چکیده:
For landslide hazard zonation and map preparation using the Nielsen method, a case study was conducted in the Chashm Khatir Kooh watershed located in the north of Semnan county. In the aforementioned region, after determining the watershed boundaries along with field operations, all landslides in the area were recorded, and their point and surface distribution maps were prepared. Then, based on the principles of the Nielsen method in landslide hazard zonation, a slope map in three classes (5-15, 0-5, and more than 15 percent) and a geological map (map of units or landslide deposits) in three classes (low or no landslide units, landslide units, and liquefaction-prone units) were prepared. Based on the Nielsen method, by comparing and integrating the slope map and the landslide unit map, a landslide hazard zonation map with five zones—stable, generally stable, moderately stable, moderately unstable, and liquefaction-prone areas—was prepared. The area of each of the mentioned zones is 596, 69, 18, 62, and 94 hectares, respectively. The results indicate that the Nielsen method is not recommended for this region because, contrary to expectations, the area of landslides in the stable and moderately stable zones is greater than the landslide area in the generally stable and moderately unstable zones, which is considered one of the flaws of this method in the region. Other flaws of this method include the existence of a stable zone for slope classes less than 5 percent in landslide units. To solve these flaws, the slope classes in the Nielsen method were modified based on the surface distribution of landslides into five classes: less than 15, 5-25, 5-45, 15-25, and more than 45 percent. Based on the matching and comparison of the new slope map and the geological map (landslide units), a landslide hazard zonation map with five zones—stable, generally stable, moderately stable, moderately unstable, and liquefaction-prone zones—was prepared. The landslide area in each of these zones is 652, 394, 263, 57, and 94 hectares, respectively, which are acceptable results and possess a higher confidence coefficient for recommendation to executive sectors in the region.
خلاصه ماشینی:
Based on the Nielsen method, by comparing and integrating the slope map and the landslide unit map, a landslide hazard zoning map with five zones—stable, generally stable, moderately stable, moderately unstable, and liquefaction-prone areas—was prepared.
Other flaws of this method include the existence of a stable zone for slope classes less than 5 percent in landslide units, which in the following, to solve these flaws, the slope classes based on the surface distribution of landslides in them in the Nielsen method are modified into five classes of less than 15, 5-25, 5-45, 15-25, and more than 45 percent have been modified, and based on the alignment and comparison of the new slope map and the geological map (landslide units), a landslide hazard zoning map with five zones—stable, generally stable, moderately stable, moderately unstable, and liquefaction-prone zone—has been prepared.
Map 5: Landslide hazard zonation of the region using Nielsen's method (A) and modified Nielsen method (B) (Refer to the page image) Methodology After preparing the point distribution map (Map (A)2) and the surface landslide distribution map (Map (B)2), the slope map (Map (A,B)3), and the landslide and non-landslide units map (Map (B)4), the landslide hazard zonation map using Nielsen's method was prepared based on Table 1 into five zones: stable, generally stable, moderately stable, moderately unstable, and liquefaction-prone areas.
Table 1: Principles of landslide hazard zonation based on Nielsen's method Comparison and matching of the prepared landslide hazard zonation map with the surface distribution map and the landslides of the region shows that the landslide area in each of the stable, generally stable, moderately stable, moderately unstable, and liquefaction-prone zones is 94, 596, 690, 18, and 62 hectares, respectively, as shown in Figure 1.
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