Mapping surface flow pathways in urban areas using UAV-based thermal imaging in combination with flooding experiments

In recent years, heavy rainfall events and resulting flash floods have increasingly caused widespread damage to public and private technical infrastructures in Germany. Flood events occurred often at smaller water bodies or as hillslope surface runoff far from the actual watercourses. During extreme events technical measures are often overloaded, so that in addition to local property protection planned emergency runoff pathways can be designated as an essential element of water-sensitive urban development.

The research project ‘Urban Flood Resilience - Smart Tools’ (FloReST), funded by the German Federal Ministry of Education and Research (BMBF), is exploring those measures to increase the resilience of infrastructures after flash floods.

The aim of this study is the development and demonstration of an experimental setup to improve high-resolution digital mapping of existing surface flow pathways in urban areas using UAV-based thermal imaging in combination with flooding experiments. For this purpose, already known critical points, i.e., dysfunctional emergency drainage sections in the urban infrastructure within the City of Trier, Germany were identified.

Within this setting, during relatively warmer or colder days, respectively, we use artificial water releases as a thermal marker of the potentially emerging surface flow pathways. Combining UAV-based visual (RGB) and thermal (infrared) imaging, high-resolution mapping of the potential surface flow paths and their Thalweg is then possible.

Using a hydrological model allows for determining extreme discharges potentially generated in the connected catchment areas. Based on a digital terrain model the locally surveyed water levels and flow paths are then scaled up to potentially occurring water levels during extreme discharges. Depending on the occurrence probability of the extreme discharges a set of high-resolution GIS-datasets of the emergency surface flow pathways around objects at risk of flooding can be generated.