Determining Environmental Flow Requirements for Rivers in the Southern Basin of Lake Urmia (Case Studies of ZarinehRood and SiminehRood Rivers)

Determining Environmental Flow Requirements for Rivers in the Southern Basin of Lake Urmia (Case Studies of ZarinehRood and SiminehRood Rivers) | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Determining Environmental Flow Requirements for Rivers in the Southern Basin of Lake Urmia (Case Studies of ZarinehRood and SiminehRood Rivers) Jafar Chabokpour, Behzad Azarafrouz This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4471269/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Environmental flow assessment (EFA) is crucial for maintaining river ecosystem health and determining the minimum water requirements for aquatic life and riparian vegetation. This study evaluates the environmental flow of the SiminehRood and ZarinehRood Rivers in the Lake Urmia Basin, Iran, using three hydrological methods: Tennant, Tessman, and Flow Duration Curve (FDC) analysis. Long-term daily discharge data from hydrometric stations were collected and analyzed. The Tennant method, recommending 30% of mean annual runoff (MAR) for low-flow seasons and 10% for high-flow seasons, provided environmental flow values inconsistent with the rivers' natural regimes. The Tessman method, utilizing a combination of mean monthly flow (MMF) and MAR, revealed exceedance probabilities below 50% during certain months, indicating inadequate environmental flow provision. The FDC method assessed low-flow ranges by calculating exceedance probabilities. For the SiminehRood River, low-flow ranges were 1.06-0.1 m3/s (Qizil Ghonbad), 1.45-0.36 m3/s (Dashband), and 2.4-0.26 m3/s (Miandoab Bridge). For the ZarinehRood River, low-flow ranges were 1.41-0.1 m3/s (Anian Bridge), 10.7-2 m3/s (Sarighamish), and 3.43-0.9 m3/s (Nezam Abad). The study highlights the limitations of solely relying on hydrological methods and the need to incorporate ecological components and field research to determine acceptable living conditions for aquatic species. Recommendations include exercising caution when using the Tennant method, modifying it to suit local conditions. Environmental flow Tennant method Tessman method flow duration curve Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction There are numerous methods for evaluating environmental flow. The EFA method creates one or more descriptions of possible flow regimes for a river, each associated with a goal depending on the health conditions of the river ecosystem. The environmental flow requirement for a river is the minimum flow necessary to enhance or maintain the survival of aquatic life and riparian vegetation. More than 200 methods have been used in various countries around the world to determine environmental flow. However, these methods are mainly classified into four general methods of Hydrological method, Hydraulic rating method, Habitat simulation method, and Holistic/integrated method that are widely used for environmental flow assessment (Akter, 2010 ). Each of these methods differs in terms of the required data, flow selection methods, ecological assumptions, and its impact on environmental flow, and they determine the hydrological regime essential for aquatic ecosystems to achieve environmental goals. Since the 1970s, there has been a gradual evolution of methods for assessing the water needs of river ecosystems (Acreman & Dunbar, 2004 ). The initial efforts included defining a "minimum flow" as a fixed percentage of average flows (Tennant, 1976 ) or statistically based on the duration of low flows (e.g., 95th percentile flow, Q95). From 1980 to 1995, the science of environmental flow advanced and was challenged by simulation methods. By the late 1990s, a general protocol for river restoration was established, and the natural flow paradigm emerged. For example, the relationship between river ecosystem health and flow diversity was the focus of the United States Instream Flow Council guidelines, but even after 30 years, the use of simple operational rules has generally been based on minimum flow (Annear et al., 2004 ). (Suwal et al., 2020 ) investigated the environmental flow of the Kaligandaki River in Nepal. In this study, hydrological methods such as Tennant, flow duration curve, mean annual flow method, and annual flow distribution method were used to evaluate the environmental flow, and the suitability of the methods was analyzed using hydrological alteration indices and environmental flow components. They stated that the annual flow distribution method and 30% of the daily discharge outperform other methods and can meet the annual dynamic demand of the river for maintaining river ecosystem health. (Chen et al., 2019 ) conducted a study to classify Chinese dams in terms of environmental flow implementation. They screened 773 dams and classified them into four classes based on environmental flow, which were: Class 1 includes dams with rare and endangered fish species downstream. This group has the highest priority for the release and regulation of environmental flows, which requires flow components for fish spawning and migration, including flow duration and flood pulses. Class 2 includes dams with significant hydrological alterations downstream. This class has the second priority for environmental flow release and regulation, requiring the simulation of natural hydrological regimes or complete restoration of flow components to optimize the flow duration curve and mitigate the impacts of regular dam operations. Class 3 includes dams with a high degree of regulation, where immediate release and flow regulation require a minimum flow guaranteed by reservoir level regulation. Class 4 includes dams with a low degree of regulation, where there is less urgency for flow release and regulation. They stated that this classification method is important for future research, including the regulation of released environmental flows and the evaluation of their effectiveness. (Książek et al., 2019 ) applied a combined approach of hydraulic and hydrological methods to calculate the environmental flow of the Wisloka River in Poland. They stated that hydraulic methods provide lower values of environmental flow compared to hydrological methods. The main issue in using hydraulic methods is the selection of criteria. The development of a set of required parameters while considering their seasonal nature shifts the method towards habitat modeling approaches. However, the range of habitat requirements of ecosystems, including the assemblage of aquatic organisms and the type of water flow, must be determined before the hydraulic method is widely used. (Akter, 2010 ) proposed a combined model. The proposed model is a combination of an economic model and an environmental model. It was stated that this model can examine environmental flows based on the economic potentials of the region. It was also claimed that the maximum profit obtained from the environmental flow in study region could be the main criterion for calculating the amount of environmental flow. (Sahoo et al., 2016 ) conducted a study to evaluate the environmental flow of the Mahanadi sub-basin in India using the Tennant method, Tessman method, Smakhtin method, Low Flow method, VMF method, and FDC method. They recommended that the river's environmental flow requirement is an average of 33% of the mean monthly flow and high flow at 23% of the mean maximum flow to ensure prevention of river ecosystem degradation under any condition. (Tan et al., 2018 ) estimated the environmental flow of the Yangtze River with a new method called the Distribution Flow Method (DFM) and evaluated the standard degree in a study. The results showed that DFM considers the intra- and inter-annual variations of natural runoff. Consequently, it reduces the impact of flow intensity and uneven flow distribution throughout the year. This method also calculates the actual runoff demand of the river ecosystem and demonstrates its superiority over traditional hydrological methods. (Jackson et al., 2017 ), through studies in the Australian region, showed that the fundamental problems and challenges in the area of large rivers are the lack of public attention to the environmental priorities of that region. This public inattention to environmental priorities is due to the lack of attention from consultants and engineers to the local people's beliefs and culture when estimating the volume of environmental flow. They stated that to calibrate environmental flow assessment models, the culture and beliefs of the target region's people, which are important factors, must be considered. (Yin et al., 2022 ), in a study on large reservoirs, stated that although the construction of dams and large reservoirs is useful for hydropower generation, their adverse effects on rivers and their ecosystems are greater. They stated that the issue of river and ecosystem protection must be considered when estimating reservoir storage capacity. They proposed a model to solve this problem and stated that this model should be calibrated based on the topographic, environmental, and other conditions of each basin for use in that basin. (Olden et al., 2012 ) in a study on environmental flow in Denmark, suggested that models calibrated based on the climatic conditions of the same region should be used to assess environmental flow in an area. They also stated that in calibrating a hydrological model, the main objective should be considered, and the influencing factors should be carefully examined so that the model can be more accurately calibrated for that objective. (Guedes et al., 2016 ) used the River 2D model to determine the environmental flow regime for a 1-kilometer reach of the Formoso River. The research results showed that the determined environmental flow of the Formoso River varied throughout the year. The minimum environmental flow was 2.85 (m 3 /s) in December, and the maximum was 4.13 (m 3 /s) in May. (Gao et al., 2018 ) investigated changes in the flow regime of the Yangtze River using environmentally friendly flow criteria. By examining the parameters with the IHA index, they concluded that the annual flow decreased during the 1968–2008 period, with a severe decrease in autumn. The amount of water released from the dam decreased after 2003 due to drought, leading to negative environmental impacts. (Seaman et al., 2016 ) discussed the DRIFT-ARID method for assessing environmental water requirements in non-perennial rivers, focusing on hydrological and ecological outputs. It emphasizes the importance of capturing the essence of river ecosystems through interdisciplinary collaboration and data collection. The study highlights the need for hydrological modeling and simulation to understand future flow regimes and ecosystem impacts. The research provides valuable insights for stakeholders and decision-makers to facilitate discussions on sustainable water management practices in arid regions. Overall, the study underscores the significance of considering environmental factors in water resource management for the long-term health of river ecosystems. (Grela & Madej, 2019 ) presented a hybrid method for determining environmental flows based on the habitat requirements of fish and macrozoobenthos in 34 research catchments in Poland. By combining habitat models and hydrological formulas, the study proposes coefficients to calculate environmental flows for different bio-periods of the year. A comparison with the Kostrzewa method shows differences in flow values, highlighting the challenges of averaging coefficients and potential limitations on water abstraction. The research emphasizes the need for a comprehensive method to determine channel environmental flows, considering the complexities of hydrological regimes and the importance of balancing water use with ecosystem conservation. (Chimtengo et al., 2014 ) investigated changes in the Rivirivi River's flow regime in Malawi. Reduced forest cover and traditional water management practices are linked to increased zero-flow days and altered flow patterns. While total water use remains sustainable, environmental flow requirements are likely compromised. (Colloff & Pittock, 2022 ) discussed challenges in water management in the Murray-Darling Basin, including environmental degradation and water injustice. It highlights the need for reforms to increase transparency, accountability, and Indigenous water entitlements. Criticisms of the Murray-Darling Basin Plan include inadequate recovery of water for the environment and complex water markets disadvantaging smaller irrigators. Policy options suggested include improved modeling, regulating interception activities, and environmental triage for sustainable water management. (Swirepik et al., 2016 ) discussed the challenges of managing water resources in the Murray-Darling Basin while balancing human and environmental needs. It introduces the Umbrella Environmental Asset (UEA) approach to establish environmental water requirements based on key ecosystem components. The UEA approach integrates existing data and allows for flexibility in incorporating new information to address knowledge gaps in flow-ecology relationships. By focusing on key sites in large river basins, the UEA approach aims to represent the broader needs of water-dependent ecosystems and promote sustainable water management practices. (Shokoohi & Amini, 2014 ) explored different methods to determine Environmental Flow Requirements (EFR) for the Kazemroud River in Iran, focusing on index species habitat protection. It compares Tennant, Q95, and hydraulic methods, finding the hydraulic method most rational but less applicable. A new combined method is proposed to balance rationality and applicability. The study emphasizes the importance of accurately determining EFR to prevent environmental catastrophe in rivers. (Fu et al., 2021 ) analyzed TEEWR along the Yarkand River Basin in China, defining ecological protection areas based on riparian forests at varying distances. It proposed a method to calculate ecological water demand for different protection zones, aiming to guide sustainable water resource management in arid regions. The study identified limitations in the calculation method and suggested improvements for future research, with references to similar studies in other regions provided. The research was supported by various funding sources and adheres to open access licensing. (Hamidifar et al., 2022 ) investigated the impact of a hydroelectric dam on the natural flow regime of the Kor River in Iran. Nine hydrological methods were used to determine the river's environmental water requirement (EWR). Two indices evaluated environmental flow allocation, revealing a deficiency of 1.92–30.2% in EWR during the spawning period of dominant fish species. The dam construction eliminated major floods, disrupting the river's morpho-ecological balance and natural habitats. The results highlight the need to consider the dam's negative environmental impact and manage dam outlets accordingly. Taking into account the literature review, the main aim of the study was to evaluate the environmental flow requirements of the SiminehRood- and ZarinehRood Rivers in the Urmia Basin of Iran using hydrological methods. Specific objectives include evaluating the applicability and reliability of Tenant, Tessman, and the Flow Duration Curve (FDC) approaches to estimate environmental flows. In addition, the study seeks to identify the advantages and limitations of relying solely on water methods, highlighting the need to incorporate ecological components and field research to determine acceptable living conditions for aquatic species. One of the main objectives was to recommend changes or alternative approaches that are more suitable for Iran's climate and environmental conditions, to address current and future water resource needs. In the end, the aim of the research was to provide insight into sustainable water management practices in the Urmia Lake basin and similar regions. 2. Materials and methods 2.1. Study Area (Southern Rivers of Lake Urmia Basin) The Lake Urmia basin is one of the closed basins in Iran, considered a major basin according to the classification of Iranian water basins. The area of this basin is 51,870 (km 2 ). Its western border is the mountainous border between Iran and Turkey. The highest elevations in this basin include Sabalan (4,811 meters) and Sahand (3,707 meters), and the lowest point is Lake Urmia at an average elevation of 1,280 meters. The average precipitation in the basin is 350 mm, originating mainly from Mediterranean currents. The Lake Urmia basin covers an area of about 21,500 (km 2 ) in West Azerbaijan Province, 19,000 (km 2 ) in East Azerbaijan Province, and around 5,000 (km 2 ) in Kurdistan Province. 33,469 (km 2 ) of this basin comprises mountainous regions, while 12,564 (km 2 ) consists of plains and foothills. Lake Urmia itself occupies an area of 5,320 (km 2 ) with a water volume of around 32 billion cubic meters. Lake Urmia is considered the largest and most valuable ecosystem in Iran. The Lake Urmia ecosystem is a prime example of a closed basin, where all surface and groundwater resources flow into the lake. The average precipitation volume in this basin is 20.74 billion cubic meters. Additionally, the average annual flow volume of the basin's rivers is approximately 4.5 billion cubic meters. 2.1.1. SiminehRood River The SiminehRood River, with a length of about 100 kilometers and a basin area of 3,500 (km 2 ), is considered one of the most important and water-rich rivers in the Lake Urmia basin. The main tributaries of the SiminehRood River include Tatavu and Kuliz (Zavehkuh). The primary sources of the river originate from the slopes of Mount Nastan, 22 kilometers from the city of Sardasht, at an elevation of 2,410 meters, known as Cham Suyinas. Another tributary, Tatavu, originates from the northern slopes of Mount Nastan and joins other minor tributaries such as Cham Ghalu and Golulan before entering the city of Bukan. After passing through Bukan, the river flows from south to north, enters the city of Miandoab, and finally discharges into Lake Urmia (Fig. 1 ). 2.1.2. ZarinehRood River The main tributaries of the ZarinehRood River are the Khorkhoreh, Saghzchi, and Sarogh rivers, which converge at the Shahid Kazemi Dam site. Sarogh River is a major tributary of ZarinehRood, with a length of about 72 kilometers and a basin area of 2,350 (km 2 ). It originates from the mountains of Takab County. The minor branches of Sarogh Chai converge in the city of Takab and flow in a northeastern direction. After passing through the village of Pahlavan, the Sarogh River receives the tributary of Cham Ghareh Ghiyeh, which originates from Mount Balghis in Takab. It then receives the tributaries of Cham Shafa, Cham Bezeh Dareh, and Karaftu, flowing through mountainous. After passing through the villages of Feyzabad and Ghorkhan, it enters the ZarinehRood River near the village of Yaminabad. The Sari Ghamish River is a seasonal river with a length of about 25 kilometers and a basin area of 120 (km 2 ), considered a minor tributary of the ZarinehRood. It originates from the slopes of Mount Bezhinak Bosar (elevation 1,936 meters), 20 kilometers north of Saghez. Its primary branches converge in the village of Darzi Vey, and then the river flows in a northeastern direction, irrigating the villages of Takan Tappeh and Sari Ghamish before joining the ZarinehRood River in the east. The Saghzchi River is another major tributary of the ZarinehRood River, with a length of about 100 kilometers and a basin area of 1,350 (km 2 ). The main branch of this river, originating from the eastern heights of Namshir, 38 kilometers southeast of Saghez County, is known as Cham Mirnaghineh. After this point, it is called Cham Saghez. Cham Saghez flows in a northeastern direction and enters the city of Saghez after joining the Khan River in the village of Tamogheh. After passing through the city, it merges with other branches under the name Altun Telagi. After crossing the villages of Dareh Pambeh Dan, Kani Cheshni, and Agh Tappeh, a small river called Seyed joins it, and it enters the Shahid Kazemi Dam in the village of Dash Alujeh (Fig. 2 ). 2.2. Used Methods to Determine Environmental Flow of the Studied Rivers As mentioned previously, there are over 207 methods for assessing the environmental flow of rivers. In this research, considering the available data, the following three hydrological methods were used to calculate the environmental flow of the ZarinehRood and SiminehRood rivers: Tennant Method Tessman Method Flow Duration Curve (FDC) Analysis 2.2.1. Tennant Method The most common hydrological method is the Tennant or Montana method. This method is currently the second most widely used method for determining environmental flow in North America. The Tennant (Tennant, 1976 ) method is also widely used as an EFA system in many other countries. In this method, a percentage of the Average Annual Flow (AAF) is used to specify the conditions for aquatic habitats. Based on the results of previous studies, it was concluded that 10% of the AAF is the minimum environmental flow for the short-term survival of fish. On the other hand, 30% of the AAF can maintain relatively good habitats, and 60% of the AAF is suitable for optimal habitats. 2.2.2. Tessman Method Tessman, (1980) (Teklu & El-Zawahry, 2019 ) adapted Tennant's seasonal recommendations by using a combination of the Mean Monthly Flow (MMF) and Mean Annual Flow (MAF) to determine the minimum required monthly flow. Tessman's proposal for determining MMF is as follows: - If MMF 40% of MAF, 40% of MAF is considered the minimum monthly flow. - If MMF > MAF, 40% of MMF is considered the minimum monthly flow. 2.2.3. Flow Duration Curves The most important feature related to river flow, which is used in assessing environmental flow variability, is the Flow Duration Curve (FDC). In environmental flow studies, data from the natural flow regime is used. The FDC is the best method for displaying the entire range of river flows, from low-flow occurrences to flood conditions. The FDC expresses the relationship between flow intensity and the time frequency at which a specific flow (during the statistical period) is equaled or exceeded, or the relationship between flow magnitude and frequency. The time unit of this frequency can be days, months, or years, yielding daily, monthly, or annual flow duration curves. Flow duration curves generated from daily time series data provide more comprehensive information for examining a river's flow regime characteristics. These curves can also be constructed with other time intervals, such as the mean m-day or m-month flow time series (Smakhtin & Eriyagama, 2008 ). Numerous low-flow indices are derived from the flow duration curve. Flows between the 70th and 99th percentile exceedance times (Q99 to Q70) are commonly referred to as low flows. The Q90 and Q95 flows are indices most frequently used as low-flow indicators. The median monthly flow (Q50) is also a common flow persistence index during the warm months of the year. 3. Results Since all the used methods in this research are hydrological, the collected data and information required included daily, monthly, and annual flow discharges of the two studied rivers, ZarinehRood and SiminehRood, obtained from the Regional Water Authority. The available monthly hydrological data for the ZarinehRood and SiminehRood rivers were analyzed for long-term periods. In this study, the required data, including long-term daily discharges from hydrometric stations were collected. From among the hydrometric stations, those with reliable long-term discharge data were also selected, and the rest were eliminated. The monthly flow potential of the SiminehRood River at three hydrometric stations, Ghizil Ghonbad, Dashband Bukan, and Miandoab bridge, is shown in Fig. 3 , and the average monthly flow potential at the hydrometric stations of both studied rivers is presented in Table 1. Table 2 Average annual flow discharge of SiminehRood River and ZarinehRood River at hydrometric stations River Name hydrometric Station Name Mean Annual Flow (m 3 /s) SiminehRood Ghizil Ghonbad 5.2 Dashband Bukan 14.4 Miandoab Bridge 15.55 ZarinehRood Anian Bridge 19.5 Sarighamish 48.35 NezamAbad 35.7 3.1. Tennant Method In this method, various percentages of the mean annual flow are proposed as the environmental flow. Considering that the acceptable value of this method is based on the declared criteria in Iran as the "acceptable condition," 30% of the mean annual runoff (MAR) was considered for early April to the late August, and 10% of the annual flow was considered for September-October. The main criterion is the six-month period, considering the dry (low-flow) and wet (high-flow) periods. However, the range of the mean of the two low-flow and high-flow periods does not correspond to the actual hydrological conditions of the studied rivers. In some months of the year, the environmental flow provided by this method exceeds the monthly average, and the probability of meeting the required environmental water needs in some months is absent. This is because the values proposed by Tennant were based on studies conducted on northern American rivers. Therefore, the determination of low-flow and high-flow seasons was based on the long-term discharge of the studied rivers at the selected hydrometric stations and the regional river flow regime. Accordingly, from late June to mid-October was considered the low-flow season, and from mid- November to mid-July was considered the high-flow season. Thus, considering the changes in the river flow regime in each region and the consequent temporal variations in low-flow and high-flow periods, in this research, 30% of the mean annual flow was considered for June to September as the low-flow period, and 10% of the mean annual flow from October to May as the high-flow period. Based on the results obtained from the study, the environmental water requirements of the SiminehRood River at the Ghizil Ghonbad hydrometric station during the low-flow and high-flow periods are 0.52 and 1.57 m 3 /s, respectively. At the Dashband Bukan station, 1.44 and 4.32 m 3 /s, and at the Miandoab bridge station, 1.55 and 4.66 m3/s. additionally, the environmental water requirements of the ZarinehRood River at the Anian Bridge hydrometric station during the low-flow and high-flow periods are 1.95 and 5.85 m3/s, respectively. At the Sari Ghamish station, 4.83 and 14.5 m 3 /s, and at the Nezam Abad station, 3.57 and 10.72 m 3 /s. The results obtained from the Tennant method for determining the environmental water needs of the studied rivers do not correspond well with the natural river flow regime data of the Simineh Rood River. However, it is observed that the data obtained from this method still differ from the actual conditions of the river, such that in some seasons, including September-October, the minimum required environmental flow cannot be met during both drought and wet periods of the river. 3.2. Tessman Method The obtained results from the proposed Tessman method indicate that the probability of exceeding monthly flow discharges in different months of year. An example of calculations for Anian Bridge is presented in Table 3 . It was found that at some months for the Miandoab Bridge station on the SiminehRood River, the flow is below 50%, indicating a lack of compliance with the environmental flow discharge. This condition is presented by the mentioned method in real situations and during low-flow seasons. For the purpose of comparing the average natural monthly flow of the ZarinehRood and Simineh Rivers at the studied hydrometric stations, the proposed flow of Tessman have been plotted in Fig. 5 . According to results of this method, the proposal for the required environmental flow for studied rivers can be outlined as bellow: - At Qizil Ghonbad hydrometric station on Simineh River: Flow of 2.44 m 3 /s, equal to 47% of MAR with an exceedance probability of 44.84% - At Dashband hydrometric station on Simineh River: Flow of 6.85 m 3 /s, equal to 47% of MAR with an exceedance probability of 58.63% - At Miandoab Bridge hydrometric station on Simineh River: Flow of 7.79 m 3 /s, equal to 49% of MAR with an exceedance probability of 50.2% - At Anian Bridge hydrometric station on ZarinehRood River: Flow of 8.88 m 3 /s, equal to 47% of MAR with an exceedance probability of 44.83% - At Sariqamish hydrometric station on ZarinehRood River: Flow of 25.4 m 3 /s, equal to 52.6% of MAR with an exceedance probability of 57.95% - At Nezam Abad hydrometric station on ZarinehRood River: Flow of 18.73 m 3 /s, equal to 52.5% of MAR with an exceedance probability of 43.17% The results obtained from the Tessman method for determining the environmental needs of the hydrometric stations of the Simineh River during drought and wet periods show that generally from (January to May) in both periods and at different stations, the probability of exceedance of flow is less than 50%. Especially at the Miandoab Bridge station, the probability of exceedance of flow in most months of the year is less than 50%, indicating that providing the environmental flow obtained from this method is not feasible. Table 3 Environmental flow of Anian Bridge station on ZarinehRood River using the Tessman method Month MMF 1 (m3/s) MMF 0.4 (m 3 /s) MAF 2 (m 3 /s) MAF 0.4 (m 3 /s) EF 3 (m 3 /s) probability of exceedance (%) October 0.55 0.22 19.5 7.8 0.55 32.7 November 5.85 2.34 19.5 7.8 5.85 17.6 December 9.13 3.65 19.5 7.8 7.8 30 January 10.84 4.33 19.5 7.8 7.8 43.5 February 18.01 7.2 19.5 7.8 7.8 63.8 March 41.06 16.42 19.5 7.8 16.42 72.3 April 73.81 29.5 19.5 7.8 29.52 85.8 May 51.71 20.68 19.5 7.8 20.68 68.5 Juan 14.02 5.61 19.5 7.8 7.8 34.4 July 1.6 0.64 19.5 7.8 1.6 33.4 August 0.54 0.22 19.5 7.8 0.54 29 September 0.24 0.1 19.5 7.8 0.24 27 Average 18.95 8.88 44.83 [1] Mean monthly flow [2] Mean average flow [3] Environmental flow 3.3. Flow Duration Curve (FDC) Method To assess the environmental flow of the ZarinehRood and SiminehRood Rivers, the monthly flow data was arranged in descending order, and then the flow duration curves (FDCs) of the studied rivers were calculated at the selected stations. Then the exceedance probabilities were calculated, and the flows with exceedance probabilities of 70, 75, 80, 85, 90, and 95% were selected, as shown in Tables 6 and 7 . As observed, the low-flow range for the SiminehRood River at the Qizil Ghonbad station is between 1.06 (Q70) and 0.1 (Q95) (m 3 /s), at the Dashband station between 1.45 (Q70) and 0.36 (Q95) (m 3 /s), and at the Miandoab Bridge station between 2.4 (Q70) and 0.26 (Q95) (m 3 /s). For the ZarinehRood River, the low-flow range is between 1.41 (Q70) and 0.1 (Q95) (m 3 /s) at the Anian Bridge station, between 10.7 (Q70) and 2 (Q95) (m 3 /s) at the Sarighamish station, and between 3.43 (Q70) and 0.9 (Q95) (m 3 /s) at the Nezam Abad station. The environmental flow of the hydrometric stations of the SiminehRood River was also determined for both wet and drought periods. The results show that the low-flow range for this river during the drought period at the Qizil Ghonbad station is between 0.85 (Q70) and 0.01 (Q95) (m 3 /s), at the Dashband station between 1.34 (Q70) and 0.2 (Q95) (m 3 /s), and at the Miandoab Bridge station between 2.23 (Q70) and 0.15 (Q95) (m 3 /s). During the wet period, at the Qizil Gombad station, the range is between 2.48 (Q70) and 0.02 (Q95) (m 3 /s), at the Dashband station between 2.3 (Q70) and 0.33 (Q95) (m 3 /s), and at the Miandoab Bridge station between 3.1 (Q70) and 1.4 (Q95) (m 3 /s). Table 6 Calculated annual flow duration curve index values at hydrometric stations of SiminehRood River Station Name Discharges of flow duration curve (m 3 /s) Discharge with excedence probability 95% Discharge with excedence probability 90% Discharge with excedence probability 85% Discharge with excedence probability 80% Discharge with excedence probability 75% Discharge with excedence probability 70% Ghizil Ghonbad 0.1 0.2 0.38 0.543 0.798 1.06 Dashband 0.36 0.5 0.65 0.84 1.1 1.45 Miandiab Bridge 0.26 0.64 1.1 1.64 2.02 2.4 Table 7 Calculated annual flow duration curve index values at hydrometric stations of Zarinahrood River Station Name Discharges of flow duration curve (m 3 /s) Discharge with excedence probability 95% Discharge with excedence probability 90% Discharge with excedence probability 85% Discharge with excedence probability 80% Discharge with excedence probability 75% Discharge with excedence probability 70% Anian Bridge 0.1 0.2 0.37 0.65 1 1.41 Sarighamish 2 3.2 4.68 6.23 7.9 10.7 Nezam Abad 0.9 1.5 1.92 2.5 2.98 3.43 All the methods employed in this research were conducted with the consideration that the required information for the evaluation methods is available for most water resources in Iran and feasible. In the Tennant method, various percentages of annual water flow or the MAR index are proposed as environmental flow. These values are 10% of annual flow for high-flow periods and 30% of annual flow for low-flow periods, deemed acceptable. The Tennant method focuses solely on the mean annual flow. Rivers that have experienced environmental degradation may not have a desirable mean annual flow and cannot maintain their natural habitats. Using the Tennant method in restoration projects is not appropriate, and employing composite models in such projects is more effective. The Tessman method is similar to the Tennant method and proposes the required environmental flow for different months by comparing the existing monthly flow with the mean annual flow. Therefore, in the proposed Tessman method, the probability of monthly flow deviations during the dry seasons (low-flow months) is less than 50%, indicating that the discharge provided by this method during low-flow months does not comply with the conditions of these rivers. - It is recommended that the Tennant method be applied with more caution or, if possible, modified to suit the climatic and environmental conditions of the country to produce desirable results. Therefore, it is suggested that further research be conducted on the physical details, including width, depth, and velocity in the river channel, to determine the optimal levels for riverine aquatic habitats, and that the Tennant method be used without calibration and only for preliminary planning purposes. - Since all the methods used in this research are hydrological methods and none of them employ ecological components in calculating environmental flow, obtaining satisfactory results necessitates conducting field research and experiments to identify ecological indicators, acceptable living conditions, and the range that the species of interest can tolerate. The assessment of environmental flow in rivers, while dependent on the collection of numerous and diverse data, must also undergo changes in environmental management and water resources management programs. To address the time-consuming nature of these processes, on one hand, two approaches are mentioned, the use of simpler models with less error and their replacement with more comprehensive models is recommended to meet the current and future water resource needs of the Iran. In this study, the capabilities of the IHA model were evaluated for estimating the environmental flow of the SiminehRood and ZrinehRood rivers. Considering the data requirements of this software and the available information in Iran, its use provides acceptable results. 4. Conclusions In conclusion, the evaluation of the methods of assessing the environmental flow of the SiminehRood and ZarinehRood rivers in the Urmia-Lake basin of Iran has revealed some critical insights. The only water approaches used, including Tennant, Tesman and Flow Duration Curve (FDC) methods, demonstrated limitations in accurately capturing river natural conditions and ecological requirements. The Tenant method, based on the average annual flow rate percentage, generated environmental flow values that were not consistent with actual river conditions. Similarly, the Tessman method, using the mean monthly flow rate, produced over flux probabilities of less than 50% during certain months, indicating insufficient flow rates. Although the FDC method provides estimates of the low flow range, the lack of ecological components in the three methods emphasizes the need to incorporate field research and identify acceptable conditions of living for aquatic species. The study emphasizes the importance of caution when applying these methods and recommends that they be modified to better adapt to local climate and environmental factors. In addition, the findings suggest the need for a comprehensive approach combining water assessments, ecological considerations, and stakeholders to achieve sustainable water management practices in the Urmia Basin and similar areas. Declarations Conflicts of interest: No potential conflict of interest was reported by the authors. Availability of data and material: The datasets generated during and/or analyzed during the current study is available from the corresponding author on reasonable request Code availability : Not applicable Authors' contributions: Data analysis, Conception or design of the work, simulation interpretation, drafting the article Ethics approval: Not applicable Consent to participate : Not applicable Consent for publication: Not applicable Funding: Not applicable References Acreman MC, Dunbar MJ (2004) Defining environmental river flow requirements–a review. Hydrol Earth Syst Sci 8(5):861–876 Akter J (2010) Environmental flow assessment for the Ganges River Annear T, Chisholm I, Beecher H, Locke A, Aarrestad P, Coomer C, Estes C, Hunt J, Jacobson R, Jobsis G (2004) Instream Flows for Riverine Resource Stewardship (revised edition): Instream Flow Council. Cheyenne, Wyoming Chen A, Wu M, McClain ME (2019) Classifying dams for environmental flow implementation in China. Sustainability 12(1):107 Chimtengo M, Ngongondo C, Tumbare M, Monjerezi M (2014) Analysing changes in water availability to assess environmental water requirements in the Rivirivi River basin, Southern Malawi. Phys Chem Earth Parts A/B/C 67:202–213 Colloff MJ, Pittock J (2022) Mind the gap! Reconciling environmental water requirements with scarcity in the Murray–Darling Basin, Australia. Water 14(2):208 Fu A, Li W, Wang Y (2021) Calculation of targeted eco-environmental water requirements in a dry inland river: A case study of the Yarkand River Basin, Xinjiang, China. SN Appl Sci 3(6):680 Gao B, Li J, Wang X (2018) Analyzing changes in the flow regime of the Yangtze River using the eco-flow metrics and IHA metrics. Water 10(11):1552 Grela J, Madej P (2019) Assessment of the possibilities for determining the channel environmental flow based on the environmental requirements of ichthyofauna and macrozoobentos. Acta Sci Pol Form Circumiectus 18:59–70 Guedes HA, Silva DD, Dergam JA, Elesbon AA (2016) Ecohydrological modeling and environmental flow regime in the Formoso River, Minas Gerais State, Brazil. An Acad Bras Cienc 88:2429–2440 Hamidifar H, Akbari F, Rowiński PM (2022) Assessment of environmental water requirement allocation in anthropogenic rivers with a hydropower dam using hydrologically based methods—case study. Water 14(6):893 Jackson W, Argent R, Bax N, Clark G, Coleman S, Cresswell I, Emmerson K, Evans K, Hibberd M, Johnston E (2017) Australia state of the environment 2016: overview, independent report to the Australian Government Minister for the Environment and Energy. Australian Government Department of the Environment and Energy, Canberra Książek L, Woś A, Florek J, Wyrębek M, Młyński D, Wałęga A (2019) Combined use of the hydraulic and hydrological methods to calculate the environmental flow: Wisloka river, Poland: case study. Environ Monit Assess 191:1–17 Olden JD, Kennard MJ, Pusey BJ (2012) A framework for hydrologic classification with a review of methodologies and applications in ecohydrology. Ecohydrology 5(4):503–518 Sahoo S, Khare D, Mishra PK, Behera S, Krishan R (2016) A comparative study on environmental flows assessment methods in lower reach of Mahanadi River. Int J Eng Trends Technol 32(2):82–90 Seaman M, Watson M, Avenant M, King J, Joubert A, Barker C, Esterhuyse S, Graham D, Kemp M, le Roux P (2016) DRIFT-ARID: A method for assessing environmental water requirements (EWRs) for non-perennial rivers. Water SA 42(3):356–366 Shokoohi A, Amini M (2014) Introducing a new method to determine rivers’ ecological water requirement in comparison with hydrological and hydraulic methods. Int J Environ Sci Technol 11:747–756 Smakhtin VU, Eriyagama N (2008) Developing a software package for global desktop assessment of environmental flows. Environ Model Softw 23(12):1396–1406 Suwal N, Kuriqi A, Huang X, Delgado J, Młyński D, Walega A (2020) Environmental flows assessment in Nepal: the case of Kaligandaki River. Sustainability 12(21):8766 Swirepik J, Burns I, Dyer F, Neave I, O'brien M, Pryde G, Thompson R (2016) Establishing environmental water requirements for the Murray–Darling Basin, Australia's largest developed river system. River Res Appl 32(6):1153–1165 Tan G, Yi R, Chang J, Shu C, Yin Z, Han S, Feng Z, Lyu Y (2018) A new method for calculating ecological flow: Distribution flow method. AIP Adv, 8 (4) Teklu S, El-Zawahry AHSA (2019) Planning for Environmental Water Allocations: Hydrology-Based Assessment in the Awash River Basin. Ethiopia Plann, 9 (11) Tennant DL (1976) Instream flow regimens for fish, wildlife, recreation and related environmental resources. Fisheries 1(4):6–10 Yin D, Li X, Wang F, Liu Y, Croke BF, Jakeman AJ (2022) Water-energy-ecosystem nexus modeling using multi-objective, non-linear programming in a regulated river: Exploring tradeoffs among environmental flows, cascaded small hydropower, and inter-basin water diversion projects. J Environ Manage 308:114582 Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4471269","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":312222753,"identity":"f7ad987f-26d5-4fa7-a145-bb7442ab9032","order_by":0,"name":"Jafar Chabokpour","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0002-6268-4415","institution":"University of Maragheh","correspondingAuthor":true,"prefix":"","firstName":"Jafar","middleName":"","lastName":"Chabokpour","suffix":""},{"id":312222754,"identity":"3ffb830d-cbbc-4036-92b1-ba7f6b138b1b","order_by":1,"name":"Behzad Azarafrouz","email":"","orcid":"","institution":"University of Maragheh","correspondingAuthor":false,"prefix":"","firstName":"Behzad","middleName":"","lastName":"Azarafrouz","suffix":""}],"badges":[],"createdAt":"2024-05-24 08:56:54","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4471269/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4471269/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":59444469,"identity":"2895d702-5888-431f-83e8-59dcbc45a6b0","added_by":"auto","created_at":"2024-07-01 22:52:20","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":656556,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLocation of the SiminehRood River Basin and its Tributary Branches\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4471269/v1/f162af1b47786cb74b8e53c0.png"},{"id":59444467,"identity":"6490ea9c-a97c-4b65-a7a6-440a8a58e320","added_by":"auto","created_at":"2024-07-01 22:52:20","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":103241,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLocation of the ZarinehRood River and its Major Headwater Streams\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4471269/v1/55cd7db8e296c3e6ba72ed72.jpeg"},{"id":59445083,"identity":"f76e53b1-ecc5-48ff-b886-23a7f5c8d69f","added_by":"auto","created_at":"2024-07-01 23:00:20","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":66566,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMonthly flow discharge of SiminehRood River at selected hydrometric stations\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4471269/v1/8603d9aee679c947697a9f6f.png"},{"id":59445084,"identity":"c21a95dd-b25c-4298-8aa4-40318591ad2d","added_by":"auto","created_at":"2024-07-01 23:00:20","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":321406,"visible":true,"origin":"","legend":"\u003cp\u003eFig. 5. (a) Monthly flow and environmental flow of Simineh River at Qizil Gombad hydrometric station,(b) Monthly flow and environmental flow of Simineh River at Dashband Bukan hydrometric station, (c) Monthly flow and environmental flow of Simineh River at Miandoab Bridge hydrometric station, (d) Monthly flow and environmental flow of Zarinahrood River at Anian Bridge hydrometric station, (e) Monthly flow and environmental flow of Zarinahrood River at Sariqamish hydrometric station, (f) Monthly flow and environmental flow of Zarinahrood River at Nezamabad hydrometric station\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4471269/v1/0d1eeef0c8cc67d61cc26472.png"},{"id":59954016,"identity":"d47d2f1c-bf09-45e3-84a2-315fd8fe0205","added_by":"auto","created_at":"2024-07-09 18:48:10","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1811120,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4471269/v1/42a30be4-28a3-41d3-af39-5b3abfd65e43.pdf"}],"financialInterests":"","formattedTitle":"Determining Environmental Flow Requirements for Rivers in the Southern Basin of Lake Urmia (Case Studies of ZarinehRood and SiminehRood Rivers)","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThere are numerous methods for evaluating environmental flow. The EFA method creates one or more descriptions of possible flow regimes for a river, each associated with a goal depending on the health conditions of the river ecosystem. The environmental flow requirement for a river is the minimum flow necessary to enhance or maintain the survival of aquatic life and riparian vegetation. More than 200 methods have been used in various countries around the world to determine environmental flow. However, these methods are mainly classified into four general methods of Hydrological method, Hydraulic rating method, Habitat simulation method, and Holistic/integrated method that are widely used for environmental flow assessment (Akter, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eEach of these methods differs in terms of the required data, flow selection methods, ecological assumptions, and its impact on environmental flow, and they determine the hydrological regime essential for aquatic ecosystems to achieve environmental goals. Since the 1970s, there has been a gradual evolution of methods for assessing the water needs of river ecosystems (Acreman \u0026amp; Dunbar, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). The initial efforts included defining a \"minimum flow\" as a fixed percentage of average flows (Tennant, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e1976\u003c/span\u003e) or statistically based on the duration of low flows (e.g., 95th percentile flow, Q95). From 1980 to 1995, the science of environmental flow advanced and was challenged by simulation methods. By the late 1990s, a general protocol for river restoration was established, and the natural flow paradigm emerged. For example, the relationship between river ecosystem health and flow diversity was the focus of the United States Instream Flow Council guidelines, but even after 30 years, the use of simple operational rules has generally been based on minimum flow (Annear et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). (Suwal et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) investigated the environmental flow of the Kaligandaki River in Nepal. In this study, hydrological methods such as Tennant, flow duration curve, mean annual flow method, and annual flow distribution method were used to evaluate the environmental flow, and the suitability of the methods was analyzed using hydrological alteration indices and environmental flow components. They stated that the annual flow distribution method and 30% of the daily discharge outperform other methods and can meet the annual dynamic demand of the river for maintaining river ecosystem health. (Chen et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) conducted a study to classify Chinese dams in terms of environmental flow implementation. They screened 773 dams and classified them into four classes based on environmental flow, which were: Class 1 includes dams with rare and endangered fish species downstream. This group has the highest priority for the release and regulation of environmental flows, which requires flow components for fish spawning and migration, including flow duration and flood pulses. Class 2 includes dams with significant hydrological alterations downstream. This class has the second priority for environmental flow release and regulation, requiring the simulation of natural hydrological regimes or complete restoration of flow components to optimize the flow duration curve and mitigate the impacts of regular dam operations. Class 3 includes dams with a high degree of regulation, where immediate release and flow regulation require a minimum flow guaranteed by reservoir level regulation. Class 4 includes dams with a low degree of regulation, where there is less urgency for flow release and regulation. They stated that this classification method is important for future research, including the regulation of released environmental flows and the evaluation of their effectiveness. (Książek et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) applied a combined approach of hydraulic and hydrological methods to calculate the environmental flow of the Wisloka River in Poland. They stated that hydraulic methods provide lower values of environmental flow compared to hydrological methods. The main issue in using hydraulic methods is the selection of criteria. The development of a set of required parameters while considering their seasonal nature shifts the method towards habitat modeling approaches. However, the range of habitat requirements of ecosystems, including the assemblage of aquatic organisms and the type of water flow, must be determined before the hydraulic method is widely used. (Akter, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) proposed a combined model. The proposed model is a combination of an economic model and an environmental model. It was stated that this model can examine environmental flows based on the economic potentials of the region. It was also claimed that the maximum profit obtained from the environmental flow in study region could be the main criterion for calculating the amount of environmental flow. (Sahoo et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) conducted a study to evaluate the environmental flow of the Mahanadi sub-basin in India using the Tennant method, Tessman method, Smakhtin method, Low Flow method, VMF method, and FDC method. They recommended that the river's environmental flow requirement is an average of 33% of the mean monthly flow and high flow at 23% of the mean maximum flow to ensure prevention of river ecosystem degradation under any condition. (Tan et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) estimated the environmental flow of the Yangtze River with a new method called the Distribution Flow Method (DFM) and evaluated the standard degree in a study. The results showed that DFM considers the intra- and inter-annual variations of natural runoff. Consequently, it reduces the impact of flow intensity and uneven flow distribution throughout the year. This method also calculates the actual runoff demand of the river ecosystem and demonstrates its superiority over traditional hydrological methods. (Jackson et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), through studies in the Australian region, showed that the fundamental problems and challenges in the area of large rivers are the lack of public attention to the environmental priorities of that region. This public inattention to environmental priorities is due to the lack of attention from consultants and engineers to the local people's beliefs and culture when estimating the volume of environmental flow. They stated that to calibrate environmental flow assessment models, the culture and beliefs of the target region's people, which are important factors, must be considered. (Yin et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), in a study on large reservoirs, stated that although the construction of dams and large reservoirs is useful for hydropower generation, their adverse effects on rivers and their ecosystems are greater. They stated that the issue of river and ecosystem protection must be considered when estimating reservoir storage capacity. They proposed a model to solve this problem and stated that this model should be calibrated based on the topographic, environmental, and other conditions of each basin for use in that basin. (Olden et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) in a study on environmental flow in Denmark, suggested that models calibrated based on the climatic conditions of the same region should be used to assess environmental flow in an area. They also stated that in calibrating a hydrological model, the main objective should be considered, and the influencing factors should be carefully examined so that the model can be more accurately calibrated for that objective. (Guedes et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) used the River 2D model to determine the environmental flow regime for a 1-kilometer reach of the Formoso River. The research results showed that the determined environmental flow of the Formoso River varied throughout the year. The minimum environmental flow was 2.85 (m\u003csup\u003e3\u003c/sup\u003e/s) in December, and the maximum was 4.13 (m\u003csup\u003e3\u003c/sup\u003e/s) in May. (Gao et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) investigated changes in the flow regime of the Yangtze River using environmentally friendly flow criteria. By examining the parameters with the IHA index, they concluded that the annual flow decreased during the 1968\u0026ndash;2008 period, with a severe decrease in autumn. The amount of water released from the dam decreased after 2003 due to drought, leading to negative environmental impacts. (Seaman et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) discussed the DRIFT-ARID method for assessing environmental water requirements in non-perennial rivers, focusing on hydrological and ecological outputs. It emphasizes the importance of capturing the essence of river ecosystems through interdisciplinary collaboration and data collection. The study highlights the need for hydrological modeling and simulation to understand future flow regimes and ecosystem impacts. The research provides valuable insights for stakeholders and decision-makers to facilitate discussions on sustainable water management practices in arid regions. Overall, the study underscores the significance of considering environmental factors in water resource management for the long-term health of river ecosystems. (Grela \u0026amp; Madej, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) presented a hybrid method for determining environmental flows based on the habitat requirements of fish and macrozoobenthos in 34 research catchments in Poland. By combining habitat models and hydrological formulas, the study proposes coefficients to calculate environmental flows for different bio-periods of the year. A comparison with the Kostrzewa method shows differences in flow values, highlighting the challenges of averaging coefficients and potential limitations on water abstraction. The research emphasizes the need for a comprehensive method to determine channel environmental flows, considering the complexities of hydrological regimes and the importance of balancing water use with ecosystem conservation. (Chimtengo et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) investigated changes in the Rivirivi River's flow regime in Malawi. Reduced forest cover and traditional water management practices are linked to increased zero-flow days and altered flow patterns. While total water use remains sustainable, environmental flow requirements are likely compromised. (Colloff \u0026amp; Pittock, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) discussed challenges in water management in the Murray-Darling Basin, including environmental degradation and water injustice. It highlights the need for reforms to increase transparency, accountability, and Indigenous water entitlements. Criticisms of the Murray-Darling Basin Plan include inadequate recovery of water for the environment and complex water markets disadvantaging smaller irrigators. Policy options suggested include improved modeling, regulating interception activities, and environmental triage for sustainable water management. (Swirepik et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) discussed the challenges of managing water resources in the Murray-Darling Basin while balancing human and environmental needs. It introduces the Umbrella Environmental Asset (UEA) approach to establish environmental water requirements based on key ecosystem components. The UEA approach integrates existing data and allows for flexibility in incorporating new information to address knowledge gaps in flow-ecology relationships. By focusing on key sites in large river basins, the UEA approach aims to represent the broader needs of water-dependent ecosystems and promote sustainable water management practices. (Shokoohi \u0026amp; Amini, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) explored different methods to determine Environmental Flow Requirements (EFR) for the Kazemroud River in Iran, focusing on index species habitat protection. It compares Tennant, Q95, and hydraulic methods, finding the hydraulic method most rational but less applicable. A new combined method is proposed to balance rationality and applicability. The study emphasizes the importance of accurately determining EFR to prevent environmental catastrophe in rivers. (Fu et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) analyzed TEEWR along the Yarkand River Basin in China, defining ecological protection areas based on riparian forests at varying distances. It proposed a method to calculate ecological water demand for different protection zones, aiming to guide sustainable water resource management in arid regions. The study identified limitations in the calculation method and suggested improvements for future research, with references to similar studies in other regions provided. The research was supported by various funding sources and adheres to open access licensing. (Hamidifar et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) investigated the impact of a hydroelectric dam on the natural flow regime of the Kor River in Iran. Nine hydrological methods were used to determine the river's environmental water requirement (EWR). Two indices evaluated environmental flow allocation, revealing a deficiency of 1.92\u0026ndash;30.2% in EWR during the spawning period of dominant fish species. The dam construction eliminated major floods, disrupting the river's morpho-ecological balance and natural habitats. The results highlight the need to consider the dam's negative environmental impact and manage dam outlets accordingly.\u003c/p\u003e \u003cp\u003eTaking into account the literature review, the main aim of the study was to evaluate the environmental flow requirements of the SiminehRood- and ZarinehRood Rivers in the Urmia Basin of Iran using hydrological methods. Specific objectives include evaluating the applicability and reliability of Tenant, Tessman, and the Flow Duration Curve (FDC) approaches to estimate environmental flows. In addition, the study seeks to identify the advantages and limitations of relying solely on water methods, highlighting the need to incorporate ecological components and field research to determine acceptable living conditions for aquatic species. One of the main objectives was to recommend changes or alternative approaches that are more suitable for Iran's climate and environmental conditions, to address current and future water resource needs. In the end, the aim of the research was to provide insight into sustainable water management practices in the Urmia Lake basin and similar regions.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1. Study Area (Southern Rivers of Lake Urmia Basin)\u003c/h2\u003e\n\u003cp\u003eThe Lake Urmia basin is one of the closed basins in Iran, considered a major basin according to the classification of Iranian water basins. The area of this basin is 51,870 (km\u003csup\u003e2\u003c/sup\u003e). Its western border is the mountainous border between Iran and Turkey. The highest elevations in this basin include Sabalan (4,811 meters) and Sahand (3,707 meters), and the lowest point is Lake Urmia at an average elevation of 1,280 meters. The average precipitation in the basin is 350 mm, originating mainly from Mediterranean currents. The Lake Urmia basin covers an area of about 21,500 (km\u003csup\u003e2\u003c/sup\u003e) in West Azerbaijan Province, 19,000 (km\u003csup\u003e2\u003c/sup\u003e) in East Azerbaijan Province, and around 5,000 (km\u003csup\u003e2\u003c/sup\u003e) in Kurdistan Province. 33,469 (km\u003csup\u003e2\u003c/sup\u003e) of this basin comprises mountainous regions, while 12,564 (km\u003csup\u003e2\u003c/sup\u003e) consists of plains and foothills. Lake Urmia itself occupies an area of 5,320 (km\u003csup\u003e2\u003c/sup\u003e) with a water volume of around 32\u0026nbsp;billion cubic meters. Lake Urmia is considered the largest and most valuable ecosystem in Iran. The Lake Urmia ecosystem is a prime example of a closed basin, where all surface and groundwater resources flow into the lake. The average precipitation volume in this basin is 20.74\u0026nbsp;billion cubic meters. Additionally, the average annual flow volume of the basin's rivers is approximately 4.5\u0026nbsp;billion cubic meters.\u003c/p\u003e\n\u003cdiv id=\"Sec4\" class=\"Section3\"\u003e\n\u003ch2\u003e2.1.1. SiminehRood River\u003c/h2\u003e\n\u003cp\u003eThe SiminehRood River, with a length of about 100 kilometers and a basin area of 3,500 (km\u003csup\u003e2\u003c/sup\u003e), is considered one of the most important and water-rich rivers in the Lake Urmia basin. The main tributaries of the SiminehRood River include Tatavu and Kuliz (Zavehkuh). The primary sources of the river originate from the slopes of Mount Nastan, 22 kilometers from the city of Sardasht, at an elevation of 2,410 meters, known as Cham Suyinas. Another tributary, Tatavu, originates from the northern slopes of Mount Nastan and joins other minor tributaries such as Cham Ghalu and Golulan before entering the city of Bukan. After passing through Bukan, the river flows from south to north, enters the city of Miandoab, and finally discharges into Lake Urmia (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\n\u003ch2\u003e2.1.2. ZarinehRood River\u003c/h2\u003e\n\u003cp\u003eThe main tributaries of the ZarinehRood River are the Khorkhoreh, Saghzchi, and Sarogh rivers, which converge at the Shahid Kazemi Dam site. Sarogh River is a major tributary of ZarinehRood, with a length of about 72 kilometers and a basin area of 2,350 (km\u003csup\u003e2\u003c/sup\u003e). It originates from the mountains of Takab County. The minor branches of Sarogh Chai converge in the city of Takab and flow in a northeastern direction. After passing through the village of Pahlavan, the Sarogh River receives the tributary of Cham Ghareh Ghiyeh, which originates from Mount Balghis in Takab. It then receives the tributaries of Cham Shafa, Cham Bezeh Dareh, and Karaftu, flowing through mountainous. After passing through the villages of Feyzabad and Ghorkhan, it enters the ZarinehRood River near the village of Yaminabad. The Sari Ghamish River is a seasonal river with a length of about 25 kilometers and a basin area of 120 (km\u003csup\u003e2\u003c/sup\u003e), considered a minor tributary of the ZarinehRood. It originates from the slopes of Mount Bezhinak Bosar (elevation 1,936 meters), 20 kilometers north of Saghez. Its primary branches converge in the village of Darzi Vey, and then the river flows in a northeastern direction, irrigating the villages of Takan Tappeh and Sari Ghamish before joining the ZarinehRood River in the east. The Saghzchi River is another major tributary of the ZarinehRood River, with a length of about 100 kilometers and a basin area of 1,350 (km\u003csup\u003e2\u003c/sup\u003e). The main branch of this river, originating from the eastern heights of Namshir, 38 kilometers southeast of Saghez County, is known as Cham Mirnaghineh. After this point, it is called Cham Saghez. Cham Saghez flows in a northeastern direction and enters the city of Saghez after joining the Khan River in the village of Tamogheh. After passing through the city, it merges with other branches under the name Altun Telagi. After crossing the villages of Dareh Pambeh Dan, Kani Cheshni, and Agh Tappeh, a small river called Seyed joins it, and it enters the Shahid Kazemi Dam in the village of Dash Alujeh (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2. Used Methods to Determine Environmental Flow of the Studied Rivers\u003c/h2\u003e\n\u003cp\u003eAs mentioned previously, there are over 207 methods for assessing the environmental flow of rivers. In this research, considering the available data, the following three hydrological methods were used to calculate the environmental flow of the ZarinehRood and SiminehRood rivers:\u003c/p\u003e\n\u003col\u003e\n\u003cli\u003e\n\u003cp\u003eTennant Method\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eTessman Method\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eFlow Duration Curve (FDC) Analysis\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ol\u003e\n\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.1. Tennant Method\u003c/h2\u003e\n\u003cp\u003eThe most common hydrological method is the Tennant or Montana method. This method is currently the second most widely used method for determining environmental flow in North America. The Tennant (Tennant, \u003cspan class=\"CitationRef\"\u003e1976\u003c/span\u003e) method is also widely used as an EFA system in many other countries. In this method, a percentage of the Average Annual Flow (AAF) is used to specify the conditions for aquatic habitats. Based on the results of previous studies, it was concluded that 10% of the AAF is the minimum environmental flow for the short-term survival of fish. On the other hand, 30% of the AAF can maintain relatively good habitats, and 60% of the AAF is suitable for optimal habitats.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.2. Tessman Method\u003c/h2\u003e\n\u003cp\u003eTessman, (1980) (Teklu \u0026amp; El-Zawahry, \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e) adapted Tennant's seasonal recommendations by using a combination of the Mean Monthly Flow (MMF) and Mean Annual Flow (MAF) to determine the minimum required monthly flow. Tessman's proposal for determining MMF is as follows:\u003c/p\u003e\n\u003cp\u003e- If MMF\u0026thinsp;\u0026lt;\u0026thinsp;40% of MAF, MMF is considered the minimum monthly flow.\u003c/p\u003e\n\u003cp\u003e- If MMF\u0026thinsp;\u0026gt;\u0026thinsp;40% of MAF, 40% of MAF is considered the minimum monthly flow.\u003c/p\u003e\n\u003cp\u003e- If MMF\u0026thinsp;\u0026gt;\u0026thinsp;MAF, 40% of MMF is considered the minimum monthly flow.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.3. Flow Duration Curves\u003c/h2\u003e\n\u003cp\u003eThe most important feature related to river flow, which is used in assessing environmental flow variability, is the Flow Duration Curve (FDC). In environmental flow studies, data from the natural flow regime is used. The FDC is the best method for displaying the entire range of river flows, from low-flow occurrences to flood conditions. The FDC expresses the relationship between flow intensity and the time frequency at which a specific flow (during the statistical period) is equaled or exceeded, or the relationship between flow magnitude and frequency. The time unit of this frequency can be days, months, or years, yielding daily, monthly, or annual flow duration curves. Flow duration curves generated from daily time series data provide more comprehensive information for examining a river's flow regime characteristics. These curves can also be constructed with other time intervals, such as the mean m-day or m-month flow time series (Smakhtin \u0026amp; Eriyagama, \u003cspan class=\"CitationRef\"\u003e2008\u003c/span\u003e). Numerous low-flow indices are derived from the flow duration curve. Flows between the 70th and 99th percentile exceedance times (Q99 to Q70) are commonly referred to as low flows. The Q90 and Q95 flows are indices most frequently used as low-flow indicators. The median monthly flow (Q50) is also a common flow persistence index during the warm months of the year.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. Results","content":"\u003cp\u003eSince all the used methods in this research are hydrological, the collected data and information required included daily, monthly, and annual flow discharges of the two studied rivers, ZarinehRood and SiminehRood, obtained from the Regional Water Authority. The available monthly hydrological data for the ZarinehRood and SiminehRood rivers were analyzed for long-term periods. In this study, the required data, including long-term daily discharges from hydrometric stations were collected. From among the hydrometric stations, those with reliable long-term discharge data were also selected, and the rest were eliminated. The monthly flow potential of the SiminehRood River at three hydrometric stations, Ghizil Ghonbad, Dashband Bukan, and Miandoab bridge, is shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, and the average monthly flow potential at the hydrometric stations of both studied rivers is presented in Table\u0026nbsp;1.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eAverage annual flow discharge of SiminehRood River and ZarinehRood River at hydrometric stations\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eRiver Name\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ehydrometric Station Name\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMean Annual Flow (m\u003csup\u003e3\u003c/sup\u003e/s)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd rowspan=\"3\" align=\"left\"\u003e\n\u003cp\u003eSiminehRood\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eGhizil Ghonbad\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eDashband Bukan\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e14.4\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eMiandoab Bridge\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e15.55\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd rowspan=\"3\" align=\"left\"\u003e\n\u003cp\u003eZarinehRood\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAnian Bridge\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.5\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eSarighamish\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e48.35\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eNezamAbad\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e35.7\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n\u003ch2\u003e3.1. Tennant Method\u003c/h2\u003e\n\u003cp\u003eIn this method, various percentages of the mean annual flow are proposed as the environmental flow. Considering that the acceptable value of this method is based on the declared criteria in Iran as the \"acceptable condition,\" 30% of the mean annual runoff (MAR) was considered for early April to the late August, and 10% of the annual flow was considered for September-October.\u003c/p\u003e\n\u003cp\u003eThe main criterion is the six-month period, considering the dry (low-flow) and wet (high-flow) periods. However, the range of the mean of the two low-flow and high-flow periods does not correspond to the actual hydrological conditions of the studied rivers. In some months of the year, the environmental flow provided by this method exceeds the monthly average, and the probability of meeting the required environmental water needs in some months is absent. This is because the values proposed by Tennant were based on studies conducted on northern American rivers. Therefore, the determination of low-flow and high-flow seasons was based on the long-term discharge of the studied rivers at the selected hydrometric stations and the regional river flow regime. Accordingly, from late June to mid-October was considered the low-flow season, and from mid- November to mid-July was considered the high-flow season. Thus, considering the changes in the river flow regime in each region and the consequent temporal variations in low-flow and high-flow periods, in this research, 30% of the mean annual flow was considered for June to September as the low-flow period, and 10% of the mean annual flow from October to May as the high-flow period. Based on the results obtained from the study, the environmental water requirements of the SiminehRood River at the Ghizil Ghonbad hydrometric station during the low-flow and high-flow periods are 0.52 and 1.57 m\u003csup\u003e3\u003c/sup\u003e/s, respectively. At the Dashband Bukan station, 1.44 and 4.32 m\u003csup\u003e3\u003c/sup\u003e/s, and at the Miandoab bridge station, 1.55 and 4.66 m3/s. additionally, the environmental water requirements of the ZarinehRood River at the Anian Bridge hydrometric station during the low-flow and high-flow periods are 1.95 and 5.85 m3/s, respectively. At the Sari Ghamish station, 4.83 and 14.5 m\u003csup\u003e3\u003c/sup\u003e/s, and at the Nezam Abad station, 3.57 and 10.72 m\u003csup\u003e3\u003c/sup\u003e/s.\u003c/p\u003e\n\u003cp\u003eThe results obtained from the Tennant method for determining the environmental water needs of the studied rivers do not correspond well with the natural river flow regime data of the Simineh Rood River. However, it is observed that the data obtained from this method still differ from the actual conditions of the river, such that in some seasons, including September-October, the minimum required environmental flow cannot be met during both drought and wet periods of the river.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n\u003ch2\u003e3.2. Tessman Method\u003c/h2\u003e\n\u003cp\u003eThe obtained results from the proposed Tessman method indicate that the probability of exceeding monthly flow discharges in different months of year. An example of calculations for Anian Bridge is presented in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. It was found that at some months for the Miandoab Bridge station on the SiminehRood River, the flow is below 50%, indicating a lack of compliance with the environmental flow discharge. This condition is presented by the mentioned method in real situations and during low-flow seasons. For the purpose of comparing the average natural monthly flow of the ZarinehRood and Simineh Rivers at the studied hydrometric stations, the proposed flow of Tessman have been plotted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e. According to results of this method, the proposal for the required environmental flow for studied rivers can be outlined as bellow:\u003c/p\u003e\n- At Qizil Ghonbad hydrometric station on Simineh River: Flow of 2.44 m\u003csup\u003e3\u003c/sup\u003e/s, equal to 47% of MAR with an exceedance probability of 44.84%\n\u003cp\u003e- At Dashband hydrometric station on Simineh River: Flow of 6.85 m\u003csup\u003e3\u003c/sup\u003e/s, equal to 47% of MAR with an exceedance probability of 58.63%\u003c/p\u003e\n\u003cp\u003e- At Miandoab Bridge hydrometric station on Simineh River: Flow of 7.79 m\u003csup\u003e3\u003c/sup\u003e/s, equal to 49% of MAR with an exceedance probability of 50.2%\u003c/p\u003e\n\u003cp\u003e- At Anian Bridge hydrometric station on ZarinehRood River: Flow of 8.88 m\u003csup\u003e3\u003c/sup\u003e/s, equal to 47% of MAR with an exceedance probability of 44.83%\u003c/p\u003e\n\u003cp\u003e- At Sariqamish hydrometric station on ZarinehRood River: Flow of 25.4 m\u003csup\u003e3\u003c/sup\u003e/s, equal to 52.6% of MAR with an exceedance probability of 57.95%\u003c/p\u003e\n\u003cp\u003e- At Nezam Abad hydrometric station on ZarinehRood River: Flow of 18.73 m\u003csup\u003e3\u003c/sup\u003e/s, equal to 52.5% of MAR with an exceedance probability of 43.17%\u003c/p\u003e\n\u003cp\u003eThe results obtained from the Tessman method for determining the environmental needs of the hydrometric stations of the Simineh River during drought and wet periods show that generally from (January to May) in both periods and at different stations, the probability of exceedance of flow is less than 50%. Especially at the Miandoab Bridge station, the probability of exceedance of flow in most months of the year is less than 50%, indicating that providing the environmental flow obtained from this method is not feasible.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab2\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eEnvironmental flow of Anian Bridge station on ZarinehRood River using the Tessman method\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMonth\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMMF\u003ca id=\"#FNLinkFn1\" class=\"FNLink\" href=\"#Fn1\"\u003e1\u003c/a\u003e(m3/s)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMMF 0.4\u003c/p\u003e\n\u003cp\u003e(m\u003csup\u003e3\u003c/sup\u003e/s)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMAF\u003ca id=\"#FNLinkFn2\" class=\"FNLink\" href=\"#Fn2\"\u003e2\u003c/a\u003e\u003c/p\u003e\n\u003cp\u003e(m\u003csup\u003e3\u003c/sup\u003e/s)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMAF 0.4\u003c/p\u003e\n\u003cp\u003e(m\u003csup\u003e3\u003c/sup\u003e/s)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eEF\u003ca id=\"#FNLinkFn3\" class=\"FNLink\" href=\"#Fn3\"\u003e3\u003c/a\u003e (m\u003csup\u003e3\u003c/sup\u003e/s)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eprobability of exceedance (%)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eOctober\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.55\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.22\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.55\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e32.7\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eNovember\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.85\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.34\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.85\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e17.6\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eDecember\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e9.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.65\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e30\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eJanuary\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10.84\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e4.33\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e43.5\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eFebruary\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e18.01\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e63.8\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eMarch\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e41.06\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e16.42\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e16.42\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e72.3\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eApril\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e73.81\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e29.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e29.52\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e85.8\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eMay\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e51.71\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20.68\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20.68\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e68.5\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eJuan\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e14.02\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34.4\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eJuly\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.64\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e33.4\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAugust\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.54\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.22\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.54\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e29\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eSeptember\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.24\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.24\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e27\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eAverage\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e\u003cstrong\u003e18.95\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e\u003cstrong\u003e8.88\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e44.83\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e[1] Mean monthly flow\u003c/p\u003e\n\u003cp\u003e[2] Mean average flow\u003c/p\u003e\n\u003cp\u003e[3] Environmental flow\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n\u003ch2\u003e3.3. Flow Duration Curve (FDC) Method\u003c/h2\u003e\n\u003cp\u003eTo assess the environmental flow of the ZarinehRood and SiminehRood Rivers, the monthly flow data was arranged in descending order, and then the flow duration curves (FDCs) of the studied rivers were calculated at the selected stations. Then the exceedance probabilities were calculated, and the flows with exceedance probabilities of 70, 75, 80, 85, 90, and 95% were selected, as shown in Tables\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e. As observed, the low-flow range for the SiminehRood River at the Qizil Ghonbad station is between 1.06 (Q70) and 0.1 (Q95) (m\u003csup\u003e3\u003c/sup\u003e/s), at the Dashband station between 1.45 (Q70) and 0.36 (Q95) (m\u003csup\u003e3\u003c/sup\u003e/s), and at the Miandoab Bridge station between 2.4 (Q70) and 0.26 (Q95) (m\u003csup\u003e3\u003c/sup\u003e/s). For the ZarinehRood River, the low-flow range is between 1.41 (Q70) and 0.1 (Q95) (m\u003csup\u003e3\u003c/sup\u003e/s) at the Anian Bridge station, between 10.7 (Q70) and 2 (Q95) (m\u003csup\u003e3\u003c/sup\u003e/s) at the Sarighamish station, and between 3.43 (Q70) and 0.9 (Q95) (m\u003csup\u003e3\u003c/sup\u003e/s) at the Nezam Abad station.\u003c/p\u003e\n\u003cp\u003eThe environmental flow of the hydrometric stations of the SiminehRood River was also determined for both wet and drought periods. The results show that the low-flow range for this river during the drought period at the Qizil Ghonbad station is between 0.85 (Q70) and 0.01 (Q95) (m\u003csup\u003e3\u003c/sup\u003e/s), at the Dashband station between 1.34 (Q70) and 0.2 (Q95) (m\u003csup\u003e3\u003c/sup\u003e/s), and at the Miandoab Bridge station between 2.23 (Q70) and 0.15 (Q95) (m\u003csup\u003e3\u003c/sup\u003e/s). During the wet period, at the Qizil Gombad station, the range is between 2.48 (Q70) and 0.02 (Q95) (m\u003csup\u003e3\u003c/sup\u003e/s), at the Dashband station between 2.3 (Q70) and 0.33 (Q95) (m\u003csup\u003e3\u003c/sup\u003e/s), and at the Miandoab Bridge station between 3.1 (Q70) and 1.4 (Q95) (m\u003csup\u003e3\u003c/sup\u003e/s).\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab3\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eCalculated annual flow duration curve index values at hydrometric stations of SiminehRood River\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eStation Name\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003eDischarges of flow duration curve (m\u003csup\u003e3\u003c/sup\u003e/s)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDischarge with excedence probability\u003c/p\u003e\n\u003cp\u003e95%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDischarge with excedence probability\u003c/p\u003e\n\u003cp\u003e90%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDischarge with excedence probability\u003c/p\u003e\n\u003cp\u003e85%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDischarge with excedence probability\u003c/p\u003e\n\u003cp\u003e80%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDischarge with excedence probability\u003c/p\u003e\n\u003cp\u003e75%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDischarge with excedence probability\u003c/p\u003e\n\u003cp\u003e70%\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eGhizil Ghonbad\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.38\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.543\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.798\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.06\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eDashband\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.36\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.65\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.84\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.45\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eMiandiab Bridge\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.26\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.64\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.64\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.02\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.4\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"colspec\" align=\"char\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"colspec\" align=\"char\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"colspec\" align=\"char\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"colspec\" align=\"char\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab4\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 7\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eCalculated annual flow duration curve index values at hydrometric stations of Zarinahrood River\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eStation Name\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003eDischarges of flow duration curve (m\u003csup\u003e3\u003c/sup\u003e/s)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDischarge with excedence probability\u003c/p\u003e\n\u003cp\u003e95%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDischarge with excedence probability\u003c/p\u003e\n\u003cp\u003e90%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDischarge with excedence probability\u003c/p\u003e\n\u003cp\u003e85%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDischarge with excedence probability\u003c/p\u003e\n\u003cp\u003e80%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDischarge with excedence probability\u003c/p\u003e\n\u003cp\u003e75%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDischarge with excedence probability\u003c/p\u003e\n\u003cp\u003e70%\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAnian Bridge\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.37\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.65\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.41\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eSarighamish\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e4.68\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e6.23\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e7.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10.7\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eNezam Abad\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.92\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2.98\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.43\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eAll the methods employed in this research were conducted with the consideration that the required information for the evaluation methods is available for most water resources in Iran and feasible.\u003c/p\u003e\n\u003cp\u003eIn the Tennant method, various percentages of annual water flow or the MAR index are proposed as environmental flow. These values are 10% of annual flow for high-flow periods and 30% of annual flow for low-flow periods, deemed acceptable. The Tennant method focuses solely on the mean annual flow. Rivers that have experienced environmental degradation may not have a desirable mean annual flow and cannot maintain their natural habitats. Using the Tennant method in restoration projects is not appropriate, and employing composite models in such projects is more effective. The Tessman method is similar to the Tennant method and proposes the required environmental flow for different months by comparing the existing monthly flow with the mean annual flow. Therefore, in the proposed Tessman method, the probability of monthly flow deviations during the dry seasons (low-flow months) is less than 50%, indicating that the discharge provided by this method during low-flow months does not comply with the conditions of these rivers.\u003c/p\u003e\n- It is recommended that the Tennant method be applied with more caution or, if possible, modified to suit the climatic and environmental conditions of the country to produce desirable results. Therefore, it is suggested that further research be conducted on the physical details, including width, depth, and velocity in the river channel, to determine the optimal levels for riverine aquatic habitats, and that the Tennant method be used without calibration and only for preliminary planning purposes.\u003c/div\u003e\n\u003cdiv class=\"Section2\"\u003e- Since all the methods used in this research are hydrological methods and none of them employ ecological components in calculating environmental flow, obtaining satisfactory results necessitates conducting field research and experiments to identify ecological indicators, acceptable living conditions, and the range that the species of interest can tolerate.\n\u003cp\u003eThe assessment of environmental flow in rivers, while dependent on the collection of numerous and diverse data, must also undergo changes in environmental management and water resources management programs. To address the time-consuming nature of these processes, on one hand, two approaches are mentioned, the use of simpler models with less error and their replacement with more comprehensive models is recommended to meet the current and future water resource needs of the Iran.\u003c/p\u003e\n\u003cp\u003eIn this study, the capabilities of the IHA model were evaluated for estimating the environmental flow of the SiminehRood and ZrinehRood rivers. Considering the data requirements of this software and the available information in Iran, its use provides acceptable results.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn conclusion, the evaluation of the methods of assessing the environmental flow of the SiminehRood and ZarinehRood rivers in the Urmia-Lake basin of Iran has revealed some critical insights. The only water approaches used, including Tennant, Tesman and Flow Duration Curve (FDC) methods, demonstrated limitations in accurately capturing river natural conditions and ecological requirements. The Tenant method, based on the average annual flow rate percentage, generated environmental flow values that were not consistent with actual river conditions. Similarly, the Tessman method, using the mean monthly flow rate, produced over flux probabilities of less than 50% during certain months, indicating insufficient flow rates. Although the FDC method provides estimates of the low flow range, the lack of ecological components in the three methods emphasizes the need to incorporate field research and identify acceptable conditions of living for aquatic species. The study emphasizes the importance of caution when applying these methods and recommends that they be modified to better adapt to local climate and environmental factors. In addition, the findings suggest the need for a comprehensive approach combining water assessments, ecological considerations, and stakeholders to achieve sustainable water management practices in the Urmia Basin and similar areas.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflicts of interest:\u003c/strong\u003e No potential conflict of interest was reported by the authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and material:\u003c/strong\u003e The datasets generated during and/or analyzed during the current study is available from the corresponding author on reasonable request\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCode availability\u003c/strong\u003e: Not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions:\u003c/strong\u003e\u0026nbsp; Data analysis, Conception or design of the work, simulation interpretation, drafting the article\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval:\u003c/strong\u003e\u0026nbsp; Not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate\u003c/strong\u003e: Not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication:\u003c/strong\u003e Not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e Not applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAcreman MC, Dunbar MJ (2004) Defining environmental river flow requirements\u0026ndash;a review. 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Fisheries 1(4):6\u0026ndash;10\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYin D, Li X, Wang F, Liu Y, Croke BF, Jakeman AJ (2022) Water-energy-ecosystem nexus modeling using multi-objective, non-linear programming in a regulated river: Exploring tradeoffs among environmental flows, cascaded small hydropower, and inter-basin water diversion projects. J Environ Manage 308:114582\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Environmental flow, Tennant method, Tessman method, flow duration curve","lastPublishedDoi":"10.21203/rs.3.rs-4471269/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4471269/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eEnvironmental flow assessment (EFA) is crucial for maintaining river ecosystem health and determining the minimum water requirements for aquatic life and riparian vegetation. This study evaluates the environmental flow of the SiminehRood and ZarinehRood Rivers in the Lake Urmia Basin, Iran, using three hydrological methods: Tennant, Tessman, and Flow Duration Curve (FDC) analysis. Long-term daily discharge data from hydrometric stations were collected and analyzed. The Tennant method, recommending 30% of mean annual runoff (MAR) for low-flow seasons and 10% for high-flow seasons, provided environmental flow values inconsistent with the rivers' natural regimes. The Tessman method, utilizing a combination of mean monthly flow (MMF) and MAR, revealed exceedance probabilities below 50% during certain months, indicating inadequate environmental flow provision. The FDC method assessed low-flow ranges by calculating exceedance probabilities. For the SiminehRood River, low-flow ranges were 1.06-0.1 m3/s (Qizil Ghonbad), 1.45-0.36 m3/s (Dashband), and 2.4-0.26 m3/s (Miandoab Bridge). For the ZarinehRood River, low-flow ranges were 1.41-0.1 m3/s (Anian Bridge), 10.7-2 m3/s (Sarighamish), and 3.43-0.9 m3/s (Nezam Abad). The study highlights the limitations of solely relying on hydrological methods and the need to incorporate ecological components and field research to determine acceptable living conditions for aquatic species. Recommendations include exercising caution when using the Tennant method, modifying it to suit local conditions.\u003c/p\u003e","manuscriptTitle":"Determining Environmental Flow Requirements for Rivers in the Southern Basin of Lake Urmia (Case Studies of ZarinehRood and SiminehRood Rivers)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-01 22:52:15","doi":"10.21203/rs.3.rs-4471269/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"9a31c09b-0d97-4a92-8b8c-c487fd7b118e","owner":[],"postedDate":"July 1st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-07-09T18:40:03+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-01 22:52:15","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4471269","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4471269","identity":"rs-4471269","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}