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Showing 5 results for Erosion and Sediment
Evaluation of the WetSpa Model Performance in Simulating Soil Erosion and Suspended Sediment Transport in Taleghan Watershed
Sh. Moradipour, H. Zeinivand, A. Bahremand, A. Najafinejad,
Volume 18, Issue 69 (12-2014)
Abstract

Evaluation of hydrologic behaviour and soil erosion as an environmental crisis is important in order to maintain watershed ecological safety at optimum level. The aim of this study is to evaluate the performance of the distributed hydrological WetSpa model in simulating erosion and sediment transport and also sedigraph in Taleghan watershed, Iran. Base digital maps and daily meteorological time series data for 9 years are the major model inputs. The calibration of global parameters was done for the first 5 years and the model validation was carried out for 4 years considering three month warm-up period at the beginning of both calibration and validation periods. The Nash-Sutcliffe criterion for the calibration and validation periods pointed out the efficiency of model simulation (82.7% and 79%, respectively). The next phase, the erosion module was calibrated for erosion and sediment transport simulation. The results showed the Nash-Sutcliffe efficiency criterion (60% and 64% for suspended sediment concentration and transport, respectively). Overall, the evaluation results reveal the good ability of WetSpa model in simulation of the hydrological processes e.g., runoff, raindrop detachment, runoff detachment, net soil loss, etc., in a given time and space


Morphologic Study of Meandering Rivers Under Controlled Flow Using RS and GIS Techniques (Case study: Zayandehrud River at the downstream of Zayandehrud dam)
M. Javahery-Tehrani, S. F. Mousavi, Kh. Hosseini,
Volume 20, Issue 77 (11-2016)
Abstract

Morphologic study of rivers is very important in stabilization and determination of river boundaries. Dams are structures which have the highest effects on river morphology. Studies of river changes are usually time-consuming and possible only in the long-term timescales. To detect these changes, using satellite images over specific time periods and cartographic methods are useful. In the present study, morphological changes of Zayandehrud River, at downstream of Zayandehrud dam, between hydrometric stations of Sad-e-Tanzimi and Pol-e-Zamankhan, were investigated through 7 series of Landsat satellite photos from 1980 to 2015 by applying ENVI 4.8 and Arc GIS10.2 software. Based on the results, the method of enhancing the contrast as saturated linear expansion, along with the edge enhancement filter, was found an appropriate method for determining the boundary between land and water. In the next step, the river path was entered into Arc GIS 10.2, and geometric parameters of the river such as wavelength, sinuosity ratio, central angle and radius of circle tangent to the curve were determined. Also, statistical analysis of geometric parameters was performed by applying SPSS software. Results showed that from 1986 up to now the sinuosity ratio has risen from 2.14 to 2.38, while the radius of river curvatures and wavelength of meanders have decreased by 5% and 11.4%, respectively. Overall, the river has decreased its arcs’ curvature and bends have been moved to downstream. The main cause of this phenomenon is constructions in the river borders (e.g. in Markadeh and Cham-Kaka), which have disturbed the natural situation of the river. In Cham-Jangal, Cham-Khalifeh and Cham-Ali regions, due to the increase in slope and improper vegetation cover, bank erosion has reached to its highest degree. In general, although flood events have been contained by Zayandehrud dam, yet the river has great potential for erosion in the meandering sections.


Prioritizing the Effective Factors on Surface Erosion Using USLE-M Integrated Model and System Dynamic (A Case Study: Sanganeh Research Center, Khorasan Razavi)
S. Esmailian, A. Talebi, M. Esmailian,
Volume 22, Issue 1 (6-2018)
Abstract
This research was aimed to simulate and prioritize the effective factors on water erosion using USLE-M in the system dynamic model. In this integrated model, by using the system dynamic simulation software (Vensim), all variables and factors involved in erosion and soil loss were considered according to the USLE-M model. After model implementation, the estimated values and observations were compared and then sensitivity analysis was done to determine the sensitive parameters. Then, calibration was performed on the sensitive parameters. This study found that that the results of the model were acceptable for soil erosion simulation due to considering all the effective factors in soil erosion. The results of the sensitivity analysis also indicated high model sensitivity to the slope and vegetation cover in high and low slopes, respectively. By investigating the changes in various parameters such as vegetation cover and slope on erosion, the optimal vegetation cover with 67 and 40% slope, was estimated to be 20 and 60%, respectively.

The Effect of Slot’s Distance of Triangular Spur Dike’s Nose on the Pattern of Erosion and Sediment
M. Dorosti, M. Shafai Bajestan, F. Amirsalari Maymani,
Volume 22, Issue 2 (9-2018)
Abstract
Scour around structures in the river is the most destructivr factor of these structures. Therefore, different methods have been studied to reduce it. A creation slot is one of these methods in the suitable position that can be modified to control the flow pattern scour. In this study, the effects of using two parallel chord rectangular slots  in the single spur dike  with the opening of the effective spur dike area of 10% and a ratio of a/b = 4 (a and b are the length and width of the slot) on two occasions were investigated, one near the bed (near the slot spur dike) and the other near the water surface (away from the nose of spur dike) on the pattern of erosion and sediment around the nose triangular spur dike in clear water conditions. In all experiments, flow depth and angle of the triangular spur dike installation angle were constant. The experiment was done in different hydraulic conditions (Froude number 0.287, 0.304, 0.322). Eventually the results of spur dike without slot (control experiments) were compared. The results showed the slot near the bed toward the slot near water surface and control experiments had a better performance in reducing the maximum depth of scour and deposition of sediments washed to the outer bank. The reduction of the maximum depth of scour at the slot near the bed in Froude numbers 0.287, 0.302 and 0.322, respectively, was  compared to the control experiments , which were 23%, 13% and 24%, respectively, and then compared to the slot near the water surface, which was 60%, 40% and 32% respectively.

Evaluation of Efficiency of Sediment Transfer Functions in GSTARS Numerical Model
F.z. Asadi, R. Fazloula, A. Emadi,
Volume 25, Issue 3 (12-2021)
Abstract
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.

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