Document Type : Research Paper
Authors
1 Professor of Physical Geography (geomorphology), University of Ardebili University, Ardebil, Iran
2 Ph.D. student of Physical geography (geomorphology), University of researcher Ardabili, Ardebil, Iran
3 Professor of geomorphology, Tabriz University, Tabriz, Iran
Abstract
Introduction
When a natural process threatens human life or property, it is called natural hazard. Disasters’ statistics have shown that their effects are, considerably, increasing all over the world. Most of such disasters originate from geomorphological events. In fact, natural disasters have been a global concern and most of them have mainly been geomorphological. Hence, developing countries, in particular, are deeply influenced by such disasters. One way of decreasing damages caused by natural disasters is identification of disaster-prone areas and prevention of their development in such areas relying on land use planning. In this research, geomorphological hazards of flood, landslide and neotectonics were investigated in Zonouzchay catchment. The catchment in an area of 323 square km has been located in political-administrative zone of Marand county.
Methodology
The aim of the present study is to evaluate geomorphological hazards in Zonouzchay catchment through preparing zoning maps of flood, landslide and neotectonics hazards. Digital evaluation model images of height (DEM), geological maps and sentinel satellite images are the most important data used in the present study. For preparation of flood and landslide hazards’ map in Zonouzchay catchment, ten variables and effective parameters on flooding and flood spreading were combined in GIS environment. These variables are considered for zoning flooding hazard factors such as height, slope, convexity of the land surface, valley depth, lithological units, drainage density, distance from the main streams, height of the runoff, use and vegetation. For zoning landslide occurrence risk, the above mentioned variables (except for stream height, drainage density and valley depth) were used along with the three variables of distance from fault, slope direction and rainfall. ANP model in GIS was used in order to combine effective variables on flooding risk and landslide in Zonouzchay catchment. Moreover, zoning relative neotecnic activities for the underlying area was conducted by using relative tectonic activity index (Al Hamdouni, et al, 2008). Relative tectonics activity index (Iat) is developed by combination of other indexes. The index classifies the perspectives in four classes of relative tectonic activities:
Class 1: too high tectonic activities with values 1 < S/n < 1.5
Class 2: high tectonic activities with values 1.5 < S/n < 2
Class 3: medium tectonic activities with values 2 < S/n < 2
Class 4: low tectonic activities with values S/n < 2.5
Results and Discussion
Zoning Relative Tectonic Activity
Results of Iat index-basedzoning indicate that neotectonic activities in Zonouzchay catchment are, generally, medium to relatively weak. Field observations also indicate that erosive processes (in spite of resistant formations) are predominate in the study area. Lack or rare dispersion of neotectonic landforms, retreat and destruction of mountain fronts and widening of the valleys are among the reasons, which show relative weakness of the active tectonic in Zonouzchay catchment. The main part of the morpho-tectonic landforms of the catchment is in line with Zonouz-Harzand fault. For most of the sub-catchments Iat values are in classes 3,4, which shows average to weak status of the relative active tectonic in the catchment.
Zoning Flood Event Risk
ANP model-based results indicate that from among the employed variables, slope, distance from river and land surface convexity are, relatively, the most important variables with coefficients 0.23, 0.19 and 0.16. Findings of the study indicate that about 4% of Zonouzchay catchment area is in too high risk class, 7.4% in high risk class, 8.3% in medium risk, 21.7% in too low risk class and 58.6% is in too low risk class. Almost all upstream parts of the study catchment are in low risk to high risk classes. In the middle parts of the study catchment, flood zones are mostly bounded to two main valleys of the catchment. Width of the valleys has increased in different periods and, consequently, flood plains have been formed in the basin of such valleys. Some parts of Miyab and New Harzand villages have been located in this geomorphologic position. In the downstream parts of the catchment, width of Zonouzchay has increased considerably and also the two main streams of the study catchment join each other in this part. Presence of low slope lands, low relative height, adjacency to the main rivers, lower values of convexity index, higher density of drainage and the valley depth are considered as the most important effective factors of this part of the catchment in terms of flood event.
Landslide Risk Zoning
According to the results of ANP model, the three variables of slope with coefficient of 0.24, lithology with coefficient of 0.22 and rainfall with coefficient of 0.16 have the key influence on landslide occurrence in the study area. Hence, about 16.6 % of the catchment area is in too low risk class, about 38.1% is in low risk class, about 23% is in medium risk class, 15.8% is in high risk class and finally 6.5% is in too high risk class. Spatial distribution of the risk classes indicates concentration of high risk and too high risk classes in the middle arts of the study catchment. This can be related to various factors. Maybe, the most important reason is related to presence of geological formations prone to landslide and appropriate slopes for occurrence of such geomorphological process. In fact, in the middle parts of the study area dominance of slope 10%-40% , presence of high alluvial terraces , also occurrence of Marens , conglomerate formulations with Maren interlayers and dispersion of Flysch type have provided appropriate conditions for landslide.
Conclusion
Results of geomorphological indexes indicate that considerable part of anomalies of this index are originated from lithological differences of the area. Moreover, active tectonic zoning of the area shows relative weakness of neotectonic processes and movement of the area’s faults along with dominance of erosive processes. Regarding flood occurrence risk, results of ANP model indicated that the variables of slope, distance from river and convexity of the land surface have higher importance in flooding. From flooding occurrence perspective, about 4% of Zonouzchay catchment is in too high risk class and 7.4% is in high risk class. The dangerous zones are accordant to valleys’ bed of the two main streams of the catchment and hence, some parts of the residents in these valleys are exposed to destructive floods. Finally, based on results of ANP model results, three variables of slope, lithology and rainfall have higher importance in probability of landslide occurrence in the study area. About 16% of Zonouzchay catchment is in high risk class, and 7% of it is in too high risk class of landslide. Landslide occurrence in the middle parts of the catchment is highly expected due to a set of conditions such as vulnerable slope and geological formations.
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