Kenta Kondo

Construction of Salt Damage Environmental Assessment Map and Its Implementation into a Digital 3D City Model

Fuminori Nakamura

In coastal areas from Hokkaido to Hokuriku, strong winter monsoon winds transport sea-salt aerosols inland, accelerating salt-induced deterioration of concrete structures. Bridge design codes such as the Specifications for Highway Bridges classify these zones as severe salt environments with high airborne salt. To maintain the many structures concentrated along shorelines, practical methods are needed to predict salt exposure and communicate results for maintenance planning.
This study aims to provide a simple way to identify the spatial distribution of airborne salt deposition in coastal settings. Focusing on Niigata and Toyama Prefectures in the Hokuriku region, we developed a salt-damage environmental assessment map that incorporates surrounding environmental conditions, and examined its relationship with existing bridge inspection records. To promote broader use, we also integrated the map with a digital 3D city model (PLATEAU) and explored visualization methods. The assessment map was built from the planar distribution of deposition while accounting for local meteorological (wind) and wave conditions, shielding effects of obstacles such as wave-dissipating blocks and windbreak forests, and distance from the shoreline. Deposition was estimated using an empirically derived equation based on field surveys of airborne salt conducted in coastal areas of the Tohoku and Hokuriku regions. Bridge condition information was taken from the MLIT bridge data platform, xROAD. For 3D visualization, we used Niigata City data from the MLIT-published PLATEAU 3D city model.
The results show that the proposed map captures regional differences in deposition driven by wind and wave climates and enables rapid evaluation that reflects obstacles and coastal distance. Overlaying bridge inspection data on the map makes it easy to confirm salt exposure for each bridge alongside inspection outcomes, supporting more efficient maintenance and management. Visualization in a 3D city model further helps interpret surrounding topography and assess airborne salt impacts in complex coastal environments.