Cleaning Up: Strategies for dredging at national waterways

Strategies for dredging at national waterways

To enhance inland water transport in the country, 111 waterways (five existing and 106 new) were notified as national waterways (NWs) under the National Waterways Act, 2016, with effect from April 12, 2016. According to the results of techno-economic feasibility studies and detailed project reports (DPRs) for NWs, the Inland Waterways Authority of India (IWAI) has identified 26 NWs as viable for cargo/passenger movement.

Dredging guidelines for major ports with standard operating procedures for capital and maintenance dredging at major ports were is­s­ued by the Ministry of Ports, Shipping and Wa­ter­ways (MoPSW) in 2021. However, the gov­ern­ment has not been able to implement advanced dredging strategies to maintain local and regional sediment levels, and recharge salt marsh areas with fine-grained dredging, as the majority of material from dredging is unsuitable for recharging salt marsh areas due to contamination. It is also uneconomical to use spoils because the channels are located farther from marshes.

Inland waterways are not yet included in the list of projects that require prior environmental approval. However, dredging, which is necessary for the development of inland waterways, requires environmental clearance.

For the past six years, the National Green Tribunal (NGT) and the Ministry of Environment, Forest and Climate Change have been deliberating on whether the government’s World Bank-financed Jal Marg Vikas Project for National Waterway (NW)-1 requires environmental clearance. The Ganga-Bhagirathi-Hooghly river system project, which was launched in July 2014, is scheduled to be completed in December 2023. Meanwhile, the NGT has rescheduled the NGT’s environmental clearance hearings 14 times.

Initiatives such as the Loktak Inland Water­ways Improvement Project in Manipur are currently under way. The NGT remarked that with the emergence of such projects in the country, the question of whether a legally binding impact assessment pursuant to the 2006 EIA Noti­fication is required or not has become critical. Thus, a judgement made in the Ganga waterway case could become a precedent for all future inland waterway developments.

Apart from routine maintenance dredging, the DCI is collaborating with the government on port development, capital dredging, reservoir and dam desilting, and fishing harbour development. Additionally, it assists the government in coastal development projects, employing dre­dged material, conducting surveys, and undertaking geophysical and geotechnical work.

National waterways – Experience and update

According to the MoPSW, the dredging of the Brahmaputra river is a major initiative aimed at making the river suitable for the smooth movement of passenger and cargo vessels. The dred­ging work has already commenced. The lWAl has undertaken the development of NW-2 at a cost of Rs 4.61 billion between 2020-21 and 2024-25. The waterway is maintained with a fairway with a least available depth of 1.5-2.5 m and a width of 45 m, as well as navigation aids and terminals for day and night navigation.

At the Brahmaputra River Conclave, the vision of developing the north-eastern region by creating waterways for the smooth passage of passenger and cargo ships was discussed. This will re-energise the region’s economic activity, paving the way for its development. National wa­ter­ways are being constructed along the Brah­maputra and Barak rivers. With this, cargo and passenger ships from Assam and the Northeast will be able to travel to Haldia, West Bengal, via Bangladesh. The construction of NW 2 enab­les the north-eastern regi­on’s water­ways to  be con­­nected to the Kolkata/­Haldia ­ports via  the Indo-Bangladesh Protocol Route.

The approved activities on NW-2 include the construction of the Jogighopa terminal, the alternative road to Pandu port and the ship repair facility at Pandu; development and maintenance of fairways; operation and maintenance of navigational aids as well as fixed and floating terminals; procurement of four Ro-PAX vessels; operation and maintenance of vessels; consultancy training; and maintenance of an e-portal. Further, the maintenance dredging project at Cochin port has progressed by 62.5 per cent. It is expected to be completed by May 2022.

In a recent development, the centre has approved approximately Rs 240 million for dredging in the Gomati, a transboundary river between India and Bangladesh, as well as the construction of 10 jetties for a waterway project. To make the projected waterway from So­na­mura in Tripura’s Sepahijala district to Daudkandi in the neighbouring country operational, a 15.5 km stretch needs to be dredged. the MoPSW has also approved the construction of 10 floating jetties between Udaipur and Sonamura in Gomati district.

In January 2022, Dharti Dredging and Infra­structure Limited and Reach Dredging Limited were shortlisted as technically qualified for dredging works on the Farakka-Tribeni stretch of NW-1 (Ganga-Bhagirathi-Hooghly river system from Haldia to Varanasi).

Technical hindrances

Dredging on NWs presents a number of technical challenges, including logistical concerns regarding the transportation of fuel/materials to the dredger, heavy siltation and recurrence of sediments.

Other hindrances include increased flood risks in downstream areas, frequent changes in river courses, morphological issues, difficulty identifying disposal grounds, strong curr­ents/rapid changes in water levels and reduction of flow discharges, increased bank erosion issues and difficulty maintaining dredging depths in upstream areas.

Operation models

The process of inland dredging begins with the Tha­lweg survey to identify shoals in need of dredging, followed by a detailed survey to de­termine the extent of the shoal patch, and then a pre-­dredging survey to determine the dredging quantity and time required for the task, selection of dredging equipment, issuan­ce of a dredging tender, monitoring of dredging performance, and ultimately, measurement of the dredged quantity.

The operation models include departmental dredgers with in-house crews, departmental dre­dgers with contract crews, departmental dre­dgers on operation and maintenance contracts, contract dredging with private dredgers, and assured depth contracts.

The techniques of measuring include pre- and post-dredging surveys (continuous siltation and collapse of side walls); dredge material measurement, which measures the availability of disposal pits or reclamation sites; and production meter measurement, which requires time-consuming installation and repair and a lengthy approval process.

The preferred dredgers are the cutter suction dredgers, which are used in vast river sections regardless of the current, and jetting dredgers, which are deployed in areas with less current. The grab dredger is a popular choice for sections with a shallow depth of cut and sections adjacent to structures.

Dredging approaches are classified into two categories – assured depth dredging and quantity-based dredging. When alignment with navigation objectives is taken into account, the assured depth dredging strategy is better suited for addressing them. The dredging requirements might vary according to seasonal siltation, allowing for additional flexibility in ensuring fairway availability. However, this strategy is uncertain contractually. It is also prone to dispute and exposes the contractor to risks. That said, it is easy for the employer to supervise the work.

Dredging based on quantity, which in­volves the removal of a certain amount of silt from the riverbed/basin, may not be successful in facilitating assured depth. But this procedure provides greater transparency, re­duces the risk for the contractor, and is also less prone to disputes.