tsubba - 15 September, 2007 | Bangalore | Infrastructure | CDP

Chapter VIII of Bangalore's NURM-CDP, on Urban Drainage Systems.

Chapter VIII Urban Drainage Systems
1 Overview
The growing geographic spread of Bangalore and accompanying construction activity has interrupted the natural valley system of the region. Construction has also resulted in filling up small water bodies and low-lying areas. The flooding of drains during each monsoon exposes its poor state and their inadequate capacity, and impacts the City’s overall infrastructure. Therefore, improving the drainage system is a key and critical element in the City’s infrastructure.

1.1 Existing Situation
The City built by Kempegowda, 468 years ago, has a well-developed natural drainage system. Bangalore had more than 400 lakes, interlinked by a system of canals that followed the natural gradient of the land in which excess water from one lake would flow through waste-weirs into the next lake/tank, thereby preventing flooding. This system could be maintained for a long time, through the colonial period, till more recent times. The features of the existing system comprise:

• Naturally undulating terrain of Bangalore City:
  • Ideally suited for development of lakes that can capture and store rainwater;
  • Each valley at the ridge top gives rise to small streams which cascade down to form major stream systems;
• Lakes form chains of reservoirs in each of the three valley systems in Bangalore:
  • Flow of the water runs from North to South-east as well as Southwest along the natural gradient of the land;
  • The lakes harvest rainwater from their catchments, and the surplus flows downstream spilling into the next lake in the chain;
  • This connectivity ensured that additional water is continuously transferred to other lakes;
  • The system serves as an excellent flood controller and storage for rainwater;
• Pipe networks carry the collected wastewater to treatment plants – V Valley on Mysore Road (180 MLD), KC Valley near HAL Airport (163 MLD), and Hebbal Valley on Bellary Road (60 MLD); and
• Incomplete sewerage systems results in sewage being let out into storm water drains or lakes, polluting the water.

1.2 Key Issues of Urban Drainage Systems
With the growth of the City, the number of lakes has reduced to 64, and small lakes and tank beds have vanished because of encroachment and construction activities. This has resulted in storm-water drains reducing to gutters of insufficient capacity, leading to flooding during monsoon. Dumping of MSW in the drains compounds the problems, leading to blockages. To control floods, it is important to remove silt and widen these storm water drains to maintain the chain flow and avoid water from stagnating at one point.

2 Strategy for Improved Service Delivery

2.1 Characteristics of Sector
Urban drainage has a direct impact on the City's image, citizens' life, and health. If the system does not work properly, it leads to environmental hazards. However, the status is that urban drainage has become a victim of rapid urbanization. Improving the urban drainage system requires not only capital infusion, but also ongoing funding for operation and maintenance. A single point obstruction in a storm-water drain would have a cascading overall impact. Citizen awareness is therefore a critical issue, and citizens and NGOs can play a key part in monitoring development in the region to ensure that drainage is not obstructed, and dumping of debris and MSW in drains does not occur.

2.2 Proposed Implementation Plan for Urban Drainage Improvement
The proposed plan includes:

i) Construction/remodeling/rehabilitation of storm water drains and road side drains;
ii) Removing silting;
iii) Constructing retaining walls;
iv) Laying of beds;
v) Provision of enabling and awareness information architecture; and
vi) Green area development.

 

3 Project Identification & Costing
The “Valley Projects” as they are called, are the most critical element of the system. Improvement of storm water drainage system and roadside drainage and breaking the interconnectivity of sewerage and storm-water are crucial elements of the project.

3.1 Investment Plan for Urban Drainage Improvement

3.1.1 Projects in Implementation Period

i) Constructing 1,500 km of roadside drains (cost of construction assumed at Rs. 30 lakh per km for a 5-metre drain);
ii) Extension of the SWD network into CMCs and TMC areas;
iii)Clearing all encroachments that come in the way of the storm water drain network in the city;
iv) Aligning the drain network and checking blockage and overflowing of drains;
v) Reviewing existing storm water drains, ensuring connectivity of primary, secondary and tertiary drains;
vi) Redesigning for current load conditions along with building barriers between roads and open drains at crossings; and

3.1.2 Estimated Capital Investment Requirement
Table 52 gives the estimated investment requirement in the JNNURM period,
while Table 53 gives the estimated investment in future blocks.

4 Implementation Framework
One of the critical issues that is to be addressed relates to the fact that inadequate drainage in a particular ULB jurisdiction may not have the impact in that ULB but elsewhere. Coordination and continuity of action between the ULBs is of critical importance.

i) The importance of inter-ULB and Agency coordination:

i-a) Inadequate drainage in a peripheral ULB may impact drainage in BMP areas;
i-b) Improper drainage of BWSSB’s system may pollute the valley system and impact quality of life across the City; and
i-c) Improper roadside drainage and cross-connectivity may similarly impair system performance;

ii) Citizens to be involved to monitor contractor's activity on clearing of drain systems in their area:

ii-a) Citizens who dump debris into storm water drains could be penalized; and

iii) Removing silt to be a regular activity before the monsoons starting with the main (primary) drain.

The City is proposing to have a coordinated action plan to address the issue of urban drainage. At present BMP is coordinating the “valley projects,” and is carrying out the works in coordination with other agencies, facilitated by the GoK.

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