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Flash Flood
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
The floods outlined above occurred in rivers and had a meteorological origin. Intense rainfall also causes direct flooding as surface water (or pluvial flooding), principally in urban areas, before the water reaches a river. In addition, flash floods in rivers have a range of different causes, notably from the failure of natural barriers including landslide dam breaks, glacial lake outburst floods (GLOFS or jökulhlaups), and the release of water from ice jams as well as the failure of constructed barriers such as dams and embankments. Each of these types or sources of flash floods is exemplified, described, and analyzed in this chapter to illustrate the range of hydrological behavior and catchments typically affected. Examples cited here provide methods of analysis that may have wider application. In conclusion, a further flash flood definition is attempted which covers the full range of flash flood characteristics and sources.
Introduction
Published in Polpat Nilubon, Opportunistic Adaptation, 2021
Apart from climate change, there are other factors contributing to an increase of flood impacts. These are related to the location, composition and distribution of the built-up areas in urban agglomerations and thus to urban planning. Planning practices of urban developments and redevelopments often ignore flood hazards and therefore are responsible for a substantial increase in flood risk which is likely to exceed the expected impacts of climate change (Storch and Downes, 2011). Furthermore, governments tend to have a ‘silo orientation’ meaning they often consider existing problems from a single dimension leading to responses which are suboptimal. A typical domain where such a multiple perspective is needed is disaster management, requiring the involvement of multiple disciplines, governance levels and spatial scales (Radhakrishnan et al., 2017; Pathirana et al., 2017). Pluvial flooding is often perceived as a result of an insufficient discharge capacity provided by the drainage system, which leads to the single conclusion that its capacity should be increased (Yin and Li, 2001; Miller, 2015; Wei et al., 2019).
Environmental and health-related building problems
Published in Duncan Marshall, Derek Worthing, Roger Heath, Nigel Dann, Understanding Housing Defects, 2013
Duncan Marshall, Derek Worthing, Roger Heath, Nigel Dann
A property does not need to be near a river or on the coast to be at risk. Most buildings are at a higher risk of pluvial (i.e. surface water) flooding rather than fluvial flooding (i.e. river or coastal flooding): Pluvial floodingoccurs when: (!) a short period of intense rainfall overwhelms the existing drainage systems; (2) a blockage occurs; or (3) poor maintenance creates a problem. This is commonly called a flash flood and is more likely to occur than fluvial flooding.Fluvial floodingis as a result of: (!) heavy rainfall causing a river or stream to overflow and burst its bank; or (2) a high tide or severe weather overwhelming sea defences. Often, a high tide and severe weather coincide to create a storm or tidal surge. Rising sea levels may increase the likelihood of coastal flooding in the future.
Flood hazards in urban environment
Published in Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, 2023
Liang Gao, Limin Zhang, Yang Hong, Hong-Xin Chen, Shi-Jin Feng
Floods are the most frequent disasters affecting urban areas worldwide. Urban flooding generally includes pluvial, fluvial, coastal and groundwater flooding. Pluvial flooding occurs when the surface runoff due to rainfall overwhelms the capability of the drainage system. Fluvial flooding occurs when the surface runoff in a river or lake exceeds the capacity of natural or artificial channels to accommodate the flow. Coastal flooding is due to tidal surges and waves. Groundwater flooding results from high ground water levels. An urban flood event can stem from a complex combination of the above causes, but storm is always the most important triggering factor, which brings abundant rainfall. A large number of catastrophic storm-induced urban flooding disasters have been reported around the world, such as floods in Mumbai (2005) and Chennai (2015) in India, in New Orleans (2005), New York (2012) and Houston (2017) in the United States of America and in Fuzhou (2005), Beijing (2012), Macau (2017) and Zhengzhou (2021) in China (Table 1). These urban disasters have caused numerous casualties and severe damages.
Impact-based classification of extreme rainfall events using a simplified overland flow model
Published in Urban Water Journal, 2023
Urban pluvial floods are caused by extreme rainstorms, with rainfall rates exceeding the capacity of urban drainage systems, and causing severe damage to urban infrastructure (Rözer et al. 2021). They are seen by many as invisible hazards (Forzieri et al. 2018; Jacobs et al. 2018; Moftakhari et al. 2017; Suarez et al. 2005), as they can often strike with little warning in areas with no recent record of flooding. The instances of pluvial flooding are rising due to a combination of global climate change, urbanisation, and a lack of investment in sewer and drainage infrastructure (Westra et al. 2014). Although many modelling software packages are available to simulate pluvial flooding in urban catchments (e.g. InfosWorks ICM (Innovyze 2020), SWMM (Rossman 2004), MOUSE (DHI 2000)), and many methods exist to describe the underlying hydrological processes (c.f. Salvadore, Bronders, and Batelaan 2015), predicting the extent and severity of pluvial floods remains challenging. This is due to an incomplete understanding of the interactions between urban and natural hydrological systems, as well as the high degree of uncertainty (Salvadore, Bronders, and Batelaan 2015).
Coping with and adapting to urban floods: experiences of flood community-dwelling households in Aboabo, Ghana
Published in Urban Water Journal, 2023
Andrews Ofosu, Kabila Abass, Harrison Kwabena Owusu, Razak M. Gyasi
Kumasi, the capital of the Ashanti Region, is characterised by informal urban development, poor planning, and poor layout of road networks. In these informal areas, storm water drains generally are of limited capacity, lack continuity and connectivity; and where available they are often choked (Abass 2020). These conditions, among others, provide a fertile ground for the occurrence of floods. The main types of floods experienced in Kumasi are pluvial and fluvial in character. Pluvial floods are associated with surface water runoff, which occurs when its generation exceeds the rate of infiltration and drainage capacity. Fluvial floods are caused by streams and rivers that traverse the city and cause flooding at the height of the rainy season. Some of these rivers and streams are Aboabo, Kwadaso, Dadan, Subin, Adoti, Parko, Sisa, and Wewe. These floods are perennial and often cause great damage to both households and public assets (Figures 1, 2, and 3). Floodwaters could rise beyond window level in some cases and persist for days or weeks.