to 0.05, respectively. Relative to the baseline period (1960–2002), the hydrological signatures in the impact period (2003–2017) changed substantially after 2003. Reservoirs induced a remarkable increase of 27.76% and 55.97% in streamflow from January to March, accompanied by a notable decrease of 6.95% and 20.92% in streamflow from September to October after 2003 at Cuntan and Yichang stations, respectively. Meanwhile, the annual streamflow range contracted, and the flow became more stable with a reduced variation in daily streamflow, extremely low flow spell duration, and extremely high flow spell duration. Consequently, our results improved the quantitative understanding of reservoir-induced alteration and informed the management and planning of reservoir construction in the UYRB under climate change. [ABSTRACT FROM AUTHOR]

Operation of the Dniester Hydropower Complex (DHC), build on the middle course of the Dniester River in the middle of the '80s of the last century and extended during last decades, on one hand, produces low-cost energy and contributes to local and regional economical development, but on the other hand, leads to modification of river flow and ecosystems in the downstream, creating a series of dilemmas that are difficult to manage and solve by bazinal countries, Ukraine and the Republic of Moldova. This research aims to assess the changes in flow, phases of the hydrological regime, water temperature and sediments’ regime due to the DHC operation. Main utilized approach was comparative analysis of hydrological time series recorded at the stations situated upstream and downstream of the DHC, for two representative time periods: before and after construction of this hydropower complex. As a result, it was estimated that the mean annual flow downstream the DHC decreased by 9.2%. Seasonal flow changed mainly by significant decrease in February-April (February - 18%, March - 40%, April - 27%), and increase in the autumn months, by 10-14%. Minimum flows upstream of the DHC, increased by 52%, and downstream have doubled, reaching 107 m3/s (compared to 51 m3/s, before the DHC construction). Maximum annual flow, in the upstream part, in the second period, has slightly increased, while towards the downstream part, there is a reduction of this parameter by about 30%. One of the direct impacts of the DHC operation is hydropeaking effect. Intraday level amplitude downstream of the DHC amounts to 52 cm and the length of the sector that is influenced by this effect is over 100 km. Also, a long river sector is subject to water thermal modifications: when upstream the average annual water temperature has risen by 0.8°C, in the downstream it has diminished by 0.44°C. On a monthly scale, there is a decrease in the water temperature in the spring-summer period, and an increase in the autumnwinter period downstream of the DHC. Sediment transport process was also altered significantly. Due to the DHC operation, suspended sediments decreased by 92-98% downstream of it. The significant decrease in sediment volumes is specific to all months of the year. The reduction of sediment transport has increased the transparency of water, which, as a result, influences the development of the aquatic ecosystems.

Climate change and human activities are two important factors in the changing environment that affect the variability of the hydrological cycle and river regime in the Yalong River basin. This paper analyzed the hydrological alteration and extremes in the Yalong River basin based on multi-source satellite data, and projected the hydrological response under different future climate change scenarios using the CwatM hydrological model. The results show that: (1) The overall change in hydrological alteration at Tongzilin station was moderate during the period of 1998–2011 and severe during the period of 2012–2020. (2) Precipitation (average 781 mm/a) is the dominant factor of water cycle on a monthly scale, which can explain the temporal variability of runoff, evaporation, and terrestrial water storage, while terrestrial water storage is also simultaneously regulated by runoff and evaporation. (3) The GRACE data are comparable with regional water resource bulletins. The terrestrial water storage is mainly regulated by surface water (average 1062 × 108 m3), while the contribution of groundwater (average 298 × 108 m3) is relatively small. (4) The evaporation and runoff processes will intensify in the future due to climate warming and increasing precipitation (~10%), and terrestrial water storage will be depleted. The magnitude of change will increase with the enhancement of emission scenarios. [ABSTRACT FROM AUTHOR]

Hydropeaking is known for its adverse impacts on river ecosystems. However, the implementation of mitigation measures is still largely pending due to conflicting priorities of ecology and economics, which require scenario building to assess trade‐offs. Therefore, widely applicable and standardized tools are needed to analyze hydropeaking hydrology in affected rivers to expedite mitigation efforts. Here, we present a novel empirical approach—PeakTrace—that can (a) detect and follow source‐specific hydropeaking waves in the downstream direction by using multiple hydrographs and (b) describe how to flow metrics of hydropeaking waves change along a river's course. In detail, PeakTrace first identifies associated flow events and then models translation and retention processes between neighboring hydrographs. Finally, the models can be combined to establish a non‐linear hydropower plant‐specific model. We demonstrate the PeakTrace method's usability in 16 Austrian case studies. The results underline the high performance of PeakTrace, describing the longitudinal development of flow metrics with high model accuracy up to 25 km or more. Ecologically‐relevant metrics, such as rate of change or amplitude, decrease with distance from the hydropower outlet regarding down‐ramping events; the same pattern can be observed for up‐ramping events too, except for the rate of change for which an intensity increase may be observed, probably due to slope and the roughness difference between base flow and peak flow. Overall, this paper underlines the usability of PeakTrace as a basis to assess hydropower plant‐specific hydro‐ecological impacts and evaluate hydropeaking mitigation measures, especially by incorporating critical flow thresholds of river biota and life stages. [ABSTRACT FROM AUTHOR]

• High-intensity dam operations have severely disturbed the power-law tails of natural river flows. • Damming reduced downstream connection duration, magnitude, accumulation, and efficiency. • Damming weakened seasonal patterns of lateral exchanges. • Increasing damming would lead to the exponential loss of downstream connectivity. • The power-law tails of natural flows have important implications for the entire ecosystem's integrity, diversity, and sustainability. High-intensity dam operations have severely disturbed the power-law behaviors of natural river flows, which have important implications for the entire ecosystem's integrity, diversity, and sustainability. This study investigated the effects of vanishing power-law tails of river flows caused by damming on downstream hydrological connectivity in the Wanquan river–floodplain (China) and determined the consequent ecological responses. A two-dimensional hydrodynamic model was established to estimate inundation regimes under different hydrological scenarios, and a statistics-based method was used to generate vanishing power-law tails. Connectivity assessments quantified the duration, magnitude, accumulation, and efficiency of connection events in the river–floodplain system for historical hydrological processes, current dam operating schemes, and simulated flow series with compressed power-law tails. The results showed significant reductions in downstream connection duration, magnitude, accumulation, and efficiency with compression of the natural power-law tail, especially for small (P < 20 %) and large (P > 90 %) connection events. Under a fully modified scenario, the cumulative large connection events were reduced by as much as 50 %. Damming also diminished the seasonal fluctuations of lateral exchanges and weakened the synergetic relationships among inflows, inundation extents and connectivity in the river–floodplain system. Furthermore, increasing damming led to an exponential and accelerated loss of downstream connectivity, with noticeable inflection points. Reduced or insulated hydrological exchanges would weaken material cycling, energy flow, and information transmission in the river–floodplain system, ultimately impacting the entire aquatic ecosystem. Our study emphasizes the importance of the power-law tail in the estimation of natural flows, which, although accounting for only a small part of the whole flow series (approximately 6 % in this case), is of great significance for maintaining the downstream connectivity necessary for healthy aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Hydrological regimes influence an aquatic ecosystem's biotic composition, structure, and functioning. But construction of dams or anthropogenic activities substantially alter the hydrologic regimes. In this study, we used a method named as the "Indicators of Hydrologic Alteration" to examine the degree of hydrologic alteration at seven flow gauge stations in the Mangla watershed. The assessment of alteration is carried out according to the Range of Variability (RVA). This method relies on analyzing hydrologic data obtained from existing measurement points (e.g., stream gauges) within an ecosystem or model-generated data. We used 33 parameters categorized into 5 groups based on magnitude, duration, frequency, timing, and rate of change to characterize hydrologic variation within a year statistically. We then examine the hydrologic perturbations by comparing the measure of central tendency and dispersion for each parameter between the "pre-impact (1967–1994)" and "post-impact (1995–2014)" periods. The results show that within the Mangla watershed, the high alteration was noted in the magnitude of monthly flows and extreme flows at Azad Pattan, Gari Habibullah, Palote and at Muzafarabad stations. The flow at Domel and Kohala stations are found in low hydrological alteration among all groups of indicators. The study indicates that Neelum Basin at Muzaffarabad has significantly high alteration with maximum negative values. On the other hand, a high frequency of alteration observed in the monthly flows and extreme water conditions. Overall, a moderate alteration is observed in the whole watershed, which may produce adverse effects on the aquatic ecosystem of the Mangla watershed. [ABSTRACT FROM AUTHOR]

This study evaluates future hydrological alterations caused by climatic changes until 2100 using climate change scenarios. The indicators of hydrologic alteration software program assess predicted changes in flow characteristics and the degree of hydrological alteration obtained through a range of variability approach analysis. The study was performed on the Hron River basin in Slovakia, using the daily discharges from the observation period of 1981–2010 and a modelled scenario of daily discharges until 2100. The time period investigated was divided into three periods among which four ranges of variability approach analysis were conducted. The study results presented assume an increased incidence of drought in the summer months. In the winter months, the period of increased flows is expected to intensify. [ABSTRACT FROM AUTHOR]

Background: A variety of anthropogenic stressors influences the ecological status of rivers wordwide. Important stressors include elevated concentrations of nutrients, salt ions, heavy metals and other pollutants, habitat degradation and flow alteration. Some stressors tend to remain underrepresented in multiple-stressor studies, which in particular is apparent for micropollutants (e.g. pesticides, pharmaceuticals) and alterations of the flow regime. This case study analysed and compared the effects of 19 different stressor variables on benthic macroinvertebrates in the two German rivers Erft and Niers (Federal State of North Rhine-Westphalia, Germany). The stressors variables were assigned to four stressor groups (physico-chemical stress, mixture toxicity of 42 micropollutants, hydrological alteration and morphological degradation) and were put into a hierarchical context according to their relative impact on the macroinvertebrate community using redundancy analysis and subsequent variance partitioning. Results: The results suggest a strong and unique effect of physico-chemical stress, yet at the same time reveal also a strong joint effect of physico-chemical and hydrological stressor variables. Morphological degradation showed subordinate effects. Notably, only a minor share of the explained variance was attributed to the mixture toxicity of micropollutants in these specific catchments. Conclusions: The stressor hierarchy indicates that management measures for improving the ecological status still need to address water quality issues in both rivers. The strong joint effect of physico-chemical stress and hydrological alteration might imply a common source of both stressor groups in these two catchment areas: lignite mining drainage, urban area and effluents of wastewater treatment plants. The findings point at the important role of alterations in the flow regime, which often remain unconsidered in hydro-morphological surveys. [ABSTRACT FROM AUTHOR]

Freshwater fish biodiversity is experiencing an alarming decline worldwide. Understanding the main factors behind its deterioration is a key step for ecosystem restoration. In this work, large‐scale and long‐term data were used to identify the causes of the decline of native species richness in Castilla‐La Mancha. This region in central Spain covers part of six river basins belonging to four of the 11 biogeographical provinces for freshwater fish in the Iberian Peninsula.Firstly, we built a dataset that associates the presence of several fish species and a wide range of environmental variables (e.g. hydrological and hydromorphological indicators, land use classes, presence of alien fish species) at selected river sites for two different time periods (1980–2000 and 2001–2020). Secondly, we conducted an exploratory data analysis to identify possible temporal trends in the dataset. Finally, we applied the random forest algorithm to predict the response of different ecological guild‐based metrics of fish richness to the selected variables.The exploratory data analysis revealed a decrease in native fish species richness in 74% of the area studied. There was no sustained temporal trend for stressor variables, except for the number of alien species, which increased in most river sites (63%). The models of the richness of native rheophilic, native intolerant, alien rheophilic, and alien limnophilic species performed satisfactorily. Magnitude of maximum discharge, presence of alien species, land use in the catchment area and altitude were the most important predictors of richness of native intolerant and rheophilic species. Alien limnophilic species proved to be sensitive to variables related to flow regime alteration, such as the presence of dams and the number of river flow reversals, while a less degraded habitat was found to be favourable to alien rheophilic species.The results suggest that the cumulative effect of persistent altered flow regimes and water pollution, coupled with a strong increase in the number of alien species, have led to the decline of native species in the area studied. The restoration of near‐natural magnitudes of high flows when implementing environmental flows emerged as a key measure to restore ecosystem integrity.Starting from a long‐term and large‐scale dataset, this study provides new, quantitative insights into stressor–ecosystem relationships in rivers and could inform future environmental policy initiatives because it has identified the main factors leading to native fish decline and alien fish proliferation. Our findings emphasise the importance of considering metrics based on fish assemblage composition and ecological functional groups in order to disentangle the effects of stressors on fish communities. [ABSTRACT FROM AUTHOR]

Anthropogenic activities and climate change have caused physical and ecological changes in lakes and have aggravated water level fluctuations, which are essential factors to consider for nutrient import, ecological protection, and biodiversity maintenance. Maintaining water levels within a reasonable range is essential for maintaining lake function and ecological health, because ecosystem stability is compromised when water level fluctuations exceed specific thresholds. Thus, the ecological water level (EWL) is an important index for maintaining aquatic habitats and biodiversity. A method for quantifying the EWL of lakes based on hydrological statistical analysis was constructed to bridge the gaps in existing studies, considering both the hydrological alteration and spatio-temporal heterogeneity of water level fluctuations. Taking Poyang Lake as an example, which has recently attracted increasing global attention owing to its water level alterations and subsequent ecological problems, the applicability of the method and rationality of the results were verified. The results indicate that hydrological alteration occurs at the water level of the representative stations, which is jointly affected by climate change and anthropogenic activities in this region. For instance, the construction and operation of the Three Gorges Project affected the water level alteration at Hukou and Xingzi station, and drought further aggravated that of Xingzi station. The calculated EWL of Poyang Lake showed obvious spatio-temporal heterogeneity, which is consistent with the topographic, geographical, and climatic characteristics of the basin. And the rationality of the EWL in this study was verified through literature reviews and satisfiability of characteristic species requirements. The proposed EWL calculation method is simple and feasible with easy data acquisition, strong universality, and broad application prospects, offering a scientific basis and quantitative reference for water resource management and lake ecosystem protection. • An ecological water level quantifying method for lakes based on hydrological statistical analysis is proposed. • Water level alteration occurs in Poyang Lake, which is jointly affected by climate change and anthropogenic activities. • The monthly ecological water level thresholds of Poyang Lake are quantified with obvious spatio-temporal heterogeneity. • The calculated ecological water level is reasonable, offering a quantitative reference for water resources management. [ABSTRACT FROM AUTHOR]

The conventional reservoir operation strategy considering hydropower production ignores the ecology of the downstream rivers and causes a series of environmental problems. To ensure the sustainable development of a reservoir, the operation strategy should consider both the economic benefits of the power station and the ecological benefits in downstream rivers, the key to which is to select suitable parameters for quantifying the ecological objectives of the rivers and incorporate them into the reservoir operation model. To this end, the ecological index (EI) based on the Indicators of Hydrological Alteration (IHA) was developed to reflect the ecology of the downstream rivers, and a reservoir ecological operation model that takes into account the power generation capacity of the power station and the degree of hydrological alteration was constructed, which can be solved using the Non-Dominated Sorting Genetic Algorithm II (NSGA-II). The results show that the mean EI values increase a lot, from 0.24 to 0.62, after the construction of reservoir, and the optimal reservoir operation strategy in each typical year can reduce the hydrological alteration significantly (the reduction rates of both the abundant and dry water years exceed 20%), while ensuring the hydropower production of the power station (the reduction rates of hydropower production are just 1.64%, 3.15%, and 3.16% for abundant, normal, and dry water years, respectively), which provides a good reference for restoring the natural hydrological situation of downstream rivers. [ABSTRACT FROM AUTHOR]

Study region: Eight rivers regulated by large dams located in three hydro-climatic zones along the Chilean latitudinal gradient. Study focus: We performed a multi-temporal scale analysis of flow records and we used data from official gauging stations to characterise the non-altered and the altered river regimes to determine the magnitude and persistence of the hydrological alteration downstream from large dams in Chile. These analyses provide relevant information to improve the understanding of such alterations, and a conceptual basis for assessing future impacts as the country plans to build a series of large dams in the coming years. New hydrological insights for the region: The mean annual runoff was reduced in all the study rivers. The monthly flows of the rivers from the northern arid zone were the most affected by the dams. The magnitude and frequency of floods decreased in all the study rivers. Moreover, northern drier river systems did not recover their hydrological conditions in the distance downstream of the dams, probably due to transmission losses and water extractions and diversions; in contrast, southern rivers partially recovered their flow regimes with distance downstream, mainly due to the inflows from permanent non-regulated tributaries. So far, this is the first study in Chile that comprehensively analyses the hydrological effects of large dams.

The construction of dams across rivers controls the magnitude of downstream floods and limits the suspended sediment transport into the downstream areas. We elucidated the downstream hydrological alterations compared to upstream after the construction of Kali Gandaki ‘A’ hydropower dam, Syangja, Nepal using continuous wavelet analysis, cross wavelet analysis and wavelet coherence. The downstream fluvial flow in winter and pre-monsoon seasons showed highest water deficit condition compared to monsoon and post-monsoon seasons. The dam-induced changes in fluvial flow with decreasing amount of sediment alter the downstream flood morphological characteristics of river reach such as flood depth, wetted perimeter of river section, flow velocity, and maximum and minimum floods together with the decrease in amount of suspended sediment. The dam-induced downstream alterations directly or indirectly create stress on the aquatic as well as terrestrial ecosystems. The findings of this study will be useful for hydropower dam gates operation that fulfils the minimum ecological threshold.

Study region: A channel fen in the Athabasca Oil Sands Area, Alberta, Canada Study focus: We assessed the hydrological changes to the hydrology of a moderate-rich fen after the construction of a road (perpendicular to flow) in 2003 and a pipeline (obliquely to flow) in 2011. New hydrological insights for the region: Flow obstruction was most prominent where the fen intersected the road. Changes to hydrophysical properties from pipeline construction were most pronounced in the top 10 cm of peat, which demonstrated significantly higher bulk density (by 170% and 112%) and lower hydraulic conductivity (by 94% and 91%) above the buried pipeline and in adjacent cleared locations, respectively, relative to areas not cleared or directly disturbed during pipeline development. Changes to water table levels from the pipeline were more pronounced farther down-gradient as the pipeline cut through the fen obliquely to direction of flow, and water tables became more variable on the side where the flow face had decreased in length. If built through peatlands, pipelines should be oriented parallel to flow direction and located along the central axis of the fen. Additional culverts should be considered in the event of building a pipeline through an already existing road to facilitate flow on either side.

Comprehensive assessment of hydrological alteration due to anthropogenic interventions is a prerequisite for sustaining the native biological profile and integrity of river ecosystems. This paper proposes a novel strategy to measurably evaluate how the dams have modified the natural flow regime at a downstream site. The Bhagirathi Basin, a part of the Himalayan ranges of the Ganga River Basin in India, is studied to comprehend the impact of multiple dams on natural river flow at Devprayag. The methodology for estimating the River Flow Health Index (RFHI) consists of four steps: (1) segregation of the flow data based on preimpact and postimpact periods, (2) identification of important hydrological parameters, (3) assessment of the alterations, and (4) development of an index indicating the health of the river flow during the altered period on a 0–1 scale. Results show that the different components of the flow regime have changed due to construction of dams across the river, and the hydrological alterations could be seen at the downstream site, Devprayag. The RFHI increased after subsequent addition of dams, i.e., 0.328 after commissioning of Maneri Bhali I hydro-electric projects (HEP), 0.374 after Maneri Bhali I HEP, Maneri Bhali II HEP, and Tehri HEP were commissioned, and 0.411 after Koteshwar HEP was commissioned in 2011. Our results may help upgrade the design and implementation of reservoir operation policies that consider downstream hydrological alterations. Further studies can be made to consider the coordination of hydrological alterations with different river ecosystem services important for the sustainable management of water assets. [ABSTRACT FROM AUTHOR]

Rivers are intensively managed worldwide through unprecedented flow regime alterations on a global scale. This has led to an increasing interest in the development of quantitative tools to assess the ecological response of organisms to flow alteration. To date, studies reflect a large diversity of responses that make the intensity and prevalence of effects difficult to generalize. The present study analysed how flow alterations caused by dams affect the structure, composition and traits of diatoms and macrophytes in three Spanish river basins (Cantabric, Ebro and Duero). By using a control‐impact design based mainly in hydrological similarity, our results showed consistent patterns of change in diatom and macrophyte communities. Our study showed a shift from resistant traits such as non‐colonial diatom forms and crust‐forming algae, which are adapted to the extreme events and natural dynamism of unregulated rivers, towards planktonic diatoms, free‐floating algae and the mass development of aquatic plants in hydrological altered sites. Both communities shared common thresholds of response to altered hydrological attributes that could be considered in a flow management context. The hydrological indices that impacted diatom and macrophyte communities the most were related with the magnitude and duration of minimum flows. However, our results also show that it is important to consider the interrelationships between the different hydrological attributes such as the seasonal variability of monthly flows, the magnitude of maximum annual extremes, the timing of flow events, and the frequency and rate of flow changes. [ABSTRACT FROM AUTHOR]

Hydropeaking by hydroelectric facilities generates sudden changes in river flows and can affect the composition, abundance and structure of fish and invertebrate populations over long distances. To assess the level of hydrological alteration, as a factor of risk of biological impacts, a synthetic indicator was developed. Based on the analysis of 97 hydrometric stations and 1575 years of unaltered flow data, rates of change in flow were calculated. Formulas representing the fastest natural variations, depending on the mean stream flow, the type of variation (increase or decrease) and the range of variation were established. Based on the analysis of 80 hydrometric stations and 491 years of flow data affected by hydropeaking, a method was developed to identify hydropeaks, essentially defined as variations with a rate of change greater than the maximum natural value computed using the formulas. A synthetic indicator differentiating five levels of hydrological alteration was developed using linear discriminant analysis based on five parameters characterizing hydropeaking regimes. Examples show that this indicator is sensitive to changes in the management of hydroelectric facilities and provides information on the spatial and temporal evolutions in hydropeaking regimes, including the progressive attenuation during downstream propagation. [ABSTRACT FROM AUTHOR]

The Tagus River basin faces a growing water management challenge, as water demand and river regulation by large multi-purpose reservoirs lead to situations of water scarcity and mediocre conditions in some water bodies. The current situation and the impacts of increasing water demands are evaluated by a detailed river basin model which covers the whole river basin and includes the main hydraulic infrastructures and water uses of Spain and Portugal. Several indicators are computed from the model results to assess water demand satisfaction and the alteration of the hydrological regime, offering a better understanding of current hydro-climatic conditions in the basin. Results show that current water management practices have significantly altered the natural river flow conditions in the entire Tagus River basin. Water managers struggle to satisfy existing waters uses and increasing water demands will further accentuate these problems. The enforcement of new and planned environmental flow requirements may alleviate the conditions of some water bodies but will decrease the level of satisfaction of non-priority water demands. As additional measures are needed to improve water bodies status, water management and allocation policies must be revised at the river basin scale to improve the balance between water consumptive uses and environmental needs. A shared knowledge base and a common vision on the basin challenges will be required to achieve these goals and the datasets and tools applied in this study contribute to this needed transboundary cooperation. [ABSTRACT FROM AUTHOR]

A reasonable assessment of the hydrological regime alteration is a prerequisite for river utilization, restoration, and protection. The hydrological alteration is quantified as changes in different indicators (IHAs) identified by Range of Variability Approach (RVA). However, RVA is unable to reveal the morphological characteristic which demonstrates the overall hydrological regime. This will lead to an incomplete assessment of the hydrological alteration. To supplement the current assessment, this work proposed a revised RVA method in three main steps: (1) to identify the morphological characteristics of each IHA; (2) to quantify the morphological alteration by comparing the Hasse matrices of different time series; (3) to combine the frequency alteration and morphological alteration of IHAs for reflecting overall hydrological alteration. A case study of the upper Yellow River shows that the revised RVA method outperforms RVA in the assessment of the hydrological regime not only because revised RVA captures the hydrological changes of certain IHAs that are not reflected by conventional RVA, but also the alteration identified by revised RVA shows more apparent differences at two stations upstream and downstream the dam than conventional RVA can provide. The revised RVA is more applicable to identify the hydrological alteration due to dam construction which could have negative impacts on river ecosystem since the morphological alteration of time series is considered. As a whole, the new method offers a better understanding of the alteration in hydrological regime, which gives beneficial guidance to river management. [ABSTRACT FROM AUTHOR]

Natural hydrological fluctuations within river floodplains generate habitat diversity through variable connections between habitat patches and the main river channel. Human modification of floodplains can alter the magnitude and frequency of large floods and associated sediment movement by interrupting these floodplain connections. The lower Wolastoq | Saint John River and its associated floodplain wetlands are experiencing anthropogenic disturbances arising from climate change, increased urbanization in the watershed, changing upstream agricultural landscape practices, and, most notably, major road and dam construction. By comparing digitized aerial images, we identified key periods of change in wetland extent throughout an ecologically significant component of the floodplain, the Grand Lake Meadows and Portobello Creek wetland complex, with significant erosion evident in coves and backwater areas across the landscape following dam construction and significant accretion around the Jemseg River following highway construction. Connectivity and hydrological regime also influenced other habitat components, namely nutrients and metals retention, as well as the composition of the local macrophyte community. These findings address two key aspects of floodplain management: (1) understanding how hydrological alteration has historically influenced floodplain wetlands can inform us of how the ecosystem may respond under future conditions, such as climate change, and (2) the mechanisms by which habitat diversity and disturbance regimes filter biological communities, with the potential for patches to host a rich biodiversity continuously supporting critical ecosystem functions.

Aim: River flow regimes are changing globally as a consequence of human use of freshwater resources. Additionally, rivers are among the most invaded ecosystems. Invasion biology predicts that the establishment and spread of non‐native species might be favoured both by new environmental regimes (niche opportunities) and by human‐mediated dispersal (propagule pressure). Here, we expand on past research by asking whether these two mechanisms act in isolation or whether they interact to facilitate the spread of non‐natives. Location: Conterminous USA. Time period: 1987–2016. Major taxa studied: Freshwater fishes. Methods: First, we examined the geography of riverine fish invasions across 1,148 watersheds spanning the conterminous USA. We focused on species richness and the life‐history strategies of non‐native (both translocated and exotic) relative to native species pools. Second, we quantified flow regime alteration as the deviation between observed and expected contemporary flow regimes, using a combination of spectral analyses on long‐term discharge data and random forest models. We focused on two biologically relevant facets of the flow regime: flow variability and flow seasonality. We also estimated metrics of propagule pressure: recreational fishing pressure and socioeconomic activity. We then compared the strength of evidence associating riverine fish invasions with flow alteration, propagule pressure, and interactions between the two mechanisms. Results: We found that alteration of flow variability and seasonality is widespread across the conterminous U.S. rivers, and has favoured invasions by filtering specific life‐history strategies. Importantly, high levels of flow stabilization and propagule pressure interacted: where co‐occurring, these two drivers were associated with higher fish invadedness levels than expected based on their individual effects. Main conclusions: Our results underscore the need to consider different drivers of invasion concurrently. Otherwise, important synergistic interactions might be missed that could explain (and guide management strategies to mitigate) the high levels of invasion in fresh waters. [ABSTRACT FROM AUTHOR]

Anthropogenic activities in the Krishna River have altered its flow regime and affected the ecosystems in the river. It is essential to maintain an optimum Environmental Flow (EF) in the river to recover from its deteriorated ecosystem. The present study is to estimate Environment Flow Requirement (EFRs) and the Hydrological Alteration (HA) (Flow changes) that take place on the Krishna River at five dam sites. Pre and post construction impact flow data are collected at five gauge stations which are located downstream of these five dams. The flow data which are impacted by climate variability are removed and the study is focussed on the impact of human activities. These EFRs are estimated using statistical relationships between the Krishna River flow regime and ecological indicator with the help of the Global Environmental Flow Calculator (GEFC). HA is used to analyse how the recommended EFRs are different in the post-impact period (after the dam construction). Hydraulic indicators like water depth and velocity are determined by importing estimated EF values into a Hydrologic Engineering Centre’s - River Analysis System (HEC-RAS) model. The habitation analysis is carried out to check whether the hydraulic indicators are providing an acceptable habitation for aquatic species in the study area. The results from HA analysis showed that the required EFRs in the Krishna River were not maintained for almost 43% of the time in the post impact period. The hydraulic analysis showed that recommended EFR is providing velocity in the range of 0.12 m/s to 1.08 m/s and water depth in the range of 0.23 m to 3.16 m throughout the basin. From the habitation study, it is observed that the results obtained from the GEFC approach is providing excellent habitation under the dams of Srisailam and Nagarjuna Sagar. Good habitation conditions are seen under Narayanapur, Ujjani, and PD Jurala dams.

Study region: The Medjerda is a transboundary catchment located in North-Eastern Algeria and shared with Tunisia. Study focus: In this study, we explore the causes of hydrological alteration of streamflow in a sub-catchment of the Medjerda in Algeria. The hydrological alteration was explored through the application of Mann-Kendall test based on possible explanatory factors, namely, precipitation, evapotranspiration, temperature, irrigation, and Normalized Difference of Vegetation Index (NDVI). Furthermore, the causal factors of streamflow variation were addressed using Convergent Cross Mapping (CCM) method. New hydrological insights for the region: Results of the trend analysis yield that the streamflow is altered during the period 1981−2012. This is consistent with the trends of the possible explanatory factors of this alteration. The Convergent Cross Mapping (CCM) method showed that streamflow alteration is unidirectionally caused by changes in patterns of precipitation, temperature, evapotranspiration, irrigation, and NDVI, and that there is little feedback from streamflow alteration to these causing factors. Overall, our assessment showed that the method used to identify the causal relationships in dynamical systems based on the CCM algorithm is suitable for exploring the drivers of the hydrologic alteration in multivariate time series, in particular when nonlinear dynamics determine the system.

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.

Accurate assessment of the effects of reservoir impoundment on the downstream hydrology and ecology is a prerequisite for the restoration of impaired rivers. However, little research has been conducted to directly link hydrological processes to biological processes. To address this knowledge gap, we used 15-year spawning records for four Chinese major carps in the middle Yangtze River; downstream of the Three Gorges Reservoir, China; and the hydrological data during these spawning events to identify the impaired components of the linkage between the hydrological processes and these fish spawning events due to reservoir impoundment. Results of this study show that the reservoir impoundment has led to a 14-day delay in the start of the spawning season, 10 fewer annual spawning days, a 2-day shortening of the duration of spawning events, and the disappearance of one peak spawning period. The delay in the spawning start date is connected to the decrease in water temperature caused by the cooling effect of the reservoir water released during the early spawning season, and the lower spawning activity throughout the spawning season is attributed to the insufficiency of the flow pulses, especially the decreases in both the duration and the rate of the flow increases. The acceptable and optimum flow criteria deduced from the pre-impoundment flow-spawning linkage can provide process-explicit environmental flow criteria for the spawning function restoration. This research presents an approach based on the flow-biotic process linkage for the assessment of impoundment-induced hydrological and ecological effects, and the process-based information can reduce the uncertainty in environmental flow management. [ABSTRACT FROM AUTHOR]

This paper aims to determine how both climate and local drivers, such as groundwater withdrawals influence surface water - groundwater interactions in Groundwater Dependent Ecosystems (GDEs). We studied the hydroperiod in eight of the most representative ponds of Doñana National Park (southern Spain) during a 21-year period. We analyzed the average flooded phase of each pond as well as the average depth of the piezometric level in nearby piezometers. In addition, we used the average precipitation as a proxy of the water inputs onto the ponds. The average flooded surface was taken by a previous analysis of satellite images and the depth to the piezometric level was field measured at a monthly time step. We found out that the average precipitation was slightly lower during the second decade (675 mm/y vs. 552 mm/y). Nonetheless, 5/8 of the ponds showed a much higher shrinking of the flooded surface that could not be explained only by a reduction in the precipitation events. Local drivers were found to be decisive in the degradation of 3/8 of the ponds: those closer to a pumping facility and located at a higher altitude. [ABSTRACT FROM AUTHOR]

River regulation by the construction of reservoirs represents one of the greatest challenges to the natural flow regime and ecological health of riverine systems globally. The Danjiangkou (DJK) Reservoir is the largest reservoir on the Hangjiang River and commenced operations in 1967. The reservoir was upgraded in 2012 to provide water resource for the South–North water transfer project through central China. However, the effect of the reservoir operations on the downstream hydrological regime and ecological health of the Hanjiang River following the upgrade (increase in dam height and reservoir capacity) has not been examined thus far. The daily discharge series from four stations along the main stem of the Hanjiang River, including a site upstream, were examined from 1950 to 2017. The study series was divided into three periods based on the difference stages of the reservoir operation: (1) 1950–1966, (2) 1967–2012 and (3) 2013–2017. The nature of hydrological alteration, ecological flow requirement and potential ecological risk during the different periods were investigated. The results clearly indicate that the DJK reservoir has significantly modified the hydrological regime in the middle and downstream section of the Hanjiang River, with most significant modifications recorded immediately downstream of the reservoir. None of the observed 'Range of Variability Approach' hydrological indicators fell within the expected range at Huangjiagang following the increase in reservoir capacity. As a result, the ecological flow requirements could not be guaranteed, and the frequency and intensity of ecodeficit increased. The river ecosystem immediately downstream of the dam was observed to be at high risk of ecosystem degradation during the post-dam periods considered. [ABSTRACT FROM AUTHOR]

Climate, land use, and land cover change can propagate alteration to the watershed environment. The interaction between natural and human activities probably accelerates the change, a phenomenon that will generate serious environmental problems. This study aims to evaluate the change in the hydrological regime due to natural and human-induced processes. The study was conducted in Brantas watershed, Indonesia, which is the largest watershed in East Java. This area is populated by more than 8 million inhabitants and is the most urbanized area in the region. An analysis of rainfall time series use to shows the change in natural phenomena. Two land-use maps at different time intervals were used to compare the rapid development of urbanization, and the discharge from two outlets of the sub-watersheds was employed to assess hydrological changes. The indicator of hydrological alteration (IHA) method was used to perform the analysis. The daily discharge data are from 1996 to 2017. The research results show an increase in flow (monthly, 1-day, 3-day, 7-day, 30-day, and 90-day flows) in the two sub-watersheds (Ploso and Kertosono) from the pre-period (1996–2006) to the post-period (2007–2017). [ABSTRACT FROM AUTHOR]

Understanding the extent to which human activities affect river flow is fundamental for enhancing effective water resources management. In past decades, various methods have been proposed to estimate naturalized flow (i.e. the expected flow if the basin is unaffected by human activities). However, there are still drawbacks to naturalized flow estimation, particularly in a highly regulated basin with incomplete hydrological observation. This study proposes a method for daily naturalized flow development at the key station of the Chao Phraya River Basin; the most highly regulated basin in Thailand. The naturalized flow is estimated by applying the Naturalization with Coarse and Fine Components (NCFC) method to perceive river flow conditions unaffected by human disturbance. The estimation is derived with the integration of five components: (1) observed river flow at the key hydrological station; (2) changes in major reservoir storage; (3) water withdrawal along the river; (4) travel time from major reservoirs to the station; and (5) the filtering technique used by Savitzky- Golay with a three-day window. [ABSTRACT FROM AUTHOR]

• Variations in DOM chemistry across the four periods were explored in Poyang Lake. • More terrestrial DOM inputs were detected during higher water levels periods. • CHOS formulas enhanced the autochthonous DOM features in the dry period. • Hydrological alteration affects DOM chemistry and its overall lability. As the largest reactive organic carbon pool, dissolved organic matter (DOM) plays an important role in various biogeochemical processes in lake ecosystems. Recently, climate change-induced extreme events (e.g., floods and droughts) have significantly modified the hydrological patterns of lakes worldwide, and regulated the quality and quantity of DOM. However, the responses of DOM chemistry to hydrological alteration in lakes remain poorly understood. Here we investigated the influences of hydrological alteration on sources, composition, and characteristics of DOM in Poyang Lake, the largest freshwater lake in China, using a combination of bulk chemical, optical and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) techniques. Results show various sources of DOM (autochthonous, allochthonous, and anthropogenic inputs) and significant variations in DOM chemistry across four hydrological periods (the retreating, dry, rising, and flooding periods) in Poyang Lake. During the retreating, rising, and flooding periods, DOM was characterized by higher aromaticity, humification degree, and recalcitrance, and exhibited pronounced allochthonous signatures. In contrast, DOM contained more S-containing molecules and aliphatic compounds during the dry period, displaying relatively stronger autochthonous features. Terrestrial inputs and the lignin-CHOS formation process are likely the primary underlying mechanisms shaping the differences in DOM chemistry in Poyang Lake. Our research demonstrates the significant impacts of hydrological alteration on DOM dynamics, and provides an improved understanding of DOM biogeochemical cycles and carbon cycling in large aquatic systems under global climate change. [Display omitted] [ABSTRACT FROM AUTHOR]

Environmental flow refers to the fundamental hydrological process that sustains the ecosystem of rivers and lakes. Safeguarding environmental flow is crucial for optimal water resource utilization and lake ecosystem preservation. The study delivers a comprehensive exploration of ecohydrology, focusing on the common analysis of runoff and water level (RWL) to evaluate ecohydrological conditions in Hongze Lake (HZL) over five decades (1970–2020). Techniques such as the change point test and wavelet analysis were employed to discern trends and periodicity in hydrological elements. A series of ecologically pertinent indicators was applied to measure the changes in RWL, assessing their impacts on the lake's ecosystem. The Budyko hypothesis and cumulative slope rate of change (CSRC) were integrated for a quantitative analysis that shed light on the ecological response to RWL variations. Differential effects of human activities and climate change on runoff were discerned through subsurface parameter analysis across different decades. The study's results indicate that human activities, particularly gate dam operations and agricultural irrigation, have precipitated a significant reduction in environmental flow components (EFCs). The gate dam manipulation during the dry season has notably influenced the lake's hydrological regime, with a substantial alteration of RWL by 37% and 41%, respectively. This hydrological modification aligns with observed ecological trends such as species population reduction, habitat fragmentation, and organism miniaturization within HZL. Analysis of subsurface parameters also reflected an increasing influence of climatic factors on runoff over time. Human activities, evapotranspiration, and precipitation were found to contribute 75.5%, 10.3%, and 14.2% to runoff alterations, and 70.1%, 11.4%, and 18.5% to water level (WL) changes, respectively. [Display omitted] • Runoff and water level exhibit significant synchronicity and correlation. • The water level rises by an average of 0.43 m during the impact period. • Downstream irrigation demand and dam regulation induce observable intra-annual alteration. • Hydrological indicators indicate a moderate 35–38% variation in both runoff and water level. • Human activities surpass climate factors accounting for 70.1–75.5% of water level and runoff changes. [ABSTRACT FROM AUTHOR]

Lake Baiyangdian, the largest natural freshwater wetland on the North China Plain, has faced multiple stressors from anthropogenic disturbances and climate change, affecting its aquatic ecosystem over the past century. An improved understanding of the relationship between environmental stresses and ecosystem responses and the mechanisms underlying ecological shifts has significant implications for managing the aquatic ecosystem in Lake Baiyangdian. In this paper, we reconstructed the ecological changes in Lake Baiyangdian over the past 70 years based on diatom assemblages in a sediment core and identified ecological shifts by the Sequential t test Analysis of Regime-shifts algorithm (STARS) and a sequential F test. Our results revealed two ecological shifts. The first ecological shift in the diatom community occurred in approximately 1963, which was associated with the rather abrupt changes, i.e., damming in the basin. This hydrological modification prolongs hydraulic residence time and accelerates nutrient retention, consequently leading to an increase in eutrophic species. Subsequently, the second ecological shift occurred in the 1990 s, which was attributed to sustained nutrient loading due to human activity intensification as well as an increase in the regional temperature. Ongoing nutrient loading finally pushed the lake toward a driver threshold, leading to an abrupt shift in the diatom assemblage. Our study details the complex trajectories of aquatic ecosystem shifts driven by hydrological alteration, increasing nutrient loading, and climate change in Lake Baiyangdian and highlights the processes by which ecological shifts occur in response to both abrupt and gradual stressors. [ABSTRACT FROM AUTHOR]

Increasing demand for renewable energy has led to a massive expansion of the small-scale hydropower plants and particularly those of run-of-river type. Meanwhile, the awareness concerning river conservation and restoration is being continually increasing. This study focuses on the assessment of environmental flows releases and energy production considering eight hydrological based environmental flows methods. The main goal of this study is to propose a practical approach that allows for quick estimation of the environmental flows releases and alteration due to water diversion for energy production, in the case of run-of-river hydropower plants. For this purpose, the indicators of hydrological alteration approach was applied to characterise flow alteration, and three economic metrics were used to assess the impact on energy production. Downstream Diversion Index was proposed to characterise the degree of water diversion due to energy production. Also, five new simplified indexes derived from indicators of hydrologic alteration approach were proposed to simplify flow alteration characterisation. The results of this study showed that a minor reduction of energy production could significantly improve environmental flows releases for the riverine ecosystem needs. Particularly, proportional dynamic approaches maximise energy production and imposes relatively less flow alteration. Also, it was concluded that following flow parameters: frequency, timing, duration and rates, can be maintained close to the natural regime without necessarily reducing the energy production by choosing the right environmental flows method. Finally, the methodology developed in this study can be a useful decision-making tool to help water managers, by including other relevant information also (i.e., biological, water supply, irrigation, and social) to choose the most appropriate method for the environmental flows determination in the case of run-of-river hydropower plants. Image 1 • Eight environmental flow methods were applied to estimate the implication on e-flow release and energy production. • Downstream Diversion Index (DDI) was introduced to characterise the degree of water diversion. • Five new indexes were derived from Indicators of Hydrological Alteration (IHA) to simplify flow alteration characterisation. • Proportional dynamic approach preserves essential flow regime parameters and maximises profitability. • Hydropower licensing should guarantee adequate e-flow release and ensure feasible investment. [ABSTRACT FROM AUTHOR]

The relationship between hydrological alteration and climate variability in the upper Yangtze River is not fully understood. In this paper, the periodicity features and the intercorrelation of annual and seasonal eco-flow metrics at the Yichang gauge station are analyzed for the period 1882 to 2013. Analysis is carried out to explore the formation of the eco-flow metrics and the possible linkages between eco-flow metrics and selected climate indices, using the cross-wavelet and wavelet coherence methods on data from 1948 to 2013. The results show that the variation of eco-flow metrics correlates well with some selected climate indices, but changes in different eco-flow metrics are complex. Most annual and seasonal eco-flow metrics correlate well with the Northern Hemisphere (N.H) and Indian Ocean Dipole (IOD) and have a significant common power in the two to four years band. In addition, most annual eco-flow metrics have an obvious phase relationship with the selected climate indices. However, the seasonal eco-flow metrics have no significant phase relationship with the selected climate indices. These findings provide a better understanding of how hydrological alterations of the streamflow and better water resource management can ensure ecosystem sustainability for the Yangtze River. [ABSTRACT FROM AUTHOR]

• We established large-scale patterns of hydrological alteration caused by dams. • We used a hydrological classification and we define types of altered regimes. • Variability of daily flows and high flow events were the most commonly altered features. • The hydrological alteration is influenced by the pre-dam nature of the altered rivers. • Types of altered regime and the purposes of the dams were not directly related. Nowadays, alteration of the natural flow regime is considered one the most widespread and damaging impacts for river ecosystems. Hence, increasing our understanding of large-scale hydrological alteration patterns would help us design more effective water use policies. The present study aims to establish general patterns of hydrological alteration caused by dams on a national level, with Spain as a case study. First, we developed a classification of the natural flow regime of the Spanish river network, which served as the reference to assess the degree of hydrological alteration of 139 altered-river gauges. In addition, using the flow series of the altered-river gauges we defined a set of 7 types of altered regimes (TARs), which allowed the stratification of the analyses. The results revealed that the magnitude and direction of hydrological alteration depended on the natural flow class of the altered rivers. In this regard, major effects of dams on Spanish rivers were related to the modification of the intra-annual variability of daily flow, the magnitude of seasonal maximum and minimum flows and the patterns of high flow events. Our results also showed that the distribution of the TARs partially followed a geographic order, but associations between TARs and natural flow classes were not straightforward. In addition, we highlighted that the nature of the hydrological alteration was independent of the registered dam uses. [ABSTRACT FROM AUTHOR]

Changes in streamflow and sediment runoffs would affect the reservoir's functional operation and the construction of soil and water conservation measures in China's Loess Plateau. In this study, the long‐term changes in streamflow and sediment were analyzed for a main stem section of the middle Yellow River where the to‐be‐built large Guxian Reservoir is to be located. Results showed that both streamflow and sediment had significant downward trends with the rates of −9.4 m3 s−1 yr−1 and −16.8 million t yr−1, respectively, during the period of 1961–2017. Using the range of variability approach, the change of streamflow regime in its postimpact period (1986–2017) was subjected to the moderate alteration, whereas the alteration of sediment regime was moderate and severe for the first (1980–1996) and second (1997–2017) postimpact periods. As an example, the attribution analyses of annual streamflow and sediment changes were conducted in a typical tributary catchment (Qingjian River) on the right bank of Guxian Reservoir. For the periods of 1980–2002 and 2003–2016, climate variability occupied the primary and secondary proportions to both streamflow and sediment reductions, respectively. Overall, human activities demonstrated the underlying contribution to the sharp declines of streamflow and sediment, accounting for 68% and 74%, respectively, during the period of 1980–2016. We suggest that, based on the operational life of warping dams (built on gully for mitigating gully erosion by raising the gully‐bed step‐by‐step), there are risks of flash flood and high sediment concentration events in the future because the streamflow/sediment‐reducing infrastructures may be damaged by extreme rainstorms and in turn become the flood and sediment amplifiers. [ABSTRACT FROM AUTHOR]

Highlights • Cause of emerging canopy gaps in the natural desert riparian forests was discussed. • Effect of hydrological alteration on the canopy gap disturbances was estimated. • Implications for ecological restoration of floodplain forests were put forward. Abstract Due to climate change and excessive human activities, runoff dynamics of the Tarim River in northwest China become more pronounced. Understanding the effects of hydrological alteration on the life strategy and dynamics of the Populus euphratica riparian forests is becoming increasingly important. Forest gaps led by such disturbances change the structure and function of the desert riparian forest ecosystems. However, there is a lack of research on the gap formation and dynamics of this special forest type, for which the main driving force of the gap disturbance has always been unknown. In this study, we investigated several parameters of P. euphratica forest gap, such as gap size, gap age, gap fraction, and gap makers to quantify the gap disturbance regimes in the natural floodplain forests along the Tarim River in arid northwest China. In the middle reaches of the Tarim River, a total number of 263 gap makers and 60 gaps in six 50 m × 50 m plots with a total area of 1.5 hm2 were investigated. The result showed that gap fraction was <5%, and approximately 28.5% of the expanded gaps were from 1.0 to 1.2 in size (ratio of gap diameter to tree height), especially when formed around 1997–2006. The median size of the expanded gap (140.57 m2) in the desert riparian forests was smaller than in tropical forests. P. euphratica was the most abundant gap maker, and its share among gap makers was 12–14 times larger than another species. Furthermore, gap makers contributed to the forest gap size, as shown by a significant correlation between the number of gap makers and the size of expanded gaps, especially those that had been created 50–60 years ago (R2 = 0.455, P < 0.01). The DBH distribution of living trees versus dead trees showed that most P. euphratica mortality occurred in small size classes. However, living trees were equally frequent in large classes, which suggested that large trees were not exclusively injured or died in these P. euphratica stands that were affected by poor habitats, such as water scarcity. We concluded that climate change and anthropogenic activities (increasing water use for irrigation) since the 1970s led to the progressive decrease in water resources at the regional scale and resulted in a higher frequency of forest gaps in the riparian forests along the Tarim River. The results of this study provide useful implications for ecological restoration of P. euphratica to improve sustainable management of desert riparian forests. [ABSTRACT FROM AUTHOR]