جستجوی مقالات مرتبط با کلیدواژه « environmental flow » در نشریات گروه « آب و خاک »

In this study, the environmental flow of the Sojasrood River (Yengikand station) at Zanjan province was calculated using the water quality )the so-called Q relationship) and M5 tree decision methods and then the results were compared with the four hydrological methods (Smakhtin, desktop reserve model, FDC shifting and single low flow indices (7Q10 and 7Q2). Evaluation of the hydrological methods showed that the FDC shifting method has the proper accuracy than other methods in determining the environmental flow of the Sojasrood River. Based on the FDC shifting method, the environmental flow (Environmental Management Class C) at Yengikand station was equal to 0.99 (m3/s), respectively, which is equal to 29/4% of MAR. The maximum value of environmental flow was obtained by the water quality method (1.48 m3/s, equal to 43.9% of MAR) and the minimum value of environmental flow was obtained by 7Q10 and 7Q2 method (0.26 m3/s, equal to 7.7% of MAR) while, the environmental flow was determined 1.11 m3/s (equal to 32.8% of MAR) based on the tree decision method. In sum, the tree decision method (M5) extracted the equations of flow duration curve and could properly determine the environmental flow and is able to provide the values of characteristic discharges of a river.

Drought is a global phenomenon that can occur anywhere and cause significant damage to humans and natural ecosystems. Therefore, the issue of hydrological drought and reduction of river flow in Ardabil province is also an important issue that requires a comprehensive study.

In this study, hydrological drought characteristics are using Severity-Duration-Frequency (SDF) curves considering four different threshold levels (constant, annual average, seasonal, and environmental flow) in 33 hydrometric stations in Ardabil province. The severities of drought events are calculated using Easy-Fit software in different return periods. In this regard, drought magnitude-duration-frequency curves are calculated and based on that, the values of drought events in different return periods are calculated and analyzed.

The highest drought event is determined for constant, seasonal, yearly, E-flow threshold levels in Samina, Mashiran, Booran, and Samian stations, respectively.  Also, the lowest occurrence of drought is associated with the Vildaragh station. The majority of drought events in all four aforementioned thresholds are mostly observed in shorter durations, especially within one-month periods. The Jonson_SB and General Extreme Value distributions were the most suitable statistical distributions. The highest intensity of drought increases with longer return periods associated with the average annual threshold level, and the lowest intensity of hydrological drought is linked to the threshold of environmental flow. The SDF curves for all stations demonstrate an increasing trend, indicating that with prolonged hydrological drought duration in all studied thresholds, the severity of hydrological drought occurrences also increases. The greatest intensity of hydrological drought is sequentially related to the annual threshold, followed by the seasonal threshold and the fixed threshold, with the threshold of environmental flow being the lowest and least. Consequently, for shorter return periods, the fixed threshold indicates greater intensity or magnitude compared to the seasonal threshold in all four stations, and for longer return periods, the seasonal threshold demonstrates higher intensity of drought events compared to the fixed threshold.

Furthermore, it can be concluded that the magnitude of hydrological drought at a fixed threshold shows less variability in all four selected stations compared to the other thresholds. It should be noted that in defining drought based on fixed, annual, and seasonal thresholds, events will have a higher number and greater intensity compared to the environmental flow threshold. The spatial changes in drought intensity are depicted on the map, indicating that most droughts have occurred in stations located in the northern and north-western regions (Borran and Dostbiglou). Separating the effects of human and climatic factors in drought assessment is a suggestion from this study that could be considered in future research.

Generally, Iran has an arid and semi-arid climate with a high population. In recent years, the shortages of surface water and groundwater have become a main national challenge in Iran. The optimum operation of reservoirs is one of the most critical challenges in water resources management. In a situation where the drying crisis of the Urmia Lake is serious, comprehensive management of water resources in this basin, allocation of environmental water rights, and the optimal operation of dam reservoirs are the most principled methods of allocation to combat the drying crisis of this lake. The choice of management policies and optimization method depends on the system specification, availability of data, type of objective function, constraints, and variables. The Eleviyan dam is located on the Sufi-Chay River and is one of the main existing dams in the Urmia Lake basin. Therefore, in this research, the performance of the Teaching Learning Based Optimization algorithm (TLBO) is compared with Improved Harmony Search (IHS) and Particle Swarm Optimization (PSO) algorithms in order to optimize the Eleviyan reservoir operation, located across the Sufi-Chay River.

Considering the vital importance of environmental flow to prevent the death of Urmia Lake, the minimum environmental flow of the Sufi-Chay River was estimated by two hydrological methods Tennant (first scenario) and Flow Duration Curve analysis (second scenario). The Teaching Learning Based Optimization algorithm, Improved Harmony Search, and Particle Swarm Optimization algorithms were used for optimization. The optimization models were written in the form of two scenarios, taking into account the complete provision of the minimum environmental flow, the municipal demands, and industry, and minimizing the severity of agricultural shortages. In order to check the performance of the studied algorithms in the optimal exploitation of the reservoir, the performance indicators of the reservoir including reliability, vulnerability, and stability index of the reservoir were used.

The results in this study showed better performance of the TLBO algorithm method compared with both scenarios. In TLBO algorithm, the objective function values for both scenarios are calculated, respectively 2.43 and 7.54. While with Improved Harmony Search algorithm objective function values are calculated respectively 2.81 and 8, and with the Particle Swarm Optimization algorithm objective function values are calculated 3.34 and 8.45 with both Tenant and Flow Duration Curve (FDC) methods. Based on the obtained results, the TLBO algorithm has been able to supply the downstream demand of the dam. So, for the first scenario, it will provide 81.40% and for the second scenario, 62.55% of the demands. The release of observation has been able to provide about 70% of the total demand and according to the situation of Urmia Lake, the current policy of the dam is not suitable and should be revised. Taking place according to the second scenario (flow duration curve method), in case of reducing about 8% of agricultural expenses and allocating it to the environmental flow, the problem of water rights of Urmia Lake from the Sufi-Chay River will also be solved to some extent.

One of the main causes of drying of the Urmia Lake is the reduction of inflow to the Lake due to the development of agricultural lands, allocation of irregular water resources to the agricultural sector regardless of the environmental right of water, and irregular yields of surface and groundwater resources. Regarding the scenarios, it seems that if the downstream agricultural demand is reduced by about 8% in methods such as lessened irrigation of gardens, changes to crop cultivation, and revising the curve of dams around the Lake, it would aid the recovery of Urmia Lake and play an important role in adequately supplying the downstream needs. The results show that managing the Eleviyan dam is required to reduce the agricultural demand through the methods such as reducing the crop area and changing the cropping patterns such as low consumption plant cultivation or changing the type of irrigation method in order to optimize the operation of water resources in the basin. Otherwise, water stress will increase in the basin. The results in this study showed a higher performance of the Teaching algorithm compared with the other methods employed in the optimum release from the Eleviyan reservoir with considering environmental flow.

Hydrological variability is of great importance for water resources management. Analyzing the instream environmental flow demand by coupling the hydrological cycle and the hydrodynamic process with aquatic ecological processes at a watershed scale remains one of the most important yet most difficult issues. Ecological water demand (environmental flow) refers to the typical—intra-annual and inter-annual natural flow regime variability—which describes the quality, quantity, and timing of flow discharge required to preserve the ecosystem and sustain essential services upon which human livelihoods and well-being depend. Therefore, ecological water demand (EWD) should be considered as a constraint in water resource planning and management.

Numerous methods and frameworks have been developed for establishing ecological water demand at regulated rivers. Hydrologically-based ecological water demand methods, because of their simplicity, data availability, and other economic and social aspects, remain the most applied ones. A suitable range of discharges environmental flow Dinavar River was estimated using advocate statistical analysis of hydrological methods Tennant, Annual Distribution Method, and Texas, coupled with habitat suitability model using the program River2D to natural flow variability need. River2D is a two-dimensional, depth-averaged hydrodynamic and fish habitat model widely used in environmental flow assessment studies. A detailed digital model of the river channel and its surrounding area was developed, including all the morphological characteristics of the river channel and its various sandy islets. Data collection was performed through GIS/GPS mapping surveys, hydro-morphological measurements (water depth, flow, substratum type, etc.), and electrofishing samplings at a microhabitat scale under different discharge conditions. Several different steady-state hydraulic simulations were conducted under typical low flow conditions, producing water depth and water velocity (direction and magnitude) maps for each discharge scenario, while results were verified with the use of field measurements. In the next step, River2D was used for the fish habitat modeling of the study area, with the application of fish preference curves developed specifically for the study area. Finally, the fish habitat modeling was conducted for the Capoeta trutta (Heckel, 1843) species, divided into two life groups, forced under the flow conditions. Also, the suitable level of ecological water demand and crucial values with different flow frequencies were analyzed, including water level, water surface width, and Weighted Usable Area.

Results show that high environmental flow releases did not necessarily provide the highest habitat availability and suitability at all seasons and fish life-stages. The adult life stage resulted in being more vulnerable to water diversion, particularly during the spring season. Shallow-water hydromorphological units suffered the highest habitat loss. Some of the environmental flow methods demonstrated inconsistent results over seasons and fish life-stages by either allowing for higher environmental flow releases. Also, the Weighted Usable Area -Discharge curve was calculated with the suitability index in medium flow conditions. From the result, the Weighted Usable Area is changed according to flowrate. In the flowrate- Weighted Usable Area/A graph, ecological flow can be determined at 1.38 m3/s for Capoeta trutta (Heckel, 1843) species. Ecological flows were calculated in the range 0.17–3.71 m3/s as the required discharge, which assures the welfare and sustainability of protected fish species populations. It was also noticed that low flow months (June to November) required more proportions of mean monthly flow than high flow months (December to May). When compared with flow-duration analysis, it is demonstrative that simulation results fitted EWD considering the quantity of available habitat for fish species. Also, the results of the study indicated that monthly EWD had an increasing trend during the flood season and a decreasing trend during the non-flood season in three sections at different suitable levels. With the increase of suitable levels, the range of EWD in the three sections also increased. The EWD and crucial values were the lowest in April with the smallest range and were the highest from June to October.

The major finding of this research is that the estimated Suitable Range of Discharges could better address environmental water requirements, rather than simply allocating single value minimum ecological flows. Results reveal that the ecohydraulic modeling of river basins should be considered as an indispensable component in sustainable water resources.

There are various methods for assessing and regulating flow in order to protect the environment. In total, 207 methods have been identified for determining the environmental flow of rivers in 44 countries around the world, which can be classified into four general methods, including the hydrological method, hydraulic rating, habitat simulation, and holistic methodologies. Among these methods, the hydrological method has been the most used due to its ease of use, access to data and short calculation time. The aim of this study is to determine the environmental flow of Balikhluchay river in Ardabil, using Tennant, Tasman and flow continuity methods. Also, the effects of Yamchi dam construction on environmental and hydrological flow in downstream of the river were investigated and analyzed using IHA software. To achieve the objectives of the present study, some hydrological methods have been used. The input data in these methods is the daily runoff data of the Pole Almas station. The research stages are based on two main steps of calculating the river's environmental flow from 1970 to 2013 without considering the Yamchi dam and applying the Tennant, Tessman and Flow duration curve methods in different months of the year. According to the Tennant criteria, values of 10, 30 and 60% of the mean annual flows, respectively, are allocated as minimum flows, for Short-term survival of fish, maintaining relatively good survival status and maintaining suitable habitat. In Tessman method, if the 40% of mean annual flow was greater than the mean monthly flow, then the average monthly flow would be considered as the minimum monthly flow, otherwise, 40% of mean annual flow would be considered as the minimum monthly flow. The flow duration curves, by presenting the relationship between the amount and frequency of the river flow, show the full range of river discharges, from drought to flood events. The flow duration curves include information on river water planning, drinking use, or construction of diversion dams. In this method, the daily average data is first sorted in descending order. The next step is to investigate and analyze the effects of the Yamchi dam construction (before and after the dam construction in 2004) on environmental and hydrological downstream flows of the river using IHA software. The results showed that the Tennant method calculates the river flow between 1.96 to 3.27 m3/s to keep the river flow regime at the optimum range for all months of the year, while Tessmann method calculates 1.31 m3/s. The results of the FDC indicate that for the protection of the river in suitable and relatively suitable conditions, the flow rate of 2.95 and 2.46 m3/s was required, respectively. The results of the flow duration curve method can be useful to simulate the historical flow regime to maintain good or moderate environmental conditions and to provide a management model for the protection of the Balikhluchay river as well as early planning. The flow duration curve method estimated the environmental flow values more than other methods. The Tenntant method also estimates the environmental flow values less than the other two methods. In all months of the year, the Tenant method estimates the amount of environmental flow less than the Q75. In some months, Tasman method has estimated the amount of environmental flow less than the Q75 and in some months more than the Q75. The results of the periodicity and continuity of the pulsating behavior of the Balikhluchay river in low and high water periods, showed that before and after the construction of Yamchi dam, the duration of low-flow pulse has little hydrological change. However, the hydrological change degree of the wetness period pulse in terms of frequency and continuity is moderate and high, respectively. Changing these parameters can cause the movement of organic and food materials between the river and floodplain, the frequency and severity of soil moisture stress for plants, the frequency and duration of plant oxygen-free activities stress, and the effect on substrate transport, channel sediment texture and duration of disturbance. The intensity of flow decrease and increase in the period after the dam construction has had moderate changes. Generally, it was found that the dam’s operation has influenced downstream hydrological and environmental parameters. The extent of these effects on hydrological parameters such as magnitude of monthly water conditions, magnitude and duration of annual extreme water conditions, timing of annual extreme water conditions, and frequency and duration of high and low pulses status were 61.38% with moderate change degree. Also, despite the dam, 51.6% of the environmental parameters such as monthly low flows, extreme low flows, small floods and large floods have changed.

Due to the increasing deterioration of river life systems because of human intervention, droughts and climate change, the recognition of the environmental flow in planning water resources development studies to maintain the health of it is necessary. The main objective of in this research is to implementation and assessment the methods of Tennant, Flow Duration Curve, Eco deficit, Aquatic Base Flow, Flow Duration Curve shifting (FDC Shifting) and Desktop Reserve Model (DRM) in estimating the environmental flow of Gharasoo River in different months of the year in the range of studies of Siahab hydrometry station to entrance to Gorgan Gulf in order to conservation and restoring of the above river. In the present study by comparing the results of suggested values of environmental flow in Gharasoo River were determined to be estimate Tennant method 0.57 m3/s for April to September and 0.19 m3/s for October to March, Flow Duration Curve method in conditions of relatively suitable (Q90) and suitable (Q75) was respectively 0.17 and 0.393  m3/s, Aquatic Base Flow method 0.57 m3/s, FDC Shifting method in relatively modest conditions with an annual average of 0.94 m3/s, Eco deficit method 0.88 m3/s and in class B DRM model 0.69 m3/s. Accordingly, by providing the ecological regime of the Gharasoo River, it is possible to maintain proper conditions for maintaining the ecosystem health using FDC Shifting method in C management class (48.5 percent of natural stream of the river).

The field of ecohydraulics is rapidly growing as the society requires a better understanding of the interrelations amongst the dynamics of the physical processes pertaining to aquatic ecosystems and the modifications observed in their habitat as well as the biological responses of the organisms. Environmental flow science is a common tool for assessing the consequences of changing the flow regime of aquatic ecosystems and providing a minimum flow of aquatic species protection. Environmental Flows assessment is a global challenge involving a number of tangible and intangible segments of hydrology, hydraulics, biology, ecology, environment, socio-economics, and several other branches of engineering including water resources management. River impoundment (dams, weirs), water diversions and consequent modifications to flow regimes have highly destructive effects on aquatic species and ecosystems.    

In this research, two most common hydrologic methods Tennant and FDC Shifting were compared with a habitat simulation method i.e. PHABSIM. Tennant method is the most popular hydrological method in rivers and is based on the historic flow data. Investigation of the relationship between hydrologic approaches and physical habitat simulation approach and presentation of new recommendations based on the ecological and hydrological data can be very useful for estimating environmental flow in planning phase of river projects. We used river habitat simulation program to model the depth and velocities around boulder clusters to evaluate the habitat for Capoeta habitat in Zarrin-Gol River. The Zarrin-Gol River is one of the rivers in Golestan province in northern Iran. The statistics required for hydrologic calculations were also collected from Zarrin-Gol hydrometry station during the 42-year statistical period (1353-1395). In this regard, after the field studies and the development of the habitat suitability model for the target species, the Habitat simulation of the flow was carried out and eventually the ecological flow regime was extracted. In order to identify the important habitat variables and assess their impact, the life pattern of fish species was divided into juvenile and adult life stages.

Based on ecological assessment, the environmental water requirement of Gharahsoo river is 30% of mean annual flow for spring and summer and 10% of mean annual flow for autumn and winter seasons. It was found that application of Tennant and FDC Shifting methods led to dramatically low discharges as fixed minimum environmental flows, while habitat simulation method gave an acceptable estimation of ecological regime. However, habitat simulation technique assesses the allowable value of extraction from river flow dynamically, considering the ecological condition and average intermediate values. River conditions including flow velocity, water depth and river bed substrate are combined to form unique habitats facilitating the survival and growth of fish species populations.  Habitat forms are observed in a wide range of rivers depending on the diet and the river type such as Pool, Riffle and Run. The destruction of the Riffle substrate causes disruption and impacts the biological integrity of the current. According to the Q-WUA curve of the Riffle habitat in high waters and flood conditions, the area available for juveniles of the target species decreases because of the flood, morphology and habitat of the river, so large and continuous floods inhibit the opportunity to rebuild habitats from the river and endanger the lives of fish. One of the factors limiting the desirability of the habitat and thus reducing the available habitat in low river flows is the low flow velocity, as well as high stream flow flows. The maximum and minimum flow regime, required to maintain the Zarrin-Gol river ecosystem according to ecological needs, was 2.49 and 0.58 m3/s in April and November, respectively, with an average value of 1.25 m3/s (59 % of natural stream of the river). In the next step, habitat suitability distribution along the stream was investigated. This was performed for the full range of discharges. Habitat suitability distribution along the stream at different discharges indicated that the upstream part of the stream had the poorest habitat condition and moving towards the downstream parts, the habitat suitability condition was improved.

Application of the Tennant method based on a hydrological system can be an inappropriate choice for determining the minimum flow to maintain the ecological environment of the river. According to the results, the PHABSIM model can simulate flow, habitat suitability of target species and the habitats dynamics accurately, which is highly required to protect the proper habitat of fish in river ecosystems.

A good understanding of the river natural flow regime plays an important role in many hydrological studies. In integrated water resources management, it is necessary to determine the environmental flow in river systems that affect the health of river habitats, water-dependent systems and aquatic life. In the present study were calculated and evaluated hydrological methods (Tennant, Q50 and Q90, Esmakhtin, flow duration curve shifting (FDC Shifting), Texas and Water Quality) and hydraulic (Wetted Primer) estimating the environmental flow of the Qarasoo River in different months of the year. Based on the results of this study, for the protection of the Qarasoo River in the minimum acceptable environmental conditions, FDC Shifting method in management class C with a flow of 0.96 m3/s (53 Percent Mean Annual Flow) in this study due to the consideration of biodiversity management classes and the proper adaptation of the pattern changes within the year of environmental flow and the mean annual flow and its flexibility with respect to changes in the monthly flows river under study. On the other hand, the efficacy, flexibility and effectiveness of the Tenntant, Q90 and Smakhtin methods are not sufficient to protect the river habitat under study due to an inappropriate estimate environmental flow. Also, comparison of water allocation for environmental flow with Wetted Primer and Tennant methods in the studied river showed that shortage of flow is observed in summer and winter seasons (river flow is less than environmental flow). Finally, it was concluded that other environmental flow methods provide values above 20% of the mean annual flow, which provide better flow protection for the river habitat. It is noteworthy that the Wetted Primer and Tennant methods, with assigning a more portion of the river flow regime to the environmental segment, should be used with caution in summer. The optimal environmental flow regime will be effective when released and provided in the river at the appropriate time to continue bio-activities, river habitat performance and the preservation of the river bed morphological conditions.

This study aims at evaluating and modifying the Texas method for allocating environmental flow. This hydrologic method, while using the minimum amount of data, is a rival for the Tenant method and has the capability of introducing an amount of discharge to maintain the ecological regime of rivers. In this paper, after distinguishing the worthiness of the Texas method and observing some differences between the results of the method and the historical regime in the case study, the method was modified in such a way that while preserving the basic principal of the original method, could propose a flow regime which was laid between the observed long-term minimum and mean monthly discharges. The new method is called the Modified Texas method. For evaluating the Texas and Modified Texas methods concerning the allocated annual volume, the equivalent scenario from the Tennant method was employed. The allocated volumes by the Modified Texas, Texas, and Tenant methods were 50%, 47%, and 40-60%, respectively. This paper, concerning the achieved results for the case study, shows that employing the Texas and Modified Texas methods instead of the Tenant method and enhancing the method to the level of a native method provides reasonable results comparable with those of the habitat simulation or holistic methods.

Iran is faced with limited freshwater resources and, on the other hand, is facing increasing demand for water for various uses. One of the most important challenges in planning water resources is the determination of the environmental flow in the rivers. The environmental flow describes the time, quality, and amount of flow needed to maintain the aquatic ecosystem. Protected rivers are widely protected with a high conservation value, aimed at preserving and restoring plant habitats. Protected areas are suitable environments for conducting educational and environmental studies. Protected River Kashafrood is part of the Qara-e-Ghom basin of Iran located in the northeast of the country and in the north of Khorasan Razavi province. The basin has 15650 km of area. To maintain ecosystems in this area, it is essential to determine the minimum environmental flow. Today, various methods for estimating the environmental flow of the river are presented in the world, which hydrological approaches are the most widely used ones. In this paper, the environmental flow of the Kashafrood Protected River is estimated on the basis of the 39-year statistical period in the Olang Asadi station using hydrostatic methods of Tessman and Transmission curve continuity flow (Smakhtin). The required flows were obtained and then, using SWOT analysis, according to the internal and external characteristics of each method, the most suitable approach for determining the environmental flow of Kashafrood River was presented. The minimum environmental flow in the Tessman method was 1. 57 and in Smakhtin method, the continuity curve was 1.85. Using the SWOT analysis, internal and external evaluation matrices of the internal and external assessment matrix were used to convey the continuity curve of 3.64 and 3.53, which was selected as the appropriate method in comparison to the method.

Assessment of river flow variation and trends is important in surface water resources management and utilization. In this study, the changes of Zahre river flow regime was assessed in Polfloor, Kheirabad, and Dehmola gauge stations using Mann-Kendall, Sen-estimator in monthly time scale, quarterly and annually during the years 1996 to 2015. The Tennant method was used to determine the environmental flow requirement, and subtracted from the recorded river flow data of the Dehmola station (adjacent to Handijan city), the volume of water taken from the river for drinking water supply of the Handijan city were determined at monthly scale. Results indicate that the flow amount in April and May had the highest volume at all stations during the year. Also, the Polfloor and Kheirabad stations had the greatest volume of discharge in spring season. While, the high river flow discharge of Dehmola station was observed in winter season. According the Mann-Kendall and Sen`s estimator the decreasing trend were observed in almost all seasons, and the steepest decreasing trend slope occurred in the spring. The results of Mann-Kendall and Sen`s estimator tests also suggest a decreasing trend in the annual flow discharge at all studied stations. Finally it was realized that the November, December, January, February and March are the wet months and suitable for water withdrawal/harvesting to supply drinking water from the river. In contrast, the summer months of June, July, August and September are low flow months and there is no water to exploit, and the base flow of the river should be maintained to support and protect the river environment and its dependent ecosystems.

Rivers have a significant impact on human life as its pollution and harming leads to the degradation of the aquatic ecosystem and eventually will cause irreparable and irreversible damage. In order to protect the stability of ecosystems in the rivers, a criterion named “environmental stream” or “environmental water requirement” is defined for the rivers which actually expresses how much current is required to maintain an aquatic ecosystem. Several methods are available for estimating this flow, however, the International Institute of Water Management Resources has classified these methods into five groups. These consist of Hydrological Methods, Hydraulic Methods, Habitat Simulation Methods, Comprehensive Methods and Combinational Methods. The purpose of this study is introduction and comparison of these methods and choosing the best methods for different regions of Iran and application of the most appropriate ones in each area.

Introduction Development of water resources projects are accompanied by several environmental impacts, among them, the changes in the natural flow regime and the reduction of downstream water flows. With respect to the water shortages and non-uniform distribution of rainfall, sustainable management of water resources would be inevitable. In order to prevent negative effects on long-term river ecosystems, it is necessary to preserve the ecological requirements of the river systems. The assessment of environmental flow requirements in a river ecosystem is a challenging practice all over the world, and in particular, in developing countries such as Iran. Environmental requirements of rivers are often defined as a suite of flow discharges of certain magnitude, timing, frequency and duration. These flows ensure a flow regime capable of sustaining a complex set of aquatic habitats and ecosystem processes and are referred to as "environmental flows". There are several methods for determining environmental flows. The majority of these methods can be grouped into four reasonably distinct categories, namely as: hydrological, hydraulic rating, habitat simulation (or rating), and holistic methodologies. However, the current knowledge of river ecology and existing data on the needs of aquatic habitats for water quantity and quality is very limited. It is considered that there is no unique and universal method to adapt to different rivers and/or different reaches in a river. The main aim of the present study was to provide with a framework to determine environmental flow requirements of a typical perennial river using eco-hydrological methods. The Barandozchi River was selected as an important water body in the Urmia Lake Basin, Iran. The preservation of the river lives, the restoration of the internationally recognized Urmia Lake, and the elimination of negative impact from the construction of the Barandoz dam on this river were the main concerns in this study.
With lack of ecological data, the environmental requirements of the Barandozchi River were investigated using five eco-hydrological methods (1- Tennant, 2- Tessman, 3- Flow Duration Indices, 4- FDC shifting, 5- DRM). Some of these methods are too simplistic and do not take into account the direct hydro-ecological interactions (e.g. Tennant method), and some have been developed for a specific country/region (e.g., DRM), and need to be adapted to a different physiographic environment before they can be reliably applied. Two ecological friendly models GEFC, and DRM were tested to estimate the environmental flow of this river. The results were compared with corresponding flows allocated for the release from the Barandoz Dam (currently under construction).
The prediction of the mean annual environmental flows from five eco-hydrological methods are presented and compared with the corresponding value reported in the downstream dam’s documents. The ultimate decision making based on the potential flows in the river, the environmental class of the river management, and engineering judgment is also recommended for the flows in the river towards the Urmia Lake. The results indicated that the flow allocation for the river environment (4% of mean annual flows) is not sufficient to meet the minimum flow requirements for any of the targeting species in the river ecosystem. In order to maintain the Barandozchi River at minimum acceptable environmental status (i.e. Class C of environmental management), an average annual flow of 1.9 m3/s (26% MAR) are to be provided. The distribution of monthly flow rates in the river is also recommended for sustaining the Barandozchi River life.
The provision for the minimum ecological flows was investigated in the Barandozchi River ecosystem. The results indicated that, in order to maintain the Barandozchi River at minimum acceptable environmental status (i.e. Class C), an average annual flow of 1.9 m3/s (26% MAR) are to be provided along the river towards the internationally recognized Urmia Lake, in Iran. Considering the construction of the Barandoz dam on this river, the pre-determined environmental flow releases from the dam are to be revised in order to increase the order of flows from 4% to 26% or more. Further investigation is necessary to take into account for the targeting riverine species and for the saving of the Urmia lake ecosystem. It is noted that minimum flow requirements are to be allocated in critical months of the year or during drought period of the river basin. Water leasing from agricultural users is an option or a necessary action whenever long-term environmental damages to the river ecosystem must be avoided.

Minimum environmental flow in rivers provides a certain level of protection for the aquatic environment. In Iran using hydraulic method of wetted perimeter could be a step forward in this field. How to identify the critical point in P-Q curve is still faced with uncertainty in this method. Slope, Curvature and Ideal Point Methods presented by different researchers in this filed. In this article beside description of wetted perimeter method, the environmental flow of Beshar River calculated by using hydraulic parameters. The average of results of Slope, Curvature and Ideal Point Methods is 23%, 8.4% and 20.6% of average annual flow of river, respectively. The results of Slope and Ideal Point Methods are in the acceptable rang of the Tennant method. But the Ideal Point method is superior choice due to the direct use of the chart and more rapidly in calculation.