Banafshe Yasrebi; Majid Soufi; Mir Khalagh Mirnia; Jahangard Mohammadi
Abstract
This research focused on studying the morphometric characteristics, topographic threshold of gullies and their relationships, dominant process of gully initiation and development stages as well, in agricultural and rangeland land uses. Also, morphometric characteristics of 120 gullies including top width, ...
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This research focused on studying the morphometric characteristics, topographic threshold of gullies and their relationships, dominant process of gully initiation and development stages as well, in agricultural and rangeland land uses. Also, morphometric characteristics of 120 gullies including top width, bottom width and headcut height and surface characteristics of gullies contributing area including vegetation, rock fragment and bare soil by 1 m2 plot and soil samples from top soil and gullies wall were collected in semi-arid part of Ilam Province. Results showed that top width–depth ratio of gullies in cropland and rangeland is 2.1 and 1.5, respectively that widening and deepening has more important role in gully growth. Top width-length ratios are 0.41 and 0.57 in croplands and rangelands, respectively that shows rangeland gullies are more elongated. Negative exponential relationship between those ratios and slope shows the effect of topographic factors especially slope on final shape of gullies. Bottom width-top width ratio in croplands and rangelands is about 0.33 and 0.3, respectively and cross section shapes are trapezoidal and V shape. Results showed that slope describes 16 percent of cross sections area variation and lateral growth of gullies in croplands and rangelands and describes 84 and 73 percent of gully volume variation. Effective factors on gully volume are sand content in top soil, land use and slope. Studied gullies in both land uses have mean fractal dimension of 1.08 and has linear growth with length and power growth with volume of gully. Power of Hack law in studied gullies in croplands and rangelands gullies are 0.5 and 0.54, respectively.
Seyed Masoud Soleimanpour; Majid Soufi; Hassan Ahmadi
Volume 1, Issue 1 , May 2009, , Pages 46-52
Abstract
Fars province has experienced gully erosion in six climate zones based on deMartonne classification method. After selecting one region from each climate zone, 15 active and representative gullies were investigated using morphometric characteristics and watershed area, slope gradient above gully heads, ...
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Fars province has experienced gully erosion in six climate zones based on deMartonne classification method. After selecting one region from each climate zone, 15 active and representative gullies were investigated using morphometric characteristics and watershed area, slope gradient above gully heads, linear advancement, form factor, particle size analysis, vegetation cover, gravel content and bare grounds were measured and sediment production was calculated. Effective factors on sediment production due to gully erosion were determined using Stepwise method provided in the SPSS software package. The results of this research revealed that four factors including slope gradient, maximum 24 hours rainfall, sand, and form factor had significant impact on sediment production with 99 percent of confidence. Slope gradient above the gully head was the most important factor on the sediment production. Slope gradient and form factor had positive relationship and maximum 24 hours rainfall and sand had negative relationship with gully development. The most important impact of slope gradient on the sediment production implies the velocity of surface runoff concentrated above gully heads. Alternative controls to decrease slope gradient would be effective on the reduction of gully development and sediment production.
