year 12, Issue 1 (Spring 2022)                   E.E.R. 2022, 12(1): 18-40 | Back to browse issues page

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khazaie poul A, zarezadeh F, moridi A. Sediment Simulation Using Soil and Water Assessment Tool (SWAT) in a Multi-reservoir Basin. E.E.R.. 2022; 12 (1) :18-40
Civil Engineering Center, Imam Hossein University, Tehran, Iran. ,
Abstract:   (340 Views)
1- Introduction
Knowing the extent of erosion in each area and the amount of sediment load they produce, especially near dams, is very important and this leads to identifying the factors affecting each area and creating solutions to control or reduce sediment load to dam reservoirs. This effort has become a necessity. Therefore, by simulating runoff and sediment in Karun basin by SWAT model and performing the calibration process and reviewing the results of the stations and their sediment load, areas with higher susceptibility to erosion were identified. After identifying the critical erosion areas and in order to reduce erosion and sediment load of the whole basin, a plant filter was used to apply the management and protection strategies of the SWAT model. Evaluation of the results in this section showed that the implementation of plant filtration in some sub-basins can reduce sediment load by up to 28%.
2- Methodology
To build and prepare the SWAT model, inputs such as topographic information, meteorology, soil, vegetation, reservoirs and management data were used. Daily temperature, precipitation information, location of meteorological and rainfall stations with dbf or txt extensions, topographic information in the form of digital elevation model with UTM coordinate system, Grid format and location of hydrometric stations and springs in tables with dbf extension were introduced to the model as well. Maps of waterways and rivers in vector form and land use and soil maps as raster from in Arc GIS 10.4 software are included in the model.
One of the parameters required to simulate the basin by the model is meteorological information. In this study, rainfall statistics of 57 rain gauge stations and 8 hydrometric observation stations with a statistical period of more than 26 years have been used in the catchment area of ​​Karun River. In this research, the characteristics of the basin have been investigated using the digital model of DEM height with a cell size accuracy of 90 × 90 m and using the GIS geographic information system. For this purpose, with the help of Arc GIS10.4 software, the physiographic characteristics of the basin such as the area and average slope of the basin and river were extracted. Based on hydrological characteristics, Karun Basin erosion studies have been divided into 49 sub-basins and 424 hydrological reaction units.
In this study, the region is classified into 5 categories. Accordingly, about 25% of the area has flat land and a slope of less than 5%; 12% have a slope between 5 to 10%; 9% have a slope between 10 to 15% and 8% have a slope between 15 to 20, and most of the area has sections with a slope of more than 20%, which covers more than 45% of the area.

3- Results
Implementing a plant filter that is densely vegetated to reduce runoff flow and trap sediments can be in the form of combinations of meadows, grass, trees and shrubs. In order to innovate in the application of filters, the width of filter strips in all sub-basins is not defined uniformly, but according to the area of each sub-basin, the amount of filter is considered different and the filters are applied equal to 40% of the area of each sub-basin. After applying the plant filter, the results obtained from the sediment of each sub-basin were compared against the amount of sediment in each basin before the application of the plant filter. The results showed that the implementation of the filter can reduce the amount of sediment up to 28% in some sub-basins in some areas. By comparing the figures that show the effect of plant filter application in reducing sediment in each sub-basin and the slope map of the area, it can be seen that the areas that had more slope had a relatively significant performance due to plant filter application. In addition, the application of plant filters has often reduced the sediment load and the average sediment load of the entire basin by an average of 10.4%.
4- Discussion & Conclusions
The purpose of this study was to estimate the amount of runoff and sediment load produced in Karun watershed and to investigate the implementation of plant filtration as one of the most effective management and conservation strategies to reduce the amount of sediment load in the entire basin. According to the topography of the region and the slope characteristics of the region, most of the area has areas with a slope of more than 20%, which covers more than 45% of the region, and land use of the region, which uses more than 46% of forests and vineyards. It has been covered with pastures with an area of ​​about 31% of the total use basin of the region and also the existence of livestock equivalent to the area which is equal to 11.29. Erosion control in this area requires strategies to reduce this sediment load, including the construction of dams. After simulation of runoff and sediment in hydrometric and sediment measurement stations and evaluation of SWAT model by good fitting coefficients (NS, R2) and uncertainty coefficients using SWAT-CUP model, the facilities and areas with higher erodibility were identified. Then, by examining the sediment load trapped behind the dams, the sediment measurement curve was modified and adjustment coefficients were applied to correct the sediment results of the area. Then, by presenting the use of plant filter as a management solution, the sediment load of the area and special erosion were reduced. The results show that the SWAT model has a high ability to simulate all the details of the area. This feature allows the model to be simulated accurately to identify any level of details in the area that the user needs. This model makes good use of the effects of rainfall, snowmelt, irrigation and withdrawal from dams or groundwater, which led to the results of good runoff fitting coefficients of acceptable values. Also, different thresholds of information layer overlaps were estimated to determine the number of hydrological units. Baes on this estimation, 696 HRU achieved better results and the use of 7-station data in determining the parameters selected for calibration increased the possibility of better spatial variation of parameters in the final calibration of results. The results of this study are given in the daily time frame; in fact, the results are estimated in 3 days, and the results are given in the daily basis.
According to the proposed maps for spatial distribution of erosion, the upstream sub-basins have less sediment and the accumulation of sediment near the reservoirs of dams is higher, which made the areas more effective. Also, as other ways, the effects of using slopes or cultivation on level lines can be examined in these areas. In addition to the slope of the region, due to the high density of livestock in Chaharmahal and Bakhtiari province, another factor of high erodibility in this area can be considered as overgrazing.
Also, the results of the MPSIAC methods were closer to the results of the SWAT model than the current method of estimating the exchange rate. However, the reports of the Water and Power Company expressed the results of the EPM model closer to the results of the flood conditions.
In this area, the SWAT model was not accurate enough in estimating sediment load due to the neglect of sediment volume in flood conditions in the sediment measurement curve. In order to solve this problem, in this study, the correction of sediment measurement curve by fitting two equations for flood and non-flood conditions was used.
In the field of management solutions, among the solutions, the implementation of plant filters has had the greatest impact on reducing sediment load and in some sub-basins alone has been able to reduce the sediment load up to 28% of the sub-basin. Of course, in this study, a fixed value for the width of the filter strips is not considered, but for better filter performance, we considered the width of the filter strip in proportion to the area of ​​each hydrological unit, which is defined as a percentage of its area. Also, with the implementation of the plant filter, the amount of change in each HRU was investigated. The results in the percentage change scale of sediment rate showed well that the application of the filter in most hydrological units had very positive effects and had reduced sediment load with an average of 10.4%.
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Received: 2021/05/29 | Published: 2022/03/12

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