Strategic BGI Framework for Flood management in Chennai | MA Urban Design and Planning
STRATEGIC
BGI FRAMEWORK FOR FLOOD MANAGEMENT IN CHENNAI
TRP6424 DESIGN DISSERTATION
Submitted in partial fulfilment of the degree of MA Urban Design and Planning, University of Sheffield September 2024
ABSTRACT
This research investigates the application of Blue-Green Infrastructure (BGI) as a strategic framework for flood management in Chennai, focusing on the neighborhood of Velachery. As rapid urbanization exacerbates flood risks, especially in developing regions like the Global South, traditional flood control methods prove insufficient. This study analyzes BGI systems at micro, meso, and macro scales to develop a multi-scalar, adaptive framework that integrates flood management into the urban fabric. Street, neighborhood, and city-scale strategies were devised, with design interventions focusing on sustainable drainage, stormwater management, and community connection with water. Key findings indicate that even narrow streets can effectively incorporate BGI to reduce stormwater runoff, while converting existing infrastructure into flood retention areas can alleviate pressure on drainage systems. The research emphasizes the importance of starting flood mitigation at the regional level through watershed management policies, increasing lake capacities, and involving the community. Despite its contributions, the study recognizes limitations, such as the lack of GIS mapping and consideration of socio-political factors. Future research should focus on accurate GIS mapping, stakeholder coordination, and cost-benefit analysis of BGI implementation in India. Overall, this project provides a foundational framework for enhancing urban resilience in Chennai, highlighting the need for integrated and adaptive strategies to combat the growing challenges of urban flooding.
1. INTRODUCTION
2. METHODOLOGY
3. LITERATURE REVIEW
4. CASE STUDIES
5. SITE STUDY
6. PRIMARY DATA AND ANALYSIS
7. DESIGN FRAMEWORK
8. DESIGN PROPOSAL
9. CONCLUSION
CONTENTS
10. REFERENCES
1.1 Research Background
Climate change and Flood risk
Seasonal variations and changes in weather patterns are a normal part of the climatic cycle. Yet, industrialisation, rapid urbanisation, deforestation, environmental degradation and resource exploitation have significantly influenced this cycle causing dramatic shifts in the past 200 years. These radical human induced changes have resulted in rising surface temperatures known as global warming. According to the United Nations (2024), the decade from 2011 to 2020 was recorded as the warmest with predictions of temperatures rising by 1.1°C by 2035. Such a drastic increase in temperature has direct effects on climate change leading to rising sea levels and extreme weather events (including storms, heat waves and cold spells). Coastal regions are particularly impacted, experiencing frequent floods and submersion (IPCC, 2015). Indirectly, climate-related disasters threaten the safety, health, food security, and livelihoods of people (WWF, 2017).
Flood risk in the Global South – Urban flooding
Flooding affects over 1.81 billion people across 188 countries, making it a global issue. A significant 89% of these individuals are from low and middle-income countries in the Global South (comprising South America, Africa, parts of Asia, the Caribbean and Oceania) highlighting the impact of adverse climate changes on developing nations (Rentschler, Salhab, and Jafino, 2022b; World Population Review, 2023). Higher-income countries can achieve a certain level of resilience against flood risk due to their financial capacity to invest in flood mitigation strategies thereby reducing their vulnerability (Rentschler, Salhab, and Jafino, 2022a). Flooding can be a natural or human-made phenomenon. Due to their low topographic elevation, regions close to rivers and seas experience pluvial flooding annually during the rainy season. Developing cities, however, are reporting more instances of urban flooding where water stagnates in densely builtup areas due to increased population, unplanned development, and reduced percolation (Ferguson et al., 2023). Muneerudeen (2017) and Zareba et al (2022) attribute this issue to an increase in impermeable surfaces, improper land use planning, unplanned growth, poor management of traditional (or existing) infrastructure, singular non-integrated systems, and a disconnect between built and natural environments. Therefore, enhancing flood resilience in developing countries requires addressing urban design, planning, infrastructure, and ecological conservation.
Flooding in India
India experiences pluvial flooding primarily from June to September (South-west monsoons) and October to January (North-east monsoons). Extreme climatic conditions like cyclones and cloudbursts lead to heavy flooding during these months. Coastal cities are more vulnerable due to rapid urbanisation, water body encroachment, decreasing green spaces, and reduced capacity of drainage systems (Gupta,2020). The cities of Ahmedabad, Surat, Mumbai, Cochin, Chennai, Vishakapatnam and Kolkata along the 7517km coastline have been frequently waterlogged in the past few decades (Dhiman et al., 2018).
Traditionally, Flood management is done in the following ways – Flood control, Flood preparedness and Disaster relief. India focuses more on Flood control and Disaster relief (R.I. Ogie, C. Adam and P. Perez, 2020). The State governments manage the construction and maintenance of structural flood control systems. In contrast, the Central government creates policies and guidelines adopted by the States and provides disaster relief (NDMA, 2005). However, poor maintenance, lack of coordination between governments, limited community involvement, and insufficient research and funding have hindered success (Mohanty, Mudgil and Karmakar, 2020). Furthermore, inadequate flood forecasting, mapping, and community awareness reduce flood resilience.
Urban floods in Chennai
Chennai, located on India’s eastern coast, frequently floods during the monsoon season. Rapid urbanisation, land use violations, ill maintenance of stormwater canals, and taking over waterbodies and natural sinks to accommodate this growth have led to 5 major floods from 1943 to 2005 (Tamil Nadu Bureau, 2015) causing severe damage to the city. The devastating 2015 flood resulted from cyclonic storms and poor government response in reservoir management, creating a man-made disaster (Kumar, 2023). In contrast during 2021 and 2023, the government religiously monitored water levels in all reservoirs to avoid a repeat of the past. However, not remediating the previous faults and inadequate provision for rainwater and stormwater management, led to recurring floods (Raghavan, 2021; Raghavan, 2022). Despite some improvements (decrease in flood duration), the persistent issues highlight the need for better flood management.
Fig 1: Exposure to flood risk across the world
Need for an Integrated Flood Management System
Traditional flood management methods, such as channelling water through sewerage and stormwater pipes, are inadequate for extreme climatic events like 50-year and 100-year rainfalls. The low infiltration levels of such systems lead to more contaminated stormwater that ultimately pollutes downstream water bodies (Pusalkar, Swamy and Shivapur, 2022). Thus, a single infrastructural system proves ineffective in the long run since any failure or lack of maintenance can render it unusable causing considerable damage to the low-lying regions of the city. Expansion of underground systems is also expensive (Sörensen, J. et al., 2016). Recurring floods take a toll on both physical and mental health of the people, necessitating multiple water management systems above-ground, integrated into the urban fabric (Abbas et al.,2015).
Blue-Green Infrastructure (BGI) combines water and green elements with urban design to manage stormwater (Washbourne and Wansbury,2023). BGI provides a multidisciplinary from residential rainwater collection to flood mitigation via wetland restoration, thus forming a cohesive framework for a larger region (Sörensen et al., 2016; Almaaitah et al., 2021). Predominantly found in the US, UK, China, and Europe, BGI’s integration in the Global South is slow due to the need for stakeholder coordination and financial support. Thus, designing holistic flood management systems is crucial for increasing resilience in the Global South.
1.2 Research Aim and Objectives
The research aims to understand BGI systems at various scales and analyse which ones can be used separately and/or in combination to form a multi-scalar, flood management strategy for Chennai. This can also become an adaptive framework to be used in other regions to create flood-resilient cities. The following research questions are proposed.
1. Where does urban flooding happen the most? What are the geographical, hydrological, and infrastructural features that determine the flood risk of a place?
2. What are the different scales at which BGI systems work and how are they interlinked?
3. How are BGI systems integrated with the urban fabric at different scales?
4. How is water management done in Chennai – past and present? Are these BGI systems? How does it connect to the urban fabric?
5. What are the sites selected within Chennai and what are their distinct characters and connecting links?
6. How can BGI systems be translated to Chennai at different scales?
The final objective is to produce BGI strategy recommendations at street, neighbourhood and city scales forming an interconnected flood management framework with drawn explorations of the street scale strategies.
1.3 Research Framework
LITERATURE REVIEW
• Flood risk characteristics
• Blue-Green Infrastructure
• Water management in Chennai
CASE STUDIES
• Rotterdam, Netherlands
• Jakarta, Indonesia
SITE STUDIES
• Site Analysis
• Site photos/videos
Location selection
Strategy selection
INTERVIEWS/SURVEY
• Semi-structured Interviews
• Online survey
DESIGN STRATEGY FRAMEWORK FOR CHENNAI
• Masterplan
• Strategy recommendations STREET SCALE NEIGHBOURHOOD SCALE CITY SCALE
• Conceptual framework
Design
CONCLUSION
• Conceptual framework
CASE STUDIES
Case studies explore flood management practices in 2 cities particularly using BGI. The systems used across all scales are explored and cross-referenced with Table 2. Inferences obtained will determine which systems can be adopted in Chennai and what their potential challenges might be.
4.1 Rotterdam, Netherlands
4.2 Jakarta, Indonesia
Rotterdam, a delta city on the New Meuse River in the Netherlands, is the country’s second-largest city and Europe’s largest port. Over 40 years, it has seen steady urban growth. Its coastal location and storms necessitate strong flood management.
Population density: 3,070 persons/sq.km. (Brinkhoff, 2024).
FLOOD MANAGEMENT IN NETHERLANDS
Delta Plan (Orr, Stodghill and Candu, 2007)
Introduced in Netherlands in the 1950s to protect coastlines from storms using dikes, storm surge barriers and closure dams to provide buffers and barriers against floodwaters.
Flood vulnerability of Rotterdam
• Urbanization and port expansion
• Reduced water retention capacity of floodplains
• High annual rainfall
• Flooding of river New Meuse
• Low elevation (up to -6m below sea level) (Dircke, Molenaar and Aerts, 2011)
• Sea rise and coastal flooding (climate change)
BGI STRATEGIES IN NETHERLANDS
Primary aim is to allow water to move through natural and urban landscapes creating a sponge.
Regional strategy
NBS systems were integrated into flood management in the 1990s
Zandmotor - Artificially widening a beach or coastline by distributing sand along the shore, spread out naturally by wind and tides.
Example - Hague coastline (The Hague & Partners, 2020).
Room for the River - Restoration project across 30 locations to increase space for water in river basins through,
• relocating dikes to increase the floodplain
• lowering floodplains
• increasing depth of the riverbed
• reducing obstructions to water flow in rivers and channels
• additional water channels
• temporary water retention basins at the mouth of the rivers
(Dutch Water Sector, 2021)
Fig 10-11: Growth of Rotterdam city and port from 1980s to 2020 (Google Earth Pro)
Absorption and Delayed runoff focused at building/ street level
Rain gardens
Water square
River restoration
Blue-Green corridors
Canals
Coastline restoration
Dikes and Storm barriers
Increase retention, drainage and infiltration at Neighbourhood and City level; Improving existing Grey systems Environmental restoration for increased detention of floodwater at regional level
Green roofs, Rain gardens, Water squares, and underground storage systems are being implemented in the Rotterdam water plan 1 & 2. Room for the River project has reduced flood risk by 25% since its implementation.
• Innovative use of rooftops for water management effective in cities with limited land and high density
• Integrating water into public spaces, allowing natural movement and flooding, enhances flood management (“Design with water, not against”)
• Multipurpose spaces offer a wide range of secondary benefits
• Water storage during floods also supports drought supply, creating balance
• Success of BGI systems requires strong stakeholder involvement, public awareness, and government financial support
Fig 14: Integrated NBS systems (Rotterdam Climate Initiative, 2013)
Fig 15: Visualisation of different roofs in Rotterdam (Roofscape, 2022)
Jakarta, a delta city on the Ciliwung river on Java’s northwest, faces increased flooding due to deforestation and loss of ecological habitats, aggravated by urban expansion. With 40% land below sea level, population density at 16,165 people/sq.km. heightens vulnerability (Waworoentoe, 2019; CNA, 2021; Siahaan, 2024).
FLOOD MANAGEMENT IN JAKARTA
Regional strategy (Octavianti and Charles, 2018)
Major strategies involve grey infrastructure - canals, drains and dams along rivers.
As part of the National Capital Integrated Coastal Development Scheme (NCICD), a sea wall is being constructed along the northern coast along with retention basins and land reclamation projects.
However, both initiatives are ineffective in reducing flood risk.
• High impermeability and less groundwater recharge
• Draining of swamps for urban growth
• Encroachments on floodplains
• Improper landuse planning of upper catchment
• Improper waste management
• Poor maintenance of canals & rivers
BGI STRATEGIES IN JAKARTA
Regional strategy
Mangrove restoration - 120 hectares restored by Wetlands International along Jakarta’s coastline since 2015, providing a barrier against rising sea levels and land subsidence (UNEP, 2023).
Ciliwung River naturalization - Initiatives since 2019 to reduce waste, raise public awareness, and restore river edges using the “Room for the River” concept. [check pg 14]
Fig 16: Location of Jakarta (Britannica, 2019)
Fig 17-18: Growth of Jakarta city from 1980s to 2020 (Google Earth Pro)
Fig 19: Masterplan from NCICD (Mezzi, 2016)
Suburbs
CASE STUDIES - JAKARTA
City and Neighbourhood Strategy
• Restoring existing water bodies: Green spaces created around reservoirs, canals, and lakes for flood control (Ministry of Public Works, 2013).
• Increasing canal capacity: Enhancements to the West flood canal and Cengkaren drain (Ministry of Public Works, 2013).
• Green open surfaces GOS (Public): Jakarta Spatial Plan 2030 proposes 20% public urban green spaces (Setiowati, Hasibuan, and Koestoer, 2018).
• Adoption of Polders for North Jakarta neighbourhoods [see pg 15]
Street/Building Strategy
Green open surfaces (Private): Proposal to convert 30% of site area to green spaces, aiming to reduce water runoff to zero and enhance rainwater harvesting under Jakarta Spatial Plan 2030 (Setiowati, Hasibuan, and Koestoer, 2018).
Rainwater infiltration wells to be accommodated in each site
Green roofs and facades to be promoted till more open space can be acquired by the government
ANALYSIS & INFERENCE
(using Table 2)
SYSTEMS USED IN JAKARTA
Green roofs Infiltration Wells
FUNCTIONS
Absorption, Storage and Delayed runoff focused at building/ street level
Green facades
Edge restoration of lakes, reservoirs, canals
Green Open Space
Green Open Space
Polder Canals
River naturalization Mangrove restoration
Sea wall
Increase retention, drainage and infiltration at Neighbourhood and City level; Improving existing Grey systems
Environmental restoration for increased detention of floodwater at regional level
• Environmental restoration: Mangroves, rivers, water bodies, and green spaces are the most effective in reducing stormwater runoff. More greenery is needed.
• Polder system: Adopted from the Netherlands, proving the BGI concept’s global applicability to similar cities (Delta, Coastal).
• Administrative challenges: Policy failures, selective implementation, and corruption hinder BGI success and flood resilience.
• Priority on grey infrastructure: Canals, drains, and dams are insufficient for current stormwater volumes; BGI integration is essential for better retention and drainage.
Fig 22: Technical Guidelines for Rainwater Management on Building Environment (Ministry of Public Works , 2013)
Fig 20: Above - Illustration of Polder (Tanuwidjaja et al., 2017)
Fig 21: Right - Proposed GOS in Jakarta (Setiowati, Hasibuan and Koestoer, 2018)
SITE STUDY
5.1 Chennai (City scale)
5.2 Velachery (Neighbourhood scale)
5.3 Individual sites (Street scale)
DESIGN CONTEXT - Location
India’s coastal cities, such as Ahmedabad, Surat, Mumbai, Cochin, Chennai, and Kolkata, are increasingly vulnerable to annual flooding during the monsoon seasons (June to September and October to December). Rapid and unplanned urbanization, encroachments on floodplains, shrinking water bodies, reduced green spaces, and the declining capacity of traditional drainage systems increases this vulnerability (Gupta, 2020).
Chennai, situated on the Eastern coast and a floodplain for three rivers draining into the Bay of Bengal, has faced frequent floods since 2005 due to the conversion of water bodies into impermeable surfaces. The most recent flood in December 2023 highlights ongoing safety and infrastructure challenges (Kumar, 2023; Dhiman et al., 2018).
Flood vulnerability of Chennai
• Low elevation (avg. 6m above sea level)
• Flooding from Cooum, Adyar and Kosaithalaiyar rivers
• Heavy annual rainfall
• Cyclonic storms
• Encroachment on water bodies
• Landuse violations
• Population growth and dense settlements
• Improper maintenance of stormwater system
• Improper waste management
Velachery in Chennai has seen rapid growth due to the IT sector over the past 20 years along with a steady decline of waterbodies. It is one of the most affected neighbourhoods during repeated floods in the last few years (Thangaperumal et.al., 2019).
Flood vulnerability of Velachery
• Low elevation (avg. 6m above sea level)
• Reduced capacity of waterbodies and grey infrastructure
• High impermeability
• Landuse violations and encroachments (Rekha, Suriya and Arul, 2022)
FIG 23: Map of India (Rajeshodayanchal, 2011)
FIG 24: Map of Tamil Nadu (Gupta, Natarajan and Berlin, 2021)
FIG 25: Map of Chennai Municipal Authority (CMA) (Rajan and Amirtham, 2021)
Velachery
Water Bodies
Marshy Land
Vegetation
Soil Fill
Built-up Area
Fig 28: Land use cover of Velachery in 2008 and 2018 (Thangaperumal et.al., 2019)
Growth pattern in Chennai
• Dense growth within City limits
• Radial pattern of growth towards North, West and South along major roads
• More growth in South due to development of IT corridor
• Pallikarnai marshlands reclaimed for city expansion towards South (decreasing boundary of marshland marked in Fig 26)
Growth pattern in Velachery (Thangaperumal et.al., 2019)
• Marshy and vegetated land in Velachery has been built up rapidly over the past 10 years. Decrease in vegetated land from 21% to 11%
• Built-up areas cover 57% of Velachery (impermeable land)
• Loss of buffer zones due to encroachments is seen around Velachery ery (major flood zone)
Ecological loss due to urbanisation and high impermeability are major factors for flood risk in Velachery
Fig 27: Change in Urbanisation in Chennai from 1973-2006 (CMA, 2006)
DESIGN
Waterbodies in Chennai form a cascading network from the West to the East i.e. if one lake reaches capacity, the excess water flows into another lake downstream via canals or natural channels and so on till the water drains into the Bay of Bengal. This was known as the Ery system as mentioned in section 3.3.
For Velachery, the cascading lakes flow into Velachery ery which ultimately drains into Pallikarnai marsh. There are no waterbodies or canals in between suggesting a missing link. This is a possible reason why the roads and neighbourhoods flood annually. Furthermore, encroachments and accumulation of silt has reduced the carrying capacity of waterbodies as shown in Fig 31.
Waterbodies draining into Pallikarnai marsh
Drains into Adyar river Velachery
Fig 29: Major Waterways and Waterbodies in Chennai (CMA, 2006)
Fig 31: Water spread area of waterbodies observed in Chennai 2023 (Bhuvan, 2024)
Fig 30: Drainage of cascading waterbodies into Pallikarnai marsh from high to low elevation (Topographic maps, 2024)
DESIGN CONTEXT - Elevation
Flow of water through Velachery
1. Areas around Velachery ery are at the same elevation as the lake and flood easily
2. Floodwaters from northern and western neighbourhoods flow into Velachery
3. Major roads through Velachery are most flooded due to low elevation and high impermeability
4. Floodwaters flow from the main road into inner residential areas of Tansi Nagar
5. Floodwaters from South Velachery and surroundings drain out into Pallikarnai marsh
Fig 32: Elevation map of Velachery (Topographic maps, 2024)
Flexible spaces that are allowed to flood, retention and drainage of roads, and buffers for low lying neighbourhoods are likely strategies for immediate flood management
Fig 26: Velachery (Google Earth Pro)
A. Encroachments around waterbodies - highly dense
Velachery is a dense, primarily residential neighbourhood in the South of Chennai. It is more concentrated around Velachery ery and becomes sparse towards the south
Defined grid pattern
Highly porous neighbourhood with narrow streets in mostly organic pattern. More vehicular usage than pedestrian on major and minor roads.
GRAIN MAP
GRID AND BLOCK MAP
Mixed use development found along major roads. Velachery borders various landuses to the north. Residential neighbourhoods have their own parks/small green spaces.
Velcahery is well connected by road. Public transport is accessible only on major roads (bus stops and MRTS line).Not very accessible for bicycle and pedestrian movement.
LANDUSE CONNECTIVITY
EXISTING INFRASTRUCTURE - BLUE, GREEN, GREY
BLUE INFRASTRUCTURE
Marshlands
No distinct edge between lake and built. Settlements at the edge are highly vulnerable. Slow maintenance.
No distinct edge between marsh and built. Settlements at the edge are highly vulnerable.
Distinct edge exists but is not activated.
Open unused areas that can be integrated with existing infrastructure
Temple tanks & Street Ponds
Temple tanks are not well maintained. Most of them are overgrown with weeds. Some have disappeared.
Fenced in pond becomes a forgotten area. No edge connection with the people and surroundings.
Most of the blue infrastructure is neglected due to being fenced off and poorly maintained. Establishing a social connection with these is essential for their revival and maintenance.
Potential for blue spaces to become multipurpose spaces - public use (residential, recreational, religious) and water retention.
Fig 33: Pallikarnai marsh
Fig 34: Velachery ery
Fig 36: Gangai Amman Koil tank
Fig 37: Nattar street pond
Fig 35: Kallu kuttai lake
Lakes (Erys)
GREEN INFRASTRUCTURE
GREY INFRASTRUCTURE
National Park Canals
Protected forest that also offers recreational facilities like a medium zoo, children’s play space, and walking trails.
Open grounds
Neighbourhood parks & Playgrounds
Open grounds of various sizes are seen in Velcahery. The cricket ground next to the marsh can become a multipurpose retention pond.
Public playgrounds for children are found in smaller neighbourhoods (or nagars). Mostly paved or filled with sand, these spaces flood during rains. Can become smaller retention and infiltration spots in the neighbourhood.
SWD (for road widths>7m)
Permeable paving for trees
Canals are not well maintained in the whole length. Spaces adjoining canals can be used for public activities. 257 SWDs connect Velachery (GCC, 2023).
DRAINAGE NETWORK IN VELACHERY
(Existing)
MRTS Parks under the railway line, a green corridor running till Thiruvanmiyur, can be adopted on other major roads and integrated with blue infrastructure as well.
Current systems all drain out into the streets due to less capacity of SWD and canals during extreme rainfall. BGI can help delay this runoff and decrease stormwater volume through retention, infiltration and storage.
Fig 38: Guindy National park
Fig 42: Veerangal canal along 100 feet road
Fig 43: Rajbhavan canal
Fig 44: Grates for stormwater drainage found along 100 feet road
Fig 45: Permeable paving along Velachery Main road
Fig 40: Bharathiyar Park
Fig 41: MRTS Park, Puzhudivakkam
Fig 39: Velachery cricket ground
Comparing Fig 46&47, 3 highly vulnerable sites are selected in Velachery to study the street level integration of BGI 1.
Fig 46: Inundated areas during 2015 floods (GCC, 2023)
Fig 46: Flood vulnerability in Zone 13 (comprising Velachery) (GCC, 2023)
Around Velachery ery 2. 100 feet road
Tansi nagar
Site 1 - Around Velachery Ery
Streets adjoining Velachery ery, Marudupandiar road and Lake view road, are the most vulnerable when the lake overflows. Even though a minimum buffer of 15m is required from the lake, many buildings sit right at the edge.
Buildings along Velachery ery are found to follow the 15m buffer at section A whereas the buildings move closer to the edge at further sections. Since the terrain is flat, the lake overflows easily during heavy rains and it is difficult for water to drain back into the lake.
Along Marudupandiar road, mixed use G+1 and G+2 buildings are found (commercial on ground floor, residential above). Majorly residential area with flat roof houses. Lake view road consists of single storey residential buildings.
Marudupandiar
Fig 47: Site section outlines (modified from Google Earth Pro)
OPPORTUNITIES
O1. Existing Blue,Green and Grey infrastructure on site can be integrated for better retention and drainage
O2. Potential for lakeside walkway along Marudupandiar road to become a major public space with integrated BGI
O3. Potential for neighbourhoods along Lakeview road to adopt a polder system (used for low-lying areas)
O4. Potential for BGI building systems to be integrated to delay runoff (green roofs)
O5. Potential to engage the surrounding residents to take responsibility of “their” BGI and “their” lake
CONSTRAINTS
C1. Poor maintenance or slow maintenance of existing lake and canals
C2. Lack of ownership and community engagement at present
C3. Lack of buffer area along Lakeview road makes it difficult to integrate BGI. Residents may face relocation while edge restoration takes place
C4. Majority of the area is paved (roads, pavements and around buildings). Transitioning to permeable paving or no paving is challenging (financially and psychologically)
Fig 48: Velachery ery and Rajbhavan canal
Fig 52: Buildings close to the edge of the lake
Fig 53: Tar road and cement pavings do not allow water to percolate
Fig 49: Lakeside walkway along Marudupandiar road
Fig 51: Weeds in lake and garbage thrown over canal
Fig 50: G+1 and G+2 residential buildings
O1
O2
O4 C1
C3
C4
One of the major roads passing through Velachery from North to South, 100 feet road is the main commercial corridor in Velachery.
The road slopes downwards from North to South. Having more paved surfaces and less vegetation, stormwater collects on this road annually.
Provision for stormwater drainage exists along the 2.5km long road but their capacity is limited and cannot handle the current density.
Overflowing sewerage lines along the road also pose a hazard to the health of the people.
(Approx values taken according to Indian Road Congress and Google Earth Pro for street widths)
Setbacks from the sides of the road till the building are paved and used for parking. SWD on Western side is raised from the road aiming to provide a barrier between floodwater and the building.
Buildings run along the road edge towards the southern end of the road due to the flyover.
Site 2 - 100 feet road
OPPORTUNITIES
O1. 100 feet road is wide enough to accommodate SUDS and other BGI drainage systems to help with stormwater drainage and reduce heat island effect
O2. Potential for paved parking areas along the road to become depaved, permeable spaces for stormwater infiltration
O3. Potential for space under the flyover to become a blue-green corridor for drainage and public use (similar to MRTS parks)
O4. BGI systems integrated along the road need to consider all users (vehicle users, pedestrians and street vendors)
CONSTRAINTS
C1. Administrative and financial constraints may arise for depaving the road and adjoining surfaces.
C2. Land owners along the road may be resistant to include BGI within their setbacks
C3. Maintenance of BGI, especially green spaces might be difficult in first few years of BGI integration due to water shortages in summer.
Fig 54: Paved parking on road sides
Fig 56: Street vendors along the road
Fig 57: Paved road and footpath found along the road. Unpaved surfaces are few.
Fig 55: Space under flyover used for vegetation. Vehicles parked next to the divider
Site 3 - Tansi nagar
Tansi nagar is a dense residential area in the south of Velachery. Due to its low elevation comparatively, the neighbourhood faces floods since water from surrounding regions drain into it. Chennai Corporation has constructed SWD drains connected from each house to the street. Water infiltration systems (SWD, individual RWH) are in place however water drainage systems are not able to handle the volume even during normal rains.
School
Waterbody
Green spaces
Unpaved surface
Paved surface
Unused space
Refer pg 26-27
F - footpath S - shoulder P - parking
(Approx values taken according to Indian Road Congress and Google Earth Pro for street widths) Inner roads of Tansi nagar are narrow with some stretches having vegetation (shrubs and trees). Houses are raised by 30-45cm from the road level and a ramp and/or steps are built from the plot edge to the road edge for access forming a discontinuous footpath. 4-wheeler and 2 wheeler parking is also accommodated along the sides. Generally, G+1 and G+2 houses are seen in Tansi nagar with a few G+3 apartment buildings.
Tansi nagar lies on both sides of Taramani Link road which houses commercial buildings. The flyover from 100 feet road ends here. A service road along some sections for commercial buildings has its own 2 wheeler parking space, raised from the road level. G+2, G+3 and taller buildings are seen. The footpath houses the SWD on both sides of the road.
G3 C2
Site 3 - Tansi nagar
OPPORTUNITIES
O1. Missing links in SWD network in the area have been rectified.
O2. Sidewalks have multiple purposes and need to be considered while integrating BGI
O3. Potential to include buffer elements on Taramani link road to decrease water flowing into Tansi nagar from the main road
CONSTRAINTS
C1. Narrow inner roads make it difficult to integrate surface level BGI for drainage or retention
C2. Community engagement and individual responsibility is key in this site for maintenance of BGI system
C3. Public awareness and response towards BGI is less (explained in section 6)
Fig 58: Velachery flyover seen from Tansi nagar
Fig 59: Typical street in Tansi nagar
Fig 61: Small grocery store on the sidewalk
Fig 60: SWD work in progress; stormwater grill on road; SWD pipe with manholes on sidewalk
Fig 62: Steps and ramp leading till edge of road; concretised sidewalk; sidewalks used for parking
Fig 63: Parking along roads; shrubs along roads
DESIGN FRAMEWORK
From the case studies it is seen that every scale of BGI has a set of distinct functions to play in flood management as shown in Fig 68.
Linear urban landscape corridors around the city forming a green network; Biodiverse and mitigates flood; Can be incorporated with existing transport network (rail lines)
The table below takes into account the inferences from case studies and site analysis and forms a strategic BGI framework which can be implemented in Chennai.
Increase biodiversity
activity
island reduction
activity
Artificial or engineered waterway to collect water from an area and transport it to a larger waterbody (river, sea etc) Drainage Increase biodiversity
Natural wetlands are highly biodiverse ecosystems; mix of water and land; natural sponge against flooding Constructed wetlands - engineered to mimic natural wetlands
island reduction
biodiversity
activity River and stream renaturation
Restoring river and stream edges from grey to green; less construction more natural vegetation Detention
biodiversity Social activity Sandy
Buffer between ocean and land; Provide natural barriers like dunes or artificial like constructed reefs for protection against tidal flooding and storm surges Buffer
Linear urban landscape corridors around the city forming a green network; Biodiverse and mitigates flood; Can be incorporated with existing transport network (rail lines)
ponds Depressions in open spaces to hold stormwater
Multipurpose bioretention area; usually a playground or field allowed to flood during rains;
Artificial or engineered waterway to collect water from an area and transport it to a larger waterbody (river, sea etc) Drainage
Parks (open green spaces)
Various sizes; can be pocket gardens to large nature reserves; owned by both public and private Infiltration Retention
biodiversity
activity
activity
biodiversity
activity
island reduction
Increase biodiversity
activity
Increase biodiversity
activity Heat island reduction
City scale Meso Green corridors
Shores
Neighbourhood scale
Fig 68: Major functions of BGI at Micro, Meso and Macro levels as seen in case studies
TABLE 3: Strategic BGI framework for flood management in Chennai Green spaces
lake Micro Green roofs
Pocket gardens
permeable paving
Vegetated roofs; can also include water elements
Open, unpaved green space in smaller scale like residential gardens or pavement gardens
Storage
Porous paving material that allow absirption and infiltration of rainwater Infiltration RWH
System of collection, purification and storage of rainwater from roofs and other paved surfaces in and around a building
Earthern shafts with concrete rings for support to collect rainwater and recharge natural aquifers
Storage
Storage
Individual green pockets for physical and mental wellbeing Heat island reduction
biodiversity in small areas
water source to balance water needs during summer and winter
water source to balance water needs during summer and winter
Open, unpaved green space in smaller scale like residential gardens or pavement gardens
biodiversity in small areas permeable paving
paving material that allow absirption and infiltration of
Linear urban landscape corridors around the city forming a green network; Biodiverse and mitigates flood; Can be incorporated with existing transport network (rail lines)
biodiversity Social activity
green pockets for physical and mental wellbeing
Open, unpaved green space in smaller scale like residential gardens or pavement gardens
and
System of collection, purification and storage of rainwater from roofs and other paved surfaces in and around a building Storage Sustainable water source to balance water needs during summer and winter
Earthern shafts with concrete rings for support to collect rainwater and recharge natural aquifers
Storage
Groundwater recharge
Drainage - flow of stormwater
Purification - natural filtering of stormwater
Detention - permanently hold stormwater Secondary benefits
water source to balance water needs during summer and winter
Retention - temporarily hold excess stormwater
Buffer - barrier elements between water and land
Storage - structures to hold excess water; smaller than detention
Velachery
Sunk wells
Meso Green corridors
Tansi nagar Micro Green roofs
DESIGN PROPOSAL
8.1 Design Interventions
8.2 Design guidance
DESIGN PROPOSAL
8.1 Design intervention Site 1 - Around Velachery Ery
Street scale BGI interventions on site
• Green roofs to be incorporated along buildings on Marudupundiar road for delayed runoff and storage. Supported by RWH systems and storage tanks for individual use. Proximity to the main road brings attention to passersby increasing awareness.
• Permeable paving along roads to decrease surface runoff. Pavements also accommodate parking, street vendors and spill out for shops.
• Edge restoration of the ery by reconstructing the ery bund, using vegetation, and reducing encroachments
• Connections to public realm through ery walkway enhanced by pocket gardens to increase stormwater absorption.
Individual systems used at Street scale
Individual systems used at Street scale
Pocket gardens along the walkway increases rain infiltration and reduces surface temperatures.
Public
Fig 71 (from top): Green roofs with low maintenance plants (Pailhès, 2023); Small scale rooftop garden (Novak, 2021); Permeable pavers (McCormack, n.d.)
Fig 69: Shops spilling out along Marudupandiar road
Fig 70: Alfred Place gardens, London (Mansfield, 2022)
8.1 Design intervention Site 1 - Around
Velachery Ery
Residences on the southern side of the ery fall within the setback area. A temporary solution till their rehabilitation is possible, would be to have an additional channel within the slope of the ery connected to Veerangal canal in the south along with pumps to drain out the neighbourhood during floods. (Adaptation of the Polder system)
Green roofs/ Roof gsrden along Ery edge
DESIGN PROPOSAL
A - Extending sidewalks on both sides
• Permeable paving along roads to decrease surface runoff. Pavements also accommodate parking, street vendors and spill out for shops.
• Front setbacks of buildings to have permeable paving and vegetation to reduce paved areas. These form an extension of the sidewalk in the following stretches.
1. Exit from Phoenix mall to 100 feet road
2. Intersection of 3rd main road and 100 feet road
Both provide opportunities for restaurants, cafes and street vendors to use the space activating the sidewalks
With permeable paving almost 50% of the street cross section can drain stormwater directly to the ground. Additional channel in the middle of the road can help move stormwater quicker during rains and potential floods.
Extended pavements on both sides promote social activity and accommodates temporary users like street vendors.
DESIGN PROPOSAL
B - Green corridor
• Space under the flyover becomes a green corridor for drainage and infiltration of stormwater on the road.
• Can be adopted on Taramani link road and 100 feet road to the west
Walkway under the flyover helps stormwater infiltration and increases biodiversity. Additional green wall along the columns will help increase air quality along the road and decrease heat island effect.
Social activity along the walkway is minimal due to heavy volume of traffic on the road. Extended footpaths also see reduced activity towards the southern end of the road (towards the intersection).
If traffic volume is decreased and adjoining spaces are more activity based (especially for the residents around), then the walkway can become an active public space.
DESIGN
PROPOSAL
8.1 Design intervention
Site 3 - Tansi nagar
Street scale BGI interventions on site
• Permeable paving along roads to decrease surface runoff.
• Green roofs (extensive, intensive, aesthetic, farming) to be incorporated along with RWH system and storage tanks.
• Increase vegetation along pavements for more absorption of stormwater
Plants or grass
Growing medium (10-15cm)
Drainage layer - water for the plants
Stormwater retention
Waterproofing
Concrete slab
Blue roofs, a type of green roof, focus on retention of water during rains and the slow release of water into the drainage system over a period of 12-24 hours to reduce pressure on the drainage network.
This can help Tansi nagar in reducing the volume of floodwaters released on streets, reducing flood volume and associated risk.
cross
F - footpath
S - shoulder
Grills spaces at regular intervals on the footpath allow stormwater to flow into the existing SWD network. For roads having width less than 7m and no SWD connection, the permeable pavement directly recharges groundwater.
Groundwater can be used through sunk wells.
Typical
section of street in Tansi nagar
Fig 72: Blue roof system (Pritchard, 2021)
Permeable surface
Blue roofs Flyover 10m
Permeable pavement
DESIGN PROPOSAL
Connection to the public realm
Neighbourhood scale BGI strategies
• Using existing playgrounds, parks and fields as retention ponds during rains. The ponds allow infiltration for groundwate recharge and slowly releases water into the drainage network.
• Integrating temple tanks into the drainage network as detention ponds
• Using transport lines - MRTS lines, flyovers etc - for green and blue corridors. These help drain the area faster and increases biodiversity in the neighbourhood
• Edge restoration of lakes, erys, canals and rivers.
City scale BGI strategies
Existing Green corridor (MRTS parks)
Existing public space (Phoenix Marketcity mall) 1. Open public space
• Using transport lines - MRTS lines, flyovers etc - for green and blue corridors. These help drain the area faster and increases biodiversity in the neighbourhood
• Edge restoration of lakes, erys, canals and rivers.
• Restoration of Pallikarnai marsh for flood detention and recreational activities (examplebirdwatching)
• Coastline protection using dunes against cyclonic storms
2&3.
ADYAR
PALAVAKKAM
VELACHERY ERY
BAY OF BENGAL
Fig 73: Interconnected BGI (Google Earth Pro)
Integrating BGI into a developed area is challenging. The following points illustrate how this can be achieved at design and policy levels.
Flood reduction starts by “working with water”. Allowing water to flow through the city needs to be the focus.
Depaving - the initial strategy
Vegetated surface - Low cost
Partially paved surfaces (using permeable pavers with spacing for grass to grow)
Paving using permeable materials (pervious concrete)
Reclaiming sidewalks, footpaths and pavements
Edges of the road can act as temporal spaces for a lot of activities and are the easiest spaces to integrate blue, green and grey infrastructure. This forms a network running through the city which not only increases sustainable drainage but also reduces surface temperatures.
Integration of pocket gardens, swales, channels, or permeable pavements differ from road to road and site to site.
Open spaces need to be flood-able
For a context that faces recurring urban floods, allowing certain spaces to flood and retain water without infrastructural damage and risk to people’s lives is necessary.
Existing parks, grounds, fields, and public spaces can be designed to retain and infiltrate water.
Consider secondary benefits of BGI
BGI provides economical and social benefits apart from environmental. Integrating BGI adds more value to a space.
Building a relationship with water
Sensory connect with water
- see water - reduce fences and blocks to the view
- hear water - provide protected spaces from traffic and noise
- feel water - steps to the edge
Activities drawing people of all ages to the edge of the water
- Play areas for children
- Community gardens
- Walkways for leisure and exercise (+ outdoor gyms)
- Community gatherings/meetings
- Eateries (cafes, restaurants etc)
Fig 74: Permeable pavements (McCormack, n.d.)
CONCLUSION
This research project aimed to understand urban floods and how Blue-Green infrastructure can be used to form a strategic framework for flood management. BGI systems at various scales were analysed to create a multi-scalar, adaptive framework for flood management and resilience in Chennai. Using the neighbourhood of Velachery as the design context, strategies were devised at street, neighbourhood, and city scale for flood mitigation.
BGI systems at Micro, Meso and Macro scales were analysed to form an initial framework. The inferences from global examples along with the site analysis were used to develop a strategic framework at street, neighboourhood and city scales for Chennai. The street scale strategies were explored through design as three interventions, each with their distinct characteristics. Strategies around Velachery ery revolved around building a connection between the water and the community while strategies employed on 100 feet road and in Tansi nagar focus more on drainage and infiltration of stormwater. It is observed that even narrow streets (width 3-5m) can integrate small-scale BGI for sustainable drainage and reducing stormwater runoff. Streets, forming an established network are the most flood-prone areas in a city and the easiest spaces to incorporate BGI, especially for a context facing rapid and unplanned urbanisation. Converting existing infrastructure into flood retention areas provide relief during rains and subsequent floods. Temple tanks, street ponds, playgrounds and parks can be turned into retention basins which will help reduce the pressure of the drainage system which in turn reduces street flooding. Environmentally sensitive areas like marshlands and wetlands are an integral part of the plan. These spaces manage large volumes of floodwaters from all over the city so it is essential to revive them, reduce encroachments on them, and restore their water-carrying capacity.
That being said, flood mitigation needs to start at the regional level involving the farthest waterbodies. Watershed management policies that increase the water capacity of lakes, including regular maintenance and community involvement should be prioritized. While this project lays out a foundational framework to integrate BGI into the urban context of Chennai, this is only a part of the broader solution for effective urban flood management.
Limitations of the research
Due to the timeline of this project, only street-scale interventions were explored through design with conceptual frameworks provided for neighbourhood and city scales. No GIS mapping of the blue-green infrastructure and flood zones has been done for analysis of the framework in the context. The framework is to be considered as a recommendation to inform future design and policies.
Various socio-political factors influence the context and their effect on the implementation of BGI in Chennai were not considered as it falls outside the project’s scope. Therefore, encroachments on waterbodies (around Velachery ery) were considered as part of the site, providing temporary solutions for flood relief. The project recognizes that these temporary solutions are not a substitute for comprehensive, long-term flood management strategies.
For the implementation of this framework, various stakeholders need to coordinate. Public awareness of larger systems of BGI is higher than individual systems. This is a possible reason for poor community engagement since the knowledge and awareness of systems that can be
handled by individuals is low. Communication links between the government and the public are also lacking. Current water management practices are split between Water Resources Department (WRD) of Tamil Nadu for macro drainage and Greater Chennai Corporation (GCC) for micro drainage. Coordination between State and City governments is poor affecting the implementation of the framework since it deals with both macro and micro drainage.
Future research
Accurate GIS mapping of the existing blue-green infrastructure and its boundaries will help create a flood management plan for the region. The masterplan needs to involve various stakeholders – government officials, urban planners, urban designers, GIS engineers etc – for a holistic approach to flood management and sustainable growth. Cost-benefit analysis of implementing BGI in India and Chennai are areas for further research.
The results of this project lay the groundwork for enhancing resilience in Chennai, highlighting the importance of integrated and adaptive approaches to address the rising challenges of urban flooding.
