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Impact of pluvial flooding and adaptation in urban transport systems

Lookup NU author(s): Dr Maria Pregnolato, Alistair Ford, Dr Oliver Heidrich, Professor Richard Dawson


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Motivation and aim Short duration, high intensity rainfall can be extreme events causing significant disruptions to transport networks and traffic operations, and climate change is projected to increase the magnitude and impact of such extreme events. Despite the severity of the phenomenon has been acknowledged by Local Authorities and the public, disruption costs of flooding are currently calculated using silo-based approaches [1]. This paper presents an integrated framework that couples simulations of flooding and transport networks, integrating hazard, vulnerability, impact and consequences [2]. It calculates the impacts of disruption and the effectiveness of potential adaptation options, like traditional (grey infrastructure e.g. floodwalls) and alternative measures (blue-green infrastructure e.g. green roofs, ponds). The findings will support local authorities in making improved business cases to adapt urban infrastructure and road networks to extreme flooding events. Methodology This study advances an integrated framework [3] to quantify the flooding risks from extreme rainfall, measured in terms of expected travel time across the road network. The method is driven by the Flood Estimation Handbook (FEH) methodology that is combined with a high resolution urban flood model, to provide depth and velocity of floodwater [4]. Hazard layers and empirical analysis of vehicle speeds in different depths of flood water are used to determine the impact of a given event on journey times, which results in a transport accessibility model. A damage function, constructed from a range of observational and experimental data sources is used to relate flood depth to vehicle speed. This allows a more realistic approach than the typical method of categorizing a road as either ‘blocked’ or ‘free flowing’. To estimate the costs and rank the adaptation options a range of options are applied across the network. A criticality index is presented which demonstrates a metric to prioritize intervention options in the road network. The benefit of climate adaptation options are measured over 50 years. Using the Green Book method of Net Present Value (NPV) to compute the long term costs and benefits, discounted to present day rates to account for inflation [5]. The NPV of the benefits in terms of risk reduction, NPVr, is calculated by summing over the disruption cost, D(x), and likelihood, ρ(x) of a range of flood events, for a life-span N of 50 years and a discount rate r of 3%: NPVr= i=1Nρ(li)D(li)dx(1+r)i (1) Results and conclusion The framework is demonstrated on Newcastle-upon-Tyne in the UK and shows that adaptation decreases delays to travelers under all scenarios. For example, grey infrastructure measures, such as the improvement of the drainage system capacity, across the network can reduce the impact by up to 50% for 1 in 10 years event (low intensity, high probability event). Results are compared by computing the NPVr for the different considered strategies, developing a tool to support decision-makers in prioritizing investment to maximize returns and make the business case. 1. Aerts, J., et al., Climate Adaptation and Flood Risk in Coastal Cities. 2013, Taylor and Francis. 2. Pregnolato, M., et al., Potential impact of climate change on flooding disruptions to urban transport networks. ASCE Journal of Infrastructure Systems, 2017. Accepted. 3. Walsh, C.L., et al., A spatio-temporal modelling framework for the integrate assessment of cities, in Earth Systems Engineering 2012: A technical symposium on systems engineering for sustainable adaptation to global change. 2012, Centre for Earth Systems Engineering Research, Newcastle University: Newcastle upon Tyne, UK. 4. Kjeldsen, T.R., The revitalised FSR/FEH rainfall/runoff method, in Flood Estimation Handbook. 2007, Centre for Ecology and Hydrology. 5. HM Treasury, The Green Book: appraisal and evaluation in central government. . 2013, HM Treasury: London (UK).

Publication metadata

Author(s): Pregnolato M, Ford A, Heidrich O, Dawson R

Publication type: Conference Proceedings (inc. Abstract)

Publication status: Published

Conference Name: 7th International Conference on Flood Management (ICFM7)

Year of Conference: 2017

Print publication date: 05/09/2017

Online publication date: 01/09/2017

Acceptance date: 01/03/2017