Surface water flooding due to the inadequacy of local drainage is a significant UK concern (DEFRA, 2005; POST, 2007). Urban flood modelling and mapping are typified by characteristic terrain difficulties (Charteris et al., 2001). These difficulties include topographic complexity (road crests and gutters; raised house pads); infrastructure (including houses, fences, garden beds, etc); and, complex underground pipe networks (Charteris et al., 2001; Mark et al., 2004a & b; Hunter et al., 2008; Neelz & Pender, 2007; Syme 2008). Designed to mitigate surface waters, drainage systems play a central role and include key features such as sewer pipes, kerbside gutter channels, gully pots and drains. These systems are often highly complex and spatially varied, simultaneously representing alternate flood pathways, hydraulic sinks and, potentially, additional flood sources (DEFRA, 2005). Accurate flood mapping (DEFRA, 2012) requires data rich modelling and, potentially, dynamic linking of models to form an integrated representation of urban surface and subsurface systems (DEFRA, 2005). Predicted data serves to estimate potential physical impacts, assessing likely damage to buildings and urban infrastructure (Kelman & Spence, 2004); or enhancing mapping further with peak velocities to provide detailed assessment of hazards to people (DEFRA, 2006; 2012). However such Integrated Urban Drainage (IUD; Gill, 2008) approaches are resource expensive (time and data requirements). Research into approaches offering more efficient representations is considered essential and timely. Therefore, the possible inclusion of proxy-model approaches offers an alternate tool for rapid hazard appraisal. Using a UK case-study approach, this Thesis addresses IUD modelling deficiencies through two specific aims: (i) examining IUD model development and impact on hazard prediction and, (ii) investigation of more resource-efficient proxy model approaches to the fully Integrated Urban Drainage model. Using TUFLOW hydrodynamic software (WBM, 2008), an IUD model of a dense UK urban area (2 sq km) is developed and examined. Firstly through small-scale IUD modelling showing improved IUD model performance with kerbside drainage and flow capture systems, particularly when based on depth-inflow criteria and, secondly, through enhanced infrastructure representation. Outputs are examined for both fluvial and pluvial source floods of the statutory 1% AEP event (HMSO, 2009). Data indicates significant IUD impact in terms of extent reductions of 56% (fluvial) and 30% (pluvial), and consequently mean peak depth reductions of 33% (fluvial) and 20% (pluvial) flood events. Velocity impacts are shown to be near negligible, recording less than 1% variation for each flood event. Examination of IUD proxy-model approaches identified inappropriate use for fluvial flood event modelling. Pluvial event surface water modelling identified approaches based on a uniformly applied adjustment of the 5% AEP Design Flood Frequency event (BS, 2008) showed most (95%) agreement to the full pluvial IUD model. This Thesis’ outcomes have supported current flood risk modelling and appraisal practice by Capita Symonds and WBM Pty Ltd (TUFLOW authors). Notable recent projects include Hereford, England (2010), Gold Coast City, Australia (2012) and Christchurch, New Zealand (2014).
|Place of Publication||Glasgow|
|Publication status||Published - 8 Jun 2015|
- urban drainage systems
- proxy-model methodologies
- surface water flooding
- urban flooding