identification of the most effective elements in rill erosion process and its occasion in ahmad-abad, mashhad

introduction soil is one of the most valuable national resources that can be wasted by erosion phenomenon. therefore, prevention of soil erosion is universally considered. erosion is a process by which soil particles are separated from their original context and can be moved to another location. rill erosion is a kind of water erosion in which detachment and movement of soil particles can be affected by concentrated flowing water. development of rill dimensions can produce water courses and gullies that generate large amount of sediment. therefore, determining the most important parameters affecting rill erosion process is necessary to manage and minimize soil losses. one of the factors of soil degradation in the hills of ahmad-abad, mashhad region is a kind of rill erosions which makes it to recognize its behavior to control that. this study’s aim is to determine the most effective elements in rill erosion of some hill slopes area in ahmad-abad, mashhad region, where rill erosion is highly noticeable. the investigated parameters are as follow: slope length, canopy cover, ground cover, soil texture (percentage of sand, silt and clay in soil sample) slope and its common effect on length. then, relations between the investigated parameters and the number of rill for one meter were investigated. study area the study area is located in the north east of iran at a distance of approximately 60 kilometres southwest of the city of mashhad. .the geological formation of the land is marl and conglomerate and its general topographical structure is low hill. the location of the study area is from 59 28 to 59 35 in east longitude and from 35 58 to 36 00 in north latitude. the average annual rainfall in the region is estimated around 251 mm. on the basis of demarten scheme (considering the volume of rainfall and temperature) climate of the region is semi-arid. unit area physiographic is low rounded hills covered with thin soil. vegetation zone, where scattered and sparse from prairie feature aspect is peanuts and lettuce fields of wild grass with hardwood such as amygdalus ebarnum, lactuca orientalis with forbs such as verbuscum songaricum, centurea virgata and so on. material and methods in this study, data has been collected through sampling. in selecting sites, the systematic analytical sampling method has been employed. in each site, the start point of transect has been located randomly, and along each transect, the parameters under investigation were measured through systematic sampling. a quadrate of 50 × 50 meters was created on the slopes in each site under research from the highest point of the ridge slopes (the highest point on the dividing line of water and water movement into the hill slope). then, 5 transects with 50 m length were established on each quadrate. the distance between each transect was 10 m. as a result, that were 5 transects with slope length of 10, 20, 30, 40 and 50 meters at each site. so, there were 7 sites containing 35 transects of 10 to 50 meters totally. ground slope was measured in each transect, at distances of 0, 10, 20, 30, 40 and 50 meters from the start point of the transect. most of plants in the region are very close to the ground surface. so the parameter of canopy cover was chosen to measure the quantity of vegetation. percentage of ground cover with regard to the percentage of gravel surface (2 cm or more in diameter) and percentage canopy cover of herbaceous plants and shrubs has been determined. this factor was measured through applying the sampling point. a rod released vertically at each transects at every 20 cm length and strike with each component of cover, gravel or bare soil was recorded. then, the data obtained for each of the components were converted to percent. due to the variability of physical properties of soil in hillside and approximately stability of these features along a transect, to determine soil texture, sampling were performed at three points along the upstream domain (length 10 m), middle (length 30 m) and lower domain (length 50 m). field observations indicate that soil to a depth of 20 cm has been affected by rill erosion. for this reason, 3 soil samples from each site to a depth of 20 cm was taken and transported to the laboratory, and soil texture of samples were measured. according to the obtained data which were normal, pearson correlation in the expression of relation between each of the factors affecting the erosion with number of rills per unit length was used. statistical minitab 16 software was used. results and discussion the results of correlation showed that most of the investigated parameters such as ground cover, canopy cover, gravel cover, amount of available clay and common effects of slope length and amount of slope have significant correlations with rill occurrence and its occasion. moreover, the amount of rills has the highest correlation with ground cover (-0.3). slope length and amount of slope were not correlated with rill occurrence and its occasion, however common effect of them showed a significant correlation (0.14). accordingly, vegetation managements and rangeland management’s have to be considered as the first step to reduce erosion potential in ahmad-abad region. conclusion one of the factors of soil degradation in the hills of ahmad-abad, mashhad region is a kind of rill erosions which makes the recognition of the behaviour and control essential. this study was conducted to determine the most effective elements in rill erosion of some hill slopes area in ahmad-abad, mashhad region, where rill erosion is highly noticeable. the investigated parameters are as follow: slope length, canopy cover, ground cover, soil texture (percentage of sand, silt and clay in soil sample) slope and its common effect on length. then, relations between the investigated parameters and the number of rill for one meter were investigated. the results of correlation showed the amount of rills has the highest correlation with ground cover. so improve vegetation cover of rangelands, especially coverage’s near the surface are effective on reduced of rill erosion. vegetation managements and rangeland management’s have to be considered as the first step to reduce erosion potential in ahmad-abad region.