Urban flooding & it's mitigation

A flood is an overflow of water onto land that is normally dry. Floods can happen almost anywhere. They can cover an area with just a few inches of water or they can bring enough water to cover the roof of a house. Floods can be dangerous for communities, lasting days, weeks or sometimes even longer.

Many different situations can cause a flood. Here are just a few:

• Heavy rainfall

• Ocean waves coming on shore, such as a storm surge

• Melting snow and ice, as well as ice jams

• Dams or levees breaking

What is Urban flooding?

occurs when city landscapes cannot absorb excess water after prolonged periods of intense rainfall, river overtopping, or storm surge. Floods cause significant life, livelihood and economic loss and erode developmental dividends that city authorities/government accrue through decades of hard work. Water prudent urban development coupled with integrated green and grey infrastructure can significantly increase a city’s resilience to urban floods. Neglecting such hybrid approaches and constructing only grey (stormwater) infrastructure to resolve urbanization and climate change driven stormwater issues will frequently bring Indian cities under water.

• Usuallly occurs due to ineffective management of city drainage infrastructure.

• Conflict of Jurisdiction between various departments.

• Open waste disposal by shops and street vendors, choking the drains

• Un levelled planning of city

• Delay in cleaning of drains post first rain showers

Preventing urban floods is impossible, but the losses resulting from flooding can be minimized through proper flood mitigation planning. This requires accurate estimations of flood extent and hazard for different flow conditions, which are essential for developing effective flood evacuation and disaster management plans.

urban flooding takes various forms, such as high-intensity rainfall, inadequate drainage, channel or river overtopping, . In coastal cities like Mumbai, severe flooding scenarios often arise from a combination of surface flooding, channel overtopping, and tidal influences. To effectively manage and mitigate coastal urban floods, it is necessary to simulate potential flooding scenarios for extreme rainfall events, different return periods of rainfall, and other design scenarios.

An integrated approach that combines computer models, Geographic Information Systems (GIS), and remotely sensed data is employed to simulate coastal urban floods. Computer models are used to predict and simulate flood behavior based on various inputs and parameters. GIS technology assists in collecting, analyzing, and visualizing spatial data related to the urban environment and flood-prone areas. Remotely sensed data, such as satellite imagery or aerial photographs, provides valuable information on land cover, elevation, and other factors influencing flood dynamics.

By leveraging these tools and techniques, decision-makers and urban planners can gain a comprehensive understanding of coastal urban flooding. This knowledge enables them to develop effective flood management strategies, implement necessary infrastructure improvements, and establish early warning systems to safeguard coastal cities from the devastating impacts of urban floods.

Big cities which suffer: Delhi, Mumbai, bengaluru, Noida, and many other cities.

Why Delhi is suffering from flooding?

The NCT of Delhi has three major drainage basins, namely, Najafgarh, Barapullah and Trans-Yamuna basins. Using the processed datasets, the SWMM model has been setup in the present study for each of the drainage basins of Delhi to simulate the inundation depths as well as their spatial locations. The model results have been validated to certain extent through the flooding location data provided by the Delhi Traffic Police.. However, it has been found that despite all our efforts there were large number of discrepancies in the drainage network. Some of these discrepancies have been removed before final simulations to analyse the drainage systems and recommend appropriate solutions.

• To alleviate the flooding conditions in various parts of the city, the stormwater infrastructure has to be made efficient. So, it is pertinent to apply corrective measures to the faulty drainage infrastructure,and introduce low cost flood preventing measures such as water bodies rejuvenation, rainwater harvesting using parks and Low Impact Development options. Further, the solid waste and the sewage has be managed in such a way that they do not interfere with the stormwater drainage.

• Institutional jurisdiction: With regard to the management of the storm water drainage system within the NCT of Delhi, there is conspicuously no single institution that bears an overall responsibility of the total system. To the contrary, the administrative authority of the capital’s drainage system is quixotically distributed amongst numerous civic bodies and various constituent departments of Government of NCT of Delhi as well as Government of India. These include (i) Irrigation & Flood Control, Delhi, (ii) Delhi Jal Board, (iii) various Municipal Corporations of Delhi, (iv) Urban Development, Delhi, (v) Ministry of Urban Development, Government of India, (vi) New Delhi Municipal Council, (vii) Delhi DevelopmentAuthority, (viii) Delhi Cantonment Board, (ix) Delhi State Industrial Development Corporation, and (x)Public Works Department, Delhi. Other departments of the Government and civic bodies whose jurisdiction does not entail any direct responsibility pertaining to the state of the capital’s drainage system but nevertheless are important, include (i) Irrigation & Flood Control, Government of Haryana, (ii) Traffic Police, Delhi, (iii) Geo Spatial Delhi Limited, (iv) Central Water Commission, Government of India, (v) India Meteorological Department, (vi) various Resident Welfare Associations (RWAs), (vii) Central Pollution Control Board of Ministry of Environment and Forests, Government of India, (viii) National Green Tribunal, (ix) National Highway Authority of India, (x) DIAL and (xi) civil society activist groups.

following are our major recommendations:

• No encroachments on storm drains :Storm drains should be treated as key public assets and no encroachment should be

allowed. Any encroachment of the drain should be immediately removed and reported

back. Department managing the storm drain should be made responsible for keeping

drain encroachment-free. Special drives to remove encroachments from the storm drains

should be taken up.

• No sewage in storm drains No natural or artificial storm drain should be allowed to carry any sewage. Only treated sewage of acceptable quality as per CPCB norms should be allowed in storm drains. All drains that are entering into NCT of Delhi (from Haryana, UP, etc.) should be only carrying storm water and treated sewage of acceptable quality as per CPCB norms. Current practice of DJB of puncturing sewer lines and draining sewage into storm drain in

the event of blockage should be stopped. DJB should resort to using latest mechanisms

such as supper suckers for de-clogging the sewer lines.

• No sewage should be allowed to enter the storm drains even from unauthorized colonies;

interceptor sewers should be set-up wherever required by DJB to trap the sewage coming

out of such colonies and take it to the nearest sewer line or STP.

• No Solid Waste or C&D waste be allowed into storm drains :No silt from the road (before or after road sweeping – manual or otherwise) be allowed to be dumped into bell-mouths/drains. Road sweeping process should be completely overhauled. Weight/volume of silt received after street sweeping should be recorded. Segments of road from where more silt is being received should be reviewed and reason of the same ascertained. If need be, possible afforestation exercise should be taken up to reduce silt on the road segment.

• No solid waste should be allowed to be dumped into storm drains.

• Construction & Demolition (C&D) waste should not be allowed to be dumped in storm

drains or depressions. Amount of waste likely to be generated from a construction or

demolition site should be assessed by the contractor in advance (along with the

permission to construct/modify house). C&D waste should be lifted by government

appointed contractors and dumped at C&D processing site.

• Effectiveness of desilting of storm drains

• It has been seen that many drains are covered fully/partially. It has been noticed that most

of the covered drains do not have access for desilting. If desilting is not carried out under

the covered potion, effectiveness of desilting of rest of the drain is reduced significantly.

Therefore, access points, if they are not there, should be provided at appropriate distance

so that desilting can be carried out.

• Schedule of desilting should be publically displayed and in a manner that is understood

clearly by general public. GSDL should use the GIS layout of the drainage network made

by IIT Delhi with cross-section and L-section to capture and display the schedule of

desilting by the contractors segment-wise and jurisdiction-wise. Crucial details such as

time schedule of desilting and the amount of silt/debris removed should also be captured

and displayed.

• No storm water should be drained into sewer systems No storm drain should ever outfall into sewer system at any cost since they are never designed for such situation and shall therefore result in surcharge of sewerage network and may flood some of the areas with sewage. All such cases should be identified and immediately addressed. No such cases (temporary or permanent) should ever be allowed. Practice of opening sewer man-holes to discharge local storm water should be banned. Adequate system to discharge storm water should be put in place and public awareness should be increased towards ill-effects of diverting storm water into sewer lines.

Additional Recommendations

It is proposed that the government should enact a law that prohibits:

1. Sidewalk and pavement hawking. There is a natural temptation to dispose of wastes into

available storm water collection system with impunity. Use of garbage disposal bags should

be made mandatory for businesses along road carriageways.

2. Roadside delis and other eating places that do not have a hygienic and an organized pantry system within the premises for cleaning and washing of utensils. Enforcement should be

rigorous and non-compliance should carry compensatory as well as punitive penalty. Further, the license to operate should also be incumbent on a demonstrable infrastructure for an orderly disposal of solid and liquid wastes.

3. Roadside auto service and repair shops as these require sophisticated waste handling,

storage, stowing and disposal infrastructure. It is commonly observed that chemical wastes

are routinely disposed off into the nearest available storm water systems.

4. Roadside auto dealerships that cater to both new as well as pre-owned vehicles. These

businesses invariably utilise public space for parking and display of goods on sale and the

damage to roadside infrastructure is indeed inevitable.

5. Collection and stacking of construction related building and other wastes on public spaces. No completion certificate should be granted unless a public inspection of the sites is able to verify compliance and adherence to building waste management norms.

6. Roadside piling of dirt and other solid wastes (road sweep) resulting from road, sidewalks

and service roads. It is a common observation that dirt is routinely swept off and stacked in

front of roadside bell mouths. Weekly markets without an installable (temporary) infrastructure to collect, store and safely stow business wastes prior to its disposal at formally designated locations and in accordance with formalized protocol. Failure to comply should result in levying punitive penalty on the organizers, individually and/or collectively.

8. Direct access to businesses from the roadside.

As part of masterplan for the future, all access to proposed community centres, markets and business centres that are planned along road carriageways should be planned with no direct access from the roadside and should be planned with basement parking. Access to shops for customers as well as delivery of stock and other inventory from/to these businesses should only be from the rear and off the main road

as shown in the Figure ES1.

Way Forward:Attention should be given at all levels of government to ensure thatefforts to mitigate urban flooding reach areas that have the highest risk of flooding and cross all economic and social levels and that locally supported steps are taken to incentivize individual homeowner mitigation efforts.

These mitigation efforts should include improved transparency, better risk communication, and more support for flood-weary residents who want to move out of harm’s way

Mains Question:

Q1.What is Urban flooding?

Q2.Urban flooding is result of institutional failure of government machinery.Comment?

Q3. What is Flood?

Q4.Suggest measures to mitigate urban flooding?

Q5.What is a smart city?

Q6..What are Sponge cities?

Q7. What is a floodplain?

Q8.Rising challenge of Urban floods is a concern for society.Comment?

Thanks for visiting!!

Refrences:

Drainage master plan for Delhi 2018 by IIT Delhi

Arnold, J. G., Srinivasan R., Muttiah R. S., and Williams J. R. 1998. Large-area hydrologic modelling and assessment: Part I. Model development. J. American Water Res. Assoc. 34(1): 73-89

Huber, W. C., Heaney, J. P., Nix, S. J., Dickonson, R. E., and Polman, D. J. 1982. Storm water

management model; User's manual, Version III , U. S. Envir. Protection Agency, Cincinnati, OhioMaster Plan Organisation, Flood Control Wing, Delhi Administration. 1976. Master Plan For Storm Water Drainage In The Union Territory Of Delhi.

Neitsch, S. L., Arnold J. G., Kiniry J. R., Williams J. R., and King K. W. 2002a. Soil and Water Assessment tool - Theoretical Documentation (version 2000). Temple, Texas: Grassland, Soil and Water Research Laboratory, Agricultural Research Service, Blackland Research Centre, Texas Agricultural Experiment Station.

htps://quigly.house.gov/media-center/press-releases/quigley-durbin-hear-from-victims-of-urban-flooding

htps://www.wricitiesindia.org/content/urban-india-going-underwater-again

Settlement geography and urban infrastructre by j.stan