پهنه‌بندي خطر وقوع زمين لغزش بر روي جاده تهران-چالوس و بزرگراه در دست احداث

Landslide hazard zoning for the Chalus-Tehran road and constructing highway

جاده توريستي چالوس، يكي از مهمترين را ه هاي ارتباطي ميان استان هاي تهران، البرز و شرق استان مازندران مي باشد. اين جاده يكي از پر ترددترين مسيرهاي داخلي كشور است. احداث بزرگراه در حال ساخت تهران- چالوس، بار ترافيكي اين مسير را كاهش خواهد داد. احتمال وقوع زمين لغزش بر روي اين جاده ها به دليل عبور از ميان رشته كوه‌هاي البرز افزايش مي‌يابد. از اين رو بررسي خطر زمين لغزش بر روي قسمت هاي مختلف جاده و بزرگراه، از اهميت بالايي برخوردار است. روند تعيين خطر زمين لغزش جاده و بزرگراه شامل دو مرحله مي باشد. در مرحله اول، پهنه بندي خطر زمين لغزش بر روي دامنه هاي كناري جاده چالوس و بزرگراه و در حوزه رودخانه چالوس صورت گرفت. براي تهيه نقشه پهنه بندي عواملي از قبيل توپوگرافي، زمين‌شناسي، گسل ها، هيدرولوژي و پوشش گياهي در نظر گرفته شد. در مرحله دوم، براي تعيين خطر بر روي جاده و بزرگراه، عواملي مانند آزيموت شيب بيشينه، فاصله جاده از خاكريزهاي كناري و مساحت موثر دامنه ها در نظر گرفته شد. جاده و بزرگراه از نظر وقوع زمين لغزش، در 4 كلاس بسيار خطرناك، خطرناك، خطر متوسط و بي خطر طبقه بندي شدند. طبق نتايج بدست آمده، از كل طول جاده در منطقه مورد مطالعه كه 66 كيلومتر است، 16 درصد داراي خطر بسيار زياد و 42 درصد، داراي خطر زياد براي وقوع زمين لغزش مي باشد. همچنين از 17 كيلومتر طول بزرگراه در حال ساخت، 12 درصد داراي خطر خيلي زياد و 33 درصد داراي خطر زياد براي وقوع زمين لغزش مي باشد.

Karaj-Chalus road is an important connection between Tehran-Alborz provinces and west of Mazandaran County. Considering tourist attractions in the north, this road is one the most crowded roads in the country. Recently a new highway is being constructed adjacent to the previous road; therefore a large portion of the traffic will be converted to the highway. Since the highway passes the high mountainous lands the roads are enormously affected and in high risk by landslides. In this study, both mentioned ways are classified according to hazard risk. This project has been performed in two steps. First, a landslide hazard zoning map has been provided for the region around the roads to detect the high risk and low risk zones, then the roads have been divided into segments that each of which has 2 kilometers length. The main parameters in landslide hazard zoning are considered such as topography, hydrology, geology, tectonics and green coverage. The landslide hazard map clearly represents the high risk and low risk areas but it is important to realize how it influences the roads. With purpose of classifying the road segments, the azimuth of the maximum slope of each side of the road has been considered. An aspect layer has been provided using the DEM of the region. In order to estimating the direction of the maximum grade of the ground, the mentioned aspect layer is applied. In order to determine the effectivity of the direction of the slope to the roads, the angle between the road segments and the maximum grade has have been calculated and is used as an important factor to determine the amount of risk for the road segments. The distance between the road axes to the trench of mountain also has been taken into account. According to the mentioned factors and the landslide hazard map, the road segments have been categorized into four zones based on the degree of accepted risk. In accordance with the results obtained from this research, 58 percent of the road has the potential of high and very high risk respectively. 45 percent of the highway has the potential of high and very high risk. Key words: Azimuth, Alborz, green coverage, topography.