Application of LiDAR Data in combination with Drone Aerial Photography for Geohazard Assessment and Mitigation in Philippine Infrastructures

Author: Ramon D. Quebral (PhD), Roy Anthony C. Luna (MSCE), Arlene Q. Buenaventura, and Trisha Leigh O. Lunas, Ramon D. Quebral (PhD), Roy Anthony C. Luna (MSCE), Arlene Q. Buenaventura, and Trisha Leigh O. Lunas

Presenter: Ramon D. Quebral

Several infrastructures in the Philippines, including power plants, transmission lines, roads and bridges, are located in areas that are highly vulnerable to meteorological and seismic hazards. Typhoons and monsoon rains regularly trigger landslides, flash floods and debris flows. The magnitude 6.5 Leyte earthquake of July 6, 2017 along the main trace of the Philippine Fault triggered landslides and caused extensive damage to several facilities due to ground rupture, ground shaking, and earthquake-induced landslides, resulting to shutdown of power plants and closure of roads.

In the past, site assessments and geohazard assessments were carried out using enlarged 1:50,000 scale topographic maps with 20-meter contour intervals and 1950s high altitude black and white aerial photographs which often had cloud covers. With the LiDAR technology, detailed topographic maps with one (1) meter contour intervals and low altitude color aerial photographs have become available. Added advantages were the capacity to see through the tree canopy and the absence of cloud covers on the photographs.

With the refinement in available remote sensing documents, new features are now being recognized:

Scars of old landslides. Although smaller in dimensions since the larger failures might be reflected in existing topographic maps, the landslide density shows which terrains are generally more susceptible to slope failure.
Gullies. Previously masked by the tree canopy, these waterways serve as pathways for flash floods, debris flows and siltation.
Gully erosion. Areas of active gully erosion are sources of material for debris flows and massive siltation. Direction of propagation of the gully erosion can be predicted and seepages can be actually identified.
Quaternary faults. Although not significant enough to be earthquake generators, some geologic structures still have to be crossed by alignment of roads and pipelines.

Having conducted a geohazard assessment and after considering other sources of information such as site development, slope, geology or hydrothermal alteration, it is now possible to assign risk ratings and prioritize sites for engineering. In the case where new facilities are proposed, the entire exercise serves as a planning tool.

Following the July 6, 2017 earthquake, LiDAR data, coupled with drone aerial photography, were used for a rapid post-earthquake damage assessment even in areas rendered inaccessible by earthquake-induced landslides. The ground rupture was recognized. Damage caused by landslides were rapidly assessed and allowing faster engineering of the slope failures. In case relocation or realignment was necessary, the documents served as tools in the assessment of the new sites.

Conference/s:

International Conference on GIS and Geoinformation Zoning for Disaster Mitigation (GIZ2018) – Auckland, New Zealand

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