THIRUVANANTHAPURAM: As Kerala begins recovering from the recent floods, demands for large-scale desilting of rivers, reservoirs and other water bodies have resurfaced, with many arguing that accumulated silt has reduced their carrying capacity and worsened flooding. Chief Minister V D Satheesan has also flagged silted rivers and reservoirs as a factor aggravating flood risk and indicated that desilting needs attention.
Owing to strict restrictions on river sand removal under the Kerala Minor Mineral Concession Rules and related Acts, the state government’s post-flood desilting projects were stalled.
However, hydrologists and experts have urged caution, warning that indiscriminate removal of river sand and sediment, without scientific assessment, could create long-term environmental problems, including groundwater depletion, riverbed degradation, saltwater intrusion in downstream stretches and damage to critical infrastructure.
Retired National Centre for Earth Science Studies scientist and former head of hydrology Padmalal D said there is no scientific evidence yet to conclude that widespread siltation alone is responsible for the recent floods. “The first question is whether there is scientific proof that rivers are heavily silted. That assessment has to come before prescribing desilting as the solution,” he said.
He said that sand beds function as natural aquifers, storing floodwater during the monsoon and gradually releasing it during summer, thereby sustaining river flow and recharging groundwater.
“If these sand beds are removed excessively, the riverbed deepens, groundwater levels fall and people eventually experience drying up of wells. It is wrong to believe that deeper rivers automatically reduce flooding,” he said.
He said that the only scientifically accepted method of limited river sand removal is ‘bar skimming’ - the removal of loose, dry sand deposited on exposed sandbars during summer. “If not done scientifically, the environmental impacts may become visible only after five, ten or even fifteen years, by which time the economic losses could be enormous,” he said.
Experts and environmentalists are also stressing the need for scientific assessment before undertaking desilting. Former executive director of Centre for Water Resources Development and Management, Manoj P Samuel, said that any intervention should begin with a comprehensive ‘sand audit’ to quantify how much sand and silt has actually accumulated in individual river stretches.
“Only after scientifically measuring the accumulated sediment should decisions be taken on how much can safely be removed. The carrying capacity of many rivers has reduced because of the accumulation of silt, organic matter and waste. Each of Kerala’s river basins should undergo a scientific audit and hotspot stretches should be identified for priority intervention,” he said.
He suggested that the most flood-affected rivers such as the Pampa, Manimala, Meenachil and Poonoor could be taken up initially on a pilot basis. “Modern technologies, including underwater drones and bathymetric surveys, can be used to estimate sediment accumulation,” he said.