From flood paths to floodways, an efficient method to map, identify and evaluate suitable floodways: A case study from Trondheim, Norway

• Published in: Journal of environmental management Vol. 346; p. 118672
• Main Authors: Skrede, T.I., Tørudstad, V., Pons, V., Alfredsen, K., Muthanna, T.M.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15-11-2023
• Subjects: Floodways; Geographical information system (GIS); Stormwater management; Sustainable drainage systems; Urban flood resilience; Urban flooding; Sustainable drainage systems; Floodways; Urban flooding; Urban flood resilience; Geographical information system (GIS); Stormwater management
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2023.118672

Due to climate change and rapid urbanisation, many Norwegian cities and urban areas suffer from pluvial flooding caused by intense rainfall exceeding the capacity of the stormwater management system. This results in increased runoff rates, volumes and peak flows in the drainage network. In response to these challenges, the authors explore the potential of utilising the urban surface's ability to transport floodwater as an integral component of the stormwater infrastructure. When the capacity of the stormwater drainage system is exceeded, the overland flow paths transporting floodwater are considered a part of the stormwater management system, as floodways. The study proposes a spatial GIS method to map existing drainage lines and identify existing surface areas that function as floodways, combined with an automated process to identify which drainage lines could be implemented as stormwater management measures. Critical points are introduced to assess the floodways' potential hazards, combined with a classification method to evaluate and sort floodways. A case study from Trondheim, Norway, was used to demonstrate how drainage lines can be identified as floodways using the proposed method. The case study is also used to illustrate how a GIS-based analysis can be extended from identifying to evaluating floodways and whether GIS is sufficient for floodway evaluation. The method enables urban planners and municipalities to identify which areas of the urban surface already function as floodways during extreme events, and to prioritise measures to secure such areas and increase the city's flood resilience. The results highlight the need to assess existing areas that function as floodways, and to implement and design needed areas as floodways. GIS-based methods combined with an evaluation scheme can be an adequate tool to map and evaluate floodways in urban areas. When using GIS-based methods, however, the corresponding hazard potential, and also the uncertainty of the floodway's spatial placement, should be considered.
•A new approach to controlled urban flooding and utilising urban flood paths can increase the stormwater system's functionality and reduce undesirous damage from extreme precipitation events.•In this study, we present an automated spatial GIS-based method to find flood paths and existing areas that function as a transporter of floodwater.•The proposed method allows urban planners and water managers to map, identify, and evaluate which surface and flood paths already function as floodwater transporter.•The results highlight the potential of utilising existing flood paths and the hazard of dormant unmanaged flood paths.