Failure to desilt riverbed chokes Yamuna, triggers flooding in city

The Yamuna has been flowing above the danger mark in Delhi for nearly a week, causing floods in the low-lying areas. Experts attribute this to the systematic choking of the river’s natural flow, primarily due to the failure to desilt the riverbed. The formation of huge sandbars, particularly near key areas like Signature Bridge and ITO Barrage, has obstructed the water’s path, exacerbating the flood situation.

Furthermore, a 22-km stretch of the Yamuna in Delhi is cluttered with three barrages and 20 bridges. Temporary paths built in the riverbed during construction of bridges are often left behind, trapping more silt and further blocking the flow.

Moreover, a February 2024 Parliamentary Standing Committee report titled ‘Review of Upper Yamuna River Cleaning Projects up to Delhi and Riverbed Management in Delhi’ highlighted that the situation is worsening due to illegal sand mining and debris dumping, citing 3,792 cases of illegal mining in Haryana in five years alone.

The committee recommended creating a coordination portal for states and exploring controlled dredging (the process of excavating silt from the riverbed) to clear the blockages.

Manu Bhatnagar, Principal Director of the Natural Heritage Division at the Indian National Trust for Art and Cultural Heritage (INTACH), emphasised the need for a detailed investigation into whether areas immediately upstream or downstream of Delhi experience similar flooding conditions.

He explained that the high velocity of water flowing from the upper stretches of the Yamuna following heavy rainfall significantly magnified the impact of the river’s increased discharge.

Bhatnagar further observed that although sand mining poses ecological threat to the river, excessive mining does not directly cause flooding.

“Mining deepens the river channel and damages the riverbed habitats and biodiversity. It can also influence the change of river course causing excessive erosion on a particular bank but it has no direct correlation with rising water levels,” he clarified.

He also highlighted that the Yamuna in Delhi has been embanked on both sides, which restricts the natural horizontal spread of water. Consequently, the excess water expands vertically, compounded by shallowing of the riverbed through sediment deposits as a result of the earlier flooding in 2023.

Such deposition was also the result of narrowing of the river channel as a result of supporting piers of several bridges and barrages. This aspect, he stressed, warrants comprehensive research.

Meanwhile, Professor PK Joshi, faculty at the School of Environmental Sciences, Jawaharlal Nehru University (JNU), explained that excessive sand mining in the upper reaches of Haryana and Uttar Pradesh lowers the riverbed, steepening the river’s gradient and accelerating flow towards Delhi.

While a steeper slope reduces travel time from Hathni Kund barrage, the loss of sand’s natural buffering capacity — its ability to absorb and slow water — results in faster downstream surges, he added.

Prof Joshi further mentioned that the flow of the river is governed by its channel width and natural gradient. Bridge piers and debris constrict the effective cross-section, impeding discharge and causing water levels to rise during peak flow.

Sediment deposits further elevate the bed, diminishing the channel’s carrying capacity and reduced velocity near such obstructions promotes backflow and localised flooding, particularly across the floodplains of East Delhi and Yamuna Bazar, he elaborated.

On the remedial measures to prevent flooding, he said Delhi requires stringent regulations to prevent waste dumping and encroachments on the Yamuna riverbed. “The channel and catchment must remain free from settlements and sand extraction, supported by regular de-silting and infrastructure designs with adequate waterway clearance for peak flows,” Joshi added.