Bihar's river silt to now help pave highways in bid to reduce flood risks

In a bid to tackle flooding in Bihar, one of India’s most flood-prone states, the National Highways Authority of India (NHAI) will desilt the state’s rivers and use the excavated material to construct national highways. 

The central and Bihar governments signed a memorandum of under­standing (MoU) on Tuesday to this effect. Desilting will be carried out using scientific methods, following detailed technical assessments of identified water bodies. 

The initiative seeks to address two problems simultaneously. National highway construction requires large quantities of earth to level or raise road surfaces, traditionally sourced from nearby land. Bihar, meanwhile, has nearly three-fourths of its area classified as flood-prone. 

Bihar Chief Minister Samrat Choudhary said floods cause annual losses of ₹10,000 crore in the state. Some rivers, he added, have accumulated more than 10 metres of silt in certain stretches. He said Bihar was the first state in India to have a Water Sources Restoration and Silt Management Policy. 

But experts caution that the proposal faces technical, ecological and economic challenges. While river desilting is more complex than clearing lakes and smaller water bodies, not all excavated sediment is suitable for road construction. Fine silt, in particular, has poor load-bearing properties and may require treatment or blending. 

They also warn that excessive dredging could destabilise riverbeds and banks, disrupt aquatic ecosystems and alter downstream sediment flows. The cost of extracting and transporting the material could further undermine the initiative’s viability.

But experts caution that the proposal faces significant technical and economic challenges. Desilting rivers is more complex than clearing lakes and smaller water bodies, while the cost of extracting and transporting the material could undermine the initiative’s viability. 

The Ministry of Road Transport and Highways (Morth) stated: “Extraction will be permitted only at approved locations and within prescribed technical limits, ensuring that river ecosys­tems, riverbanks, embank­ments, bridges and other structures are not adversely affected.” 

NHAI has identified significant potential for using excavated silt in national highway projects in Bihar, the ministry added. Under the initiative, 243,000 cubic metres of suitable silt will be used in 16 ongoing projects. Another 835,000 cubic metres is proposed for use in 27 future projects, subject to technical suitability and requisite approvals.

“Bihar has several rivers which have accumulated silt over the years, which results in lack of water holding capacity, impact on irrigation, and increased likelihood of floods. On the other hand, national highway construction requires earth/sand at a massive scale, for which fertile agricultural land is used,” said Anil Chaudhary, NHAI member.

The exercise will be undertaken at no cost to the state government, with contractors responsible for desilting, Morth minister Nitin Gadkari said. He added that the move would mitigate the environmental damage associated with sourcing material for highway construction, which often involves digging into agricultural and mountainous land.

The last such agreement by the highways ministry was signed nine years ago. Under that arrangement, contractors were allowed to excavate soil, silt and sand from local rivers, streams and lakes in Maharashtra without paying royalty. The initiative was aimed at addressing water scarcity in Buldhana, in the drought-stricken Vidarbha region.

The excavated material was used to construct nearby national highway embankments. According to a statement by the minister in 2020, more than 225,000 cubic metres of material had been excavated, increasing local water storage capacity without requiring public funds for desilting.

Currently, 39 NHAI projects covering approximately 1,561 kilometres, with an estimated investment of ₹58,340 crore, are under construction in Bihar. Another 11 projects, covering around 1,982 kilometres and involving an estimated investment of ₹1,85,200 crore, have been proposed.

The suitability of excavated silt for highway construction will be established through appropriate testing in accordance with applicable Morth specifications and relevant Indian Roads Congress (IRC) codes, the government said.

Experts, however, caution that desilting rivers is considerably more challenging than desilting lakes and smaller water bodies. They also say the Buldhana initiative is not directly comparable with the Bihar agreement.

Himanshu Thakkar, coordinator of the South Asia Network on Dams, Rivers and People (SANDRP), said the initiative could hold promise, provided it does not run into problems of economic viability because of high transportation costs.

“Rivers have a combination of silt, sand, boulders and other organic matter too. Removing that and transporting it over long distances could prove to be an economic challenge,” Thakkar said, adding, the results of NHAI’s pilot project would need to be assessed before its wider viability could be established.

Transportation costs would be a concern, and the authority would try to keep them as low as possible by identifying suitable projects, a government official said. Gadkari said in his address that the silt would be used for projects located near rivers.  

Aparna Roy, fellow, climate change and energy, Centre for New Economic Diplomacy, Observer Research Foundation (ORF), said the project appeared technically and economically feasible, with some caveats. “Not all dredged material is suitable for road construction. Fine silt often has poor load-bearing properties and can become unstable when saturated. Some material may be appropriate for embankment filling after treatment or blending, but not for structural pavement layers,” Roy said.

However, she warned that river sediment was not simply waste waiting to be removed. "It is integral to river morphology, floodplain fertility, aquatic habitats and downstream sediment balance. Excessive or poorly planned dredging can destabilise riverbeds and banks, increase turbidity, disturb aquatic ecosystems and alter erosion patterns. Removing sediment from one stretch can also affect its deposition elsewhere," she said.

The beneficial reuse of dredged sediment is an established international practice, with widespread applications in France and the Netherlands, experts added.