Urban Hazards – Flash Floods

Subsequent disasters generate increasing criticism directed not only at those responsible for risk management and disaster prevention, but also at the establishment responsible for urban planning. When disasters are deadly, with significant numbers of deaths involved, and stark images of horror, suffering, and loss widely exposed by the media, then criticism will rise to a crescendo of “mismanagement and negligence.” Deadly flash floods sounded alarm bells for urban planners to pay attention and pay more attention to environmental standards in rapid urbanization and industrialization. The full breadth of environmental realities and the state of natural resources along with the steps that ensure human safety should have provided the general framework for making decisions related to transportation, industry, and urban construction. (Yo)

Managing the challenges of flood risks in densely populated areas has been a constant historical factor in human settlements. Most of the cities are located in the valleys, floodplains and coastlines. Cities, due to their nature of having large impervious areas, produce large runoffs that the drainage network cannot accommodate and are potentially exposed to flooding. It has been recognized that the damage potential of flooding in cities is extraordinarily high. Given the high population density in urban areas, even small-scale flash floods can cause considerable damage. At the extreme end of the disaster spectrum, urban flash floods can trigger disasters that dramatically slow development. With climate change and global warming resulting in increased frequency and magnitude of flooding, continued urbanization and disproportionate growth, the economic costs of flash flooding will skyrocket. Sustainable management of urban flood risks is becoming an increasingly challenging task for city and municipal authorities. (iii)

Flash floods are clearly characterized by a very rapid rise and fall, associated with debris flows and landslides, occurring along channels and rivers with a small drainage area. Its distinctive features paint a stark picture. Flash floods occur suddenly, easily and frequently, are very destructive and difficult to protect against. Lately, flash floods have led to extremely destructive disasters, for example, the recent flash floods in Istanbul, Turkey. In most cases it is a break in the flood protection installation.

Rapid economic growth compounds the dangers of flash flooding. As new construction takes over arable land and urban population density increases, infrastructure growth may not go hand in hand. The growth of urbanization inevitably reduces vegetation, wetlands, and other habitats for flood prevention.

Urban flash flood patterns are almost identical in their strength. Small streams, canals, canals and drainage ditches turn into fast-flowing dangerous rivers. Where the terrain is flat, primary and secondary roads are inundated with torrents of flooding, streets and parking lots become rivers of moving water. As the connotations imply, flash floods increase rapidly within a few minutes or hours of heavy rain. As the water rises rapidly and moves quickly, it carries cars, rips trees out of the ground, and even destroys roads and bridges.

Disaster risk reduction in identified potentially flood-prone areas should focus on the degree of exposure and vulnerability. Exposure of nearby urban dwellers to river currents, including infrastructure (roads, bridges, dams, power plants) located in the same area requires further attention. Vulnerability could be minimized by increasing preparedness through flash flood guidance, community awareness campaigns, early warning systems, and planned coordinated emergency procedures. The World Conference on Disaster Reduction held in Kobe in January 2005 called for the early warning system to be people-centered, providing timely and reliable warnings to people at risk.

Although they are usually natural phenomena, flash floods are increasingly the result of human activities or poorly designed infrastructure. Very few countries have a flash flood management action plan. Among those that do, China stands out with severe penalties for negligence. Flash floods are a frequent feature in China, as two-thirds of the Chinese territory is mountainous, recurring natural disasters are aggravated by monsoon weather, fragile mountainous terrain and increased human activity. The threat faces a total of 74 million inhabitants exposed to flash flood hazards in the mountainous region. In a period of four decades (1950-1990) a total of 225,000 people died in floods in China. (iii) The action plan requires approval of any new construction in town planning contingent upon completion of a flash flood assessment.

Before approving construction projects, city/municipal authorities may examine the conditions affecting the construction area. Best practices in flash flood management in urban areas justify improving the disaster management chain and ensuring that they extend to urban planning. Among some authorities, the focus includes helping municipalities prepare for climate change. (iii)

In other places, such as West Africa, there is a growing awareness that “urban growth feeds floods” if not planned and organized. The Guediawave suburb of Dakar was a dry area 30 years ago. Today, it is a different story. Residents of this densely populated suburb endure flooding every rainy season. (v) Explosive population growth, urban mismanagement, urban congestion and indiscriminate construction in green areas add up to shorten the fuse of disaster. Overpopulation in northern Nigeria causes people to build houses on waterways and the natural drainage system becomes blocked with rubbish. Despite construction bans in Dakar’s “cap vert” wetlands, this flood-prone area received waves of rural-urban migration in the wake of the 1970s and 1980s drought across the Sahel. Now the region is full of buildings and roads that block watercourses and natural basins.

References:-
(i) Zaman of today. Klaus Jurgens. The limitations of urbanism: Have we reached the limitations of urbanism?
(ii) The Associated Program for Flood Management (APFM).
(iii) Flash flood management in urban China, Xu Jianchu and Li Zhuoqing, Kunming Institute of Botany, Chinese Academy of Sciences.
(iv) Prediction and management of flash floods in urban areas (URBAS), Thomas Einfalt, Andreas Wagner, Fritz Hatzfeld, Jörg Seltmann.
(v) IRIN, West Africa, Urban surge feeds flooding, Dakar, September 14, 2009.