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

T I Skrede; V Tørudstad; V Pons; K Alfredsen; T M Muthanna

doi:10.1016/j.jenvman.2023.118672

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

J Environ Manage. 2023 Nov 15:346:118672. doi: 10.1016/j.jenvman.2023.118672. Epub 2023 Sep 28.

Authors

T I Skrede¹, V Tørudstad², V Pons², K Alfredsen³, T M Muthanna⁴

Affiliations

¹ Department of Civil Engineering, Norwegian University of Science and Technology (NTNU), S.P. Andersens Veg 5, 7031, Trondheim, Norway; Norconsult AS, Vestfjordgaten 4, 1338, Sandvika, Norway. Electronic address: thea.ingeborg.skrede@norconsult.com.
² Department of Civil Engineering, Norwegian University of Science and Technology (NTNU), S.P. Andersens Veg 5, 7031, Trondheim, Norway.
³ Department of Civil Engineering, Norwegian University of Science and Technology (NTNU), S.P. Andersens Veg 5, 7031, Trondheim, Norway. Electronic address: Knut.Alfredsen@ntnu.no.
⁴ Department of Civil Engineering, Norwegian University of Science and Technology (NTNU), S.P. Andersens Veg 5, 7031, Trondheim, Norway. Electronic address: tone.muthanna@ntnu.no.

PMID: 37776813
DOI: 10.1016/j.jenvman.2023.118672

Abstract

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.

Keywords: Floodways; Geographical information system (GIS); Stormwater management; Sustainable drainage systems; Urban flood resilience; Urban flooding.