year 12, Issue 1 (Spring 2022)                   E.E.R. 2022, 12(1): 41-57 | Back to browse issues page

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jafari G, Karimi Z. Estimation of soil loss due to water erosion of Jazlachai catchment using three models FSM, Fargas, BLM. E.E.R.. 2022; 12 (1) :41-57
URL: http://magazine.hormozgan.ac.ir/article-1-665-en.html
Zanjan University. Zanjan , jafarihas@yahoo.com
Abstract:   (280 Views)
1- Introduction
The word erosion means the abrasion of the earth's surface, during this process, soil particles are separated from their main bed and transferred to another place with the help of one or more transfer agents. Soil particles can be transported by water, wind or glaciers. Particles transferred and accumulated elsewhere are called sediments. Soil erosion reduces arable land fertility and causes harmful damage. Soil water erosion is a natural phenomenon that has become one of the most important environmental threats in the world today due to unwise human activities, such as the irrational transformation of the earth and the destruction of vegetation
The study basin is one of the Ghezel Ozan River branches in Tarom region, which is more prone to erosion due to the special lithology of this region (marl and tuff lithology) and heavy rainfall.
The purpose of this study is to investigate erosion in Jazla chay catchment, which is one of the Ghezel Ozan basins. Due to the current situation and successive droughts, erosion in this basin can cause irreparable damage to the villages of this basin. Basin erosion is estimated by comparing three models (BLM, Fargas and FSM)
2- Methodology
Jazla Chay catchment area with an area of ​​149.61 square kilometers is under the Ghezel Ozan tributaries in Tarom region. To study the erosion in the study basin, software (Arc GIS 10.5), Google Earth and geological map of 1.100000 and topography of 1.50000 area have been used. First, basic maps including geological maps, topography, waterway, land use have been prepared. Using Arc GIS software, Fargas, BLM and FSM models have been implemented for erosion zoning in Jazla chai catchment area. A field visit was made to the study basin to observe erosion in the environment. Geological maps, land use, topography in digital Gis and land environment were referenced and using tables related to three models FSM, Fargas and BLM, the layers were scored and erosion zoning maps were prepared and then compared.
The Fargas model was introduced by Fargas et al. In 1997. The following steps are required to implement this model: 1- Determining the erodibility index of the basin: At this stage, the amount of erodibility is determined for each stone unit. 2- Placing water maps and rock units and evaluating the amount of drainage density in each rock unit provided by Fargas et al. 3- Determining the risk of erosion using the evaluated coefficient for rock resistance to erosion and drainage density in each rock unit.
The BLM method was developed by the US Office of Land Management. Using this model, the erosion status can be scored according to the sum of the scores of seven factors (soil mass movement, litter cover, surface rock cover, reinforced rock fragments, surface grooves, waterway shape and development of moat erosion) and accordingly the factors of the general erosion status are determined for each type of erosion.
In FSM model, 5 factors of geology, topography, vegetation, moat erosion and basin shape are used to calculate the sedimentation of the basin. The scores of each factor are shown as low, medium and high with the numbers 1, 2 and 3, respectively, which are determined using field navigation, topographic and geological maps. After scoring the five factors, the value of FSM coefficient will be obtained by multiplying the factors in each other and using this coefficient, the erosion rate of the basin will be calculated
3- Results
To evaluate the BLM model, seven factors have been considered, of which 4 factors are related to surface erosion, one factor is related to furrow erosion, one factor is for canal erosion and the seventh factor is related to moat erosion. Mountains and foothills have high erosion and are moderate in the plain. The slope factor changes significantly from one piece to another. The average slope in these different parts is not equal and its amount gradually decreases from the upstream to the downstream parts. Adjusting the balance profile from the bottom up means that most of the reversal operation (regressive or ascending erosion) takes place. In the study basin, the slope increases from downstream to upstream, which indicates the dominance of regressive erosion in the basin. In the BLM model, it can also be seen that erosion has increased in the upstream part (mountain and foothills unit). The amount of slope varies in different parts based on the available lithologies, which according to the lithologies of the basin, the amount of slope increases from the downstream, which is the lithology of the conglomerate, to the upstream lithology, which is sandston tuff, tuff and silt . The profile of the studied basin is drawn from upstream to downstream, which indicates an increase in slope upstream.  Fargas model is based on geology and two factors of erosion (drainage density factor) and erodibility factor (rock susceptibility factor to erosion) which according to Fargas model, erosion in the catchment area Jazla chay is violent. The FSM model uses 5 factors of topography, lithology, ditches, basin shape and vegetation that have different scores and is estimated through topographic and geological maps and field visits and according to the model. Erosion rate in Jazla chay catchment is estimated to be 699.08 tons per square kilometer per year.
4- Discussion & Conclusions
Given the current situation in Iran, which is threatened by drought and severe erosion, the assessment of erosion in its sub-basins can determine the rate of erosion in different sectors. In this study, Jazlachai basin has been selected from Ghezel Ozan sub-basins in Tarom region (Zanjan) to investigate the severity of erosion. To measure the intensity of erosion in the study basin, three models Fargas, BLM and FSM have been used. The results obtained from the Fargas model, based on the geology of the basin, show that the maximum area of ​​the basin is 82% with severe erosion and 13% with erosion. High and 5% has very severe erosion. Results of BLM model (using seven factors, 4 of which are related to surface erosion, one factor related to furrow erosion, one factor for canal erosion and the seventh factor related to moat erosion) in Jazlachai catchment in three units Topography (mountain, foothills and plains) indicates that the intensity of erosion is moderate in the plain unit and high in the mountain and foothill units. Evaluation of basin erodibility using FSM model in 5 factors of vegetation, basin shape, topography, lithology and ditches in the basin indicates that the basin erodibility rate is equal to 699.08 tons per square kilometer in Is the year. Among the factors that are effective in the intensity of erosion and sediment production and flooding of basins, the physiographic and topographic characteristics of the basin, including the condition of waterways, height and slope of the basin. The central part of Jazlachai catchment has a high slope, the slope factor increases the erosion in this part by increasing the speed of water flow. The western and southwestern part of the basin has a gentle to steep slope and the formation of this part is semi-resistant. As can be seen in the map obtained from Fargas and BLM models, this area has high erosion and regressive erosion dominates in the study basin and leads to further erosion of the main riverbed. According to the field visits and the results of the implementation of these models, the BLM model is more compatible with the erosion that prevails in the Jazlachai catchment.
 
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Type of Study: Research |
Received: 2021/08/14 | Published: 2022/03/12

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