NDMA Guidelines on Urban Flooding in India

Urban flooding differs from rural flooding as urbanisation leads to developed catchments which increases the flood peaks and flood volumes. As a result, flooding occurs very quickly due to faster flow times, sometimes in a matter of minutes. As urban areas are centres of economic activities, any damage to vital infrastructure has a bearing not just locally but could even have global implications. Both rich and poor living cities suffer due to flooding. Urban flooding associated with damage to property and loss of life. There is a possibility of secondary issues of possible epidemics and exposure to infections. Therefore, management of urban flooding has to be accorded top priority.

Urban Flood Risk in India

In the past several years, there is an increasing trend of urban flood disasters in India. The notables of them are Hyderabad in 2000, Ahmedabad in 2001, Delhi in 2002 and 2003, Chennai in 2004, Mumbai in 2005, Surat in 2006, Kolkata in 2007, Jamshedpur in 2008, Delhi in 2009, Guwahati and Delhi in 2010, and Chennai in 2015. Heavy rainfall during monsoons is a special feature in India. Storm surges can also affect coastal cities/ towns. Sudden release or failure to release water from dams can also have severe impact. The urban heat island effect and global climate change is resulted in episodes of high intensity rainfall events occurring in shorter periods of time. Coastal cities are also facing threat from sea-level rise.

Issues with urban flooding

Storm water drainage systems in the past were designed for rainfall intensity of 12 – 20 mm. But the average rainfall in Indian cities far exceeds the capacity of drainage system. The designed system capacities do not work due to poor maintenance. Encroachments are another big problem in many cities and towns. Consequently the capacity of the natural drains has decreased, resulting in flooding. Improper disposal of solid waste, including domestic, commercial and industrial waste and dumping of construction debris into the drains also contributes significantly to reducing their capacities.

Role of Science and Technology

The management of urban flooding has to be treated holistically in a multi-disciplinary manner. Science and technology can play a significant role for improved monitoring, modeling/ forecasting and decision-support systems. One method for improving the preparedness for urbanflooding is by setting up a vulnerability-based geospatial framework to generate and analyse different scenarios. It helps in identifying and planning for the most effective/ appropriate actions in a dynamic way to incorporate day-to-day changes that take place in urban areas, having the potential to alter the prevailing vulnerability profile.

NDMA guidelines on management of urban flooding

The National Disaster Management Authority (NDMA) has issued guidelines on management of urban flooding in 2010. Key guideline was to create a National Hydro-meteorological Network. The guidelines say that for providing early warning, the Central Water Commission (CWC) should maximize the real-time hydro-meteorological network to cover all the urban centers in dealing with urban flooding. The requirement should consider all cities/ towns which are particularly located on river banks, upstream and downstream of major and medium dams and island cities. Based on that assessment, CWC will initiate the process to prepare a plan and implementation strategy.

Other recommendations:

1. Use of Doppler Weather Radars to be expanded to cover all urban areas in the country.
2. Coordination mechanism to be established among all agencies for deriving maximum benefit from the efforts of each individual organization.
3. A dedicated high bandwidth communication channel is to be built, for ensuring smooth underlying sensor web flow of all available information and products.
4. State-of-the-art automatic water level recorders must be installed throughout the drainage network of the watershed, which may sometimes extend beyond the administrative boundary of the ULB.
5. Technical Umbrella for urban Flood Forecasting and Warning to be established at national and state level.
6. An inventory of the existing storm water drainage system to be prepared. The inventory will be both watershed based and ward based.
7. Catchment to be the basis for planning and designing the storm water drainage systems in all ULBs.
8. Contour mapping of urban areas to be prepared at 0.2 to 0.5 m contour interval for detailed delineation of the watershed/ catchment for planning drainage systems.
9. Pre-monsoon desilting of all major drains to be completed by March 31 each year.
10. Suitable interventions in the drainage system like traps, communitors, trash racks can be provided to reduce the amount of solid waste going into the storm sewers.
11. All future road and rail bridges in cities crossing drains to be designed such that they do not block the flows resulting in backwater effect.
12. Inlets to be provided on the roads to drain water to the roadside drains and these has to be designed based on current national and international practices.
13. Every building in an urban area must have rainwater harvesting as an integral component of the building utility.
14. Concept of Rain Gardens to be incorporated in planning for public parks and on-site stormwater management for larger colonies and sites those are to be developed.
15. Low-lying areas in cities have to be reserved for parks and other low-impact human activities.
16. Encroachments on the drain should attract penal action.
17. Flood hazard assessment has to ascertain level of acceptable risk of flooding on the basis of projected future scenarios of rainfall intensities and duration and land use changes.
18. Flood damage has to be according to the physical characteristics of the area such as land use, topography, drainage area, outfall system and the capacity of the existing stormwater drainage system.
19. Ward level Information System has to be developed using high resolution satellite images/aerial photos, integrated with socio-economic data covering natural resources and infrastructure facilities on appropriate scale (1:1000) at community level.
20. States/UTs have to build partnerships with public/ private insurance companies and civil society to sensitive communities about available schemes and also develop appropriate micro-insurance schemes targeted at low-income groups.
21. The database of the National Urban Information System (NUIS) will be expanded to cover infrastructure facilities at community level integrated with socio-economic data.
22. Urban Flooding has to be dealt as a separate disaster, de-linking it from riverine floods which affect the rural areas.
23. Storm water drainage concerns will be made a part of all EIA norms.
24. Buildings have to be designated as Flood Shelters and all necessary arrangements have to be ensured ahead of the flood season. Children, women, the aged and the differently-abled persons has to be given special attention.
25. Post-floods, restoration of power, telecommunications, road and railway transport will get top priority.
26. Media, corporate, NGOs has to be involved in awareness generation.