بررسي علل ايجاد آبكندها و عوامل موثر بر گسترش آنها ﴿مطالعه موردي : شهرستان كوهدشت، حوزه شورآباد﴾

چكيده انگليسي :

88 An Investigation on Causes of Gullies Formation and Effective Factor on Their Development Case Study Shurabad Catchment Kuhdasht Region Seyyed mehdi seifi tizabi sm seifitizabi@yahoo com Department of Natural Resources Isfahan University of Technology Isfahan 84156 Iran Degree M Sc Language Farsi Supervisor H R Karimzadeh h karimzadeh@cc iut ac ir AbstractGully erosion is a highly obvious form of soil erosion that affects on soil productivity restrictsland use and can endanger roads fences and buildings Gullying is a complex process controlledby a variety of closely related factors such as lithology soils climate topography land use andvegetation cover Gully erosion is often the main source of sediment on a catchment scale andmay also act as a sensitive indicator of environmental change the rate of gully growth is one ofthe most important indicators used for assessing the area destroyed by gully erosion andevaluating the many kinds of damage it causes This study investigated the causes ofgully erosion in the Shurabad watershed located in Kuhdasht city Lorestan province We studiedeffect of physiographical and soil factors on the rate of gully erosion Twelve gullies randomlyselected and classified in two form single heads and multiple heads The physiographicalcharacteristics length width and upstream slope floor slope and gully characteristics slope elevation landuse and geology were measured for each gully Three parts of gullies includingupstream middle and downstream were selected and their cross section was drawn For eachgully we drilled a soil profile with 1 5 m in depth and took soil samples from four profilelayers 0 25 25 50 50 100 and 100 150 cm Soil characteristics such as texture electricalconductivity EC saturated moisture content SP pH amounts of calcium and magnesiumions the rate of lime gypsum organic matter bulk density sodium and percentage of soil texturecomponents were measured The relationship between gully length and erosion volume wereinvestigated using regression analysis and erosion thresholds determined The results showed thatgully erosion mostly occur in Quaternary and Bakhtiary geology formation and under road rangeland and agricultural land use Although number of gullies were same in different landusebut they produced different sediment rate Average sediment rates in road rangeland andagricultural landuses were 4 4 2 and 1 1 m3 respectively Erosion rates were significantlydifferent in agricultural units in relation to road and rangelands Most gullies occur in slopes lessthan 5 percent Sediment rate increase in slopes less than 10 percent Numbers of multiple headsgullies are more in Quaternary formations in relation to others The soil erosion increased insandy loam soils and decreased in silty clay soils There is a negative relation between percentof silt and erosion rate but there is a negative relation between soil erosion and clay in layer 1 andsaturation moisture in layer 2 and a positive relation with sand in layer 3 We didn t find anyrelation between soil erosion and soil characteristics in layer 4 In general we find that thepercent of SP the rate of lime silt organic matter Coarse sand and clay increase the rate ofsoil erosion but the amount of fine sand very fine sand and sodium decrease the rate ofsoil erosion and there are no significant relationship between the pH EC and amounts ofcalcium and magnesium ions and rate of soil erosion There is also a significant relationshipbetween gully length and soil erosion rate in study area Keywords Soil erosion Gully erosion Soil texture Shurabad watershed

سيفي تيزابي، مهدي

بررسي علل ايجاد آبكندها و عوامل موثر بر گسترش آنها ﴿مطالعه موردي : شهرستان كوهدشت، حوزه شورآباد﴾

فرسايش آبكند , فرسايش خاك