Environmental Flow Components Research Articles

Applying a Holistic Approach to Environmental Flow Assessment in the Yen River Basin

Environmental flow assessment is an essential tool in water resource management. This study employs a holistic approach to evaluate the environmental flow in the Yen Basin, Thanh Hoa, Vietnam. Based on information gathered from a field survey, the Yen River system is divided into five reaches, and environmental objectives and ecological assets are identified in each reach. Hydrological and hydraulic mathematical models are applied to simulate the flow regime in the river, demonstrating their potential to assess environmental flow, especially in basins with limited data. The detailed results from the mathematical model facilitate selecting environmental flow components to address specific objectives for each river reach. By analyzing and selecting the flow regime, this study aims to ensure environmental protection while also considering basin development requirements, laying the groundwork for defining prescribed flow regimes in basin water management.

Using game theory algorithm to identify critical watersheds based on environmental flow components and hydrological indicators

Using game theory algorithm to identify critical watersheds based on environmental flow components and hydrological indicators

Analysis of driving forces on ecohydrological regime and environmental flow changes in Hongze Lake, China

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.

Potential impacts of climate change on ecologically relevant flows: a case study in the Himalayan River basin

Abstract Understanding the potential impact of anthropogenic climate change on the hydrological regime of the Koshi River Basin (KRB) is very important for sustainable water resources and ecosystem management. The hydrological studies are mainly focused on the annual, seasonal, and peak flows of the hydrological regime; however, the ecologically relevant flows of the hydrological regime are less explored. In this study, we analyzed the different flow characteristics based on the magnitude, intensity, and duration using the Indicator of Hydrologic Alterations (IHA) under the influence of shared socio-economic pathway (SSP) scenarios. We found that the KRB will experience a shift in hydro-climatic events, an increase in rise and fall rates of flow, increase in monthly low flows of the hydrological regime, eventually affecting the livelihoods and ecosystem of the basin. This study highlights the importance of environmental flow components (EFCs) in a hydrological regime to better understand the flow characteristics during the future hydro-climatic variability.

Comprehensive evaluation of environmental flows in the Yangtze River regulated by two large dams

The ecological sustainability of rivers and floodplains depends on their natural flows. Dam construction on rivers has dramatically altered the hydrologic regimes, in turn affecting aquatic ecosystem integrity. The environmental flow components was applied to exam the impacts of the two dams (i.e., the Gezhouba Dam and the Three Gorges Dam) on downstream flows of the Yangtze River, China. Due to the operation of the two dams, the Yangtze River's flow regimes became homogenous through increasing streamflow during the dry season and decreasing streamflow in the flood season. The monthly low flows from January to April significantly increased by 14-31%, while October and November low flows significantly decreased by 18-25%. We observed the decreased duration and frequency of extreme low flows and floods, particularly the disappearance in large floods. These homogenous flows strongly influence the aquatic biodiversity. To alleviate the hydrologic alteration and minimize the negative ecological influence, low flows should be lower and floods should be reestablished as a natural state. The flow characteristics of duration, timing and rate of change should also be incorporated into the environmental flow recommendations. Our results could provide a potential solution to the tradeoffs between water resources exploitation and natural water requirement in the highly regulated rivers.

Intensified regulation of large reservoirs accelerates river ecohydrological regime transition: based on the long–short-term memory model

Abstract Although previous studies have analyzed ecohydrological changes, external pressure sources on the ecohydrological regime have rarely been clarified, and knowledge about the individual impacts of large reservoir regulation is still insufficient. In this study, we reconstructed the natural flow in the middle reaches of the Yangtze River (MRYR) not regulated by the Three Gorges Reservoir (TGR) based on a long–short-term memory model. We then evaluated the dynamics of ecohydrological regimes using environmental flow components and ecohydrological risk indicators and quantified the impacts of the TGR. The results showed that the hydrological stability has increased after TGR construction, with significant decreases in the frequency and duration of extremely low-flows, large floods, and small floods. In addition, there is a high ecohydrological risk in the MRYR, with a higher ecodeficit and showing a continuous upward trend. The impact of the TGR on environmental flow components decreases along the river, averaging 42.1%, with the strongest impact on small floods, accounting for 56.2%. Overall, reservoir regulation has counteracted the increased eco-risk caused by climate change. Considering only the TGR, the ecosurplus in the spring and winter seasons increased, while the ecodeficit increased in the autumn season, with corresponding contribution rates of 81.4, 82.7, and 53.1%, respectively.

Modelling of hydrological and environmental flow dynamics over a central Himalayan river basin through satellite altimetry and recent climate projections

AbstractThe Himalayan region is vulnerable to climate change, which is triggering extreme hydrological events. To understand the impact of climate emission scenarios on different hydrological flow dynamics of the Himalayan region, a thorough hydrological investigation is needed for improved water resource management. Hence, this research exemplifies the use of remote sensing, modelling techniques, and recent climate projections (CMIP5 and CMIP6) for the assessment of hydrological flow dynamics in the central Himalayan catchment. The SWAT model is calibrated/validated using gauge observation and satellite altimetry‐derived river discharge and used for long‐term hydrological simulations (1979–2100). CMIP6 models predicted that there would be a steady rise in high flows in all the projected scenarios. Flow duration curve for CMIP5 and CMIP6 models depicted that high flow of short duration would be frequent in future. The environmental flow components (EFCs) were calculated using the indicator of hydrologic alteration tool. The SWAT model simulations of hydrological and EFCs under CMIP6 climate projections are found to be significantly more vulnerable to climate warming than CMIP5, which could be due to socioeconomic pathway emission scenarios.

Evaluation of ecohydrological regime and its driving forces in the Dongting Lake, China

Study regionThe Dongting Lake (DTL) wetland, China. Study focusAt present, there are few studies on ecohydrological assessments based on the collaborative study of flow and water level. The focus of this study is to use ecologically meaningful indicators (Environmental Flow Components method and Range of Variability Approach method) to evaluate the dynamic process of flow and water level components, whose changes have a negative impact on the DTL wetland ecosystem. In addition, we quantitatively expressed the ecological response process of flow and water level under changing environments, and proposed to use the underlying surface parameters to further clarify the impact of human activities and climate change (evaporation and rainfall) on runoff in different time periods. New hydrological insights for the regionAfter the construction of the Three Gorges Dam, the components of environmental flow in DTL were reduced and the overall change of the flow and water level of the DTL was 37% and 36%, respectively, The results of the wetland ecological response coincided with the trend of habitat fragmentation and miniaturization of fish individuals in DTL. The underlying surface parameters show that the weight of the impact of climate change on runoff is increasing, and the contribution rate of driving forces (human activities, evaporation, and rainfall) to runoff are 49.32%, 20.88%, and 29.80% respectively, and to water levels are 60.00%, 21.3%, and 18.7%, respectively.

Modeling long term response of environmental flow attributes to future climate change in a North African watershed (Bouregreg watershed, Morocco)

Environmental flows are unanimously considered to be one of the most comprehensive indicators of the rivers health and their capacities to provide ecosystem goods and services. In this study, the objective was to predict the response of environmental flow components in a typical North African rivers network to future climate change. The study watershed is Bouregreg watershed (BW) in Morocco. To achieve this objective, a hybrid approach was build based on the semi-distributed model Soil and Water Assessment Tool (SWAT) and the Indicators of Hydrologic Alteration program (IHA). Data of two emissions scenarios (RCP4.5 and RCP8.5) from a downscaled Global Circulation Model were used to force the hybrid SWAT-IHA to calculate modifications of BW's environmental flow components in 2085-2100 period. Results showed that BW will experience climatic changes under both scenarios. Most of the environmental flow attributes will be modified within the study period: loss of natural flow variability due to shift in exceedance probability of low flows (up to 40%), decrease of monthly low flows, forward shift in high flow timing (up to 50%), and alteration of both the duration and the rise rates of floods. BW's streams responded unequally to the simulated changes in terms of the altered attributes as well as the degree of the alteration. This study confirmed the ability of the developed modeling approach to monitor environmental flow parameters for the first time in Morocco, and contributed in highlighting the necessity of proactive long term strategies to protect riverine ecosystems in North Africa watersheds.

Which Aspects of Hydrological Regime in Mid-Latitude Montane Basins Are Affected by Climate Change?

This study analyzed the long-term alterations in runoff regime, seasonality and variability in headwater montane basins in Central Europe in response to the manifestations of climate change. We tested the common hypotheses on climate change effects on surface runoff dynamics in the Central Europe region, assuming that (i) recent climate warming will result in shifts in the seasonality of runoff, (ii) the runoff balance will remain without significant changes and (iii) that higher variability in runoff can be expected. The analyses were done on eight montane catchments in four mid-latitude mountain ranges in Central Europe, based on the uninterrupted time series of daily discharge observations from 1952 to 2018. We used 33 indicators of hydrologic alteration (IHA), 34 indicators of environmental flow components, the baseflow index, the calculation of surplus and deficit volumes and the frequency of peak and low flows. Homogeneity testing using Buishand, Pettitt and SNHT tests was applied to test the response of the hydrological alteration indicators to climate warming. We have proved the significant shifts in runoff seasonality, coinciding with the timing of the air temperature rise, marked by earlier snowmelt, followed by a decline in spring flows and a prolonged period of low flows. There was detected a rise in the baseflow index across the mountain ranges. Unlike the common hypotheses, the expected rise of runoff variability and frequency of peak flows was not demonstrated. However, we have identified a significant change of the flood hydrographs, tending to steeper shape with shorter recessing limbs as a sign of rising inner dynamics of flood events in montane catchments.

Reservoir Construction Effect on the Fish Spawning Events

The process of rising flow and the water temperature are the important factors affecting the richness of fish seedlings after the construction of the reservoir. The changes of ecologically significant environmental flow components in the lower reaches of the Hongshui River before and after the construction of the reservoir are compared and analyzed. The study analyses and compares the changes of environmental flow components of spawning period before and after the spawning period in order to find out the distribution characteristics of environmental flow components of during the main spawning period before and after the construction of the reservoir. Using the ZSN to standardize the flow and water temperature, and then analyzing whether to cooperate between the flow and water temperature, and whether it is beneficial for fish spawning and reproduction of fish under the combined effect of the rising water and water temperature.

Hydrological Foundation as a Basis for a Holistic Environmental Flow Assessment of Tropical Highland Rivers in Ethiopia

The sustainable development of water resources includes retaining some amount of the natural flow regime in water bodies to protect and maintain aquatic ecosystem health and the human livelihoods and wellbeing dependent upon them. Although assessment of environmental flows is now occurring globally, limited studies have been carried out in the Ethiopian highlands, especially studies to understand flow-ecological response relationships. This paper establishes a hydrological foundation of Gumara River from an ecological perspective. The data analysis followed three steps: first, determination of the current flow regime—flow indices and ecologically relevant flow regime; second, naturalization of the current flow regime—looking at how flow regime is changing; and, finally, an initial exploration of flow linkages with ecological processes. Flow data of Gumara River from 1973 to 2018 are used for the analysis. Monthly low flow occurred from December to June; the lowest being in March, with a median flow of 4.0 m3 s−1. Monthly high flow occurred from July to November; the highest being in August, with a median flow of 236 m3 s−1. 1-Day low flows decreased from 1.55 m3 s−1 in 1973 to 0.16 m3 s−1 in 2018, and 90-Day (seasonal) low flow decreased from 4.9 m3 s−1 in 1973 to 2.04 m3 s−1 in 2018. The Mann–Kendall trend test indicated that the decrease in low flow was significant for both durations at α = 0.05. A similar trend is indicated for both durations of high flow. The decrease in both low flows and high flows is attributed to the expansion of pump irrigation by 29 km2 and expansion of plantations, which resulted in an increase of NDVI from 0.25 in 2000 to 0.29 in 2019. In addition, an analysis of environmental flow components revealed that only four “large floods” appeared in the last 46 years; no “large flood” occurred after 1988. Lacking “large floods” which inundate floodplain wetlands has resulted in early disconnection of floodplain wetlands from the river and the lake; which has impacts on breeding and nursery habitat shrinkage for migratory fish species in Lake Tana. On the other hand, the extreme decrease in “low flow” components has impacts on predators, reducing their mobility and ability to access prey concentrated in smaller pools. These results serve as the hydrological foundation for continued studies in the Gumara catchment, with the eventual goal of quantifying environmental flow requirements.

Classifying Dams for Environmental Flow Implementation in China

The implementation of environmental flows is of the utmost importance for ecosystem protection and restoration in dammed rivers. A key challenge in optimizing dam regulation is the uncertainty of the ecohydrology relationship between flow release and ecological response. In the present paper, we develop a framework of dam classification to organize the categories of the ecohydrology relationship for implementing environmental flows. Dams are classified from three major categories that differ in dam properties, hydrological alteration, and downstream hydrobiological diversities based on the relationship of hydrology and ecology. Finally, 773 dams in China are screened and ranked into four classes involving a great diversity of environmental flow components. A classification of dams that utilizes the implementation of environmental flows is presented. (1) Class 1 includes dams with rare and endangered fish species in the downstream. It is the category with the highest priority for environmental flow releases and regulation, requiring continuous flow and flood pulse components for fish spawning and migration. (2) Class 2 includes dams with significant hydrological alteration in the downstream. It is the category with second priority for environmental flow releases and regulation, requiring natural hydrological regimes simulation or complete flow component recovery for optimizing the flow duration curve and mitigating adverse impacts of dam operation. (3) Class 3 includes dams with a high degree of regulation where there is urgency for environmental flow releases and regulation, requiring that minimum flow is guaranteed by cascade reservoir regulation. (4) Class 4 includes dams with a low degree of regulation where there is less urgency for environmental flow releases and regulation. This classification method is important for future research, including environmental flow release regulation and the effectiveness evaluation of environmental flow adaptive management. It will be useful for guiding the implementation of environmental flows.

Impact assessment of climate change on environmental flow component and water temperature—Kikuchi River

The Japanese archipelago extends over a large distance from north to south exposed to the effects of climate change. The aim of this study was to assess the impacts of climate change on environmental components by using hydrological indicators. The future climate change in the region was initially projected using HadGEM2-ES and MICRO5 models in three 20-year periods (2021–2040, 2041–2060 and 2061–2080), considering two representative concentration pathways (RCP4.5 & RCP8.5). The Kikuchi streamflow was then simulated using Soil and Water Assessment Tool modelling for the baseline (1986–2016) and future periods. Finally, the magnitude, duration, timing, and frequency of extreme flows were analysed using Indicators of Hydrologic Alteration software. The results showed a decrease in discharge under both models; however, a 2 m3/s increase was predicted under HadGEM2-ES (RCP4.5) in 2041–2060. Changes in river flow affect habitat suitability in aquatic ecosystems, and might have further impacts if the effects of water temperature are also considered. In our case study, water temperature was predicted to increase by up to 4 °C by 2080. This phenomenon will change habitat suitability, because important environmental flow components, such as the peaks of high flows and large flood frequency, will also increase.

KARAKTERISTIK HIDROLOGI PADA DUA DAS KECIL DI WILAYAH UPT PSDA DI SURABAYA : ANALISIS MENGGUNAKAN INDICATORS OF HYDROLOGIC ALTERATION (IHA)

This research proposes to evaluate whether there has been a change in hydrological regimes of the watershed. The research was conducted at the the administrative area of UPT PSDA Surabaya. Furthermore, Surabaya-Perning and Lamong-Simoanggrok watersheds were used as a sample for this study. The analysis was conducted using the Indicator of Hydrologic Alteration (IHA). The main input is the daily discharge data series from the two watersheds. The discharge data range from 1996 to 2015. Then, the time series data is divided into two periods, the pre-impact period (1996-2005) and the post-impact period (2006-2015). A total of 33 IHA parameters classified into 5 categories were used to evaluate the change. The results of the assessment are then used for RVA (Range of Variable approach) calculations. RVA calculations were used to discover changes occurring from the pre-impact period to the post-impact period. The data series from the two watersheds also analyzed using Environmental Flow Components (EFC) and Flow Duration Curves (FDC). The result of the research shows the difference in parameter value that indicating the hydrological change between the pre-impact period and the post-impact period. RVA analysis results show an increased flow in the Surabaya-Perning watershed from January to September and December. RVA analysis results also show an increased flow in the Lamong-Simoanggrok watershed from January to July and December. The results of the EFC analysis can provide information about flows that have the potential to cause floods and droughts. The Surabaya-Perning watershed has the potential to encounter a small flood with a value 254,7 m3/s which last for 9 days with a chance of occurring 0,5 times every 2 years.

Changes in Environmental Flow Components under the Effect of Sabalan Dam in the Qarehsou River of Ardebil Province

Changes in Environmental Flow Components under the Effect of Sabalan Dam in the Qarehsou River of Ardebil Province

Conceptualization and pilot application of a model-based environmental flow assessment adapted for intermittent rivers

Environmental flow assessments (EFAs) are widely researched and applied worldwide. However, model-based frameworks integrating the flow requirements of multiple ecosystem components have been primarily developed for perennial watercourses, being inherently inapplicable in intermittent rivers (IR), which are common worldwide and may dominate arid, semi-arid and mediterranean-climate regions. In this study, we conceptualized and pilot-applied a model-based EFA in a naturally intermittent Mediterranean river reach (Evrotas, southern Greece), guided by two fundamental principles: (1) environmental flows in IR should be delivered during specific aquatic states (AS) and (2) baseflows should be provided during prolonged dry periods to prevent artificial deviation from the natural AS-sequence. The habitat preferences of benthic macroinvertebrates and of three endemic fish species were evaluated, and a two-dimensional hydrodynamic-habitat model was applied to simulate habitat suitability at various discharges. We modelled the baseflow required to maintain disconnected water pools during dry periods and the optimal baseflow required to ensure the presence of suitable habitats after flow resumption. The results show that baseflows at the 25th percentile of the abundant-riffles state can provide adequate habitat for the IR-specific communities. During prolonged dry periods, surface–groundwater interactions should be also considered for robust predictions. We highlight the use of hydrodynamic-habitat models in IR-based EFAs as a key-tool to estimate the AS timing and duration and, consequently, the timing-duration of the respective environmental flow components. Future studies should, inter alia, (1) include the aquatic-riparian vegetation to provide information on high flows-floods, and (2) incorporate groundwater models to account for surface–groundwater interactions towards a widely accepted IR-specific EFA framework.

Multicriteria decision analysis framework for hydrological decision support using environmental flow components

Assessing the quantity and quality of water available in water stressed environments under various potential climate and land-use changes is necessary for good water and environmental resources management and governance. We present a novel approach with which to assess water quantity in the Luanginga basin, a subbasin of the upper Zambezi River, using existing results of hydrological modelling based on climate change scenarios, hydrological indicators, and multicriteria decision analysis. Flexible input criteria and open-source software are used to the greatest degree possible. Scenarios are represented through a combination of model input data and parameter settings in the hydrological model, and preferences are represented through criteria weighting in the multicriteria decision analysis. The resulting methodology, combining hydrological indicators with MCDA, is thus adaptable, in terms of both application platform and subject matter. The method results were largely as expected. When a decision maker expressed a preference for wetter conditions, the RCP 4.5 scenarios were generally deemed most suitable, and thus ranked highest. When drier conditions where preferred, the RCP 8.5 scenarios, resulting in less streamflow and less frequent flood events, were ranked highest. Validation of the results is not possible, due to the methodologically exploratory nature of the research being undertaken. The promising results do, however, allow for further research that builds upon the work undertaken here, to be envisaged.

Applying the environmental flow components approach to the River Murray in South Australia

ABSTRACTRiver regulation has degraded the River Murray’s riverine ecosystems. Environmental flows are now being delivered to restore these ecosystems to a more natural, pre-regulation state. To guide the development of environmental flow recommendations, I calculated 28 Environmental Flow Components for the River Murray in South Australia, comparing simulated flow data for natural and present conditions. Regulation has caused complex changes to the rivers’ hydrology. Under present conditions, the inter-annual frequency of extreme low flows (<4150 ML/day) and high flow pulses (15,000–55,000 ML/day) has increased, whilst for small floods (55,000–100,000 ML/day) and large floods (>100,000 ML/day) frequency has declined. The magnitude of low flows (4150–15,000 ML/day) has been reduced for all months, and extreme low flows and high flow pulses occur later in the year. The duration of high flow pulses, and both small and large floods, have also declined under present conditions. Restoring more natural extreme low flows and high flow pulses will require new events to be engineered, whilst environmental water can be used to enhance monthly low flows and small floods. In addition to providing environmental flows, changes to river operations, particularly instituting weir pool manipulation, is required to maximise ecological outcomes.

Identifying hydrological regime and eco-flow threshold of small and medium flood of the Xiaoqing River in Jinan city

It was known that hydrological regime was the main influencing factor of river ecosystem, but the regime of different flow rates of urban rivers was poorly understood. We collected daily inflows at the Huangtai station of the Xiaoqing River from 1960 to 2014 and divided the data into three periods. Then we calculated hydrological parameters by the method of EFCs (Environmental Flow Components) and analyzed the tendency and change rates of each component respectively in the three periods. Combined with the ecological significance of environmental flow components, we identified the small and medium flood had the greatest impact on the river regime and ecosystem. And then we used the hydraulic parameters in the good ecosystem period as control conditions, to calculate the ecological threshold of the flow component under the current situation. This study could provide technical support for restoring and improving hydrological regime and ecological environment of the Xiaoqing River in Jinan city.