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Dam removal is one of the methods of restoring the river ecosystem. The decision to remove a dam is based on the multidisciplinary indicators and the type of dam body and its location, as well as the downstream conditions and the type of dam removal method. In the present study, the removal of the Voshmgir Dam on the Gorganrud River, Iran, was considered, because of the high volume of sediment deposition in the reservoir and the loss of its useful life. Three scenarios were selected for the removal of the dam: 1- complete removal; 2- stepped removal of the spillway; and 3- removal with stable sediments. In the first step, numerical modeling for river morphological changes was performed using the HEC-RAS model for unsteady flows with sediment transport. The erosion and sedimentation processes were simulated in six reaches (from the Voshmgir Dam to the Caspian Sea), with total length of 128 km. The results indicated that the second scenario (stepped removal of the spillway) is the best alternative due to the gradual processes of river-bed changes. In the present research, the two-dimensional hydrodynamic and water quality model CE-QUAL-W2 is used for qualitative modeling of Gorganrud River in three scenarios of dam removal, within 128 km downstream of Vashmgir dam to the Caspian Sea Estuary. Qualitative modeling was performed for the existing conditions of Gorganrud (without removing the Vashmgir dam) at two hydrometric stations of Aqqala (68 km downstream of the Vashmgir dam) and and Basirabad (112 km downstream of Vashmgir Dam), where a set of water level and water-quality data was available for model calibration. Model results are presented in the period of rapid river changes after dam removal up to 60 days. Based on the results of qualitative modeling, the amount of dissolved oxygen (DO) has increased in three scenarios of dam removal in two sections of the river (Aqqala and Basirabad). The amount of biochemical oxygen demand (BOD) in the first scenario (complete removal) and the second (stepping removal) has increased slightly (less than 10% of the river conditions before removal). In the third scenario (removal with stable deposition), no significant change in BOD occurred. In three scenarios and in both study periods, the pH changed very little in the two periods, before and after the removal of the dam. The total amount of soluble solids (TDS) in the early days of the simulation is equal to or greater than that before removal. The TDS rate is to be decreased by time. The overall results indicated that the second scenario of the dam removal (i.e. stepped removal of the spillway) is the best alternative due to the less impacts on the river-bed changes, and the gradual processes of river-ecosystem rehabilitation.

Having knowledge on the quantitative amount of watershed sediment yield is one of the most basic information to deal with soil erosion and conservation as well as design of dams. In Iran, the estimation of suspended sediment load is often based on measurement curve methods. Since sediment discharge data are random and discontinuous, in practice, their internalization and extrapolation is associated with many errors. This review is to evaluate the number of data available to estimate daily sediment load with Loadest regression models. Therefore, daily discharge data of Ghazaghli station in Gorganrood forest watershed were used. So that different percentages of available data were accidentally deleted and the amount of sediment load was estimated by 11 methods. According to the evaluation results (Taylor diagram), model number 2 has the best accuracy and in the absence of up to 50% of the daily sediment data, the correlation coefficient of more than 0/5 in the annual sediment estimation and only for the first year And in the rest of the years under study the correlation coefficient is unacceptable. Therefore, the use of sediment measurement curve methods with the data available at the level of Iranian stations, if the number of data available to construct the measurement curve is less than 185 will be associated with very little accuracy. Also, the higher the amount of available data belonging to the periods of low sediment transport (autumn and dry years), the lower the efficiency of the Loadest method will be.

Nowadays, the environmental structure has been changing and natural disasters, including sudden floods increasing. Due to the crossing of Gorganrood River in the city of Aq’qala, it has always been in the risk of flood in the spring and summer. In this study for time series flood zones and flood’s map area calculating which occurred in 23rd March 2019, we used Sentinel-2 and Landsat-8 data because of high spatial resolution and free accessibility. For removing noise and clouds applied the atmospheric and radiometric correction on images and then used MNDWI and NDWI indexes for identifying of water and high moisture soil. The results shown the MNDWI index was better than the NDWI index for identify the moody water and high moisture zones. Flood zones maps produced by MNDWI index are shown more flooding area than NDWI index map. The area of flood maps for Aq’qala county and Aq’qala city were 262.453 and 51.091 Km2, respectively. The maximum flow rate discharge with 50 years returns period was 739 m3/s that the northern and eastern of Aq’qala city were flooded. When the flood is muddy, using MNDWI index is 50 percent better than NDWI index.

Water resource development plans (such as dams) has the numerous environmental effects, which altering the natural regime of river and river flow reduction is the most important. One of the most important environmental challenges in water resources planning is river water rights estimation affected by natural variables, understanding the importance of protecting water resources, variety biological and ecosystems related to river flow. Environmental flows is meaning time, quality and amount of required current to protect freshwater, estuarine ecosystems, human welfare and livelihoods related to water. The main aim of this study is estimation of environmental water right Gorganrood river (Aq Qala station) based on 33-year period, using hydrological methods Tennant, Tessman, aquatic base flow, flow duration curve and duration curve change in different months of years. The results show that at least the Gorganrood river flow (Aq Qala station) to provide environmental flows using the above methods, respectively should equal to 27/2, 8/1, 51/5, 47/4 and 33/3 (class C) cubic meters per second. This study has shown that in the absence of information on the ecological, hydrological indices can be used for preliminary estimation of environmental flows.

Water management and best use are among the topical issues today and for this human should reverse and mitigate the negative trends they have caused to water quality. We have tested various water quality improvement scenarios in this research. We selected nine water quality factors and generated an initial set of 41 independent variables relating to landform، physical and biological plus landscape metrics of the surrounding environment of the rivers. Regression and correlation analyses helped narrow down the independent variables and define equations between dependent and independent variables. Five management items were devised based on the regression relationships and expert opinions including: decreasing fractal dimension of remnant tree patches، pasture extension onto bare land، decreasing area under agriculture based on a special multi-criteria analysis (MCE)، decreasing road density based on a pattern suggested through least cost algorithm and increasing area under pasture management and the number of tree patches. To balance the results of the scenarios and select the optimum one، LP approach was adopted during which the analytical hierarchy process was applied and the 32 scenarios were analyzed through technique LP. The best scenario was found to be the one including incress NP onto bare land and decrease of fractal dimension of the remnant tree patches. These were the best in terms of the selected criteria for water quality improvement.

Loess Deposit is one of the most important Quaternary Deposits of northeastern parts of Iran which have high erosion rate. This study was performed with field- Rainfall- Simulator which has a plot area of 1 m2 in Gorganrood Drainage Basin to determine the effective factors on sediment yield. Landuse، slope and erosion feature maps were overlaid in GIS to obtain land unit map. Then on work units، rainfall simulator analyses were performed. The produced runoff and sediment in 69 points on work units were collected and were measured. Adjacent to each rainfall simulator plot، samples of surface material were collected in the field to analyze for physical and chemical characteristics. In the field، descriptive tables were prepared for different work units in which locality، slope percentage، elevation، depth of A horizon of the soil and other necessary informations were recorded. In order to determine logical relationship between different variables، regression and correlation analyses were performed. In statistical analyses، it was found that slope percentage has the highest correlation coefficient and has the highest direct relationship with sediment yield and sediment production and silt amount is the second factor. The investigation of multiple regression analyses generated a model which shows %80 of sediment production variations. In this model slope percentage، cation exchange capacity and silt have possitive relationship and Calcium cation has negetive relationship with sediment yield.

The amount of sediment load significantly changes along a river due to environmental effects. This variability should be considered to estimate the amount of sediment load. In this research، spatial and seasonal variation of sediment load along of Gorganroud river were evaluated based on the information of 7 hydrometry stations sited in main branch of the river namely، Tamar، Hajighoshn، Gonbad، Voshmgir، Aghghala and Basirabad. Since the amount of sediment load is directly correlated with water discharge، for assuming the effect of water discharge، linear form of sediment rating curve is used where the linear form is produced by the logarithm transformation. Based on this linear relationship with possibly different slopes، the generalized analysis of covariance with logarithm of discharge as its covariate was used to compare the logarithm of sediment load as its response. In order to precisely estimate the amount of sediment load and adequately modify the sediment rating curve، the spatial comparison was drawn separately at low، middle and high rate of water discharge. Spatial evaluation demonstrated an increase in sediment load from Tamer station to Basirabad but there are some distinctive areas between mentioned stations with noticeably decreasing (80% in average) in their sediment load mainly due to reservoir building. For seasonal evaluation of sediment load، the percentage of sediment yield at different seasons was compared. This evaluation revealed that spring with at least 50% and at most 70% of total suspended sediment discharge has the highest amount of suspended sediment yield in this river.