Dredging is the removal of sediments and debris from the bottom of lakes, rivers, harbours and other waterbodies for maintaining or increasing the depth of navigation channels to ensure the safe passage of vessels. With the upcoming berths and terminals at existing ports and other greenfield ports, there are ample opportunities available to dredging players.
Tata Consulting Engineers
Tata Consulting Engineers (TCE), a subsidiary of the Tata Group, has completed over 7,500 successful projects globally since its inception.
In the maritime sector, the company has undertaken various projects such as project management consulting for the deepening of the channel between the Jawaharlal Nehru Port Trust (JNPT) and Mumbai port, the transportation of coal via National Waterway-3 from the coal handling plant and jetty in Farakka, the review and structuring of the fourth container terminal at JNPT, and the preparation of detailed project reports and master plans for the Kandla and Paradip smart industrial port cities.
In order to describe an ideal dredging project, two scenarios have been assumed by TCE – a port with heterogeneous soil and a port with homogeneous soil. The key features of these projects are described below.
Case I: Capital dredging in a port with heterogeneous material
Capital dredging at channels and anchorages should be undertaken without disturbing vessel traffic and daily operations at the berth. Underwater obstructions, if any, should be detected and removed to achieve the proposed design depth. The choice of the dredger to be deployed should be based on the soil condition, weather condition, properties of the equipment to be used and the experience gained from previous projects. The company should also reduce maintenance dredging works during the capital dredging phase itself. Assessing the soil type, in soft clay, a trailing suction hopper dredger (TSHD) should be deployed in both low and high siltation area. In the weathered rock also the deployment of a TSHD is more economical for longer distances. However, in fresh rock, a combination of dredgers can be used.
For an ideal project, the port authority should disclose all possible obstructions that could be encountered during capital dredging. However, the contractor should also assess the sufficiency of the data prior to bidding and carry out his own investigation if he is not satisfied.
Case II: Capital and maintenance dredging in homogeneous soil
Dredging is comparatively easier in homogeneous soil types as compared to heterogeneous. However, maintenance dredging is required round the year since there is high sedimentation and siltation in the approach channels. Capital dredging at berths should be undertaken without disturbing vessel traffic and daily operations at the berth. The capacity of the dredger to be deployed should be such that it can carry out dredging operations during the period of highest sedimentation.
For dredging inside a creek, the quantity of capital and maintenance dredging should be mentioned clearly and in the case of an item rate contract, the quantity should be mentioned along with (+/-) variations. The governing factors for dredging operations inside a creek are vessel traffic and berth availability for capital and maintenance dredging.
Krishnapatnam Port Company Limited
Krishnapatnam Port Company Limited (KPCL) is the port operation company of the Navayuga Group, and is promoted by the Hyderabad-based C.V.R. Group.
Krishnapatnam is an all-weather port, located 180 km north of Chennai. Phase I of Krishnapatnam port was commissioned in a record time of 16 months. The port currently has a maximum draught of 18.5 metres and is capable of handling capesize vessels of up to 200,000 deadweight tonnage. Krishnapatnam port has 10 operational multi-purpose berths at present, and another three are currently under construction.
Krishnapatnam port’s dredging project is planned to be undertaken in three phases. Until now, 66 million cubic metres (mcum) of material has been dredged at the port, of which approximately 15 mcum has been reclaimed. During Phase I, 14 mcum was dredged and 6 mcum was reclaimed. Currently, the port is in the process of completing Phase II of the dredging project, in which 52 mcum has been dredged and 9 mcum has been reclaimed till now. During Phase III, 63 mcum of quantity is expected to be dredged, of which 29 mcum will be reclaimed.
For dredging projects, planning is done in-house by KPCL and the company has its own high capacity dredgers and other associated equipment. The port has a fleet of six dredgers – three TSHDs and three cutter suction dredgers (CSDs). The average capacity of the fleet is 60,000 cubic metres per day. Apart from this, the company also owns four work boats, one survey boat and one jack-up barge with a capacity of 500 tonnes and a bathymetric survey unit. KPCL followed a flexible and innovative approach in conducting the dredging project as both dredging and port operations were under the direct control of the port.
Some of the challenges faced by KPCL while executing the project were a shortage of trained manpower, lack of awareness among locals on environment-friendly dredging methods, an absence of workers for repair works, and lack of workshops and suppliers. Due to these challenges, TSHD utilisation was for only 77 per cent of the time, while for CSDs it was 62 per cent.
KPCL took a number of measures to optimise dredging operations such as the introduction of preventive maintenance systems and dredge monitoring systems, the identification of critical areas of technical problems, the development of local workshops, an adequate stock of spares and quality control on dredging operations.
Apart from Krishnapatnam port, KPCL has undertaken dredging projects at other ports as well. Capital and maintenance dredging at Chennai port and capital dredging at Gopalpur port was done by KPCL. Two upcoming dredging projects at other ports to be undertaken by KPCL are capital dredging at Machilipatnam port and Astaranga port.
Rock dredging at Visakhapatnam port
Dharti Dredging and Infrastructure Limited (DDIL) is a specialist in underwater rock dredging. About 1 mcum of rock dredging work has been undertaken by DDIL in the past 10 years.
One of the biggest rock dredging projects undertaken by the company was at Visakhapatnam port. The dredging project was divided into three phases. Phase I dredging was completed by DDIL in 2005 with the channel attaining a depth of 11.8 metres. Phase II, which required the deepening of the inner harbour channel to 13.8 metres, was initiated in 2008. However, the project could not be successfully completed and the leftover work was awarded along with Phase III to DDIL in 2013. The estimated cost of the contract was Rs 2.12 billion and the targeted depth of Phase III was 16.1 metres.
The inner harbour channel of Visakhapatnam port is 1,540 metres in length with a minimum width of 110 metres, while the inner harbour turning circle has a diameter of 440 metres. The project involved 0.45 mcum of rock dredging and 0.15 mcum of soft soil dredging in the inner harbour channel. Further, the inner harbour turning circle involved rock dredging of 0.03 mcum and soft soil dredging of about 0.23 mcum. The channel had been divided into nine zones for the purpose of dredging. DDIL was awarded a level-based contract wherein the same rate was taken for rock dredging and soft soil dredging.
DDIL adopted conventional drilling and controlled underwater blasting due to the restricted area, wherein the company could not use big barges and equipment. The dredged material was dumped offshore at a designated location identified 5 km from the site. According to the contract, the dredging was done on alternate days and the payment was made to DDIL on a pre-survey quantity level basis.
DDIL deployed three backhoe dredgers (BHDs) and a heavy duty grab dredger and TSHD. Apart from this, the company also deployed six hopper barges with total capacity of 5,400 cubic metres, tugboats, survey boats and workboats.
DDIL faced a number of challenges while executing the project. The inner harbour has a very narrow entrance channel and a rocky bottom along with old marine structures on both sides of the channel which made dredging difficult. Further, busy operations at the port hampered work. The company also faced objections from the local people which impacted progress.
Based on a presentation by Devdatta Bose, Group Sector Head, Ports & Harbour, Tata Consulting Engineers; Captain Pradeep Gaur, President (Marine) and Deputy Conservator, KPCL; Saraj Tulla Shariff, Dredging Consultant, DDIL