Stochastic evaluation of the impact of sewer inlets’ hydraulic capacity on urban pluvial flooding

  • João P. Leitão
  • Nuno E. Simões
  • Rui Daniel Pina
  • Susana Ochoa-Rodriguez
  • Christian Onof
  • Alfeu Sá Marques


Sewer inlet structures are vital components of urban drainage systems and their operational conditions can largely affect the overall performance of the system. However, their hydraulic behaviour and the way in which it is affected by clogging is often overlooked in urban drainage models, thus leading to misrepresentation of system performance and, in particular, of flooding occurrence. In the present paper, a novel methodology is proposed to stochastically model stormwater urban drainage systems, taking the impact of sewer inlet operational conditions (e.g. clogging due to debris accumulation) on urban pluvial flooding into account. The proposed methodology comprises three main steps: (i) identification of sewer inlets most prone to clogging based upon a spatial analysis of their proximity to trees and evaluation of sewer inlet locations; (ii) Monte Carlo simulation of the capacity of inlets prone to clogging and subsequent simulation of flooding for each sewer inlet capacity scenario, and (iii) delineation of stochastic flood hazard maps. The proposed methodology was demonstrated using as case study design storms as well as two real storm events observed in the city of Coimbra (Portugal), which reportedly led to flooding in different areas of the catchment. The results show that sewer inlet capacity can indeed have a large impact on the occurrence of urban pluvial flooding and that it is essential to account for variations in sewer inlet capacity in urban drainage models. Overall, the stochastic methodology proposed in this study constitutes a useful tool for dealing with uncertainties in sewer inlet operational conditions and, as compared to more traditional deterministic approaches, it allows a more comprehensive assessment of urban pluvial flood hazard, which in turn enables better-informed flood risk assessment and management decisions.


Sewer inlets Clogging Urban pluvial flooding Flood hazard Stochastic risk analysis GIS 



Rui Pina acknowledges the financial support from the Fundação para a Ciência e Tecnologia—Ministério para a Ciência, Tecnologia e Ensino Superior, Portugal [SFRH/BD/88532/2012]. Susana Ochoa-Rodriguez acknowledges the support of the Interreg IVB NWE RainGain project. Special thanks are due to AC, Águas de Coimbra for providing rainfall and sewer data of the pilot location and to Innovyze for providing research licences of InfoWorks ICM software.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  1. 1.Eawag: Swiss Federal Institute of Aquatic Science and TechnologyDübendorfSwitzerland
  2. 2.MARE, Department of Civil EngineeringUniversity of Coimbra, Rua Luís Reis Santos - Pólo IICoimbraPortugal
  3. 3.Department of Civil and Environmental EngineeringImperial College LondonLondonUK

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