Over time, debris can build up at the bottom of water bodies, making it hard for boats and ships to pass through. To address this problem, a process called 'Dredging' is used, which removes the debris and sediment from the bottom of the water. Even though dredging is considered beneficial, it impacts the environment.
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Understanding Dredging and its Environmental Impact
Dredging is defined as the process of removing debris and sediment from the bottom of water bodies to maintain channels and deepen them. It is considered crucial for maintenance and construction. Ports, canals, and bridges can be brought into existence by using such methods.
Dredging also ensures safe passage for ships and boats by deepening the existing channels that can help pass larger ships pass through. Land can be reclaimed using dredged materials, which can be further used for the development and creation of new ecosystems.
Even though dredging is considered a crucial phenomenon, it still causes several environmental issues, as highlighted by a recent article in the Encyclopedia of Sustainability Science and Technology. Dredging can destroy aquatic habitats like coral reefs and spawning grounds, which in turn leave a negative impact on marine life.
Water is also polluted since dredging material contains pollutants that are released into the water during the process. Sediments are also released into the water during the process, which can reduce water clarity and increase turbidity.
Sustainable Dredging Techniques
Over time, sustainable dredging techniques have been introduced to minimize their environmental impact. There are several different sustainable dredging techniques, which depend on the dredging project requirements.
Hydraulic dredging includes cutter suction dredgers that suck the sediment up through a pipe to a disposal site using rotating cutting heads. Trailing suction hopper dredgers also work similarly by dragging a suction pipe along the bottom of the waterway to collect sediment, which is stored and then transported to a disposal site. While trailing suction hopper dredgers may quickly dredge huge expanses of land, cutter suction dredgers are thought to be more efficient than standard suction dredgers.
Suction dredging, which includes venturi dredging, involves the use of a venturi nozzle to create a vacuum that sucks up the sediment. Alongside this, pneumatic dredging uses compressed air to suck the sediments. Suction dredges are less environmentally disruptive since they do not re-suspend as much sediment in the water.
Finally, precision dredging includes GPS-guided dredging, which can precisely control the position of the dredge bucket, making it more accurate and less disruptive. Another precision dredging technique is multi-beam sonar dredging, which uses multi-beam sonar to a 3D image of the bottom of the waterway. Precision dredging is mostly used to dredge around sensitive habitats.
Environmental Monitoring and Assessment
Environmental monitoring is crucial to ensuring that the effects of dredging projects are minimized, and, where possible, eradicated. To guarantee that environmental factors are incorporated into project design and execution, these analyses must be carried out early in the planning phase.
Among these techniques for monitoring and evaluating the environment are baseline assessment, which collects information on the current status of the environment; scoping, which pinpoints the primary environmental issues; impact assessment, which projects the consequences on the environment; the efficacy of the mitigating measures, which lessen the impact on the environment, is ensured by the deployment of monitoring and assessment programs to track the environmental impact of the dredging operation.
Habitat Restoration and Enhancement
Habitat restoration and enhancement are used to mitigate the negative effects of dredging on the environment and to enhance natural biodiversity. Dredged material, for instance, might be utilized to rebuild damaged ecosystems or to establish new wetlands or oyster reefs.
An extensive, multi-agency initiative to enhance and restore the San Francisco Bay ecosystem called the SFRBIP has been initiated by the California State Coastal Conservancy. Numerous dredging operations are part of the program, and they are being utilized to lower the danger of flooding, enhance water quality, and restore lost habitat.
The Eden Landing Ecological Reserve Restoration effort is one instance of an effective SFRBIP dredging effort. Over a million cubic yards of silt had to be dredged for this operation to repair a tidal marsh that had been weakened by agriculture and development. Both the new marsh habitat and the quality of the already-existing marsh habitat were enhanced by the utilization of the dredged material. This case shows how, even in densely populated places, dredging can be utilized to enhance and restore habitats.
Regulatory Frameworks and Compliance
Regulatory frameworks and compliance mechanisms play a pivotal role in ensuring responsible dredging. Governments and international organizations have set regulatory frameworks to reduce the negative effects of dredging operations on the environment.
The International Maritime Organization (IMO) has created several agreements and guidelines to address dredging-related environmental issues. The International Convention for the Control and Management of Ships Ballast Water and Sediments (BWM Convention) sets standards for ballast water management to prevent the spread of invasive species through dredging.
As per the research published in the Global NEST Journal, many countries in a similar fashion require thorough Environmental Impact Assessments (EIA) before the commencement of dredging projects to assess the environmental impacts and propose mitigation measures. For instance, the European Union's EIA Directive ensures that dredging projects within EU member states are thoroughly assessed before approval. Several international organizations, including the Central Dredging Association (CEDA), have developed Best Management Practices (BMP) guidelines for sustainable dredging. These practices offer technical guidance to minimize the environmental footprint of dredging operations.
The Port of Rotterdam, Netherlands, serves as an example of the application of sustainable dredging techniques. Rotterdam's port authorities have invested in advanced dredging technologies that minimize environmental impact.
Modern dredgers equipped with precision instrumentation allow for accurate depth measurements and sediment removal, reducing unnecessary disturbances to the marine ecosystem. Instead of disposing of dredged sediments in open waters, Rotterdam has employed innovative approaches to manage sediment by using dredged material in construction projects, habitat restoration, and land reclamation.
This approach helps to create sustainable infrastructure in addition to cutting waste. Rotterdam has actively engaged in ecosystem restoration projects. Dredged sediments are utilized to create new habitats for marine life, supporting biodiversity in the region. By incorporating ecological considerations into dredging activities, the port ensures a healthier marine environment.
The Port of Rotterdam's sustainable dredging practices have been successful in minimizing the environmental impact of its dredging activities. For example, the port has reduced its turbidity levels by over 50% in recent years. The port has also created over 10 square kilometers of new habitat for wildlife through its beneficial use sites.
Prospects and Innovations
Sustainable dredging has a bright future thanks to new developments that have the potential to lessen costs, increase efficiency, and have a positive environmental impact. Dredging activities can be completed by autonomous vessels without requiring a crew, which lowers fuel and pollution.
Environmentally friendly dredging machinery, such as electric dredges, emits no pollutants and is quieter than dredges that run on diesel. We can reduce the environmental impact by integrating renewable energy sources into dredging operations, but this effort is still under development.
Environmental Impact of Dredging: Balancing Progress and Conservation
References and Further Reading
California State Coastal Conservancy, (2021). Phase 2 South Bay Salt Pond (SBSP) Restoration Project. [Online]
Available at: https://scc.ca.gov/webmaster/ftp/pdf/sccbb/2021/2105/20210527Board09_SBSPRP_Eden_Landing.pdf
[Accessed 13 October 2023].
Dede. P. et. al. (2018). Dredges' management: Comparison of regulatory frameworks, legal gaps and recommendations. Global NEST Journal. 20(1). 88-95. Available at: https://journal.gnest.org/sites/default/files/Submissions/gnest_02358/gnest_02358_proof.pdf
Vogt, C. et. al. (2019). Dredging Practices and Environmental Considerations. Encyclopedia of Sustainability Science and Technology. Springer. 325-351. Available at: https://doi.org/10.1007/978-1-4939-2493-6_438-3
Port of Rotterdam Authority. (2022). Highlights Annual Report 2022 - Port of Rotterdam. [Online] Available at: https://reporting.portofrotterdam.com/FbContent.ashx/pub_1011/downloads/v230309104726/Highlights-annual-report-2022-Port-of-Rotterdam-Authority%20goed.pdf