Environmental Flow Calculator Research Articles

Mapping and assessment of river water quality under varying hydro-climatic and pollution scenarios by integrating QUAL2K, GEFC, and GIS

Water quality modelling has proved to be effective method for managing river water quality. But the most effective and comprehensive approach involving integration of river water quality simulation and pollution visualization with the objective of pollution reduction and maintenance of environmental flow strategies has gained less attention. Thus, the objective of this study was to employ an integrated approach for mapping and analysing river water quality under various hydro-climatic and pollution scenarios. Specifically, this approach involved the integration of a river water quality simulation model, QUAL2K, Global Environmental Flow Calculator (GEFC), and Geographical Information System (GIS) to develop water quality index (WQI) based map charts of water quality. The calibrated QUAL2K model was utilized to simulate WQI parameters including water temperature, pH, electrical conductivity, dissolved oxygen (DO), biological oxygen demand (BOD), nitrates (NO3), ammonia (NH4), and alkalinity. To analyse the WQI, the Weighted Arithmetic-Water Quality Index (WA-WQI) method was employed for various individual and combined pollution scenarios, environmental flow (Eflow), and climate change scenarios. The developed integrated approach was applied to the Bhadravati segment of Bhadra River, India. The findings revealed that the prevailing WQI status of the study stretch ranged from poor to unsuitable for drinking purposes. This deterioration can be attributed to the impact of both industrial and municipal effluents. By maintaining the effective Environmental Management Class (EMC) flow rates (class C flowrate of EMC (40.32 m3/s)) in conjunction with appropriate Pollution Reduction (PR) level (10% PR) at headwater and incoming drains, the stream self-purification capacity was enhanced resulting in the Bhadravati River stretch water quality transitioning to favourable water quality condition.

Hydrological methods in environmental flows. Is it really simple? a critical study of selected catchments in central Europe

The paper presents the analysis of problems regarding the calculation of EFs using selected hydrological methods. It was conducted in 14 catchments in the Vistula and Oder River basins in Poland. The Kostrzewa, Tennant, Q90%, and 7Q10 methods were used for the analysis. The analysis showed a significant trend in the hydrological time series. The sensitivity of different applied methods to time series length was shown. High differences were observed between environmental flow (EF) values calculated for periods defined by break points. The hydrological drought and its impact for EFs were also observed for half years in the period. Finally, different values of water deficit characteristics were presented depending on the method used for EF calculation.

Watershed environmental impact assessment for extreme climates based on shared socioeconomic pathway climate change scenarios

Abnormal climate phenomena that exceed conventional weather observations occur worldwide, such as severe floods, droughts, and environmental issues, and have attracted increasing attention. To avoid indiscriminate industrialization and achieve sustainable development, environmental experts have presented various opinions based on climate change scenario data. In this study, shared socioeconomic pathway (SSP) climate change scenarios that consider socioeconomic conditions were used to assess the environmental impact of extreme climate conditions on watersheds. Using the UK Earth System Modelling (UKESM1) SSP scenarios, we analyzed the following: 1) Heat index for each SSP climate change scenario using the H-Index; 2) extreme climate for each SSP climate change scenario using the standardized precipitation index (SPI); 3) the impact of extreme climate on non-point pollution using event mean concentration (EMC); and 4) the environmental flow caused by extreme climate by combining the K-water Distributed RUnoff Model (K-DRUM) and global environmental flow calculator (GEFC) models. According to the heat index analysis regarding SSPs climate change scenarios, the heatwave index will continue to rise if high carbon emissions persist. Temperature serves as an important indicator that has the most meaningful impact on ecosystems. The SPI analysis showed an increase in “extremely dry” conditions, and overall, more severe droughts are likely to occur due to high carbon emission-induced climate change. The nonpoint source pollution is also higher in climate change scenarios with high carbon emissions. The extreme drought event assessment using SPI and environmental flow revealed a shift from the “moist conditions” category to grade C. Our assessments in this study conclusively indicate that drought frequency will increase along with nonpoint source pollution. Furthermore, environmental flows will shift to grade C, resulting in the disappearance of some sensitive ecological species and an increase in invasive species. These analyses determined that high carbon emission-induced climate change caused leads to severe droughts and significant alterations in the overall water circulation, thereby complicating water resource management. Furthermore, we identified watersheds that are highly vulnerable to climate change and designated these as “mid-watersheds” that first require non-point pollution management. Here, the aquatic ecosystem environment can be affected by climate change without any artificial environmental influence. Various research-based analysis methods based on modeling have been presented using SSP climate change scenarios, and are highly beneficial for establishing policies and coping strategies for environmental preservation and sustainable development.

Environmental Flow Assessment (EFA) of Tawi River Discharge at the Jammu Location Using the Global Environmental Flow Calculator (GEFC)

The water, food, and energy demands are the basic requirements of society. These demands are increasing daily due to an increase in population or lifestyle changes. To fulfill these ever-increasing demands, several water resource projects have come up which require the storage or diversion of river water. These interventions have caused widespread degradation of aquatic ecosystems. Due to the degradation of the aquatic ecosystem, several programs all around the globe began. In this series, Brisbane Declaration (2007) provided a more holistic definition of Environmental Flows (EFs) as the quantity, timing, duration, frequency, and quality of flows required to sustain freshwater, estuarine and near-shore ecosystems and the human livelihoods and well-being that depend on them. The present study was envisaged to assess for environmental flows of the Tawi river with a major objective of assessing the environmental flows of the Tawi river using the Global Environmental Flow Calculator developed by IWMI. The method provides E-Flows for different Environmental Management Classes. For the western Himalayan region, the river stretches in Environmental Management Class ‘B’ and ‘C’. The assessment provides E-Flows in two ways: (i) the percentage of Mean Annual Runoff and (ii) average monthly environmental flows. E-Flows were estimated as 42.34% to 56.96% of Mean Annual Runoff and varied from 5.73 cumecs during November to 68.23 during August.

A Practical Approach for Environmental Flow Calculation to Support Ecosystem Management in Wujiang River, China.

To promote ecosystem protection in the Wujiang River, this paper proposes a practical approach for calculating the environmental flow. The proposed approach combines the idea of the “guarantee rate” of the flow duration curve (FDC) method and the grading idea of the Tennant method. A daily flow series of the Wujiang River was compiled from 1956 to 2019 and used to compare the effect of the proposed approach versus the traditional approaches in four selected sections along the river. The results show that the environmental flow of the Wujiang River can be divided into five levels by the T-FDC method, with a level-by-level disparity, and all levels can capture the temporal and spatial variability of river flow. Additionally, the calculated basic environmental flow process ranges between the historical minimum and second minimum monthly average flow, and the threshold width of the optimal flow is more reasonable than the Tennant method. The T-FDC method can provide technical support for Wujiang River ecosystem management and sustainable development.

Environmental flow estimation through a hydrology-based method in the Tamas River at Bakiya Barrage, Madhya Pradesh, India

AbstractThe River Tamas is a right-bank tributary of the River Ganga flowing through the states of Madhya Pradesh and Uttar Pradesh, India. It originates in Jhukehi village in the Satna district of Madhya Pradesh and after 268 km it joins with the River Ganga at Sirsa, Prayagraj, Uttar Pradesh. The river has a diverse habitat and harbours a variety of flora and fauna. More than 70 fish species reside in the river, along with other biotic communities. A barrage, named Tons and situated at Bakiya village, was commissioned in 1992 for hydro-electric purposes. The continuity and volume of water in the river have been disturbed due to the construction of this barrage and it has changed the ecology and biodiversity. Keeping the ecosystem intact requires that environmental flow calculations be made of the river at the barrage. An attempt has been made to estimate the environmental flow requirement using a desktop hydrological method. Based on the flow duration curve (a hydrological method of flow estimation), the environmental flow for the River Tamas has been calculated using Global Environmental Flow Calculator software. Our calculation are based on flow discharge data received from the Tons Barrage Authority at Bakiya for the period January 2006 to December 2017. Average annual discharge was calculated from the recorded maximum (151.46 cumecs in 2016) and the minimum, 13.53 cumecs in 2007. Mean Annual Runoff was calculated as 1607 Million Cubic Meter with Coefficient of Variation =0.799. To maintain the river in the “slightly modified” class of Environmental Management Class, 27.8 % of Mean Annual Runoff discharge should be released into the river to largely maintain the biodiversity and habitat, while about 57% of Mean Annual Runoff discharge is required to maintain this river in pristine condition. This is a preliminary study to determine the water requirements for healthy habitat and biodiversity of the Tamas river.

Environmental Flow Assessment of a Tropical River System Using Hydrological Index Methods

Tropical rivers and wetlands are recognized as one of the greatest and most abundant ecosystems in terms of ecological and social benefits. However, climate change, damming, overfishing, water pollution, and the introduction of exotic species threaten these ecosystems, which puts about 65% of river flow and aquatic ecosystems under a moderate to high level of threat. This paper aims to assess the environmental flow of the Selangor River based on the hydrological index method using the Global Environmental Flow Calculator (GEFC) and Indicators of Hydrological Alterations (IHA) software. The daily flow data collected by the Department of Irrigation and Drainage (DID), Malaysia, over a 60-year period (1960–2020) was used in this study to assess the Selangor River flow alterations. As per the results, the river flow has had two distinct periods over the last 60 years. In the first period, the river flows without any alteration and has a natural flow with high flood pulses and low flow pulses. While in the second, or post-impact, period, the flow of the river has a steady condition throughout the year with very little fluctuations between the dry and wet seasons of the year. From the overall comparison of the pre- and post-impact periods, it can be concluded that the minimum flow in the dry seasons of the year has increased, while the maximum flow has decreased in the monsoon seasons during the post-impact period. As a result, the Flow Duration Curve (FDC) and Environmental Management Class (EMC) analysis of the river flow recommends that the Selangor River be managed under EMC “C” to provide sufficient water for both human use and ecosystem conservation, which would also help to avoid a water level drop in the reservoirs. However, further holistic studies are suggested for a detailed analysis of the effects of the dams on aquatic biodiversity and ecosystem services in the Selangor River Basin.

Modelling of environmental flow requirements using hydraulic and habitation models

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.

Environmental Flows Assessment in Nepal: The Case of Kaligandaki River

Environmental flow assessments (e-flows) are relatively new practices, especially in developing countries such as Nepal. This study presents a comprehensive analysis of the influence of hydrologically based e-flow methods in the natural flow regime. The study used different hydrological-based methods, namely, the Global Environmental Flow Calculator, the Tennant method, the flow duration curve method, the dynamic method, the mean annual flow method, and the annual distribution method to allocate e-flows in the Kaligandaki River. The most common practice for setting e-flows consists of allocating a specific percentage of mean annual flow or portion of flow derived from specific percentiles of the flow duration curve. However, e-flow releases should mimic the river’s intra-annual variability to meet the specific ecological function at different river trophic levels and in different periods over a year covering biotas life stages. The suitability of the methods was analyzed using the Indicators of Hydrological Alterations and e-flows components. The annual distribution method and the 30%Q-D (30% of daily discharge) methods showed a low alteration at the five global indexes for each group of Indicators of Hydrological Alterations and e-flows components, which allowed us to conclude that these methods are superior to the other methods. Hence, the study results concluded that 30%Q-D and annual distribution methods are more suitable for the e-flows implementation to meet the riverine ecosystem’s annual dynamic demand to maintain the river’s health. This case study can be used as a guideline to allocate e-flows in the Kaligandaki River, particularly for small hydropower plants.

Optimisation of cascade reservoir operation considering environmental flows for different environmental management classes

Abstract Most commonly, hydropower operation focused on the economic and social benefits of the humankind, whereas neglecting the riverine ecosystem conservation. This conventional approach of operation led to the degradation of the riverine ecosystem. As research progressed, adoption of natural flow variability in the operation of reservoir gained momentum. Flow variability is a major driver of the healthy river ecosystem, whereby discharging a certain amount of water could potentially reduce the adverse effect of reservoirs and dams on the riverine ecosystem. On this preface, the study presented here constitutes a multi-objective optimisation model of cascade reservoirs to maximise the power generation while minimising the shortage of environmental flows considering five environmental management classes. This paper analyses the case studies for Liujiaping-Yumitan cascade reservoirs. The environmental flows regarding each environmental management classes were calculated using “Global Environmental Flow Calculator”, the model was solved using an anon-dominated sorting genetic algorithm (NSGA-II). The NSGA-II helps to find Pareto optimal sets of solutions, NSGA-II, however, cannot be used solely for taking a comprehensive decision. Therefore, the Projection Pursuit Cluster (PPC) model has been used additionally for the optimal sequencing of the compromised optimal solutions. The maximum annual power production considering five environmental management classes were respectively: 1.121, 1.109, 1.103, 1.109, and 1.117 (x108 kWh) with environmental flows shortage of 2060.82, 616.497, 200.52, 28.88, and 0.004 (x104 m3) respectively. Findings resulted from this study, highlight the necessity for power production compromise for a better degree of environmental protection. In contrast, the environmental benefit is more important not only for the sustainable operation of the hydropower but also for fulfilling the universal needs of the riverine ecosystem. Therefore, the outcomes of this study can be a guideline for decision-makers to improve the comprehensive benefits of the Liujiaping-Yumitan cascade hydropower station along with the conservation of the environmental health of the river.

Modeling the impact of climate change on the environmental flow indicators over Omo-Gibe basin, Ethiopia

The study focuses on climate change impacts on the environmental flow indicators from hydrologic method point of view using IWMI’s Global Environmental Flow Calculator and Indicators of Hydrologic Alteration. It also discusses how the changes in flow magnitude and duration of annual extreme conditions, timing of annual extreme water condition, frequency and duration of high and low pulses, rate and frequency of water condition changes will affect the ecosystem. Climate change disturbs the ecology by directly affecting the functions of individual organisms (growth and behavior), modifying the population (size and age structure), and altering the ecosystem structure, functioning (e.g., decomposition, nutrient cycling, water flows, and species composition and species interactions) and its distribution within landscapes (Gitay et al., 2002). Ecosystem regime shifts can occur naturally and by anthropogenic factors (Muenich et al. in Ecol Model 340:116–125, 2016). Climate change effects on flow regime are expressed by different indicators such as mean annual runoff, mean river discharge, low and high flows, mean seasonal discharge, and changes from permanent to intermittent flow or vice versa. Understanding of changes in flow regimes is important for the well-being of humans and freshwater-dependent biota with respect to water and habitat availability (Doll and Schmied in Environ Res Lett 7(1):14037, 2012). Even though the basin is rich in fish species, peoples living in lower Omo-Gibe basin and Turkana region are undertaking a traditional fishing culture. Wildlife in the parks, pastoralist communities using the flood recession farming and livestock farming are dependent on the river. The environmental flow that sustains these activities is inevitably necessary for the survival of the biodiversity. Understanding of the flow variability helps to protect the freshwater biodiversity and maintenance of goods and services that the river provides.

Integrated Software Development and Case Studies for Optimal Operation of Cascade Reservoir within the Environmental Flow Constraints

Reservoir optimal operation considering aquatic ecological protection is a hot topic in current research. This paper proposes an improved minimum monthly average runoff method (IMMR) for calculating environmental flow and an improved invasive weed optimization algorithm (IIWO) for optimizing complex problems. An integrated software consists of three modules, which is developed in this paper, i.e., IIWO convergence test module, environmental flow calculation module, and cascade reservoir operation module. Three test functions are included in the IIWO convergence test module. The minimum monthly average runoff method (MMR), IMMR, Tennant Method, Q90, and Q95 are included in the environmental flow calculation module. The IIWO and invasive weed optimization algorithm (IWO) are included in the cascade reservoir operation module. Wujiang River Basin in China is studied as a case in this paper. The results show that the environmental flow of cascade reservoir calculated by IMMR is 1871 m3/s, the maximum and the minimum are calculated by T-O and T-M, respectively. The power generation of cascade reservoir calculated by IWO is less than IIWO. The conclusions that IIWO has better convergence than IWO in solving cascade reservoir model, and the water volume of environmental flow has no obvious influence on cascade reservoir operation are drawn.

Planning for Environmental Water Allocations: Hydrology - Based Assessment in the Awash River Basin, Ethiopia

The research is financed by the Egyptian Government through the Nile Sector bilateral cooperation project Abstract With expanding water demand due to rapid socio-economic growth and shrinking supplies due to pollution and climate change impact, there is an increasing strain on the water resources of the Awash river basin. Furthermore, flow alterations due to the existing and the ongoing water resources infrastructure projects may adversely impact the natural life cycle of aquatic ecosystems in the river basin. In order to manage these consequences, compensation releases or allocation of environmental flows may be mandatory and calls for the establishment of environmental flows framework in Ethiopia. In this study, the environmental flows at selected five existing and proposed dam sites in the Awash river basin were investigated using six worldwide used hydrology-based methods, viz.: Desktop Reserve Model (DRM), Global Environmental Flow Calculator (GEFC), Tennant, Tessman, 7Q 10 and Q 95 . The environmental flow volumes from the six methods were compared on mean annual, monthly average and monthly basis and it is found that the predictions from the DRM and GEFC are more reliable than the others. Comparative results indicate that minimum annual average flow rates of 4.4 m 3 /s (15 % of Mean Annual Flow (MAF)), 10.5 m 3 /s (19 % of MAF), 16.4 m 3 /s (22 % of MAF), 2.5 m 3 /s (17 % of MAF) and 24.2 m 3 /s (26 % of MAF) are required at the immediate downstream reaches of Melka kuntre, Koka, Awash Compensation, Kesem and Tendaho dams respectively. Accordingly, the annual average environmental flow throughout the basin varies from 15-26 % of the natural MAF. Although preliminary, being the first attempt in the Awash river basin, this study is expected to stimulate dialogue among experts and decision makers in Ethiopia. Keywords: EFR, EFA, Tennant, Tessman, Q 95 , 7Q 10 , DRM, GEFC Software, Awash DOI : 10.7176/JEES/9-11-08 Publication date: November 30 th 2019

Assessment of environmental flows using hydrological methods for Krishna River, India

Krishna River is significantly affected due to Srisailam dam from past 30 years. The impact of this hydraulic structure drastically reduced the minimum flow regime on the downstream, which made the river nearing to decaying stage. In the present paper, Environmental Flow called minimum flow values released for the dam are estimated with the help of three hydrological methods viz., Range of variability Approach (RVA), Desktop Reserve Model (DRM), and Global Environmental Flow Calculator (GEFC). DRM method suggested considering the intermediate values obtained from among the three methods to preserve the ecosystem on the downstream of the river, which amounts to an average annual allocation of 9378 Million Cubic Meter (MCM) which is equal to 23.11% of mean annual flow (MAF).In this regard GEFC and RVA methods accounted for 22 % and 31.04% of MAF respectively. The results indicate that current reservoir operation policy is causing a severe hydrological alteration in the high flow season especially in the month of July. The study concluded that in the case of non-availability of environmental information, hydrological indicators can be used to provide the basic assessment of environmental flow requirements. It is inferred from the results obtained from the study, that the new reservoir operations can fulfil human water needs without disturbing Environmental Flow Requirements.

Assessing environmental flows of coordinated operation of dams and weirs in the Geum River basin under climate change scenarios

The International Panel on Climate Change (IPCC) has predicted frequent and severe droughts and floods caused by irregular climatic conditions in the future, making water resources management difficult. Within the field of integrated watershed management, the concept of ‘environmental flow’ is being increasingly studied. In Korea, the Four Major Rivers Restoration Project was carried out as part of the plan to manage future water resources, particularly in response to climate change. In order to improve comprehensive water resources management, there is an interest in integrating into the operation of the existing dams the multi-functional weirs constructed under the said project. To date, there is an absence of studies comprehensively considering climate change, run-off volume, reservoir operations, and environmental flow, with most of the existing studies focusing only on one or the other of these factors. In this study, we presented a method to evaluate the river environment that considers all the said factors. To evaluate how environmental flow is influenced by the changes in river flow due to climate change and hydraulic structure operation, the Streamflow Synthesis and Reservoir Regulation (SSARR) was used as the hydrological model, HEC-ResSim was used as the hydraulic structures operational model, and the Global Environmental Flow Calculator (GEFC) was used as the method to evaluate environmental flows. RCP climate change scenarios, provided by the Climate Change Information Center (CCIC), a branch of the Korea Meteorological Administration, were applied to analyze the future watershed runoff characteristics of the Geum River Basin under different hydraulic structure operation modes. This study concludes that efficient use of water resources can be achieved through the integrated operation of the dams and multi-functional weirs in times of water shortage. Comparing the results of modelling under a no‑carbon reduction scenario on one hand, and a scenario in which emissions were reduced on the other hand, differences were found in flows during floods, in the mean annual runoff ratio in accordance with the environment management class, and in the environmental flow rating. It appears that a new water resources management plan is required to respond to climate change as indicated by the shift of the flow duration curve to a lower environmental management class (EMC) under climate change scenarios.

Determination of environmental flows in rivers using an integrated hydrological-hydrodynamic-habitat modelling approach

We propose the novel integrated modelling procedure 3H-EMC for the determination of the environmental flow in rivers and streams; 3H-EMC combines Hydrological, Hydrodynamic and Habitat modelling with the use of the Environmental Management Classes (EMCs) that are defined by the Global Environmental Flow Calculator. We apply 3H-EMC in the Sperchios River in Central Greece, in which water abstractions for irrigation cause significant environmental impacts. Calculations of the hydrodynamic-habitat model, in which the large and the small chub are the main fish species, suggest discharge values that range from 1.0 m3/s to 4.0 m3/s. However, hydrological modelling indicates that it is practically difficult to achieve discharges that are higher than approximately 1.0–1.5 m3/s. Furthermore, legislation suggests significantly lower values (0.4–0.5 m3/s) that are unacceptable from the ecological point of view. This behaviour shows that a non-integrated approach, which is based only on hydrodynamic-habitat modelling does not necessarily result in realistic environmental flows, and thus an integrated approach is required. We propose the value of 1.0 m3/s as the “optimum” environmental flow for Sperchios River, because (a) it satisfies the habitat requirements, as expressed by the values of weighted useable area that are equal to 2180 and 1964 m2 for the large and small chub, respectively, and correspond to 82 and 95% of their respective maximum values, (b) it is consistent with the requirements of Environmental Classes A and B, whose percentiles are higher than 75% for discharge (77.2%) and for habitat availability (>83.5% for the large chub and >85.0% for the small chub), (c) it is practically achievable from the hydrological point of view, and (d) it is higher than the value proposed by the Greek legislation. The proposed modelling approach can be applied to any river or stream using the same or similar modelling tools, which should be linked via suitable coupling algorithms.

Optimal selection of the most ecologically relevant hydrologic indicators and its application for environmental flow calculation in Lake Dongting

水文改变指标（IHA）能够较为全面地描述水文状况，在评估水文情势改变及其生态系统影响方面具有广泛的应用.尽管该指标体系较为完善，但是数量众多的水文变量仍然存在信息冗余问题.根据洞庭湖城陵矶水文站1955-2014年的径流量数据，采用主成分分析（PCA）筛选了生态最相关水文指标（ERHIs），结合ERHIs改进了用于估算环境流量的变化范围法（RVA），并将其应用在洞庭湖出口的环境流量估算中.基于PCA选取了年最大90日流量、年最小3日流量、年最小流量出现时间、3月流量、6月流量、流量逆转次数和低流量年内平均历时7个变量作为洞庭湖出口的ERHIs.纵向和横向的对比分析都表明选取的ERHIs是合理的.ERHIs不仅有效缓解了IHA的冗余性问题，还有利于抓住最关键的生态水文变量.根据ERHIs改进的RVA方法在设定洞庭湖出口环境流量时，极大地简化原来的众多管理目标，对生态水文研究、水资源管理和生态保护都具有重要的参考价值和借鉴意义.;The method of indicators of hydrologic alteration (IHA) provides a relatively comprehensive way to describe the full range of hydrological regimes and is used globally to assess hydrological alteration and its ecosystem influence. This method is relatively sound, while it still has potential redundancy problems caused by a large number of variables in it. Therefore, the principal component analysis (PCA) was used to select the most ecologically relevant hydrologic indicators (ERHIs), based on the flow data at Chenglingji, a standard observation station of Lake Dongting, from 1955 to 2014. The method of range of variability approach (RVA) was improved by the selected ERHIs and was used to estimate environmental flow in the outlet of Lake Dongting. Based on the results of PCA, seven ERHIs were selected:annual maximum 90-day flow, annual minimum 3-day flow, Julian date of each annual 1-day minimum, March flow, June flow, number of hydrologic reversals and median duration of low pulses. It was proved that the seven selected ERHIs were reasonable with the comparison to previous studies and the redundancy analysis. ERHIs not only reduce the redundancy of IHA but also help to grasp the key component of eco-hydrological variables. Moreover, the improved RVA method greatly simplified the original management targets in estimating environmental flow in the outlet of Lake Dongting. This study is of great value and significance for eco-hydrological research, water resources management and ecological protection.

Assessment of environmental flow release from Deduruoya reservoir to mitigate possible impacts on downstream ecosystem

River ecosystems are interlinked with river hydrology. However, construction of dams can modify the natural flow patterns which can lead to unpredictable consequences. Environmental flow (EF) releases can restore ecosystems or reverse the already occurred degradation. Having understood the importance of EF, large number of methods has been developed to estimate the EF. The objective of this study was to make a comparison between these methods to identify the most comprehensive method and to develop a novel approach to estimate EF based on the concept of minimum information requirement. Among the EF calculation methods studied, holistic method was identified as the most reliable category and the building block methodology (BBM) was identified as the best holistic method which requires more resources or data. The new methodology developed to assess EF basically based on BBM but efforts were taken to identify minimum data requirement approaches to calculate individual water uses. It consists of the flow requirement of riverine flora and fauna, social and cultural water requirement, wetland water requirement, longitudinal connectivity, flushing flow requirement, groundwater recharge and coastal water requirement. The EF requirement of downstream of DeduruOya reservoir was estimated using the developed method. The results were compared with the EF calculated using the Sri Lanka Environmental Flow Calculator model developed by IWMI. There was a significant difference between the EF calculated using new method and the results obtained using model developed by IWMI. Hence, it is recommended to further improve and verify the findings of the new method.

Environmental flow requirements and impacts of climate change-induced river flow changes on ecology of the Indus Delta, Pakistan

Modification of Indus River flows to meet anthropogenic needs has seriously undermined the ecological benefits the river generates in the deltaic region. This paper provides an assessment of ecological conditions of the Indus Delta under different climate change scenarios by using ecological health of the Indus River as a proxy. First, we assessed the existing state of deltaic ecology and categorised it into an arbitrary environmental management class (EMC). Then, using Global Environmental Flow Calculator, we determined the Environmental Flows (E-flows) that are required for the Indus delta in (i) the present, and (ii) in the future under two climate change scenarios. Our analysis shows that due to inadequate and inconsistent release of E-flows downstream of Kotri barrage, deltaic ecosystems have deteriorated overtime. Our analysis reveals that under climate change Scenario 1, more flows may be available that can bring river flows close to natural E-flows. Under Scenario 2, there may be reduced river flows to the extent that E-flows required under prevailing conditions would not be possible. The study concludes that if the current deterioration of aquatic ecology continues, it will be challenging to maintain present, or achieve higher ecological management class (EMC), regardless of the changes in river flows in the future. In this light, there is a need to interlink economic and development needs of communities with environmental needs of Indus River in the deltaic region. Most importantly, there is a need for ensuring climate-compatible e-flows in water regulating sites such as Kotri Barrage.

The Sri Lanka environmental flow calculator: a science-based tool to support sustainable national water management

As Sri Lankan water resources are being increasingly exploited, particularly for hydropower and irrigation, ecologists, water practitioners and policymakers alike are realizing the importance of protecting these resources and setting environmental sustainability thresholds. Environmental flows (EF) – the concept that helps define such thresholds – has now become an integral part of environmental impact assessments of river basin development projects. Considering EF is especially vital in the context of the accelerated infrastructure development program, launched after the end of the war in the north and the east of the country in 2009. This paper describes a simple, user-friendly software tool that facilitates quick, first-hand estimation of EF in Sri Lankan rivers. The tool uses ‘natural’ or ‘unregulated’ monthly flow time series, at any river location to construct a flow duration curve that is then modified depending on the desired condition of a river – an environmental management class – to generate an EF time series. The tool includes historical flow records from 158 gauged locations, but users may also feed in (observed/simulated) external data. The paper illustrates the application of the tool at two locations of existing/planned infrastructure projects and discusses its usefulness as a policy tool.