Identifying High-Water Marks in Post-Disaster Reconnaissance Using Multispectral Imagery

Flooding annually causes thousands of fatalities and billions of dollars in damage globally, while predicting future floods has become increasingly challenging due to changing urban environments and land surface conditions. Furthermore, due to climate change and associated shifts in rain patterns, severe floods are likely to increase. High-water marks collected post-flooding provide key information for advancing our understanding of flood impacts and developing mitigation strategies. However, collecting high-water marks after a flooding event can be complicated due to access issues related to destroyed infrastructure, and detecting high-water marks becomes increasingly difficult with time passing after a flood event. This leads to significant loss of data or risk to personnel entering these recently flooded areas. Here, we present initial data demonstrating the use of multispectral imagery in rapidly collecting and mapping high-water marks post-flooding for different commonly used building materials. This work builds on the exploratory deployment of multispectral imagery during the Geotechnical Extreme Event Association (GEER) response to the July 14, 2021, Western European flood. Additional images were collected in a controlled lab setting to test these initial observations and the potential to extract high-water marks using multispectral imagery of materials commonly used in building façades. These materials included clay bricks, plywood, maple and pine planks, concrete, and steel. Materials were soaked for 48 h after which images were collected at predetermined specific time intervals to establish if and how the signal associated with the high-water mark evolved. For all materials, with the exception of steel, the high-water mark was clearly expressed in the multispectral imagery. Specifically, the blue band (wavelength 465−485 nm) and red-edge band (wavelength 712−722 nm) show the clearest manifestation. Current research is focusing on how the high-water mark can be significantly enhanced and clearly identified through linear combinations of spectral bands. This will enable the development of material-specific indices for rapidly mapping spatially varying flood depths and extents in urban areas during post-disaster reconnaissance. Furthermore, follow-on testing will use sediment-laden water such that the influence of soil adhering to structure surfaces can be incorporated into identifying high-water marks on various structure and foundation surfaces.