Virugambakkam-Arumbakkam canal

Urban Flooding, Hydrological Disruption, and the Limits of Engineering-Led Fixes in Chennai

Urban flooding in Chennai is frequently attributed to extreme rainfall events, yet such explanations obscure the deeper structural transformations that have rendered the city increasingly vulnerable to water-logging. The Virugambakkam-Arumbakkam Canal (V-A Canal), a relatively modest but hydrologically significant channel within the Cooum sub-basin, offers a revealing case study of how urban waterways are progressively compromised through encroachment, infrastructural misalignment, and governance fragmentation. The flooding associated with this canal is not an isolated malfunction, but a systemic outcome of how urban growth has been layered onto fragile hydrological systems.

Situating the Canal Within Chennai’s Waterscape and Unequal Risk

Series of images and maps showing the location of the Virugambakkam-Arumbakkam canal in the Cooum sub-basin and the watersheds surrounding it.

The Virugambakkam–Arumbakkam Canal is part of the Cooum River sub-basin and functions as a minor channel within Chennai’s broader drainage network. Originating near Nerkundram, the canal flows through Virugambakkam, Arumbakkam, and Aminjikarai before joining the Cooum River near Nelson Manickam Road. Spanning approximately 6.3 kilometres and draining a catchment area of nearly 13.7 square kilometres, the canal plays a critical role in conveying stormwater from densely built neighbourhoods.Historically, such canals were integral to Chennai’s hydrological logic, designed to intercept surface runoff and route excess water into rivers and wetlands. However, as the city expanded, these channels were increasingly reclassified from ecological infrastructure to residual urban space, vulnerable to narrowing, obstruction, and pollution.

Mapping of the canal’s watershed reveals its intersection with multiple drainage basins, including the Cooum River, Otteri Nullah, and Adyar River watersheds. Settlements located within the V-A Canal watershed are disproportionately exposed to flooding, as any disruption along the canal directly translates into water backing up into streets and homes. This spatial unevenness underscores an important dynamic: flooding is not distributed randomly across the city but is shaped by watershed boundaries that often cut across administrative wards. As a result, governance responses framed at ward or zonal levels frequently fail to address upstream-downstream interdependencies, leaving canal-adjacent communities particularly vulnerable.

The Narrowing of a Canal and Bottlenecks

One of the most significant factors contributing to flooding along the V-A Canal is the drastic reduction in its effective width. Originally measuring approximately 19 metres wide, the canal has, in several stretches, been constricted to barely 5 metres. This narrowing has occurred through a combination of formal and informal encroachments namely residential buildings, compound walls, and infrastructure projects that progressively eat into the canal’s buffer zones. The implications of this transformation are quantifiable. The canal’s carrying capacity has dropped from an estimated 1,700 cubic feet per second (cusecs) to around 800 cusecs. During periods of intense rainfall, this reduced capacity is quickly overwhelmed, causing water to spill into adjacent neighbourhoods. Flooding, in this sense, is not a failure of rainfall management but a foreseeable consequence of spatial constriction.

Bridges crossing the canal, intended to enable connectivity, have emerged as critical chokepoints. Of the 24 bridges identified along the canal, at least 11 are characterised by narrow vents, some less than 2 feet wide and under 5 feet high. These structures significantly impede water flow, especially when debris accumulates during monsoon events. Rather than facilitating continuity, such bridges fragment the canal hydraulically, creating localized backflow and stagnation. The problem is not merely one of maintenance but of design: bridges were constructed without adequate consideration of flood discharge requirements or future urban intensification. This reflects a broader tendency to treat water channels as static features rather than dynamic systems that respond to seasonal and climatic variability.

Pollution, Hydraulic Failure, Governance Fragmentation and Reactive Management

Image from left to right: Dumping of municipal waste on the canal has become a common practice; Encroachments have also significantly contributed to the reduction in the canal's width.

The canal’s ability to function as a drainage conduit is further compromised by chronic pollution. Untreated sewage from residential colonies and commercial establishments is routinely discharged into the canal, increasing sedimentation and reducing flow velocity. Municipal and construction waste dumped into the channel exacerbates this problem, physically blocking water movement and raising the canal bed over time. These practices transform the canal from a flowing watercourse into a sluggish, silt-laden drain. During heavy rainfall, accumulated waste acts as a dam, intensifying flooding upstream. Pollution thus becomes not only an environmental concern but a direct contributor to hydraulic failure.

Institutional responsibility for the canal has historically been fragmented. While the Water Resources Department (WRD) oversaw the canal earlier, its maintenance was recently transferred to the Greater Chennai Corporation (GCC). This shift has enabled more focused interventions, including desilting approximately 2.5 kilometres of the canal and removing an estimated 1,100 tonnes of silt from identified choke points. However, these actions remain largely reactive. Desilting addresses symptoms rather than underlying causes such as encroachments, bridge design flaws, and land-use pressures. Moreover, enforcement against illegal dumping and construction remains inconsistent, allowing degradation to recur even after interventions.

Engineering Solutions and Their Limits

Proposed solutions include demolishing narrow bridges, constructing new bridges with higher arch culverts capable of carrying up to 1,300 cusecs of water, and building compound walls to prevent encroachment and dumping. A cut-and-cover diversion drain has also been proposed to divert part of the canal’s flow directly into the Cooum River, reducing pressure on downstream stretches. While these measures may improve flow efficiency in the short term, they raise critical questions about the limits of engineering-led fixes. Without addressing land-use governance, sewage treatment, and watershed-scale planning, such interventions risk becoming cyclical; repeated after every major flood event without achieving long-term resilience.

Rethinking Urban Waterways: From Containment to Coexistence

The question is not merely why the Virugambakkam-Arumbakkam Canal floods, but what its flooding reveals about the city’s relationship with water. The canal’s constriction, pollution, and fragmentation mirror the broader erasure of hydrological thinking from urban development processes. As climate change intensifies rainfall variability, Chennai’s canals will increasingly test the limits of current planning practices. The choice before the city is stark: continue managing floods through incremental engineering responses, or reimagine urban waterways as central to resilience, equity, and sustainability. The future of neighbourhoods along the V-A Canal and countless others like it depends on which path is taken.