Dredging activities have considerable environmental consequences such as changes in coastal and river morphology, changes in currents and wave climate, impact on wildlife habitat, changes in coastal defence, and impact on water quality and benthic fauna. Thus, appropriate management of dredged material plays an imperative role in preventing harsh environmental outcomes and ensuring environmental sustainability.
Current practices for handling of dredged material
During the capital dredging phase, ports first conduct investigations such as physical characterisation of the area, chemical characterisation of water and biological characterisation. In the case of offshore disposal, dispersal plume analysis is often conducted, while in the case of reclamation, dredging is done based on physical characterisation and available capacity. Besides, bathymetry and topographical surveys are also conducted for the area to be dredged. In the second stage, ports apply for an environmental clearance (EC). Once the EC is obtained, the dredging work finally starts. For the entire process, a monitoring system is put in place as per the conditions laid out in the EC.
During the maintenance dredging phase, ports commonly carry out bathymetry and topographical surveys for land reclamation, after which the dredging work starts. However, certain issues have been observed during this phase. First, the physical, chemical and biological characterisation of the soil is not conducted to assess its quality. Besides, ports continue to dispose of the dredged material at locations allotted in the EC even after the clearance expires. Despite the fact that ports have their own systems for reporting environmental issues, proper adherence to norms is often found to be lacking due to a fear of an increase in the financial burden.
On the west coast of the country, during maintenance dredging, almost 100 per cent of the disposal is done offshore, with no reclamation activities taking place. On the east coast, although Chennai port does not undertake a lot of dredging activity, the disposal is done close to the shoreline for beach replenishment. Visakhapatnam port also uses most of the dredged sand for beach replenishment, while at Paradip port disposal is typically a mix of offshore and beach replenishment. In contrast, Kolkata and Kamarajar ports conduct completely offshore disposal of dredged material. Under capital dredging, while there is 100 per cent offshore disposal on the west coast, the east coast ports adopt a mix of offshore disposal and reclamation, depending on the soil type.
Potential use of dredged material
Dredged material has many potential environment-friendly applications. It can be used for land creation; land improvement; expansion of beach size; protection of beaches; development of offshore berms, dykes and dams; capping of contaminated dredged material; for aquaculture; and for use as replacement fills, construction material and topsoil.
However, there is still a long way to go for Indian ports to ensure that the dredged material is optimally handled and utilised. Essentially, there is no framework for the assessment of dredged material in the country. Hence, such a framework needs to be developed with provisions for characterisation of soil, assessment of contamination status, study of beneficial use options, site selection, and assessment of technical feasibility and regulatory acceptability. The framework should also incorporate a cost-benefit analysis, treatment methodology and parameters to choose a cost-effective technology, as well as put in place appropriate monitoring impact assessment systems. Besides, the general framework should also be adapted to individual ports, since each port has different characteristics. Further, economic, engineering, environmental, regulatory and social aspects need to be considered while undertaking reclamation activities. Lessons also need to be learnt from the global and domestic experience on optimal handling of dredged material. For example, Rotterdam port in the Netherlands uses a large-scale storage site for polluted dredging sludge. The municipality of Rotterdam has also entered into discussions with companies to minimise emissions. This approach has halved the amount of polluted sludge from the port area that is deposited in the depot every year. Similarly, another best practice in handling of dredged material is the case of Kochi where fine clayey material has been used for land reclamation.
The way forward lies in the development of a dredged material management strategy which includes a long-term management plan. Besides, there needs to be a plan for the physical, chemical and biological mapping of parameters for both capital and maintenance dredging projects. There should also be appropriate classification of the dredged material based on its characteristics and expected environmental impact. Source control needs to be put in place as well to reduce pollution. The financial aspect of material handling solutions needs to be studied as well to ensure that the provisions are sustainable in the long run.