Environmental Flow Assessment Research Articles

Ecohydrological indicators and environmental flow assessment in the middle and lower reaches of the Huai River, China

The vitality of river ecosystems is vital for the sustainable development of river basins, with the assessment of environmental flow (EF) playing a pivotal role in eco-informatics. This study delves into the middle and lower reaches (MLR) of the Huai River basin (HRB) in China, utilizing hydrological data spanning from 1950 to 2020. Its principal objective lies in the selection of ecohydrological indicators to refine the estimation of EF in the HRB. Employing principal component analysis (PCA), ecologically relevant hydrological indicators (ERHIs) were discerned and scrutinized for their hydrological characteristics. The analysis extended to evaluating hydrological shifts at different stations using ERHIs, determining suitable EF in the MLR, and delineating the trajectories of appropriate intra-annual flows in different hydrological years through HEC-RPT. Based on a variety of mutation test methods, the change point of runoff sequence was determined in 1991. The PCA analysis identified eight ERHIs, reflecting hydrological changes of 49.79 % and 56.26 % at Bengbu and Sanhezha, respectively, which indicate a moderate alteration. Based on ERHIs, the other stations in the HRB exhibited hydrological alterations ranging from 33 % to 47 %, notably highlighting substantial changes in maximal 30d flow and flow fall rate. The optimal flood pulse discharge in the middle reaches is 4150 m3/s, 3140 m3/s and 2150 m3/s in wet, dry and dry years, respectively. Downstream, flood pulse flow in wet, normal and dry years should exceed 4070 m3/s, 3110 m3/s and 1980 m3/s, respectively. The research contributes significantly to the management of rivers and the sustainable conservation of the ecological milieu.

Environmental flow assessment for the Musi River, India

Environmental flow assessment for the Musi River, India

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.

A fish biodiversity protection based approach for assessing environmental flow regime in rivers

Available environmental flow assessment methods are not able to integrate the impacts of flow regime on the fish biodiversity which means improving these methods is necessary. This study proposes a novel approach to assess environmental flow regime in which the fish biodiversity index is simulated in the structure of the environmental flow assessment for protecting the fish biodiversity values in the case study. Due to considerable impact of water quality parameters as well as physical flow parameters, two combined physical flow and water quality indices were considered as the inputs of simulating fish biodiversity index. Adaptive neuro fuzzy inference system (ANFIS) as well as hydraulic simulation were applied to simulate combined indices of physical flow and water quality. Moreover, a multiple linear regression (MLR) model was utilized for simulating the fish biodiversity index. Due to necessity of simulating natural flow regime in the representative river reach, soil and water assessment tool as a known hydrological tool was applied as well. According to evaluation indices of the case study, ANFIS model as well as SWAT and MLR are reliable to assess environmental flow considering the fish biodiversity. The minimum environmental flow in the study area was assessed 40% of mean annual flow in which the difference between fish biodiversity index between the natural flow and environmental flow is less than 10%. However, significant improvement of water quality is a prerequisite before implementing the proposed environmental flow regime. High computational complexities is one of the weaknesses of the proposed method.

Estuarine environmental flow assessment based on the flow-ecological health index relation model: a case study in Yangtze River Estuary, China.

Environmental flow (e-flow) is the water demand of one given ecosystem, which can become the flow regulation target for protection and restoration of river or estuarine ecosystems. In this study, an e-flow assessment based on the flow-ecological health index (EHI) relation model was conducted to improve ecosystem health of the Yangtze River Estuary (YRE). Monitoring data of hydrology, biology, and water environment in the last decades were used for the model establishment. For the description of the YRE ecosystem, an EHI system was developed by cumulative frequency distribution curves and adaption of national standards. After preprocessing original flow values into proportional flow values, the generalized additive model and Monte Carlo random sampling were used for the establishment of the flow-EHI relation model. From the model calculation, the e-flow assessment results were that, in proportional flow values, the suitable flow range was 1.05-1.35, and the optimum flow range was 1.15-1.25 (flows in Yangtze River Datong Station). For flow regulation in two crucial periods, flows of 42,630-65,545 m3/s or over 14,675 m3/s are needed for the suitable flow of YRE in summer (June-August) or January, respectively. An adaptive management framework of ecological health-based estuarine e-flow assessment for YRE was contrived due to the limitation of current established model when facing the extreme drought in summer, 2022. The methodology and framework in this study are expected to provide valuable management and data support for the sustainable development of estuarine ecosystems and to bring inspiration for further studies at even continental or global levels.

Integration of social and cultural dimensions in the assessment of environmental flows: case of the Ouémé delta in West Africa

The use of environmental flows as a technique for the diagnosis and sustainable management of aquatic ecosystems in West Africa is relatively new and cautious, despite being broadly implemented for many years in Western countries and Southern Africa. The present study, the first to evaluate the environmental flows in Benin, concentrates on the deltaic region of the Ouémé River. The assessment utilises the Building Block Methodology approach, and incorporates ecological, socio-cultural, and religious dimensions. The assessment focuses on the alterations in river flows and the impact on local communities’ livelihoods, beliefs, and cultural and religious practices. The results indicate that the population of the Ouémé Delta are significantly impacted by changes in the river’s flow. Indeed, floods play a crucial role in people’s daily routines and livelihoods, while a significant decrease in river flow results in economic instability. Moreover, there is a strong link between specific religious customs in the area and the river’s flow. To maintain the current provisioning, regulating, and cultural ecosystem services in the Ouémé delta, The study recommended to allocate 100% of the River Ouémé’s natural flow during low-water periods (December to May) and 50% of the natural flow during high-water periods (June to November). This allocation ensures that the environment’s water needs are met and will contribute to preserve the Ouémé delta’s ecosystem, ensuring the sustainability of its ecological habitats and biodiversity. However, the implementation of these recommendations would require more debate and a real consensus on the priority between development and environment.

Environmental flow assessment, evaluation, and suggestions for dying riverine ecosystem of the transboundary Amudarya River, Central Asia

The Amudarya River (ADR) is the largest source of freshwater in Central Asia providing livelihood to millions of people by extracting water for agriculture. However, the over-exploitation has created some critical environmental issues. For example, almost no water for the delta and the Aral Sea, which was once the 4th largest lake in the world. The present study focused on the assessment of environmental flow requirements (E-flows) in the basin. However, the main challenges in the accomplishment were the unavailability of natural streamflow, which is necessary for E-flow assessment, and sparse and limited hydroclimatic data. A hydrologic model was configured to simulate naturalized streamflow using the meteorological data from the Climate Research Unit. Four hydrological methods (i.e., Tennant, low flow index (7Q10), flow duration curve analysis (Q90, and Q95), and flow duration curve shifting (FDCS)) and all-method mean were applied to estimate E-flows at 34 sites on all tributaries of the ADR. According to FDCS, 7Q10, Q90, and Q95, E-flows should be 46%, 37%, 30%, and 25% of naturalized mean annual flow (NMAF), respectively, and on average, it should be 35% of NMAF, assessed by the all-methods mean. For low-flow (October–March) and high-flow (April–September) months, E-flows were determined to be 20–30% and 40–98% of NMAF, respectively. E-flow evaluation with the current environmental conditions showed very serious concerns because no sites met the environmental flow requirements below Kerki. This study will be guidelines to improve the riverine ecosystem and for future sustainable development in the region.

An integrated reservoir operation framework for enhanced water resources planning

Climate change induced spatiotemporal variation in global water availability modifies the proposed design criteria of water infrastructure structures like dams and reservoirs. Although reservoir operation is treated as a potential adaptation option, obsolescence of existing operation rules in the climate change scenarios could cause devastating situation through faulty water management practices. Presently onboard simulation–optimization based reservoir operation schemes fail to capture the uncertainty involved in the climate change scenario. Hence, there is a need to identify the limiting application scenario of the existing reservoir operation rule, and subsequently, revise the operation framework to address the future supply–demand uncertainty adequately. This research develops an integrated Soil and Water Assessment Tool (SWAT) (hydrologic), HEC-ResSim (hydraulic), and genetic algorithm (GA) (optimization) based adaptive reservoir operation framework, which is competent enough in accounting the future supply–demand uncertainty. Incorporation of the newly proposed environmental flow assessment approach in the reservoir operation would assist the decision makers in guiding the reservoir release for maintaining the water quality and sustenance of the downstream aquatic species. Certainly, corresponding to the existing operation rules under both the baseline and future climate change scenarios of RCP 4.5 and 8.5, the developed SWAT-HEC-ResSim-GA based reservoir operation scheme could improve the performance of the Kangsabati reservoir with the time and volume reliability estimates of 0.631 and 0.736, respectively. Conclusively, the developed approach in this study could be the best feasible alternative for hydrologic characterization in complex reservoir catchment-command regions with the option for enhanced reservoir planning in global catchment-command regions.

EPiC grasshopper: A bottom-up parametric tool to quantify life cycle embodied environmental flows of buildings and infrastructure assets

Reducing the embodied environmental flows of built assets is becoming increasingly important and is a key priority for actors in the built environment to improve life cycle environmental performance. Policies and related targets for embodied environmental flow reductions are emerging. Despite this, tools for quantifying the life cycle embodied environmental flows of built assets are limited in variety and scope. Parametric life cycle assessment (LCA) tools have emerged to address some of these limitations. These tools can enhance decision making, be embedded directly into CAD programs, and offer real-time LCA calculations across multiple design variations. Yet, existing parametric tools for LCA rely on process-based material environmental flow data, limited geometries, limited real-time data visualisation capacity, and often require specialised technical expertise to use. These gaps limit their ability to provide transparent, robust, and rapid assessments. This paper introduces EPiC Grasshopper, an open-source, open-access, bottom-up, parametric tool that enables the quantification of life cycle embodied environmental flows at the early stages of built asset design, bridging the aforementioned gaps. The key characteristics and functionalities of the tool are described, followed by verification (checking that calculations are correct), validation (checking that results are representative of reality), and demonstration of its application to two built asset case studies, i.e. parametrically-defined Australian house and road. The paper shows how the tool can be used to generate designs to meet specific embodied environmental flow targets as well as streamline and increase the uptake of embodied environmental flow assessment and considerations in built asset design workflows.

Linking catchment and hydrodynamic models for environmental flow analysis in hypersaline lakes

Abstract This research work proposes a novel method of environmental flow analysis in hypersaline lakes in which the outputs of the hydraulic rating method considering the base flow as a known approach for environmental flow assessment in rivers are analyzed in terms of providing suitable aquatic habitats in the lake by linking a continuous hydrological model and a hydrodynamic model of salinity simulation. Soil and Water Assessment Tool (SWAT) as a hydrological model was applied to simulate the natural inflow of the lake's ecosystem in the simulated period. Moreover, a hydrodynamic model was applied to simulate the salinity distribution of the lake in the same simulated period. Based on the results of the models and monthly analysis of the environmental flows, both models are robust for simulations. The Nash–Sutcliffe Efficiency (NSE) of both hydrological and hydrodynamic models average more than 0.5, which means that they are reliable for simulating the natural inflow and salinity distribution respectively. Furthermore, outputs indicated that using the hydraulic rating method considering the base flow for assessing the environmental flow of rivers is not able to provide environmental requirements in the lake's ecosystem of the case study.

ENVIRONMENTAL FLOW ASSESSMENT MODEL ON SUSTAINABILITY PLANNING STRATEGIES, KENYIR LAKE BASIN, MALAYSIA

The study presents the Environmental Flow Assessment (EFA) model on sustainability planning strategies to reduce damage in the main area of Kenyir Lake Basin. The XPSWMM model have been used to simulate the EFA in this study. Based on simulation in the Terengganu River, which has a most effective discharge of 42.78 m3/s with depth on 3.94 m and a water velocity of 0.54 m/s, which are expected to meet the development needs of fish species, the analysis for both study rivers found the minimum river discharge values with the frequency probability in the period of 20 years needs to be maintained. While, based to the simulation in the Petuang River, the maximum discharge is only 0.08 m3/s, the maximum depth is 0.4 m, and the maximum water speed is 0.04 m/s, which is adequate for a small number of small-sized fish species. With output deficiency of less than 20% from an actual situation, the two lowest values later obtained were adopted as input in low flow analysis. A more effective management approach ensures the ecosystem's sustainability and maintains an optimal equilibrium among the many uses. Environmental flows aren't considered a luxury but instead an integral component of contemporary water management given the global misuse of water resources and the resulting degradation of ecosystems and their functions. It is a strategy that requires widespread adoption.

Environmental Flows Assessment Based on the Coupling of Water Level and Salinity Requirements for Maintaining Biodiversity: A Case Study from the Ouémé delta in West Africa.

The present study carried out on the Ouémé delta in West Africa, addresses the implementation of the BBM approach for the determination e-flows in a context of high data limitation. It also highlights the potential challenges for the implementation of the recommended e-flows in West Africa countries. To do this, we first established the current ecological status of the delta based on data collection, measurements and scientists' observations. Then, we formulated ecological objectives for e-flows based on the environmental management vision for the delta. And finally, we determined the water requirements for the sustainability of the biodiversity and ecosystem services using a simple 2D hydrodynamic model. The results indicate that 100 and 50% of the average natural flows are required respectively in low-water and high-water periods (3.4 billion m3 per year) to maintain the Ouémé Delta in its current environmental management class. This recommendation for e-flows allocation is in direct competition with the water requirements for the economic development of the delta, which is estimated to be over 3.0 billion m3 per year in the Master Plan for Water Development and Management. While it is clear that the establishment of e-flows recommendations must be accompanied by measures to limit the degradation of ecological habitats, it is even more clear that the economic development remained the main concern of policymakers. The integration of environmental flows into water resources management policies in developing countries requires linking water needs for economic development with water needs for the ecological sustainability of rivers and their associated ecosystems.

Environmental flow assessment for intermittent rivers supporting the most poleward mangroves

The most vulnerable and dynamic ecosystems in terms of response to climate change and fluctuations in hydrological conditions are mangroves, particularly those located on the edge of their latitudinal range limits. The four primary Iranian mangrove forest sites: Nayband, Qeshm, Gabrik, and Govatr, located in the northern part of the Persian Gulf and the Gulf of Oman already exist near the limit of their tolerance to extreme temperature, precipitation, and salinity. Due to extreme climate conditions at these locations, the mangrove trees are usually smaller and less dense as compared with mangroves closer to the equator complicating their monitoring and mapping efforts. Despite the growing attention to the ecological benefits of mangrove forests and their importance in climate change mitigation, there are still a few studies on these marginal mangroves. Therefore, we investigated whether the variation in mangrove ecosystem health is related to the changes in physical parameters and differs between estuarine and sea-side locations. We developed a comprehensive database on NDVI values, associated rainfall, temperature, and river flow based on in-situ and remote sensing measurements. By understanding the normal hydrologic patterns that control the distribution and growth of mangroves in arid and semi-arid regions, we are questioning the need for environmental flow allocation to restore mangrove ecosystem health. This brings us to the second gap in the literature and the need for further studies on Environmental Flow assessment for intermittent and ephemeral rivers. Alike other mangroves studied, forests showed greenness seasonality, positively correlated with rainfall, and negatively correlated with temperature. As there was no clear difference between estuarine and marine sites, freshwater influence in the form of river flow, unlike temperature, cannot be considered a major limiting factor. Nevertheless, during prolonged droughts mangroves could benefit from the recommended allocation of Environmental Flow during the cold period (November–March).

Environmental Flow Assessment using multiple criteria: A case study in the Kumbih river, West Sumatra (Indonesia)

Water withdrawal from rivers is a key resource for agriculture, industry, and power generation. However, in order to maintain riverine ecosystem, withdrawal should not exceed certain thresholds, and normally a requirement is made that a certain amount of water be left in the river, to be assessed via Environmental Flow Assessment (EFA) procedure. In spite of the crucial importance of this task, little or no international standard exists to assess minimum values of the EF. Rather, general guidelines are provided, with large subjectivity entailed. Here, focusing on the case study Kumbih river, in Sumatra, Indonesia, we apply a multiple criteria approach to EFA procedure, testing the values of EF assessed with hydrological methods in a previous study, with a focus on a relevant target species, i.e. the fish Tor Soro. Based upon a two-dimensional hydraulic model, we explore 6 indicators, covering some most important criteria to ensure the welfare of the fish fauna. Indicator II, weighed usable volume, slightly modifies the well-known method PHABSIM. Indicators IIi.IIIII target water depth needed to ensure welfare of target species, whereas criteria IIV-VI target flow velocity, and sediment removal. Use of multiple indicators as shown here, albeit still subjective, may provide more consistent values of EF, and even an outlook of the disparity in terms of flow requirements given by the several criteria. Here we found that the maximum estimated EF under IV (flow velocity), is over twice as large as the flow estimate from II. Overall however, initial EF estimates from the hydrological criterion seem adequate against the criteria proposed. Our study is among the few covering EF for Indonesia, and the only one regarding Kumbih river, and our results are of interest, also as a benchmark for other EFA studies in the region.

Mapping Community Perception, Synergy, and Trade-Off of Multiple Water Values in the Central Rift Valley Water System of Ethiopia

Individuals and communities use and value water in multiple and complex ways. In Sub-Saharan Africa (SSA), the pluralistic nature of water values is poorly documented, and the existing and potential value trade-offs are unidentified. This study was undertaken in the Central Rift Valley (CRV) of Ethiopia to understand and map water values, priorities, risks, and trade-offs in a multi-stakeholder engagement process to provide the basis for more transparent and accountable decision-making. Integrated assessment methods, combining bio-physical and social methods, were applied. The results show 24 community-perceived and articulated water values that are diverse but interconnected, including values of water, landscapes, the river system, and downstream water bodies. Connections between people and landscape structures are articulated. In terms of priority water values, the overall results reflect the primary but basic need for water for food security and domestic uses. The results further illustrate the pluralistic nature of water values and the dichotomy of preferences among people of different backgrounds. The scenario-based Environmental Flow (EF) assessment exercise integrated into community value preferences and the event calendar that was used show that the river systems in CRV (Ketar, Kulumsa, and Gusha-Temela) have different ecological and socio-cultural flow requirements and that there are marked water value trade-offs. The conclusions of the study suggest that overlapping governance structures are affecting people’s perceptions of water and the way they articulate water values. Policy directions and decision-making need to recognize and acknowledge the multiple water values and competing uses of water in the CRV as a starting point to reconcile trade-offs that will then improve water security. Findings suggest that EF estimation and decision support tools can be customized to local ecological requirements through engaging local stakeholders in the assessment process.

Environmental flow assessment for benthic macroinvertebrate communities using pseudo‐2D hydraulic habitat modelling at a green small hydropower plant

AbstractThe determination of minimum flow requirements for green small hydropower plants (GSHP) in China primarily relies on hydrological methods such as the Tennant method with no seasonal variation. However, the direct application of hydrological methods without local ecological data for calibration lacks ecological validity, potentially resulting in unsuitable minimum flow recommendations for local aquatic biota. Hydraulic‐habitat modelling (HHM) is assumed to provide more ecologically relevant and reliable environmental flow recommendations (EFRs), but benthic macroinvertebrates (BMs), crucial in the aquatic food web, have rarely been the focus in HHM studies. Moreover, the strong subjectivity in HHM processes hinders the comparison of EFRs across different biota and geographical regions. This study aims to investigate the ecological validity of using the Tennant method to set minimum flow requirements for local BM communities and the impacts of various methods used in HHM on derived EFRs. To achieve this, a pseudo‐2D HHM approach is employed, integrating the 1D hydraulic models HEC‐RAS and CASiMiR with the habitat model HABFUZZ. The EFRs downstream of Jiufeng reservoir, one of China's first GSHPs, are derived for wet (April–June) and dry seasons (July–September). Our findings highlight that setting minimum flow alone is inadequate for preserving BM community integrity downstream of GSHPs. It is crucial to incorporate more diverse environmental flow criteria, including minimum flows and peak flows, into GSHP assessment standards, with recommended flow levels varying across different seasons. Additionally, the development of a standardized HHM methodology is essential to mitigate the inherent subjectivity in HHM and facilitate the comparison of EFRs generated from different studies. This study's innovative modelling framework and findings will enhance the optimization of minimum flow assessment criteria for GSHP in China, deepen understanding of seasonal e‐flow requirements of BM communities, and refine the methodology used in BM HHM for e‐flow recommendation.

Research on the improvement of wetted perimeter method and application in seasonal rivers-a case study of Fenhe River, China.

Environmental flow is vital for maintaining river ecosystem health and ensuring the normal growth of aquatic organisms. The wetted perimeter method is indeed very useful in the assessment of environmental flow due to consideration of stream forms and minimum flow for aquatic life habitat. In this study, a river with obvious seasonality and external water diversion was selected as the typical research object; taking Jingle, Lancun, Fenhe Reservoir, and Yitang hydrological sections as control sections, we improved the existing wetted perimeter method in three aspects: (1) We improved the selection of hydrological data series. The selected hydrological data series should be of a certain length and can well reflect the hydrological changes of wet, normal, and dry years. (2) Different from the traditional wetted perimeter method, which only gives one environmental flow value, the improved method calculates the environmental flow month by month. (3) The improved wetted perimeter method establishes the relationship between native fish survival and environmental flow. Results indicated that the improved wetted perimeter took the survival of the main fishes into consideration, the ratio of the calculated results by the slope method to the multi year average flow was greater than 10%, which can ensure the fishes' habitat is not being destroyed, and the results are more reasonable. Furthermore, the monthly environmental flow processes obtained were better than the annual unified environmental flow value determined by the existing method and are consistent with the natural hydrological situation and water diversion situation of the river. This study shows that the improved wetted perimeter method is feasible for research of river environmental flow with strong seasonal and large variation of annual flow.

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 Procedure for Assessment of Environmental Flows Incorporating Inter- and Intra-Annual Variability in Dam-Regulated Watersheds

A Procedure for Assessment of Environmental Flows Incorporating Inter- and Intra-Annual Variability in Dam-Regulated Watersheds

Minimum Instream Environmental Flow in Shatt Al-Hillah River

To maintain river flows necessary to meet social and ecological objectives, instream environmental flows are frequently used as a strategy. The capability of three alternative historical flow approaches to protect against low flows is shown in this study using gage stations in the Shatt Al-Hillah River in Iraq. The extension of the Shatt al-Hillah River is the focus of this research discussion on environmental flow assessment. The available data on discharge in this research were adopted for ten years from 2012-2021. Different flow methods were adopted to establish a minimum environmental flow in the Shatt Al-Hillah River. Three hydrological-based approaches: Tennant, modified Tennant, and low-flow metrics like 7Q10, were used to compare the results of the methods with the provision of a minimal environmental flow. The Tennant method relies on 30 % of the annual discharge rate as the minimum environmental instream flow. The modified Tennant method is based on 30% of the monthly average discharge rate as a minimum environmental instream flow. The 7Q10 method is based on the lowest daily discharge rate in 7 consecutive days for ten years. The results showed that the minimum instream environmental flow given by the Tennant method is 42.26 m3/s while the lowest value of the minimum instream environmental flow obtained from modified Tennant was 37.2 m3/s in January, and the largest value was 47.22 m3/s in August. The one obtained by the 7Q10 method was 50 m3/s in this research.