جستجوی مقالات مرتبط با کلیدواژه "تغییرات بستر" در نشریات گروه "آب و خاک"

Geometric and morphological characteristics of each river are its main characteristics by which the management planning of the basin and the conservation of natural resources around it is done. Estuaries are formed at the mouth of rivers in a border area between sea and land. Deformation of estuaries due to sedimentation and erosion changes the pattern of river flow. In this research, the hydrodynamic model (HD) is used to calculate the flow rates and velocity and the sediment transport model (ST) is used to calculate the suspended load and bed level. The results of the hydrodynamic model showed that the maximum speed at 17 km of Shalmaneh station (beginning of the third interval) is approximately 4.7 m /s. This value decreases to about 1.5 meters per second as we approach the end of the estuary. Due to the importance of the role of floods in bed changes, the model was implemented using the 25-year flood discharge of Shalmanrood River (355 cubic meters per second) for a period of one year. After that, the river route was divided into three parts and the behavior of Shalmanrud river was studied according to the deformation created in the sections of each part. The maximum amount of sediment in the first part is 0.41 m in non-flood condition and 1.1 m in flood condition. In the second part, sedimentation increases and in non-flood state reaches 0.8 meters and in flood state reaches 2 meters. In the third part, the amount of sediment will be more than the first and second parts. The maximum amount of sediment in this part is 0.53 m in non-flood condition and 1.4 m in flood condition.

Investigating and understanding river change issues is one of the important factors in sediment hydraulic sciences and river engineering. These studies can be done with the help of physical, mathematical models, or both, but due to financial and time constraints, mathematical models are more general and often used. In this study, the GSTARS model was used to investigate erosion and sedimentation and select the most appropriate function in 12.5 km in length from the Talar river in Mazandaran Province. Simulation using the 55 sections taken in 2006, the daily flow data of the hydrometric station of the Shirgah, located at the beginning of the rich and characteristics of the river sediment, was done. The calibration and validation of the model with cross sections taken in 2012 showed that Yang's sediment transport equation has the highest correlation with reality and can be used to predict river change. The amount of sediment depleted from the case study using the Yang equation is estimated at 8590 tons per year. Also, the study of longitudinal profiles of the river with different sediment transfer functions showed that the study reach at the end range has an erosion trend and is not capable of sand and gravel mining.

Spur dikes as one of the main structures in river restoration practices are used for protecting and shaping the river banks and main channels. These structures growing from the river natural banks, having suitable length and angle relative to the flow direction and cause deviation of the flow from the riversides and driving it to the central axis of the river. In this study, the numerical hydrodynamic and sediment transport model “CCHE2D” was used to simulate the flow pattern and streambed changes around the spur dikes. Two separate series of experimental data were used to assess the numerical model outputs. The accuracy of the model outputs were evaluated through common statistical parameters including RMSE, MARE, REmax and R2. Comparison of the experimental results with the simulated values revealed that the CCHE2D was reasonably capable to simulate the flow pattern around the both of single and series of spur dikes with high accuracy (correlation coefficient=0.755-0.955). The bed changes around the series of spur dikes were simulated with acceptable accuracy, revealed that the CCHE2D model could precisely predict the maximum scouring depth with correlation coefficient of 0.990, but overestimated the width of scour hole around the spur dike in comparison with experimental observations. Furthermore, both the numerical results and experimental observations showed that the erosion depth of main channel had a direct relation with the length of spur dike.