Exchange between drainage systems and surface flows during urban flooding: Quasi-steady and dynamic modelling in unsteady flow conditions

Vasileios Kitsikoudis,Sebastien Erpicum,Matteo Rubinato,James D Shucksmith,Pierre Archambeau,Michel Pirotton,Benjamin Dewals

doi:10.1016/j.jhydrol.2021.126628

Vasileios Kitsikoudis, Sebastien Erpicum + Show 5 more

Open Access

https://doi.org/10.1016/j.jhydrol.2021.126628

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Abstract

The accurate modelling of urban flooding constitutes an integral part of flood risk assessment and management in residential and industrial areas. Interactions between drainage networks and surface runoff flows are commonly modelled based on weir/orifice equations; however, this approach has not been satisfactorily validated in unsteady flow conditions due to uncertainties in estimating the discharge coefficients and associated head losses. This study utilises experimental data of flow exchange between the sewer flow and the floodplain through a manhole without a lid to develop two alternate approaches that simulate this interaction and describe the associated exchange flow. A quasi-steady model links the exchange flow to the total head in the sewer pipe and the head losses in the sewer and the manhole, whilst a dynamic model takes also into account the evolution of the water level within the manhole at discrete time steps. The developed numerical models are subsequently validated against large-scale experimental data for unsteady sewer flow conditions, featuring variable exchange to the surface. Results confirmed that both models can accurately replicate experimental conditions, with improved performance when compared to existing methodologies based only on weir or orifice equations.

Highlights

Urban flooding events tend to become more frequent due to the in crease of urbanization and changes in rainfall patterns linked with climate change
This study developed a quasi-steady and a dynamic model for the determination of the exchange discharge between a sewer pipe and the surface floodplain through a manhole in a typical setup of an urban drainage system
When compared to the commonly utilized weir/orifice approach to calculating exchange volumes (Nasello and Tucciarelli, 2005; Seyoum et al, 2012), the quasi-steady model explicitly accounts for the head losses along the flow path from the sewer pipe to the surface and links the exchange flow to the total head in the sewer pipe minus the occurring head losses

Summary

Introduction

Urban flooding events tend to become more frequent due to the in crease of urbanization and changes in rainfall patterns linked with climate change. Hydrodynamics associated with flood events is complex because such events commonly include in teractions between surface flows/runoff and flows within urban drainage networks (Schmitt et al, 2004; Rubinato et al, 2019). The risk of flooding is commonly evaluated using hydraulic modelling tools, which utilize a number of empirical and semi-empirical relationships (and associated parameters) to simulate processes such as runoff and frictional/turbulent energy losses, including relationships to describe interactions between surface flows and drainage networks (Djordjevic et al, 2005; Leandro et al, 2009; Seyoum et al, 2012). Typical datasets consisting of point depth of flow obser vations during flood events are insufficient to fully overcome parameter non-identifiability/equifinality issues in complex flood models, or pro vide a detailed evaluation of modelling representations for individual model components such as above/below ground flow exchange (Beven, 2006; Dottori et al, 2013; Arrault et al, 2016)

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