URBAN FLOODS

Frequent flooding since 2000 (even during normal rainfall) is a consequence of the increase in impervious area due to land use changes in the catchment from open space to impervious surfaces with the high-density urban developments. This is coupled with lack of drainage upgrade works with the changes in enhanced run-offs, the encroachment and filling in the floodplain on the waterways, obstruction by the sewer pipes and manholes and relevant structures, deposits of building materials and solid wastes with subsequent blockage of the system and also flow restrictions from under capacity road crossings (bridge and culverts). The lack of planning and enforcement has resulted in significant narrowing of the waterways and filling in of the floodplain by illegal developments.  This has subsequently caused flooding to other properties that have not previously been flooded, new properties in the flood plain built below the high flood marks (designated flood levels), these being frequently flooded and restrictions of options for future flood mitigation including widening of waterways.

Reclamation of lakes for various developmental activities has resulted in the loss of interconnectivity in Bangalore district leading to higher instances of floods even during the normal rainfall. Analyses of Bellandur and Ulsoor drainage network (figure 9.1) showed that the network is lost due to conversion of Chelgatta tank into a golf course. Similarly the drainage network between Madivala and Bellandur revealed of encroachment and conversion that has resulted in the loss of connectivity between Yelchenhalli kere and Madivala (figure 9.2).

Figure 9.1: Ulsoor–Bellandur–Varthur (a) drainage network (b) lakes overlaid on 10 m DEM showing their missing interconnectivity

Figure 9.2: Madivala–Bellandur–Varthur (A) drainage network (B) lakes overlaid on 10 m DEM showing their missing interconnectivity

Increased peak discharge and higher frequency of floods are the consequences of urbanization due to lack of provisions for infiltration. As land use changes from vegetation and wetlands to impervious layer (built-up, roads, etc.), it loses its ability to infiltrate/absorb rainfall. Urbanisation has increased run off  3 to 6 times over what would occur on natural terrain in some pockets of Bangalore (Ramachandra and Mujumdar, 2009). During periods of urban flooding, streets become swift moving rivers, while low lying residential areas and basements become death traps as they fill with water. Conversion of water bodies to residential layouts and encroachment of storm water drains have further exaggerated the problem.

Ulsoor–Belandur catchment: This catchment has 6 lakes – Sankey, Ulsoor, Chalghata, Chinnagara and Varthur and was classified into three major land use types – built up, vegetation and others (comprising open land, waste land etc). The total rainfall yield in this catchment is 240 Mm3, percolated water is 90 Mm3 and water overflow is 150 Mm3. The SRTM DEM data were resampled to 10 m resolution and the volume of each lake was computed assuming the depth to be 1 m and the mean annual rainfall to be 850 mm. The total volume of all the 6 lakes in this catchment is 73 Mm3. Hence there is surplus overland flow of 77 Mm3, which cannot flow to downstream due to disruption of natural drainage (removal of lakes and blockage of storm water drains) resulting in flooding (even during normal rainfall).

Madivala–Varthur catchment: Similar analysis was done for  Madivala catchment which has 14 lakes – Venkatapura, Yellakunte, Bandepalya, Begur Doddakere, Madivala, Hulimavu, Marenahalli, Govindanaikana kere, Tank north of Doresanipalya, Gittigere and Vaddarpalya. The total rainfall yield is 247 Mm3, percolated water is 97 Mm3 and the remaining 150 Mm3 water flows as overland flow and storage in lakes. The total volumes of all the lakes considering 1 m depth is 110 Mm3  resulting in the excess of 40 Mm3 from the catchment leading to artificial floods. In addition to rainfall, Belandur-Varthur watershed receives untreated municipal sewage to the order of 500MLD.

Flooding in urban areas has caused large damage at buildings and other public and private infrastructure (evident during 1997, 2002 and 2007). Besides, street flooding can limit or completely hinder the functioning of traffic systems and has indirect consequences such as loss of business and opportunity. The expected total damage; direct and indirect monetary damage costs as well as possible social consequences is related to the physical properties of the flood, i.e. the water level above ground level, the extent of flooding in terms of water volume escaping from or not being entering the drainage system, and the duration of flooding. Table 6 summarises the causal factors for poor drainage system and remedial measures to be undertaken to improve the condition.

Table 8.1: Causal factors and key impacts

Conservation and Management of Wetlands: The loss of ecologically sensitive wetlands is due to the uncoordinated pattern of urban growth happening in Greater Bangalore. This could be attributed to a lack of good governance and decentralized administration evident from lack of coordination among many Para-statal agencies, which has led to unsustainable use of the land and other resources.  Failure to deal with water as a finite resource is leading to the unnecessary destruction of lakes and marshes that provide us with water. This failure in turn is threatening all options for the survival and security of plants, animals, humans, etc. There is an urgent need for:

• Restoring and conserving the actual source of water - the water cycle and the natural ecosystems that support it - are the basis for sustainable water management
• Reducing the environmental degradation that is preventing us from reaching goals of good public health, food security, and better livelihoods world-wide
• Improving the human quality of life that can be achieved in ways while maintaining and enhancing environmental quality
• Reducing greenhouse gases to avoid the dangerous effects of climate change is an integral part of protecting freshwater resources and ecosystems.

A comprehensive approach to water resource management is needed to address the myriad water quality problems that exist today from non-point and point sources as well as from catchment degradation. Watershed-based planning and resource management is a strategy for more effective protection and restoration of aquatic ecosystems and for protection of human health. The watershed approach emphasizes all aspects of water quality, including chemical water quality (e.g., toxins and conventional pollutants), physical water quality (e.g., temperature, flow, and circulation), habitat quality (e.g., stream channel morphology, substrate composition, riparian zone characteristics, catchment land cover), and biological health and biodiversity (e.g., species abundance, diversity, and range).

The suggestions for conserving and managing wetlands to mitigate frequent floods as per the recommendations of the Lake 2010: Wetlands, Biodiversity and Climate Change (22-24 December 2010) organized at Satish Dhawan Auditorium, Indian Institute of Science Campus and, Brainstorming session for evolving the strategies for the conservation and management of lakes (26th Sept 2009) at Centre for Infrastructure, Sustainable Transport and Urban Planning [CiSTUP], Indian Institute of Science. Lake 2010 forum discussed the recommendations of Lake Symposiums (Lake 2008, Lake 2006, Lake 2004, Lake 2002, LimGIS 2001, Lake 2000, 1998 symposium) and Brainstorming Session (Ramachandra, 2009 a, b) apart from discussing the draft notification of the Regulatory Framework for Wetlands Conservation of The Ministry of Environment and Forests, Government of India. Policy interventions required to conserve fragile ecosystems – wetlands are:

1. Carrying capacity studies for all macro cities: to adopt holistic approaches in regional planning considering all components (ecology, economic, social aspects) in rapidly urbanizing macro cities such as Greater Bangalore, etc.
2. Demarcation of the boundary of water bodies: The existing regulations pertaining to boundary demarcations within different states need to be reviewed according to updated norms and based on geomorphology and other scientific aspects pertaining to individual water bodies. Maximum Water Level mark should form the boundary line of the water body. The buffer zone should be treated as inviolable in the long term interests of the water body and its biodiversity. This requires
• Declare and maintain floodplains and valley zones of lakes as no activity regions
• Remove all encroachments – free flood plains, valley zones, storm water drains, etc. of encroachments of any kind.
• Ban conversion of lake, lake bed for any other purposes.
• Urban wetlands, mostly lakes to be regulated from any type of encroachments.
• Regulate the activity which interferes with the normal run-off and related ecological processes – in the buffer zone (200 m from lake boundary / flood plains is to be considered as buffer zone)
3. Mapping of water-bodies: The mapping of water bodies should also include smaller wetlands, springs etc. The neglect of these hydrological systems could cause considerable impoverishment of water flow in the river systems as well as turn out to be threats to rare kinds of biodiversity.
4. Holistic and Integrated Approaches – Conservation and Management: Integration of   the activities with the common jurisdiction boundaries of Government Para-statal Agencies for effective implementation of activities related to management, restoration, sustainable utilization and conservation. This  necessitates common jurisdictional boundary for all Para-statal agencies. To minimise the confusion of ownership – assign the ownership of all natural resources (lakes, forests, etc.) to a single agency – Lake Protection and Management Authority (or Karnataka Forest Department). This agency shall be responsible for protection, development and sustainable management of water bodies). There is a need to maintain catchment integrity to ensure lakes are perennial and maintain at least 33% land cover should be under  natural Vegetation.
5. Documentation of biodiversity: The biodiversity of every water body should form part of the School, College, People’s Biodiversity Registers (SBR, CBR, PBR). The local Biodiversity Management Committees (BMC) should be given necessary financial support and scientific assistance in documentation of diversity. The presence of endemic, rare, endangered or threatened species and economically important ones should be highlighted. A locally implementable conservation plan has to be prepared for such species.
6. Mitigation of Floods: This entails maintenance of open spaces (vegetation, water bodies).  Mitigation necessitates restoration of  wetlands, removal of blockages in the drainage network, removal of encroachments (storm water drains, wetlands), prevention of indiscriminate disposal of  solid waste (including building debris) in storm water drains, lake beds, catchment of wetlands and restoration of the connectivity of lakes
7. Preparation of management plans for   individual water bodies: Most large water bodies have unique individual characteristics. Therefore it is necessary to prepare separate management plans for individual water bodies.
8. Implementation of sanitation facilities: It was noted with grave concern that the water bodies in most of India are badly polluted with sewage, coliform bacteria and various other pathogens.
9. Restoration of lakes: The goals for restoration of aquatic ecosystems need to be realistic and should be based on the concept of expected conditions for individual  eco-regions. Further development of project selection and evaluation technology based on  eco-region  definitions  and  description  should be  encouraged and supported by the national and state government agencies.
10. Protection of riparian and buffer zone vegetation: Any clearances of riparian vegetation (alongside lakes) and buffer zone vegetation (around lakes) have to be prohibited.
11. Restoration of linkages between water bodies: The process of urbanization and neglect caused disruption of linkages between water bodies such as ancient lake systems of many cities. Wherever such disruptions have taken place alternative arrangements should be provided to establish the lost linkages.
12. Rainwater harvesting: Intensive and comprehensive implementation of rain water harvesting techniques can reduce taxation of water bodies and also minimize electricity requirements. The country needs in principle a holistic rainwater harvesting policy aimed at directing water literally from “roof-tops to lakes” after catering to the domestic needs.
13. Environment Education: Lake associations and citizen monitoring groups have proved helpful in educating the general public. Effort should be made to ensure that such groups have accurate information about the causes of lake degradation and various restoration methods.
14. Adopt Inter-disciplinary Approach:  Aquatic ecosystem conservation and management requires collaborated research involving natural, social, and inter-disciplinary study aimed at understanding various components, such as monitoring of water quality, socio-economic dependency, biodiversity and other activities, as an indispensable tool for formulating long term conservation strategies. This requires multidisciplinary-trained professionals who can spread the understanding of ecosystem’s importance at local schools, colleges, and research institutions by initiating educational programmes aimed at raising the levels of public awareness of aquatic ecosystems’ restoration, goals and methods. Actively participating schools and colleges in the vicinity of the water bodies may value the opportunity to provide hands-on environmental education, which could entail setting up of laboratory facilities at the site. Regular monitoring of water bodies (with permanent laboratory facilities) would provide vital inputs for conservation and management.