Scientific authority is not conferred by degrees or institutional prestige, but earned through scientific integrity, professional judgement and non-partisan analysis. The role played by expert agencies in the controversial Mamallan reservoir project, which seeks to turn a biodiverse tidal marsh into a freshwater reservoir, reveals how easily institutional reputation can be used to legitimise conclusions that extend well beyond what the underlying science actually demonstrates.
To claim exemption from Coastal Regulation Zone (CRZ) notification’s prohibition of reclaiming, bunding or disturbing the natural course of seawater, the state government has described the project as a structure for ‘prevention of salinity ingress and freshwater recharge.’ The notification requires the structure to be “based on [study] carried out by any agency to be specified by MoEF.’ But instead of commissioning a study to establish those functions, it tasked IIT-Madras with providing a technical evaluation of Water Resources Department’s (WRD) proposal ‘for further processing of CRZ clearance.’
Barely three days after it received WRD’s work order, the IIT submitted a report asserting that the project ‘will indirectly augment groundwater recharge, check seawater intrusion and directly supplement the Chennai city water supply.’ The report further claims that the reservoir will ‘aid in the management of flood water’ in the sub-basin. IIT’s authority allows these claims to be read as settled science.
A close reading of the report suggests otherwise, that its only scientifically grounded conclusion is that there is enough runoff in the Kovalam sub-basin to fill the reservoir, a finding unrelated to the basis on which CRZ clearance is sought.
For that, the report must demonstrate that a reservoir built within a wetland ‘influenced by tidal waters and freshwater flows from the hinterland catchment’ will reliably perform all the functions claimed for it. Despite being authored by an ocean engineer, the report focuses solely on freshwater flows from the west, ignoring the Bay of Bengal, the dominant hydraulic force governing the site. The sea enters the analysis only as a sink for surplus floodwaters through the report’s potentially fraught recommendation that ‘direct outlets from the reservoir to the ocean at different locations need to be considered to release surplus water during flood events.’
Critical engineering questions remain unanswered: Will the reservoir continue to function during the compound extremes that define this coast — monsoon floods coinciding with high tides, cyclonic storm surges and coastal flooding? Will floodwaters be drained or trapped when sea levels rise at the estuary? Will the direct outlets recommended by IIT become inlets for seawater during storm surges – an eventuality that can salinise the reservoir and aggravate flooding? Will seawater displaced from the enclosed marsh simply shift flooding and salinity risks elsewhere in the basin?
On groundwater recharge, the EIA’s own studies reveal that soils in the project site have only low-to-moderate infiltration rates, and high water-holding capacities, characteristics suited to water retention structures rather than for groundwater recharge.
Ignoring the agency of the sea in its own territory exposes the report’s assertions to charges of dangerous overreach unsupported by analyses of the coastal and estuarine processes that govern those claims.
Science is not merely about calculations and conclusions. It is also about professional judgement - about what factors to consider, what assertions can be substantiated, what remains uncertain, and what questions still need to be asked. The sea deserves that respect, and the public deserve those distinctions to be made clearly, especially when ecological futures, public money and public safety are at stake.