Freidoon Soleimani; Majid Soufi; Aziz Arsham
Abstract
Introduction: Khuzestan province with 4.6 million hectares area has suitable agricultural lands that gully erosion destroyed some parts of them. One of the major basins in which much of its agricultural land threatened by gully erosion is located in Modarres watershed of Shushtar. Gully erosion progression ...
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Introduction: Khuzestan province with 4.6 million hectares area has suitable agricultural lands that gully erosion destroyed some parts of them. One of the major basins in which much of its agricultural land threatened by gully erosion is located in Modarres watershed of Shushtar. Gully erosion progression in this basin causing the loss of farmland and thus the farmers are leaving farming and consequently would lead to poverty and migration to urban areas and social consequences. Therefore, presenting a model to determine the factors that impact on gully erosion and erosion hazard zonation for conserving and stability of the land need to research and investigate on gullies of Khuzestan province.
Materials and Methods: Study area is located in Shahid Modares basin that large parts of these farm lands destroyed by gully erosion. The aim of this project is to identify the main factors affecting on linear gully development and modeling them. For this purpose, distribution maps of climate and the gully was determined. Then a Watershed from each climate class with the highest losses was selected. At last Haddam watershed with warm-arid climate and Sharif watershed with warm-semi arid climate were selected. And 15 gullies were selected from each watershed then some parameters studied and measured in these gullies. Finally relationship between the length and volume development of gully with watershed characteristics, Physio-chemical soil properties, the percentage of vegetation cover, pebbles, bare soil, litter, slope and upstream area of head cuts, rainfall and different land use area a 20-year period (1993-2012) were analyzed. Modeling of the gully development was done using multivariate regression.
Results and Discussion: The results showed that in Haddam watershed the gully number A17 had most elongation (78.8 meters) while the gully number B2 had lowest elongation (3.8 meters). In Sharif watershed the gully number B3 had the most elongation (108.1 meters) while the gully number B4 had the lowest elongation (1993-2012). Gully clustering results showed that gullies of Haddam’s watershed were in two clusters and gullies of Sharif’s watershed in the three clusters. The final equation for the development of Haddams gullies in the cluster one shows the amount of development in these gullies depends on three variables including upstream area of initial point (X4), the percentage of bare soil (X6) and slope of initial point (X2). At cluster two the amount of progress in these gullies depends on silt percent (X18) and PH(X23). The final equation for the development of Sharif’s gullies in the cluster one shows the amount of progress in these gullies depends on upstream area of head cut(X3). At cluster two the amount of development depends on two variables upstream area of initial point (X4) and Sodium content (X22). In Haddam’s watershed more than 80 percent of land use is covered by rain fed and irrigated land. Unlike Sharif’s watershed that more than 80 percent of pasture land form. In addition, measurement of upstream watershed area reflects very poor range condition. In this region, due to the slight slope in gully head cut the surface runoff has not velocity but also due to lack of canopy cover in gullies’ watershed and low soil permeability because of silt frequency and high salinity in the soil profile increases the risk of gully development. In this research, slope of head cut upstream and slope of initiates point is less than 5 percent at total gullies that are correlated with development of gully elongation. However, due to poverty and lack of vegetation cover conditions provided for gully linear growth.
Conclusions: Gully erosion is a form of progressive erosion that allocated the largest portion of soil degradation in different climates to itself. Gullies behavior against its spreading and growth is affected by different environmental factors. In this research, available data analysis in Haddam’s watershed showed that the most important factors on the gully development were watershed characteristics on gully headcut (area and slope), the fine geological formation (silt), acidity and high soil salinity. These factors along with poor vegetation cover and agricultural land had created an excellent platform for gully elongation so that over a 20 year period have at least 3.8meter per year and a maximum elongation 78.8 m. In Sharif ‘s watershed showed that the most important factors on gully development were upstream area of head cut, upstream area of initiate pointed amount of sodium which caused to 10.1 and 108.1 meters minimum and maximum linear development respectively.
H. Karimi; A. Lakzian; Gh. haghnia; H. Emami; M. Soufi
Abstract
Introduction: Soil erosion by water is one of the most widespread forms of land degradation and it has caused many undesirable consequences in last decades. On steep slopes, rill erosion is the most important type of erosion, which produces sediment and rill flow. It can be also considered as a vehicle ...
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Introduction: Soil erosion by water is one of the most widespread forms of land degradation and it has caused many undesirable consequences in last decades. On steep slopes, rill erosion is the most important type of erosion, which produces sediment and rill flow. It can be also considered as a vehicle for transporting soil particles detached from upland areas. Recent studies indicate that soil detachment rates are significantly influenced by land use. It is also known that there is a major difference between detachment rates of disturbed and natural soils (Zhang et al., 2003). Plowing rills especially in steep slopes increases sediment production. Sun et al. (2013) reported that the contribution of rill erosion in hill slope lands in china was more than 70%, which was approximately 50% of total soil erosion. In addition, measured soil loss is statistically related to hydraulic indicators such as slope, water depth, flow velocity, flow shear stress and stream power (Knapen et al., 2007). This study aims to evaluate the effects of hydraulic variables (shear stress and stream power) on spatial-temporal soil detachment rate. The focus is on the plowing rills in hillslope areas under wheat dry farming cultivation.
Materials and Methods: The study area is located in hilly slopes with the slope of 22.56% under dry farming wheat cultivation at 60 km of west of Shiraz, Iran. Top-down conventional plowing was carried out in order to create 10 meters furrows. Slope and cross sections of rills were measured throughout the experiment at 1 m intervals by rill-meter. Water was added to the top of the rills for 10 minutes and inflow rates were 10, 15 and 20 L min-1. Hydraulic parameters such as shear stress and stream power were calculated measuring rill morphology and water depth. Flow velocity and hydraulic radius along the different rill experiments were also calculated. Sediment concentrations were measured in three equal regular time and distance intervals (measurement points (MPs)), they were considered to calculate sediment detachment rate in different times and sections of each rill experiment for spatial and temporal soil detachment rate evaluation. One-way analysis of variance (ANOVA) was employed to test the significance of differences of sediment detachment rate among different treatments.
Results and Discussion: The results showed that the maximum values of shear stress and stream power were 14.07 Pa and 10.29 Wm-2 and the minimum values were 7.41 and 2.77 respectively. This research also indicated that changes in longitudinal profile of these hydraulic parameters along the rills affected the soil detachment rate values. Obtained average, minimum and maximum of the soil detachment rate were determined as 0.09, 0.02 and 0.22 kgm-2s-1, respectively. Due to Detachment-Transport Coupling mechanism, there was a significant difference between the initial and following MPs (P
S.M. Soleimanpour; M. Soufi; H. Rahimi
Abstract
Abstract
Gully erosion is a kind of water erosion that has high priority in Fars Province due to sediment production and enormous damages to land, roads and infrastructures. In this study, 15 gullies were selected and their morphometric characteristics, such as catchment area, soil, cover vegetation ...
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Abstract
Gully erosion is a kind of water erosion that has high priority in Fars Province due to sediment production and enormous damages to land, roads and infrastructures. In this study, 15 gullies were selected and their morphometric characteristics, such as catchment area, soil, cover vegetation and climate were measured. In order to determine influential factors on the sediment production and gully development, relationship between gully volume as dependent variable and gully characteristics such as, length, width, depth and watershed characteristics such as area, slope, form factor, particle size, vegetation cover and maximum raining during 24 hour as independent variables were analyzed by using step wise method in SPSS (recipe 13) software. The results revealed that sediment production due to gully development was related to five variables of clay, sand, silt, slope and cover vegetation of the watershed above the gully heads. This result implied on the impact of the characteristics of soil, geology and watershed on the sediment production of gullies. Impact of soil and geologic factors indicated were more important than watershed characteristics. Investigation on the topographic threshold indicated that positive environmental than exponent implied that sub surface runoff is dominant on gully development. These results also indicate the impact of field observations proved the dominance of subsurface acting due to tunneling the geological formation on the gullies sediment yield.
Keywords: Gully Erosion, Sediment Yield, Topographic Threshold, Konartakhte, Fars Province
