Smart Governance
Infra Concern
Q. What is an urban flood? How is it different from rural flood or any other flood?
A. The term urban flood consists of two parts-‘ urban’ and‘ flood’. According to the Census of India, 2011, an urban area is defined as( a) all statutory places with a municipality, a corporation, a cantonment board or a notified town area committee, etc.; or( b) all other places satisfying all three conditions: i) a minimum population of 5,000; ii) at least 75 per cent of male working population engaged in non-agricultural pursuits; and iii) a density of population of at least 400 per sq. km.
Flood is defined as“ an overflow of a large body of water over areas not usually inundated”. Thus, flooding in urban areas is caused by intense and / or prolonged rainfall, which overwhelms the capacity of the drainage system. Our cities are densely populated, and an urban flood affects a large number of people in a very small area. In addition, an urban flood results in inundation and damage to vital infrastructure, and disruption to roads and services, thereby affecting all walks of life. It often leads to major economic losses which have both local and global implications. Outbreak of diseases is yet another hazard after a major urban flood.
The extent of flooding in a rural flood may be quite large and there may be agricultural losses but the number of people affected is much lower in comparison to urban areas. Moreover, the flood peaks in urban areas are about two-eight times and flood volume is about six times when compared with the rural floods.
Q. What causes urban flooding?
A. Urban flooding is caused by three main factors – meteorological, hydrological and human factors. Meteorological factors include heavy rainfall, cyclonic storms and thunderstorms. Hydrological factors include presence or absence of overbank flow channel networks and occurrence of high tides impeding the drainage in coastal cities. Human factors include land use changes, surface sealing due to urbanization( which increases run-off), occupation of flood plains and obstruction of flood flows, urban heat island effect( which has increased the rainfall in and around urban areas), sudden release of water from dams located upstream of citizen towns and the failure to release water from dams resulting in backwater effect. The indiscriminate disposal of solid waste into urban water drains and channels is a major impediment to water flow during the monsoon season.
Q. There are multiple agencies which claim authority over waste disposal systems. Is there a system in place currently where different agencies work together and mitigate the risk?
A. In Mumbai, the Municipal Corporation of Greater Mumbai has designated a Chief Engineer exclusively in charge of solid waste management. The solid waste department ensures that solid waste is collected and transported to the solid waste disposal site. Other cities may think of adopting a similar administrative structure so that their solid waste is swiftly and effectively transferred to the solid waste disposal site.
Q. Which parts of the country are more prone to urban flooding?
A. All our cities are vulnerable to flooding. Most of them have now reached a saturation point in terms of population growth and accommodation, and the developmental activities have now shifted to low-lying areas and areas next to the riverbanks. Thunderstorms and heavy rainfall can occur anywhere. So, whenever a city experiences a large amount of rainfall within a short time, there are
November 2016 20 www. smartgovernance. in