The utilization of dredging for rehabilitating lakes and aquatic habitats severely impacted by eutrophication is well-documented. Although dredging practices have been under scrutiny for an extended period, the global research community has only recently linked them to water quality. Dredging can exert both positive and adverse effects on water quality. Evaluating the benefits against the associated risks is crucial in making informed decisions regarding the most suitable technique.
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Introduction to Dredging and Water Quality
Dredging is the process of removing sediment, debris, or other materials from the bottom of water bodies such as lakes, and rivers. As per the United States National Oceanic and Atmospheric Administration, it is commonly employed to deepen waterways, establish new ports, and maintain existing ones.
Dredging is primarily done to sustain the water level by enhancing the depth of water channels. It is helpful as a safe water level ensures smooth operation of boats. Furthermore, dredging also removes harmful pollutants and contaminants from the water. This stops the spread of detrimental substances and ensures the survival of aquatic ecosystems.
Dredging affects the water quality, particularly in environments sensitive to turbidity, such as coral reefs, filter-feeding communities, and seagrasses. The dynamics of sediment dredging can influence various crucial aspects of water quality, encompassing parameters like turbidity, dissolved oxygen, pH, and nutrient concentrations. These parameters significantly affect the water quality and aquatic life.
What are the Different Techniques for Sediment Management?
The dredging process consists of four essential steps: excavation, vertical transportation, horizontal transportation, and material disposal or utilization. Mechanical and hydraulic dredging are the two most famous techniques utilized for a long time.
Mechanical dredging often involves excavators or cranes with open digging or clamshell buckets mounted on barges or flexi-floats. These machines remove sediments and deposit them at the designated locations.
Alternatively, hydraulic dredging involves transporting sediments in a slurry form through temporary pipelines facilitated by dredging pumps. In cases where the discharge slurry velocity needs enhancement, boosters may be employed to maintain optimal material transport. The dredging method's selection depends on the reservoir's specific characteristics and accumulated sediment.
Various types of dredges are employed for sediment removal, each designed to suit specific applications. The plain-suction dredge is the most common, relying on suction to remove loose debris without penetrating or cutting the water body's bottom.
On the other hand, cutter-suction dredges feature a cutting tool that loosens material from the bottom and transports it to the suction apparatus. Auger-suction dredges utilize a rotating auger to bore holes into the bed, effectively loosening and suctioning up debris. Jet-lift advanced sediment removal equipment employs a high-volume stream of water to pull in nearby water, silt, and debris. The selection of the dredge type depends on the nature of the sediment and the specific requirements of the dredging project.
Effectively managing sediments is essential for maintaining or enhancing water quality. Excessive amounts of sediments can harm the organisms in the water body, and many pollutants can decrease the water quality. In this regard, dredging is essential to keep a safe level of sediments and remove pollutants effectively.
Case Studies: Positive Impacts of Dredging and Sediment Removal on Water Bodies
Researchers published a chapter in the Wetlands: Ecology, Conservation and Management book series in which they highlighted the use of dredging to improve the water quality of a polluted lake in Sweden.
Lake Trummen, situated in Sweden, was heavily polluted and a micro-pollutant center until 1970. The water was unusable for domestic purposes, and no aquatic life could survive. Suction dredgers were used to save the lake during 1970-1971.
The cyanobacterial blooms, characterized by summer transparency levels of 15–20 cm, disappeared, giving way to a plankton community with diverse species. The ecosystem, as a whole, recovered into a functional unit. The water quality was increased, evidenced by a balanced aquatic ecosystem.
In the Journal of Environmental Sciences, researchers from China used dredging to improve the water quality of Lake Yuhea, which was severely affected by eutrophication. The research team utilized dredging practices and compared the lake water content before and after dredging.
The post-dredging results showed a significant decrease in phosphorus and organic pollutants. The zooplankton community structure swiftly adjusted to the environmental changes primarily induced by dredging. Consequently, there was a notable decline in the abundance of rotifers. Hence, dredging is a suitable practice to increase the water quality of affected lakes.
Potential Impacts and Challenges of Dredging
Researchers have found that although dredging is primarily done to increase the water quality, it may sometimes be more damaging. A major concern is the process of sediment resuspension, which increases the turbidity levels in the water, leading to a collection of sediments on the water surface. This increased turbidity can hinder light penetration into the water, adversely affecting aquatic plants and animals.
Furthermore, dredging activities have sometimes led to the release of accumulated contaminants in the sediment into the water bodies. These contaminants mainly include heavy metals, pesticides, and other pollutants, threatening aquatic and human health.
However, several effective methods to mitigate the negative impacts of dredging have been employed during various projects. In some instances, opting for hydraulic dredging over mechanical dredging has significantly minimized sediment resuspension. Treating dredged sediment before disposal is an effective strategy to reduce the release of contaminants into the water. These practices contribute to a more environmentally sustainable approach to dredging activities.
The International Association of Dredging Companies has highlighted the importance of Environmental Dredging Equipment, a recent technological advancement to preserve nature and water quality.
During dredging practices, managing turbidity is a significant challenge. The novel environmental dredging techniques aim to minimize turbidity to protect surrounding waters and contain the spread of contamination. This specialized equipment is designed precisely to achieve a high concentration of dredged sediment while keeping turbidity as low as possible.
The standard equipment is modified and engineered to remove thin layers accurately, ensuring that only the necessary amount of material is dredged, minimizing environmental impact.
The efficient removal of sediments is essential for sustainable dredging practices as it is key in enhancing water quality by decreasing the concentration of pollutants and nutrients in the water. Choosing the dredging technique equipment and safely disposing of the dredged material affects the water quality and requires thorough research beforehand.
Read More: The Different Methods of Monitoring Water Quality
References and Further Reading
GeoForm International, (2023). DREDGING 101: WHAT IT IS, HOW IT WORKS, BENEFITS & MORE. [Online] Available at: https://geoforminternational.com/sediment-removal-101/ [Accessed 27 November 2023].
U.S. Aqua, (2023). Sedimentation Management: Reservoir and Dam Dredging. [Online] Available at: https://www.usdredge.com/learn/sedimentation-management-reservoir-and-dam-dredging [Accessed 28 November 2023].
Zhang, S. et al. (2010). Effects of sediment dredging on water quality and zooplankton community structure in a shallow of eutrophic lake. Journal of Environmental Sciences, 22(2), 218-224. Available at: https://doi.org/10.1016/S1001-0742(09)60096-6
Björk, S. et al. (2010). Restoration of lakes through sediment removal, with case studies from lakes Trummen, Sweden and Vajgar, Czech Republic. Restoration of lakes, streams, floodplains, and bogs in europe: Principles and case studies, 101-122. Available at: https://link.springer.com/chapter/10.1007/978-90-481-9265-6_8
United States National Oceanic and Atmospheric Administration, (2023). What is dredging? [Online] Available at: https://oceanservice.noaa.gov/facts/dredging.html [Accessed 25 November 2023].