Namma Metro, Namma Mess: What causes Bengaluru’s Silk Board Junction to sink when it rains?

Bengaluru: A Metro pillar in the middle of a major drain — this is the crux of a fierce blame game between BBMP and BMRCL on the now-infamous flooding at Central Silk Board junction, which forced the closure of a flyover, led to water gushing into homes, and resulted in a traffic mess affecting lakhs of commuters.

Saying Namma Metro construction at the junction has obstructed water flow at several points, former Bengaluru mayor BN Manjunath Reddy accused the Metro operator of inaction, despite raising the issue two months ago. "BMRCL engineers should be held accountable for the mess at Silk Board. A pillar was erected at the point where water from BTM Layout joins major stormwater drains, blocking the flow. This obstruction caused flooding in Dollars Colony, KAS Officers' Colony, and Silk Board quarters. Moreover, no shoulder drains were provided near Silk Board Metro station, worsening the waterlogging. Water receded only after concrete blocks were broken to allow it to flow."

Transport minister Ramalinga Reddy told TOI Namma Metro also blocked drainage on the Madiwala side. "They built a pillar blocking the natural flow of water. Instructions have been issued for immediate remedial action."

At Silk Board junction, BMRCL constructed a Metro station on RV Road to Bommasandra route. A curved ramp was built as part of a double-decker flyover in the area. Ongoing works include the Blue Line Metro station and the connecting ramp from HSR Layout to BTM Layout.

Maheshwar Rao, BBMP chief commissioner and BMRCL MD, told TOI: "Near the station, there's reverse flow of water. The area forms a ‘saucer' near the station. During rain, water pushes back into the station when the stormwater drain (SWD) is full. When the primary drain is completely full and the secondary drain cannot take the excess load, flooding becomes inevitable."

The chief commissioner said they need to assess whether the drain capacity can be increased as some drains are clogged. A team will be formed to discuss solutions with the additional chief secretary. "We'll look at options to manage both primary and secondary systems. In the meantime, we'll continue to explore temporary solutions," he added.

Last year, even after heavy rain, water would recede within an hour, but that's no longer the case. "At Roopena Agrahara, a drain was constructed to divert water and prevent it from reaching Silk Board junction. While this helped reduce the flow rate theoretically, that solution was handed over to BMRCL. Now, we must consider that there may not be a single solution — we need to explore multiple options," he said.

Tushar Giri Nath, BBMP administrator, told TOI: "The primary reason for flooding at Central Silk Board junction is the ongoing Metro work. The primary drains don't have the capacity to carry heavy volume of water flowing from KC Valley. Moreover, the secondary drains aren't fully connected, which causes water to reverse on to the streets, leading to severe flooding. Additionally, several drain sections have pillars constructed over them. There is a significant amount of construction debris in the area. This has led to blockages and has aggravated the flooding issue."