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Impact of Urbanization on Flooding
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
As reported by “World Population Prospects” (United Nations, 2017), the world population in urban areas can be expected to add close to 1.5 billion people in the next 15 years, and three billion by 2050, but the world's rural population has already stopped growing. Although the increasing concentration of people in urban settlements can facilitate economic and social development with good planning and governance, it also offers opportunities to threaten sustainable development when the necessary infrastructure is not developed to protect the environment and ensure that the benefits of city life are equitably shared. For example, urban flooding occurs due to the overflow of rivers and lakes, snowmelt, stormwater, water released from damaged water mains, or backed-up water from sewer pipes, toilets, and sinks. In addition, floodwater constitutes a hazard to both the population and infrastructure. The recently catastrophic flooding in the Houston metropolitan area (Figure 5.1) was caused by Hurricane Harvey in August 2017. This disaster highlights the impacts of urbanization on flooding.
State of the art in urban flood modelling
Published in Vorawit Meesuk, Point Cloud Data Fusion for Enhancing 2D Urban Flood Modelling, 2017
Urban flooding can happen when discharges exceed riverbank capacities leading to overflows from rivers and reservoirs (fluvial floods); or when intensive rainfalls exceed capacities of drainage systems (pluvial floods); or when massive coastal surges and high tides strike shorelines (coastal floods); or when combinations of these events occur. Hydrodynamic models can play an important role in simulating water level rise, estimating the evolution of inundation extents, and indicating hazard areas of high floods. These simulation results can adequately be used as supporting information for evaluating flood damages from the past, or for predicting floods in the future. An appropriate quality of urban-flood simulation results should replicate and represent key behaviours of flow dynamics as close to reality as possible. In this chapter, approaches to urban flood modelling are introduced in Section 2.1. Principles of 1D urban flood models and quasi 2Dmodelling approaches are described in Section 2.2 and 2.3, resp. Principles of 2D urban flood models (Section 2.4) and advances in coupled 1D-2D models (Section 2.5) are then given. Some simulation results of hypothetical cases are compared in Section 2.6. Issues concerning complex urban flood modelling are discussed in Section 2.7.
Coastal megacities, environmental hazards and global environmental change
Published in Mark Pelling, Sophie Blackburn, Megacities and the Coast, 2014
Urban flooding has multiple, often interacting causes, mainly storm surges, river overflows or intense rainfall. Coastal regions are particularly vulnerable to the impact of urban flooding, due to a combination of natural and man-made factors (Cashman, 2011; Nicholls, 2004; Wisner et al., 2004). Drains are often blocked by solid waste and debris, drainage systems are inadequate, and urban land cover is generally impermeable and compact, thus limiting space for water storage (Sherbini et al., 2007). Floods can also increase pollutant levels in water supplies (e.g. reservoirs, rivers), and disproportionately affect those settlements located on floodplains (Rosenzweig et al., 2011).
Sub-catchment-based urban flood risk assessment with a multi-index fuzzy evaluation approach: a case study of Jinjiang district, China
Published in Geomatics, Natural Hazards and Risk, 2023
Xuejin Ying, Ting Ni, Mingxia Lu, Zongmin Li, Yi Lu, Olusola Bamisile, Mark Pelling
Urban flooding occurs when the excess surface runoff caused by floods or rainstorms surpasses the capacity of the urban drainage system, which is the most frequent and serious natural hazard in cities worldwide. Globally, 20% of urban residents are exposed to a 100-year flood, and more than 600 cities are likely to be completely inundated by a 100-year flood (United Nations Human Settlements Programme (UN-Habitat) 2022). Urban flooding events result in traffic network paralysis (Kogure 2016; Zhou et al. 2021), property damage to residential and public buildings (Jakoubek 2007), and even casualties (Xu et al. 2022). Globally, coastal cities are hotspots that face high economic and non-economic losses from urban flooding. However, with intensifying climate change and increasing probability of extreme precipitation, many inland cities in China face more flooding hazards than they have not previously had the opportunity or rarely encountered (Ministry of Water Resources of the People’s Republic of China 2019). On July 20 last year, a heavy rainstorm flooded the whole Zhengzhou city and caused 380 deaths or missing and 40.9 billion CNY in direct economic losses (State Council Disaster Investigation Team 2022). Compared with coastal cities, the natural drainage capacity and the standard of urban drainage infrastructure in inland cities are generally lower. Therefore, it is necessary to analyze the spatial and temporal distribution of flooding in inland cities, identify potential high-risk areas at the local level, and develop suitable adaptation strategies and measures (IPCC 2022; Jia et al. 2022).
LID coupled design of drainage model using GIS and SWMM
Published in ISH Journal of Hydraulic Engineering, 2021
The conventional solution to minimize urban flooding involves increasing the capacity of the drainage system by upgrading or expanding the existing system. However, this solution becomes impractical in most of the highly urbanized areas due to its space requirement. Thus, there is need to employ some new best management practices (BMPs) for storm water management, which helps to minimize urban flooding by reducing the total runoff volume (Jia et al. 2012) and creates sustainable development by accelerating the ground water recharge processes. Low impact development (LID) is one of the most widely used source control practice for reducing storm water runoff and imperviousness. The LID helps to achieve pre-development conditions and reduces runoff by providing storage, retention, infiltration, ground water recharge and evapotranspiration processes (Palla and Gnecco 2015). There are several types of LIDs are being practiced (e.g. pervious pavements, green roofs, grass swales, bio-retention cells, rain barrels or rooftop rainwater harvesting, detention ponds, etc.) which are proven to be effective for minimizing the urban flooding by reducing total flood volume and peak flow rates (Jia et al. 2012; Qin et al. 2013). The implementation of such techniques in combination is more effective as compared to a single LID (Guan et al. 2015). However, an optimal combination of different LIDs is depended upon the specific project goals and local site conditions (Li et al. 2019).
Assessment of the growing threat of urban flooding: a case study of a national survey
Published in Urban Water Journal, 2021
Jayton L. Rainey, Samuel D. Brody, Gerald E. Galloway, Wesley E. Highfield
This study considers urban flooding as impacts from inundation exacerbated or caused by the human-built environment. FEMA defines urban flooding as ‘the inundation of property in a built environment, particularly in more densely populated areas, caused by rain falling on increased amounts of impervious surfaces and overwhelming the capacity of drainage systems. The definition excludes flooding in undeveloped or agricultural areas, but instead focuses on situations in which stormwater enters buildings through (a) windows, doors, or other openings; (b) water backup through pipes and drains; (c) seepage through walls and floors’ (State of Illinois, Department of Natural Resources 2015). The definition has been expanded to include specific issues, such as sewer water backing up into homes, water seeping through foundation walls, clogged street drains, and overflow from sound walls, roads, or other barriers that restrict stormwater runoff. Urban flood loss related to the built environment is caused by multiple triggers; aging and inadequate drainage systems, failure to maintain drainage systems, sewage and stormwater backups, changes in overland flow conditions, and increases in local and region runoff.