Zeinab Sheikhi; Aliakbar Nazari Samani; Haji Karimi; Reza Bayat
Abstract
Gully erosion is a typically threshold process which is important in land degradation and sediment contribution. Having knowledge on driving conditions and affected lands by gullies are crucial for land degradation management. In this research to prepare the gully erosion map over Iran land mass about ...
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Gully erosion is a typically threshold process which is important in land degradation and sediment contribution. Having knowledge on driving conditions and affected lands by gullies are crucial for land degradation management. In this research to prepare the gully erosion map over Iran land mass about scientific references (article, thesis and report) were investigated in order to scrutinizing of spatial data base and gullying map. Location of 2719 gully headcuts under different climate and land use were identified. Environmental attributes including: soil, climate, rainfall and temperature were collected through using of DEM (12.5 and 30 m), and landuse by using of maps, scientific reports, research studies were extracted. The frequency of gullies was investigated in relation to literature investigation. Topographic threshold conditions were determined and the relative frequency of gully area under mentioned environmental factors were analyzed. The results show that the total gully area in Iran is about 1,328,852 ha. The most occurrence of this erosion is in semi-arid climates, with annual rainfall is 250-350 mm, high silt content, low slope (<5%) and under dry farming landuse. The lowest threshold coefficient () in both arid and semi-arid climates is related to ranglands. The coefficient varies from 0.06 to 0.37 in arid climate and from 0.002 to 0.46 in semi-arid climate, which is indicating of mixing process (surface and subsurface) on gully developing. The resistance of sandy soils (due to permeability) and clay soils (due to cohesion) is higher than silty ones The degradation of canopy cover and runoff generating are two main driving forces, which will be more important under climate change in the near future.
parisa farzi; maryam azarakhshi; ali rasoulzadeh; mehdi bashiri
Abstract
Characteristics of stones forming the earth's surface contribute significantly to environmental changes such as soil erosion and movements of soil particles. This study seeks to investigate the main and reciprocal effects of geological units and slope gradient on runoff and sediment production in Senobar ...
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Characteristics of stones forming the earth's surface contribute significantly to environmental changes such as soil erosion and movements of soil particles. This study seeks to investigate the main and reciprocal effects of geological units and slope gradient on runoff and sediment production in Senobar watershed using rainfall simulator. To this aim, the geological map was created in Arc GIS 10 software and three dominant units i.e. green tuff, sandstone, marl (Et), Orbitolina Limestone (Kl) and Conglomerate, Sand stone (Ngcs) were identified. Besides, to study the effect of slope gradient, the slope map was provided in three classes: 0-10, 10-30 and more than 30%. Then, the rainfall intensity equal to 0.9 mm min-1 (10- years return period) was created by rainfall simulator. Analysis of variance showed significant differences between geological units for runoff, sediment yield and sediment concentration at 5% significant level. It was found out that there is significant difference between different slope gradients in runoff and sediment production; however, there was no significant difference regarding sediment concentration. The results of interaction between geological units and slope gradient for runoff volume was significant at the 95% level of confidence but regarding sediment yield and sediment concentration interaction effects were not significant. Generally, it was found that the type of geological units and slope of the study area impacted on soil erosion process. Also, the impressibility of runoff variable was more than that of the sediment.
