Development of 3D Inundation Hazard Map

Asia Air Survey Co., Ltd.

Publication date	March 31, 2023 (Posted on December 25, 2023)
Sector	Natural Disasters and Coastal Areas

Company Overview

Climate Change Impacts

In recent years, various issues such as climate change, biodiversity, response to natural disasters, and social infrastructure maintenance and management have become more prominent within and outside of Japan. In 2020, combined disasters such as widespread floods and landslides in the Kyushu and Chubu regions had a major impact on society and the natural environment.

Adaptation Initiatives

We developed a "3D Inundation Hazard Map" that overlays 3D hazard information with a 3D building model with realistic photo textures, in order to provide risk information that is easy to understand. This includes information such as how far an individual’s house will be inundated and which building to evacuate to in the event of a vertical evacuation, which cannot be identified with conventional 2D hazard maps.

The 3D Inundation Hazard Map is created by superimposing the data of "various landmarks (evacuation sites and other major facilities such as roads)," "3D urban city models," and "results of inundation analysis" on the base software of "LandViewer NX" (*1), a highly accurate 3D viewer that we developed (Fig. 1).

• Data acquisition of various landmarks
  Using the latest aerial survey camera, the Oblique Aerial Camera, nadir and four oblique view (forward, backward, leftward, and rightward) images are simultaneously taken in a single shot (Fig. 2). The use of oblique view images enables acquisition of 3D spatial information such as building sides.
• 3D urban city models
  Realistic replication of real space in 3D by employing a multi-view stereo method that automatically extracts pixel feature points from multiple photographs to create a 3D model.
• Results of inundation analysis
  An inundation analysis was conducted utilizing a distributed runoff model (*2). Rainfall data was added to this analytical model to reproduce the surface flow of the watershed during rainfall in detail (Fig. 3). We further improved the accuracy of the surface flow analysis by utilizing microtopographic information obtained from aerial laser measurements. This analysis method is particularly effective for understanding local inundation characteristics (inundation area, inundation depth, inundation time, etc.) caused by torrential rains.

The 3D inundation hazard map created by this project is being used in Koriyama City, Fukushima Prefecture, and a 3D animation of major points in the city created using LandViewer NX is available on the city's website for local residents.

Effects / Expected Benefits

Conventional inundation hazard maps generally superimpose the results of inundation analysis and information on evacuation sites on top of two-dimensional topographic maps and aerial photographs. The 3D Inundation Hazard Map allows the user to switch the time line and check the status of damage (flooding under the floor, flooding above the floor, etc.) from any perspective. Since it is possible to check flood damage over time, the maps can also be used as reference material for evacuation plans.