Homogeneous road segment mapping

4.3 Homogeneous road segment mapping

  Roads are also important element-at-risk to consider next to buildings. Therefore, it is important to assess the susceptibility of multi-hazards for road segments within hazards prone area. Different road segments may experience different degree of susceptibility by different hazard types, and therefore the correct subdivision of the road network into more or less homogenous segments is important. However, in mountain areas, the road alignment and it’s topology is not as simple as in flat area. Generally, most of road segments in a mountain region are built in sloping terrain with heterogeneous land cover and geology, resulting in road cuts, and fills that are not present in any of the input maps. Therefore, an automated approach of homogeneous road segments is difficult and also required detailed information. In this study Roads are also important element-at-risk to consider next to buildings. Therefore, it is important to assess the susceptibility of multi-hazards for road segments within hazards prone area. Different road segments may experience different degree of susceptibility by different hazard types, and therefore the correct subdivision of the road network into more or less homogenous segments is important. However, in mountain areas, the road alignment and it’s topology is not as simple as in flat area. Generally, most of road segments in a mountain region are built in sloping terrain with heterogeneous land cover and geology, resulting in road cuts, and fills that are not present in any of the input maps. Therefore, an automated approach of homogeneous road segments is difficult and also required detailed information. In this study

  (a) Rock cliffs with open joint

  (b) Damaged section due to landslide

  (c) Road surface damaged due to bad drainage

  (d) Road passes through an active landslide

  Figure 4.18: Road condition of some segments of Pasang Lhamu Highway after the 2015 earthquake Experiencing the actual field condition of the important road, an attempted was taken to perform manually

  approach road segments analysis. To avoid the complexity of automated road segment analysis, only a manual approach was used to generate homogenous road segment. To do that, the results of automated terrain unit mapping (which has the information of slope steepness, land cover and hazard runout path) was combined with information on road cuts, drainage and landslides within a 3D oblique view of Google Earth to digitize the different homogeneous road segments. The road segments are classified into six categories with unique characteristic as shown in Table 4.4.

  Based on the above classification, the Pasang Lhamu Highway was manually segmented by on screen digitization of Google Earth images (Figure 4.19). It shows that most of the segments don’t have any disruption from surrounding which has been classified as normal segment. By visualizing the slope map with road layer, it is observed that this class road segments are located almost within moderate slope

  steepness (between 15 0 – 35 0 ) region. Although, this type of road segment doesn’t have any disturbance

  from landslides or rockfall or road cuts, the road surface condition is very poor as because most of the parts blacktop surfaces was damage due to heavy traffic movement.

  Table 4.4: Classification of manual homogeneous road segment

  Type of Road segment

  Criteria

  Normal segment