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.
Ebrahim Omidvar; Ataollah Kavian
Abstract
Landslides are the major natural hazard, causing significant damage to properties, lives and engineering projects in all mountainous areas in the world. In order to estimate the role of the landslides in erosion processes and evaluation of their risks, it is necessary to quantify landslides. This quantifying ...
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Landslides are the major natural hazard, causing significant damage to properties, lives and engineering projects in all mountainous areas in the world. In order to estimate the role of the landslides in erosion processes and evaluation of their risks, it is necessary to quantify landslides. This quantifying can be performed by applying the probability distributions that show the landslide size against the probability density. This study was investigated the behavior of landslide areas and volumes on Frequency distributions in Mazandaran province. Also total number, area and volume of landslides that have occurred over time were estimated using the approach suggested by Malamud et al. Result of cumulative frequency distribution of landslide area and volume revealed the significant proportion of large landslides in determining the total landslide area and volume. According to Malamud et al. approach total number of landslides were estimated to be 9823±2323. These landslides have been obliterated over the time by soil erosion, vegetation growth or by human activities and total of their affected area and volume by these landslides were 31.5±7.1 km2 and 0.232±0.052 km3, respectively. The obtained results also presented an area of 2×10-3 km2 as a critical threshold area for transition between resistances against slope failure.
