The Mamallan reservoir project in Chennai’s Kovalam-Nemmeli backwaters has exposed a conflict at the heart of urban water infrastructure: a project intended to manage water could also alter the wetland systems that store, drain and sustain it. According to Palluyir Trust for Nature Education and Research, ongoing dredging and bund work has affected a key habitat for migratory waterbirds and may have implications for flood drainage in south Chennai.
The trust’s representation to the Water Resources Department is based on a survey conducted on September 29 by four naturalists and zoologists. The team recorded around 3,500 waterbirds belonging to 51 species in the project area. The findings included more than 1,500 garganey ducks and over 700 greater flamingos. The trust said 25 of the recorded species were migratory species protected under the UN Convention on Migratory Species.
The numbers matter because they challenge the idea that the project site is an inactive or degraded stretch of water. Palluyir Trust described the Kovalam-Nemmeli wetland as an important stopover site for birds travelling along the Central Asian Flyway during the August-September migration season. The presence of thousands of foraging birds, it said, indicated that the area contained biologically active mudflats, even though that function had not been recognised in the coastal zone management plan.
That gap between what a planning document records and what a wetland does on the ground is central to the Mamallan reservoir controversy. Wetlands are not defined only by their visible water spread or by whether they carry a formal conservation label. Their value can also lie in the less visible movement of tides, sediment, vegetation, prey and floodwater. When these processes are not reflected in planning documents, construction can proceed without fully accounting for the urban services the landscape is already providing.
The trust said dredging and bunding for the reservoir had removed brackish and halophytic vegetation. Such vegetation had previously acted as a buffer between waterbirds and traffic and human activity, according to the organisation. Its removal therefore affects more than the appearance of the site. It can change the distance between wildlife and disturbance, while also altering the edge conditions through which water, sediment and organisms move.
The proposed reservoir is also being assessed by the trust as part of a tidal system rather than as an isolated storage structure. It said that blocking tidal flow could affect the movement of marine organisms during high tide and reduce prey availability for waterbirds. The supplied report does not establish the scale or duration of such an impact, but it identifies a specific ecological mechanism: changing the movement of water can change the food chain that supports the birds using the wetland.
This is where the project’s urban significance extends beyond bird conservation. South Chennai has experienced rapid development around the Old Mahabalipuram Road corridor, commonly known as OMR, alongside continuing pressure on drainage infrastructure. In such a landscape, the performance of a backwater is connected to the performance of roads, housing, commercial development and neighbourhood drainage. A change at one point in the system can affect how water moves through adjoining areas, although the exact consequences for the Mamallan project require technical assessment.
Palluyir Trust specifically raised concerns about the project’s implications for flood drainage in south Chennai. It cited warnings by scientists from Anna University’s Centre for Climate Change and Disaster Management regarding extreme weather and the possibility of severe cyclonic events in the Bay of Bengal. The organisation said that blocking a crucial flood channel could increase flood risks in the region around OMR.
The claim is significant, but it remains a representation by the trust rather than an independently published assessment included in the supplied material. That distinction is important. The report establishes that the trust has identified a possible connection between the project’s bunding and the region’s drainage capacity; it does not establish that flooding will occur or quantify any increase in risk. Those questions would require hydrological modelling, project design documents, flood-channel mapping and an assessment of how tidal exchange is expected to operate after construction.
The underlying policy question is whether urban water projects are being evaluated only for their intended engineering function or for their effect on the wider landscape. A reservoir may be assessed for storage, bund stability and construction progress, while the surrounding wetland is assessed separately, if at all. But in a coastal urban system, storage, drainage, tidal exchange and ecological productivity can occupy the same geography. Treating them as separate categories can make an infrastructure project appear simpler than it is.
The coastal zone management plan is especially relevant in this context. Palluyir Trust said the biologically active mudflats identified during its September survey had not been recognised in the plan. The report does not specify why the mudflats were omitted, whether the plan is under revision, or what statutory process governs changes to the project area. It does, however, point to an institutional challenge: planning classifications can lag behind seasonal or ecological realities.
Migratory waterbirds provide one visible indicator of that reality. The survey recorded birds arriving during the August-September migration period, including garganey ducks that migrate from temperate regions such as Russia and Mongolia. Their presence does not by itself determine whether construction is permissible. It does show that the site is being used during a defined seasonal window and that project activity overlaps with that use.
The more difficult question is how the project should account for seasonal variation. A site may look relatively empty outside the migration period but perform a different ecological function when birds arrive. Similarly, a drainage channel may appear manageable during ordinary rainfall but become critical during intense rain or a cyclone-related event. Infrastructure decisions based on average conditions can therefore miss the periods when wetlands matter most.
The Mamallan project also illustrates the administrative complexity of urban water governance. The representation was submitted to the Water Resources Department, while the ecological concerns involve coastal planning, wetland functioning and migratory species. Flood risk around OMR involves yet another layer of responsibility, including drainage planning and the management of urban development. The supplied report does not indicate how these agencies have responded or whether a joint assessment has been ordered.
That absence of a documented response is itself a limitation in the current public record. The trust has set out the survey findings and its concerns, but the material supplied does not include the Water Resources Department’s reply, the project’s environmental assessment, construction drawings, a tidal-flow study or an official flood-risk analysis. Without those documents, it is not possible to determine whether the identified ecological and drainage risks have already been considered in the project design.
What can be established is that the project site performs several functions at once. It is a construction zone for a proposed reservoir, a wetland used by migratory birds, a landscape containing mudflats and vegetation, and part of a drainage system serving a rapidly urbanising part of Chennai. The tension is not simply between development and conservation. It is between different infrastructure objectives that depend on the same water system.
For Chennai, the broader lesson is that flood resilience cannot be measured only by the amount of concrete added to a drainage or storage network. It also depends on whether natural channels remain connected, whether tidal movement is preserved where it is functionally necessary, and whether seasonal ecological evidence enters project decisions before construction changes the site. The report does not prove that the Mamallan reservoir project will fail on these counts. It shows that those questions now require clear technical and administrative answers.
The next stage should therefore be judged by the evidence made public: the project’s hydrological design, its treatment of tidal flow, the status of the coastal zone management plan, and the authorities’ response to the survey conducted on September 29. Until those details are available, the Mamallan reservoir project remains both a water-infrastructure proposal and a test of whether Chennai’s planning system can account for the ecological and drainage functions already operating at the construction site.
