Proxy-methods representing integrated urban drainage systems in large-scale urban flood models

Research output: Contribution to conferenceAbstractpeer-review


The outputs of hydraulic flood modelling (peak depths, extents and velocities data) are key in producing hazard mapping (DEFRA, 2005). The development of this hazard data is often combined with identification of diverse flooding pathways, potentially from multiple sources, and requires increasingly complex models and computational power. Surface water modelling of rainfall flood hazard should include urban drainage infrastructure representation where possible. Key urban drainage systems includes infrastructure such as sewers, gullies and drains; these components may represent both additional flood pathways and, potentially, hydraulic sources and sinks (DEFRA, 2005).
Typically the dynamic linking of several hydraulic models is employed in order to form an integrated representation of the urban surface and drainage infrastructure. These Integrated Urban Drainage (IUD; DEFRA, 2008) studies now form a critical tool in assessing surface water flood impacts. Yet the data, modelling techniques and the models themselves are frequently poor, unavailable or unfit for purpose (MSfW, 2005). Fundamental to the modelling process is the application of appropriate levels of surface and subsurface component detail, and any associated complexity, and the applied boundary conditions and urban hydrology. This must be balanced against the scale of model of flooding impact reviewed and the levels of model resolution required. Consideration of scale and detail requirements is often overlooked in favour of more multifarious and detailed models, capturing accurately all topography features and drainage infrastructure with high resolution models.
Using a UK-based case study of an urban development area, TUFLOW (WBM PTY, 2008) 2D hydrodynamic software is employed to create a hydraulic, linked 1D-2D IUD model of a dense, city centre, urbanised area. This model is used to assess hydraulic flood hazard results in terms of inundation impact; focusing on extent and maximum depths at the development scale. The 2D surface model representing the urban area (2sq km) is dynamically linked to a large, data rich 1D drainage and subsurface sewer network model. Responding to a simulated statutory 1in100yr return period rainfall flood event (HMSO, 2009), IUD model surface water flooding outputs indicate significant extents of impact, with significant overland flows and surface water flooding observed. Mean depths of surface water flooding between 0.15-0.20m (peak 1.20m) and extents of 167,900 m2 were observed, leading to predictions of significant flood hazard at several key locations. These results form a baseline data against which the proxy approaches are compared.
In seeking new methodologies for simplifying modelling processes for large scale urban flood hazard models yet maintaining the same levels of accuracy as a fully IUD model, this paper reviews proxy approaches focusing on modification of the applied boundary conditions and urban hydrology against the baseline results. Aiming to reduce complexity and, potentially, the need for a subsurface drainage network model, a series of proxy hydrology techniques based on adjusting the applied rainfall are examined. Based on road drainage standards (Highways Agency, 2000; BS, 2008), these rainfall hyetograph proxy-techniques compare and contrast: (1) uniformly applied variations and (2) spatially varied approaches. Impacts on surface waters are considered by examining variation on baseline results and, consequently, model flood hazard predictions.
Results from the extreme rainfall event surface water modelling identify approaches based on a uniformly applied adjustment of the 1in20yr return period Design Flood Frequency event (BS, 2008) as showing most agreement (95%) when compared to the full IUD model. This research’s impact will provide the surface water flood modelling community with alternatives to developing fully IUD models at large scales, offering proxy-modelling approaches suitable for rapid assessment and pilot models. As many water engineering consultancy firms, water utility and service providers, as well as local and regional authorities, are involved in the provision of flood risk assessment mapping and guidance ideally including consideration of the role and impact of drainage systems on flooding, this paper offers timely guidance on possible alternatives to time consuming and resource intensive modelling work.
Original languageEnglish
Publication statusPublished - 15 Apr 2015
EventInternational Water Association UK Young Water Professionals Conference - Technology Innovation Centre, Glasgow, United Kingdom
Duration: 14 Apr 201517 Apr 2015


ConferenceInternational Water Association UK Young Water Professionals Conference
Abbreviated titleIWA UK YWP
Country/TerritoryUnited Kingdom


Dive into the research topics of 'Proxy-methods representing integrated urban drainage systems in large-scale urban flood models'. Together they form a unique fingerprint.

Cite this