Farhang Azarang; Abdolrasoul Telvari; Hossein Sedghi; Mahmoud Shafai Bajestan
Abstract
Introduction: The critical role of the rivers in supplying water for various needs of life has led to engineering identification of the hydraulic regime and flow condition of the rivers. Hydraulic structures such dams have inevitable effects on their downstream that should be well investigated. The ...
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Introduction: The critical role of the rivers in supplying water for various needs of life has led to engineering identification of the hydraulic regime and flow condition of the rivers. Hydraulic structures such dams have inevitable effects on their downstream that should be well investigated. The reservoir dams are the most important hydraulic structures which are the cause of great changes in river flow conditions.
Materials and Methods: In this research, an accurate assessment was performed to study the flow regime of Karkheh river at downstream of Karkheh Reservoir Dam as the largest dam in Middle East. Karkheh River is the third waterful river of Iran after Karun and Dez and the third longest river after the Karun and Sefidrud. The Karkheh Dam is a large reservoir dam built in Iran on the Karkheh River in 2000. The Karkheh Reservoir Dam is on the Karkheh River in the Northwestern Khouzestan Province, the closest city being Andimeshk to the east. The part of Karkheh River, which was studied in this research is located at downstream of Karkheh Reservoir Dam. This interval is approximately 94 km, which is located between PayePol and Abdolkhan hydrometric stations. In this research, 138 cross sections were used along Karkheh River. Distance of cross sections from each other was 680m in average. The efficient model of HEC-RAS has been utilized to simulate the Karkheh flow conditions before and after the reservoir dam construction using of hydrometric stations data included annually and monthly mean discharges, instantaneous maximum discharges, water surface profiles and etc. Three defined discharges had been chosen to simulate the Karkheh River flow; maximum defined discharge, mean defined discharge and minimum defined discharge. For each of these discharges values, HEC-RAS model was implemented as a steady flow of the Karkheh River at river reach of study. Water surface profiles of flow, hydraulic parameters and other results of flow regime in HEC-RAS model were obtained for the conditions before and after the construction of the Karkheh Reservoir Dam and then it was reviewed and analyzed.
Results and Discussion: By exploiting the Karkheh Reservoir Dam, the river flow was changed from the natural condition to the regulatory situation. The results indicate that the river flow was considerably declined because the regulatory effect of the reservoir dam which has contributed to the great alternations at hydraulic parameters of the river. For example, the mean annual discharge of the Karkheh River shows 44pecent reduction during the time period of simulating (after the dam construction in comparison with the natural river flow before construction of reservoir dam) in PayePol hydrometric station. Flow velocity of Karkheh River is influenced by discharge, slope of the river channel and geometry of cross section. By increasing the river flow, the flow velocity has increased and there is a significant difference between pre and post-dam condition at the mean velocity of river flow in different sections. The flow area is directly influenced by river discharge and there is a significant difference in the maximum defined discharge before and after dam construction. The width of water surface is a parameter of the geometric situation of the river cross section that also shows the maximum width of the cross sections, passing discharge through the desired cross section. Since Karkheh River has a relatively large water surface width, it has a high wetted perimeter. For this reason, the Karkheh river hydraulic radius is usually low. The significant reduction of all these quantities is for reduction of flow rate by construction of Karkheh Reservoir Dam. Studying the water surface profiles represents reduction of water level in the longitudinal profile of Karkheh River and water level of hydrometric stations by construction of the Karkheh Reservoir Dam. Also, due to the reduction of the discharge in the downstream of Karkheh Dam, all hydraulic parameters of the river such as flow velocity, flow area, width of surface water, hydraulic depth, shear stress and the hydraulic radius have been changed. In general, it can be concluded that the construction of a large dam such as Karkheh Reservoir Dam has a significant effects on the flow regime conditions at river downstream. Our survey would be helpful for environmental, geological and ecological experiments on effects of dam construction and for engineering next hydraulic structures on such rivers.
B. Salavati; H.R. Sadeghi; A.R. Telvari
Abstract
Abstract
Flood is among phenomena which result considerable damages to resources and is a serious issue among hydrologists. The proper estimation of runoff is necessary for designating appropriate approaches for its control or optimal management. Various problems have been reported in application of ...
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Abstract
Flood is among phenomena which result considerable damages to resources and is a serious issue among hydrologists. The proper estimation of runoff is necessary for designating appropriate approaches for its control or optimal management. Various problems have been reported in application of empirical models. The regional analysis of runoff with different return periods by applying watershed characteristics is an alternative with numerous applications. In this study, mean discharge data of 7 hydrometric stations in Kurdistan Province watersheds, Iran, were collected for a period of 30 years and discharges with return periods of 2, 5, 10, 20, 25, 50, 100 and 200 years were consequently calculated using SMADA package. The relationship between mean discharges with different return periods and 26 physiographic and climatic factors were evaluated by using bivariate and multivariate regression models using SPSS 13.5 package and their partial influence were also determined. The results of the study showed that the nonlinear models performed better than linear regression. The main variables include the area, main waterway length and Gravellius factor. Data analysis also revealed the possible change of variables and their importances in determination of monthly mean discharges with different return periods.
Keywords: Kurdistan Province, Physiographic characteristics, Return Period of flood, Flood modeling
L. Gholami; H.R. Sadeghi; A. Khaledi Darvishan; A. Telvari
Abstract
Abstract
Application of empirical models is a must owing to complexity of process, different features, spatial and temporal variation of soil erosion and non-existence or lack of pertaining data. In this study, the efficiency of rainfall and runoff variables of 11 storms during winter 2006 and spring ...
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Abstract
Application of empirical models is a must owing to complexity of process, different features, spatial and temporal variation of soil erosion and non-existence or lack of pertaining data. In this study, the efficiency of rainfall and runoff variables of 11 storms during winter 2006 and spring 2007 in explanation of storm-wise sediment yield in Chehelgazi watershed of Gheshlagh Dam basin in Kurdistan province was evaluated with the help of bivariate and multivariate regression models by using different transformed data. The models’ efficacy was then assessed by using coefficient of determination, error of estimation and verification. The results showed that bivariate regression models, using different transformed data with determination coefficient of beyond 66%, and respective error of estimation and verification of below 40 and 30%, had a better efficiency in estimation of storm-wise sediment yield than multivariate regression models. The results also verified that the rainfall variables could explain storm-wise sediment yield variations better than runoff relating factors with overall contribution of some 80%.
Key words: Sediment yield, regression models, Gheshlagh dam, Chehelgazi watershed, Kurdistan province, Iran
