Underpasses: Under par, under water

Poor design, placing and maintenance coupled with grossly inadequate drainage mechanisms have left most underpasses in the City extremely vulnerable to flooding during heavy downpours.

Fifty unsuspecting bus passengers stood dangerously close to a disastrous watery end to their journey. Trapped in an underpass near Anand Rao Circle, they helplessly stared in extreme horror. A record 130 mm downpour on September 26 had come horrendously close to submerging their buses. Totally!

Fire and Emergency Services personnel eventually rescued them after much struggle. They survived to ask a million questions to the city’s civic agencies. About the quality of the underpass construction, about its poor maintenance record, and yes, about the authorities’ rain preparedness found extremely wanting!

It was clear that a dangerous mix of faulty design, below par upkeep and a record rainfall had pushed the city to the edge yet again. Thoroughly exposed was the engineers’ limited understanding of storm water management in extreme situations. Commuters eventually paid for all those lapses.

Lessons are hardly learnt even when disasters strike with monotonous regularity, year after year. Despite the inherent defects with underpasses built with little or no natural gradients, many more are planned across the City. Existing ones are rarely redesigned and restructured.

Last November, flooding of the Kino Theatre underpass had triggered another vehicular gridlock, a ritualistic, annual repeat of heavy rain and after-effects. But for once, BBMP had zeroed in on the culplrit: A piece of plastic that blocked the small drain in close proximity to the underpass. Water had stagnated to reach monstrous levels in good time.

Quickfix solutions

The Palike had talked about a solution, made public after a visit to the spot by the commissioner and the district incharge minister Ramalinga Reddy: To build a new parallel drain that would connect to the storm water drain passing close to the Karnataka Slum Clearance Board office.

In July 2013, BBMP had made another assurance of rectifying a fault with the underpass near Le Meridien on Sankey road. The facility was closed due to water-logging triggered by a blocked storm water drain. Commuters suffered for weeks and harried traffic policemen complained of unending vehicular queues.

As urban experts point out, problems such these shouldn’t recur if the Palike knows how water, sewage, electrical and telecom lines criss-cross an area. The Geographical Information System, for instance, should help the project engineers plan and fix an underpass’ location accordingly.

But good design goes even beyond. The location of the underpass should meet natural gradient requirements so that the excess water drains out due to gravity. If this is not possible, high discharge pumps should be placed for quick evacuation. The water flow, measured in volume per sec should be calculated in advance to see how much will get into a SWD and how quickly, explains retired BWSSB chief engineer, MN Thippeswamy.

Natural gradients 

Urban architects emphasise the need for grilled vents inside every underpass to help the flood waters reach the natural gradient. But these vents too should be well designed. “Flooding happens when the vent openings are not adequate enough. Debris might block them. They can’t be too wide either due to safety reasons,” notes a Water Board Assistant Engineer.

Most underpasses in the city are without water actuated pumps that should be permanently fixed with backup. “At the bottom of the underpass, there should be collection sumps. Once the water level reaches a predetermined level, it should get automatically pumped and drained out to a higher level,” informs architect Naresh. His choice is not to have underpasses at all in the City. “Bangalore needs better solutions to mobility. A city such as New York with far more traffic has no flyovers or underpasses. Ideally, such grid separators should be built only over a railway line, a ring road intersection or over water.”

Design shortcomings

Hurriedly planned short-sighted solutions to the city’s ever-rising traffic problems have meant more flyovers and underpasses. As commuters, traffic policemen and experts assert, this strategy is not going to change anytime soon. So, the best option would be to identify the big faults in the current designs.

Traffic expert, MN Sreehari finds that most underpasses have narrow width and lack adequate cross and longitudinal slopes at the bottom. This invariably holds up water, slowing down drainage. Grilled vents are rarely provided at both approaches. The cross drainage mechanism too is not designed scientifically. If the drains are not desilted regularly -- which is usually the case --, the flooding threat during heavy downpours looms larger. 

Strategies to combat flooding in low-level underpasses is not rocket science. Motorists such as Domlur resident Prashanth Purohit or Basavanagudi resident, Shibani Bhonsle are experienced enough to suggest better desilting of drains. As Bhonsle explains, heavy rains usually drag mud and other debris to lower areas, clogging drain openings. Scientifically designed slopes and alignments are a must as well.

Corrupt nexus

Yet, the quality of most underpass structures in the city leave much to be desired. An architect with many years of experience with BBMP projects blame a corrupt nexus of contractors, bureaucrats and politicians for the emergence of inferior, poorly located underpasses built with minimal expertise. One expert is brutally frank to even state that the “engineers don’t know the ABCD of scientific planning and design.”

The design imperfections are clearly exposed in “A study of vehicular underpasses in the City” carried out by the Centre for Infrastructure, Sustainable Transportation and Urban Planning (CiSTUP), Indian Institute of Science. The study had found that 58 per cent of underpasses built by the Bangalore Development Authority (BDA) and an even higher 64.3 per cent executed by BBMP did not meet the vertical clearance standard of 5.5 metres mandated by the Indian Road Congress (IRC). 

Half of the BBMP underpasses also fail to meet the width standards of IRC. For single lanes, the IRC requirement is 3.75 metres. For double lane roads, the width required is 7.5 metres. As if these weren’t enough, both BDA and BBMP were found wanting in maintenance of the underpasses. Only 33 per cent of the projects measured up to the IRC’s maintenance standards.

The study did refer to clogging and poor drainage records of most projects. Having endured nightmarish drives and rides through the city’s flooded underpasses year after year, Bangaloreans now want BBMP, BDA and the state government to break out of their studied silence and get into action mode.