Introduction
The Tamil Nadu Government has sanctioned ₹91 crore for a new flood mitigation project in South Chennai. The tender for this project was opened on July 8, 2025, with an expected completion timeline of 18 months. This effectively means the project is not designed to prevent floods during the 2025 or even 2026 monsoon seasons. This delay raises serious questions about the intent, feasibility, and efficiency of the project—especially given the track record of Tamil Nadu Water Resources Department (WRD) in completing flood management infrastructure on time.
Critical Observations on the Proposed Straight-Cut Canal Project
The current proposal by the Water Resources Department (WRD) envisages a straight-cut canal intended to drain floodwaters from the Buckingham Canal into the Bay of Bengal. However, a detailed review of the tender documents reveals significant limitations and engineering challenges associated with the proposed solution.
1. Inadequate Hydraulic Capacity
According to the hydraulic specifications published in the tender documents, the proposed canal—entirely designed as an underground vented drain beneath the road surface—has a maximum carrying capacity of just 550 cusecs. This limited capacity raises serious concerns about its effectiveness during high-intensity flood events, especially considering the magnitude of runoff generated from the Pallikaranai catchment and adjoining areas.
Moreover, implementing such an underground cut-and-cover system is capital-intensive, making it an expensive and constrained option for flood mitigation with minimal room for future augmentation.
2. Unfavorable Terrain and Elevation Profile
A major engineering constraint is the terrain profile:
- The Buckingham Canal lies at approximately +2.5 m MSL.
- The proposed alignment cuts across the East Coast Road (ECR), which has an elevation of +6 to +8 m MSL.
- The coastal outfall point is at or near sea level.
This configuration offers no natural gradient for gravity-based drainage. Without sufficient head, efficient discharge toward the sea would be infeasible, and would likely require pumping systems, further increasing operational costs and complexity.
3. Risk of Seawater Intrusion
The high tide level along the Chennai coast is typically around +1.5 m MSL, while the Buckingham Canal sits at +2.5 m MSL. Currently, natural sand dunes along the shoreline act as barriers, preventing tidal waters from pushing inland and protecting the low-lying Pallikaranai Marsh, which in some sections lies below sea level.
Introducing a permanent open channel through these protective coastal dunes could compromise this natural buffer, allowing high tide backflow into the canal and potentially leading to saline water intrusion into ecologically sensitive and densely populated lowland areas.
4. Geotechnical Challenges of Coastal Soil
The sandy coastal soils present along the alignment pose a considerable geotechnical risk. Sandy strata are highly permeable, structurally unstable during excavation, and susceptible to collapse or subsidence unless proper shoring and dewatering techniques are implemented. These factors complicate the construction and long-term stability of an underground canal system.
5. Littoral Drift and Sand Blockage
The Chennai coastline is highly dynamic, with significant littoral drift driven by seasonal monsoon winds:
- Southwest monsoon winds (May–Sept) generate northward sediment movement.
- Northeast monsoon winds (Oct–Jan) induce a weaker southward drift.
This bidirectional drift leads to the regular closure of natural river mouths (Adyar, Cooum, and Kosasthalaiyar) due to sand deposition. Even Chennai Port requires breakwaters to manage sediment movement and ensure navigability.
In this context, any proposed sea outlet—especially if not adequately engineered—faces a high risk of blockage by coastal sand, rendering it ineffective for flood discharge without continuous maintenance and dredging.
6. Risk of Canal Overflow and Sheet Flooding
In the event of excess floodwater inflow beyond the canal’s design capacity, the system could experience backflow or overtopping. Given that the canal is entirely underground and passes through densely built urban areas, such overflow could manifest as sheet flooding, inundating wide swaths of surrounding neighborhoods. The shallow cover and limited surface drainage paths further amplify the risk of prolonged waterlogging and damage during storm surges or intense rainfall.
Why This Might Not Work: A Look Back
This is not the first flood mitigation project proposed for this region. Several past efforts—either left incomplete or abandoned entirely—reveal the persistent issues of poor planning, cost overruns, and ineffective execution.
1. Flood Water Management under JNNURM (2009)
As part of the Jawaharlal Nehru National Urban Renewal Mission (JNNURM), ₹633.03 crore was sanctioned for macro-drainage improvements across Chennai. Ten packages were planned to improve flood protection, especially along the South, North, and Central stretches of the Buckingham Canal. A performance audit by the Comptroller and Auditor General (CAG) in 2014 highlighted significant implementation gaps.
One key component was the widening of the South Buckingham Canal from 20 meters to 100 meters between Okkiyamaduvu and Muttukadu, intended to boost the canal’s discharge capacity from 3,500 to 9,000 cusecs.
- CAG Finding: As of February 2013, only 7.51 km of the 13 km stretch had been widened.
- Current Field Observation: Our team found only 2.5 km widened up to the Injambakkam Bridge. Beyond this, the canal remains partially dredged with an obstructing bund, dividing the channel into two parts (35–40 m wide).
- Reason for Incompletion: Non-availability of funds and a cost escalation from ₹78.14 crore to ₹104.4 crore due to design changes and revised estimates.
Another dropped component was a shortcut drainage diversion from Okkiyam Maduvu to the sea, which aimed to divert 3,500 cusecs of water. The plan was shelved due to a high land acquisition cost of ₹100 crore.
2. IWAI’s Development Work in South Buckingham Canal (NW-4)
In 2014, the Government of India sanctioned ₹123 crore for developing a 37 km stretch from Sholinganallur to Kalpakkam under National Waterway-4 (NW-4). Led by the Inland Waterways Authority of India (IWAI), the project aimed to enhance navigation through dredging, terminal construction, and embankment strengthening.
However, field assessments revealed no evidence of dredging, jetty construction, or embankment work. The canal remains heavily silted and encroached.
- RTI Findings: IWAI claimed ₹4 crore was spent on preliminary works, but subsequent RTI responses contradicted this, attributing the amount to a different project altogether. Delays were reportedly due to lack of cooperation from the state government on land and clearances.
Why the Proposed Flood Canal is Inefficient Compared to Widening the Buckingham Canal
The newly proposed underground straight-cut canal is a high-cost, low-impact project. Compared to improving the existing Buckingham Canal, it lacks capacity, speed, and efficiency.
- Extremely Limited Capacity
- Proposed canal capacity: 550 cusecs
- Current Buckingham Canal capacity: 3,500 cusecs (expandable to 9,000 cusecs per CAG)
- The new drain delivers just 6% of the improved canal’s potential at several times the cost.
- Implementation Time & Disruption
- Buckingham Canal widening could be completed in 3–4 months with minimal disruption.
- The underground canal requires 18 months of road excavation, causing severe public inconvenience and offering no flood relief until project completion.
- Engineering Risk
- The underground canal involves high-risk construction in sandy coastal soil.
- The return on investment is questionable given its limited capacity and engineering complexity.
Accountability of Engineers in Public Water Infrastructure Projects
Government engineers from departments like PWD and WRD play a central role in designing and executing flood mitigation infrastructure. Yet, repeated failures expose systemic lapses:
- Poor Design Justifications: Ignoring site-specific factors.
- No Performance Audits: Absence of post-project evaluations.
- Lack of Accountability: Failures rarely lead to professional consequences.
- Ignored Escalations: Concerns raised by citizens or audits are not acted upon.
In a recent interview with Times of India, Mr. Kanthimathinathan, the Disaster Management Department coordinator, called the ₹91 crore flood mitigation project the only viable option for southern Chennai. Yet, he provided no supporting data to demonstrate how much risk it would reduce, nor any justification for not pursuing lower-cost alternatives.
This raises critical questions:
- Were cheaper or nature-based solutions considered?
- Why were they rejected?
- If the ₹91 crore project fails, will he or the engineers be held accountable?
Legal and Institutional Gaps
Existing legal frameworks like the Tamil Nadu Transparency in Tenders Act or Civil Services Conduct Rules do not effectively hold engineers accountable for flawed designs. The Vigilance Department focuses on financial corruption, not technical inefficiency. Even CAG audits carry only recommendatory weight, without enforcement power.
Conclusion
Instead of building a costly, low-capacity underground canal that may take years to deliver results, the government should prioritize enhancing the existing Buckingham Canal—a solution that is faster, more effective, and far less disruptive.
Flood mitigation in Chennai demands urgency and scale. The Buckingham Canal improvement offers both. The proposed project, unfortunately, offers neither. Engineers play a vital public role—but without institutionalized accountability mechanisms, technical lapses result in social, environmental, and financial disasters. Bridging the gap between design responsibility and accountability requires urgent structural reform, performance audits, and public oversight.
