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

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.

Monitoring and evaluation of hydrological drought has become a necessity due to its frequent occurrence in various basins of Iran, and in order to prevent and manage the resulting crisis. In most studies, drought indices have been used to investigate it. Drought indices like Streamflow Drought Index, using statistical calculations on river flow data, ultimately leads to a number that does not have the ability to completely investigate and analyze drought in the studied area. Low flow or minimum river flow is one of the most important drought indices that using different criteria can get a comprehensive understanding of the hydrological drought situation in the region. In most studies, deficit characteristics or low flow frequency analysis have been used. Using different low flow indices is necessary to recognize different aspects of drought and its management. Therefore, the aim of this research was to study hydrological drought of Armand river using all of the low flow indices including flow duration curve, deficit characteristics, low flow frequency analysis and base flow index, which can be used to determine characteristics such as dry and wet periods, amount of flow during drought, drought threshold, duration of drought, volume and intensity deficit and frequency of low flows. Also, in this study, the environmental flow of river was calculated and analyzed.

The Armand River basin with 9961 Km2 area located in Chaharmahal and Bakhtiari province was selected as the study area and the daily flow statistics of the Armand hydrometric station were used from 1957 to 2013. First, by plotting the flow duration curve, three low flow indices Q70, Q90 and Q95 also, the river status including wet, normal and drought periods was determined. Then, the minimum environmental flow was calculated based on the two indices Q75 and Q90, and the deficit characteristics using the threshold level Q70. In order to estimate the return period of low flow series (AM7), a suitable two-parameter gamma distribution function was considered appropriate. Finally, the base flow index was calculated using recursive digital filter method in different time scales.

Based on the results, the Armand River in 28, 22 and 14 years (from 57 years of statistical period) has a flow of less than Q70, Q90 and Q95, respectively (45, 32 and 27 m3/s). Due to the gentle slope of the flow duration curve of basin, also the high value of the BFI index (0.95), it was concluded that groundwater had a high participation in the river flow. The dry period in this river begins when the flow reaches less than 45 m3/s (the threshold level Q70). The results showed that the deficit volume and intensity increased over the past 50 years. Based on the frequency analysis of low flow, in the return periods of 2, 5, 10, 20, 50 and 100 years, the low flow was 34.26, 26.8, 23.1, 21.1, 19.1 and 17 m3/s. Comparison of these values with the minimum environmental flow showed that the river flow becomes less than its minimum environmental flow on average every two years.

Despite the sustained flow in the Armand River (due to the snow-rainy regime of the region, the ability of the basin to save water and drain it during the dry season), the dry periods with different intensities occurred over the past 57 years. Also, the severity of drought has increased due to the increase in the volume deficit of the river in recent years, and if this continues in the future, the severity and frequency of the drought occurrence will increase and the overall flow of the river will decrease.

Due to the effects of climate change on water resources and hydrology, Changes in low flow as an important part of the water cycle, is of interest to researchers, water managers and users in various fields. Changes in characteristics of low flows affected by climate change may have important effects on various aspects of socioeconomic , environmental, water resources and governmental planning. There are several indices to assess the low flows. The used low flow indices in this research for assessing climate change impacts, is include the extracted indices from flow duration curve (Q70, Q90 and Q95), due to the importance of these indices in understanding and assessing the status of river flow in dry seasons that was investigated in Tang Panj Sezar basin in the west of Iran.
In this paper, the Tang Panj Sezar basin with an area of 9410 km2 was divided into 6 smaller sub catchments and the changes of low flow indices were studied in each of the sub catchments. In order to consider the effects of climate change on low flow, scenarios of temperature and precipitation using 10 atmospheric general circulation models (to investigate the uncertainty of GCMs) for both the baseline (1971-2000) and future (2011-2040) under A2 emission scenario was prepared. These scenarios, due to large spatial scale need to downscaling. Therefore, LARS-WG stochastic weather generator model was used. In order to consider the effects of climate change on low flows in the future, a hydrologic model is required to simulate daily flow for 2011-2040. The IHACRES rainfall-runoff model was used for this purpose . After simulation of daily flow using IHACRES, with two time series of daily flow for the observation and future period in each of the sub catchment, the low flow indices were compared.
Results According to results, across the whole year, the monthly temperature in the future period has increased while rainfall scenarios show different variations for different months, also within a month for different GCMs. Based on the results of low flow indices, in most cases, the three indices of Q70, Q90, and Q95 will show incremental changes in the future compared to the past. Also, the domain simulation by 10 GCMs for all three indices is maximum in Tang Panj Sezar and less for other sub catchments, which is related to better performance of IHACRES model in smaller sub catchments. In order to investigate the uncertainty of type changes in different indices in every sub catchment, changes in any of the indices were considered based on the median of GCMs. To achieve the correct type of changes in low flow indices, the amount of error in a simulation of the indices of IHACRES rainfall-runoff model should also be taken into consideration. Therefore, considering the error, the three indices Q70, Q90 and Q95 in all sub catchments (except for Tang Panj Sezar) will have the relative increase in the future period. The improvement of low flow state in the future period is related to the changes occurred in the state of climate scenarios. As the results indicated, most often, there is an increase in rainfall in dry seasons. Also, in different months of the wet season wet season, if the result of changes in quantity of rainfall is incremental, it can lead to an increase in river flow through groundwater recharge. On the other hand due to the limestone and karst forms in most of the basin area, water storage ability and increase the amount of river flow during low water season in this area is expected. The study on rainfall quantity in Tang Panj Sezar sub catchment also indicated that, there will be no significant increase or decrease in the quantity of rainfall in the dry season. Thus, it is expected that there will not be significant changes in low flow indices. In this sub catchment, changes in various low flow indices do not match perfectly, so more difficult to obtain reliable results. With regard to incremental changes of Q95, low flow index with less uncertainty, as well as improving indices of low flow in other sub-basins, it is possible to predict a relatively better state for low flow indices of Tang Panj Sezar in the future period.
Using temperature and rainfall scenarios to simulate river flow in the future, a relative increase of all three low flow indices Q70, Q90 and Q95 was predicted compared with the past period. Although all three of mentioned indices show the amount of low flow in the dry season, it is recommended that only two indices of Q90 and Q95 to assess the effects of climate change be considered. Q90 and Q95 indices are more suitable indices than Q70 for studying the effects of climate change on low flow state. These two indices indicate less quantity of flow in dry seasons; therefore, the changes of the two indices are more important in identifying the low flow state. However, there is less uncertainty in the estimation of the two Q90 and Q95 indices than Q70.