Architecture and Planning: Urban floods

In recent years, Indian cities start facing urban flood during monsoon season. Every year from July to august many parts of the Indian region face the flood and other impacts from it. In the western region state of Gujarat and Maharashtra, eastern states like Bihar, West Bengal, Odisha, Assam and eastern part of Uttar Pradesh and in southern states like Karnataka and Kerala have faced the floods. Bihar is the most vulnerable state in all of them. In the year 2017, Rajasthan followed by West Bengal, and Bihar are amongst top three states affects in terms of land areas while Bihar is a topmost state in terms of population affected i.e. approximately 17.2 million followed by west Bengal having 8.7 million (https://data.gov.in/resources/stateut-wise-damages-caused-floods-across-country-data-available-central-water-commission).There is a significant increase in urban flooding in India. Urban flooding is different from Natural flooding.

The major cause of urban flooding is the increase in population and unplanned urbanization. Construction activities in low lying area and interference in catchment areas and floodplains change the course of natural drainage routes is a major concern. Urban flooding is typically characterized by

1. Increase in flood peaks by 2-8 times;

2. Increase in flood volumes by up to 6 times;

3. Decrease in time required to reach flood peak;

4. Excessive economic losses (in the form of damage to property and loss of productivity)

Cities	Flooding Years
Ahmedabad	2001
Bangalore	2005, 2009, and 2013
Chennai	2004 and 2015
Delhi	2002, 2003, 2009, 2010, 2013, 2016
Guwahati	2010 and 2011
Hyderabad	2000, 2001,2002, 2006 and 2008
Jamshedpur	2008
Kolkata	2007 and 2013
Mumbai	2005, 2007, and 2015
Srinagar	1992, 2014 and 2015
Surat	2006 and 2013

Source: https://smartnet.niua.org/sites/default/files/resources/FS%203_Urban%20Flooding.pdf

For the intensity of rainfall of 12-20 mm, stormwater drainage systems were previously designed. When higher intensity rain has been received, these capacities have failed very quickly. Furthermore, because of inadequate maintenance systems very often do not work at the designed capacities. Accommodations started to flourish into urban communities by rivers and bodies of water. This resulted in an increase in water flow proportional to watershed urbanization. To accommodate the greater flows of stormwater, the natural drains should ideally have been broadened. As a result, the capacity of natural drains was diminished, and flooding occurred. Improper management and dumping of construction waste to drains of solid waste, including domestic, commercial, and industrial waste, also significantly contributes to the reduction in capacity. Better operations and maintenance measures are absolutely crucial.

Floodwater surrounds the premises of Aluva Siva Temple, Kochi

The Chennai International Airport runway was also built directly over the river Adyar. Most of the airport was built on the riverine floodplains, which resulted in massive flooding during the Chennai floods in 2015. Similarly, developments such as the Amaravati Capital City Project of Andhra Pradesh had proposed that large areas be developed on the Krishna River floodplains.

Urban flood Impacts:

1. Traffic jams

2. Damage to public and private property

3. Mixing of solid waste in floodwaters causing further choking of drains

4. Vector and waterborne disease

5. In coastal cities, increased inundation of low lying areas during high tide reduced capacity of drains to discharge stormwater

6. Disruption of power supply and telecommunication

7. Mixing of fecal matter in the flood water due to open defecation

Responsibilities and Challenges

The reality is that our big cities were built with hardly any regard for the natural topography and there is seriously a lack of integrative initiative. Also, with regulations on rainwater harvesting, sustainable urban drainage systems, etc., in regulatory systems such as the Environmental Impact Assessment (EIA), Notification 2006 or almost every state's building bylaws, adoption at the end of the user and local law enforcement remains a problem. Cities such as Mumbai suffer from a substandard urban infrastructure issue, as they have organically expanded its boundaries over the years. In recent years, Gurugram has seen an exponential growth of both the urban population and the infrastructure. Throughout the year's water bodies and wetlands have declined as a consequence of inadequate planning, unchecked development, and mismanagement of natural resources. From 644 in 1956, the number of bodies of water fell to 123 in 2018. Green coverage is just 9%, which would preferably have been at least 33%.

Measures to tackle urban flooding:

· National Disaster Management (NDMA) Guidelines: In 2010, NDMA had issued guidelines on Urban Flood Management in India -to create a National Hydro-meteorological Network for providing early warning, use of Doppler Weather Radars to be expanded to cover all urban areas in the country, an inventory of the existing stormwater drainage system to be prepared, economic loss, etc.

· Rainwater harvesting and other check measures: on-channel storage of rainwater in storm drains, artificial recharge trenches, retention basins, deepening of ponds and lakes etc.

· Sustainable usage of land: Low-lying areas in cities have to be reserved for parks and other low-impact human activities, restrict encroachments in natural drainage areas; clearance of river beds, proper implementation of Coastal Regulation Zone rules. Planting drought resistant and flood-resistant sturdy trees in vulnerable areas also help.

· Utilizing international best practices: Implementing ‘Mobile Walls’ like in Germany, and ‘sponge’ cities in line with cities in China which involves replacing concrete pavements with porous pavements to ensure better filtration.

CONCLUSION

Lack of planning vision and expansion of cities to accumulate population moving towards them without proper infrastructure has induced the demand for sewage and stormwater management strategy in urban areas. Unorganized development on flood plains and natural wetlands leading to flash fools during monsoon season in India every year. Lack of integrated flood control strategy and lackadaisical attitude of local governing bodies have contributed to the urban flood. Policymakers, planners must learn from the growing case of slood in Indian cities and must prepare various plans at different levels to successfully mitigate and reduce the impact of floods for everyone.

Architecture and Planning

Urban floods: Drowning of Indian megacities

Cities

Flooding Years

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