Environmental Erosion Research
Year:2011 | Volume:1 | Issue:1|Papers Count:7

Vegetation is an important component of global ecosystem and the knowledge about its cover and fraction are essential in understanding of land-atmosphere interactions and their effects on environmental issues. The main objective of this study was to estimate the vegetation fraction (Fv) of an arid area in central part of Iran (Sheitoor- Yazd) by using satellite images and artificial neural networks (ANN). To do so, the percentage of vegetation fraction for 52 randomly selected plots (50 meters by 50 meters), were measured on the field in July 2009. Next, an ALOS (AVNIR) image collected on 18 July 2009 and multilayer perceptron network were used to estimate the percentage of vegetation cover. Two types of transfer function, 12 training functions and six different combinations of spectral bands of satellite image as input were used to select the optimal network. Furthermore, the number of hidden neurons varied from one to six. Field measurements were used as target values to the network. To evaluate the effect of randomly selected training and test data, 30 and 35 out of 52 observed plots were considered as training data sets, and 22 and 17 plots as test data sets, respectively. Then, using linear regression models between the measured field data and estimated values, coefficients of determinations and RMSEs were calculated. Moreover in order to validate the results and remove possible errors due to random selection, cross validation algorithm was used. Results demonstrate that ANN can be used for accurate estimation of the percentage of vegetation cover in arid areas (R2>0.74 and RMSE <2%).

Gezir Watershed is located in Hormozgan Province and its area, is 225/05 km2, is one of the famous and significant watershed in this province because of its gully erosion "Gully erosion development in agricultural lands" and "high dependence of local people livelihood into agriculture" are two main reasons for choosing this watershed as the case study. In this research is study soil characteristics and catchment's topography and their relationship with information and morphometry of Gullies.According to the gully erosion analysis morphologic characteristic of gullies were measured and their profiles were delineated; soil characters such as PH, SAR, salinity and also silt, lime, and clay percentages were measured; and data relating to well drainage and discharge were collected. Results show that increasing the soil and water salinity, decreasing the underground water table, rainfall shortage, and also intense short duration rainfall are the main factors caused to gully development in Gezir Watershed. According to soil characteristic measurements, increasing the silt and clay percentage is another reason for gully development. Consequently, some important environmental change occurred due to less traditional soil and water conservation such as increasing the gully area, well numbers, water salinity, ratio between inactive and active wells, salinity and usefulness, and decreasing the high annual discharge of wells.

Discharge rain above or below the long term average often leads to either flood or drought, two extreme climate events, each with severe ramification on public lives encountered widely across large parts of Iran. Prediction of drought, even with considerable error, can alleviate some of the devastating consequences. Meteorological drought is often experienced first and its data analysis could therefore be used to predict different aspects and types of drought in general. In this study, carried out on karoon-1 basin, an empirical model is proposed for prediction of meteorological and hydrological droughts in the basin using long-term data prepared from the local hydrometric and pluviometer stations and standardized precipitation index (SPI) and surface water supply index (SWSI). The model was found to have RMSE and R2 of 0.16 and 0.92, respectively, and hence can be considered as an effective model for the basin.

Water erosion has a fundamental and important role in environmental degradation and in order to prevent of its effects the knowledge of soil erosion process is needed. Stream erosion is one of the most important types of water erosion. In this study the role of environmental factors including slope, hypsometric classes, slope aspect, geological formation and soil erodibility in drainage density as stream erosion characteristic were investigated in Kojoor, Firoozkolay region. In view of this, drainage density layer were overlaid with independent variables and drainage density were determined in different classes. The relationship of drainage density and independent variables were investigated using regression models. Effective classes (effective clusters) in drainage density and the assigned clusters were tested using cluster analysis (CA) and discriminant analysis (DA), respectively. The results showed that vegetation type has a direct affect on water erosion so that length frequency and erosional density is higher in rangeland compared to forest cover. The results of regression model showed a significant exponential correlation between drainage density and slope, hypsometric class and slope aspect. Hierarchical CA grouped the 25 variables from rangeland and 29 variables from forest into four and three clusters, respectively based on the similarity of catchment characteristics. DA provided an important data reduction affording more than 79% and 56% correct assignations in rangeland and forest, respectively to discriminate between the clusters of catchment characteristics in the study area.

Erosion means the harvesting, transportation and movement of eroded material. The concept is very extensive erosion that has different definitions in different disciplines. The purposes of this paper is finding a brief definition of "erosion" concept in different perspectives and comparing it in Geomorphologic and Natural Resources point of views. To achieve this goal, we try to use the library documents, analyze and compare the findings of this work with each other. Results show that most differences between these approaches, different time, place, is corrosive agents and erosion processes. In Geomorphologists view of point, erosion is a natural phenomenon and Sformation of it is slow and makes landscapes and landforms that are environmental resources suitable for human life. But the erosion in the point of Natural Resources Science view is destruction of fertile soils and have negative effects on the lives of many inhabitants of the plan. Natural Resources Science specialists believe that soil erosion phenomena even is a destructive force for civilizations. General concept of erosion according to the type and scope of the study has significant differences from the perspective of Natural Resources Science and Geomorphology.

Study area is Cheshme-Ali Damghan, one of the main watersheds of Haj-Ali-Gholi subcatchment located in central drainage basin of Iran. Research was carried out via generating needed informative themes, detecting location of water samples and overlaying and interpreting themes. The effect of geological formations on water quality was analyzed after geometric overlaying of themes and assessing water resources distribution. Informative themes included maps of: geology, geological formation sensivity, drainage net, deposits and its bedrock, and water samples. Results showed that the main destructive agent of surface water quality is Neogene marly formations (Ngm) which are mostly expanded over west part of watershed. Also marly formation extension as bedrock of pediment and playa deposits is the main cause of groundwater quality degradation.

Investigating the factors affecting the occurrence of mass movements, help to identify sensitive areas and providing solutions and ways to control and proper management, partly to prevent the occurrence of mass movements. This research tried to recognize the factor affecting the occurrence of mass movements in the Forest Park Abidar watershed. In this research, information layers including lithology, elevation, slope gradient, aspect, rainfall, land use, rivers, faults, roads, soil and landslides distribution, is prepared by use of geographical information system (GIS), topographic maps, aerial photographs and field study. Then, factors affecting the occurrence of mass movements are recognized by using the method of multivariate linear regression. The use of multivariate linear regression is to find the best fitting function to describe the relationship between the mass movements (dependent variable) and a set of environmental parameters (independent variables). The effect of each parameter on mass movements occurrence is assessed from the corresponding coefficient that appears in the regression function. The interpretations of the coefficients showed that lithology, soil, land use, distance from road, distance from faults, distance from rivers, play a major role in determining landslide occurrence and distribution in study area.