پديد آورندگان :
صفاري، امير نويسنده دانشجوي دكتراي دامپزشكي safari, amir , عليمرادي ، مسعود نويسنده كارشناسارشد ژيومورفولوژي، دانشگاه اصفهان , , حاتمي فرد، رامين نويسنده كارشناسي ارشد ژيومورفولوژي دانشگاه اصفهان Hatamifard, Ramein
چكيده لاتين :
Introduction
The increasing growth of urban and rural development has caused some natural anomalies in the Earthʹs inhabitants. Mass movements, especially landslides, are one of the most damages of them that have had the increasing momentum together human manipulation in natural systems in recent decades. So that it is one of the principal geomorphic processes in the mountainous areas. Landslide phenomenon occurring in many parts of the world and Iran in the favorable conditions causes the destruction of vegetation, orchards, farmlands, and even human casualties. Burying of Abikar village of Charmahal-o-Bakhtiari Province in spring 1997 year is one of the clear samples of landslide human damage. Since the exact predication of landslides occurrence isn’t possible by human sciences, thus, we can prevent from the damages of this phenomenon by identification of landslide susceptible areas and prioritizing them. Landslide hazard zonation maps can help the environmental designers and engineers to select a suitable place for development projects implementation. The results of these studies can be used as fundamental information by environmental managers and planners.
The purposes of this study are the recognition of effective factors in landslide and the zonation of Marbor River Basin in terms of the occurrence of this phenomenon Using Multivariate Regression Method. Therefore, selection of criteria and standards, providing of factors raster layers, preparing landslide hazard zonation map and to obtain more accurate predictive models of the basin are the major objectives of this research to determine sensitive sites that have the maximum occurrence probability of landslide.
Methodology
The studied area is the Marbor River Basin, which has been located in the 30o 41ʹ 48" to
31o 3ʹ 20" North latitude and 51o 23ʹ 48" to 51o 52ʹ 54" East longitude. Marbor basin area is about 800 km2 and is located 55 kilometers south of the city Semirom. The study area in the southernmost part of the Isfahan province and approximately north of Fars province. At first, study area was investigated and determined its extent using 1:50000 topographic maps. Then, the map of landslide hazard zonation was prepared by interpretation of aerial photographs, Satellite Images and field studies. In the next step, according to the landslide location, Environmental characteristics of study area, using comparative studies, results of other researchers and expert opinions, 9 factors and 54 parameters were identified to achieve the goals.
Then the collected dates to draw maps were imported into GIS and were digitized. The needed Layers of landslide hazard zonation were prepared using Arc GIS 9.3 software. These layers are slope (SLP), aspect(ASP), distance from stream (DRN), distance from way (ROD), distance from fault (FLT), lithology of Earth material (LIT), land use (LUS), isohyets map (RAN) and vegetation cover (RNG). After digital layers preparation of effective factors and landslide dispersion using linear multivariate regression, zonation model of study area was drawn.
Results and Discussion
Multivariate regression relationships between independent variables (factors) compared with each other and with the dependent variable (occurrence of landslides) are considered together. Effective factors maps by using 1:50000 and 1:250000 topographic maps, 1:100000 geological maps, digital layers of geology, Digital elevation model, interpretation of aerial photographs 1:40000 and Final report of investigative scheme Research center of agriculture and natural resources of Isfahan (2005) were drawn. Isohyets map was developed with a 30-years period at stations in the study area and by interpolate method in Surfer software. To landslide hazard zonation Marbor´s basin by using multiple linear regression, was overlaid Effective factors and Landslides distribution layers and then to obtain homogeneous units map using method of Union in ARC GIS software, and finally created 27466 homogenous units. Number of variables used in landslide risk analysis, are quantitative (for example, linear elements, rainfall, slope) and some of them are qualitative (aspect, vegetation, land use, lithology). Because linear regression methods using quantitative data is performed. Thus, qualitative data must be converted into quantitative data. Dummy variables are used for this purpose. In this method, after obtain homogeneous units map, Units where the landslide occurred are 1 and 0 for other units (non landslide).In multivariate regression, Stepwise method with confidence more than 95% was chosen. Finally, among the 54 parameters involved in the regression, 23 parameters with coefficient of less than 95% were excluded from the equation, and 31 parameters with coefficient 95-99%, involved in the regression. That is perfectly acceptable.
Results of Integration of landslide hazard zonation map with observed landslide map have been showed. Models evaluation was done with use of landslide index (LI) and density ratio (DR).
Conclusion
The landslide phenomenon is one of environmental hazards which occur in Marbor basin in most times. Therefore, creation of one regional strategy is very necessary to reduce its damages and maintains natural and human resources. Furthermore, landslide hazard zonation map can help research centers in environmental management and planning. In this study, linear multivariate regression model have been used to achieve goals. Multivariate regression relationships between independent variables (factors) compared with each other and with the dependent variable (occurrence of landslides) are considered together. According to weight of homogeneous units and effective factors in landslide occurrence, the study area was zoned as various layers. Finally, landslide occurrence zones were classified into five classes (very high, high, moderate, low, and very low). The regression coefficients obtained show that the distance from fault (0-1500 m) and precipitation (850-1000 mm) respectively had the greatest and least effect on the occurrence of landslides of the study area. According to presented model, final zonation map, about 32 % (256 ?Km?^2) of the Marbor basin area have the occurrence of moderate risk and the occurrence of low risk 31% (equal to 248.7 ?Km?^2). Furthermore the occurrences of high risk 25.5 percent (203 ?Km?^2). The results obtained evaluation of the accuracy and precision of the model show that it has significant accuracy for zones identification with landslide very low, low and average.
