Flooding is one of the most destructive natural disasters, threatening lives, causing untold property damage, and potentially causing substantial disruption to public services, including electricity and clean drinking water. This article will explore the critical role of dredging in flood prevention and its environmental considerations in the face of rising flood risks and climate change.
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Flooding can have disruptive effects that go far beyond the immediate area by restricting the movement of products and people. Flood damage makes up approximately one-third of global economic losses caused by natural hazards worldwide. Between 1980 and 2018, more than 220,000 people died due to floods, and economic losses exceeded $1 trillion.
Climate Change and Flooding
Floods and their devastating impacts are expected to increase for several reasons. First, the forces of climate change will significantly alter the water cycle, causing more extreme rainfalls and severe storm surges as the sea level rises. While there is substantial uncertainty regarding the scale of these climate change impacts, they have the potential to drastically ramp up the threat of flooding.
Changes in land use will significantly increase the risk of flood damage. For instance, urbanization of vegetated land lowers infiltration and raises overland flow.
Given the current and potential future impacts of flooding, mitigation measures are more important than ever, and dredging is a proven tactic that should be used cautiously.
Understanding the Link Between Dredging and Flood Prevention
Dredging involves the removal of fine gravel and silt materials from a riverbed, coastline, reservoir, or other body of water. Dredging helps to increase water flow and transport capacity in a river. An extreme form of dredging involves realigning a river by carving out water channels. This is typically carried out to move potential floodwater past essential areas.
River dredging has been done for many years, and not just as a flood prevention measure. Other reasons to dredge a river include increasing land drainage, maintaining water flow to mills, and mining material for construction. When it comes to flood prevention, dredging is most effective in combination with other flood risk management tactics and any comprehensive catchment-oriented approach.
The Role of Dredging in River Management
Many regions and countries worldwide use dredging as a river management solution.
Taiwan is one place where dredging plays a crucial role in river management. The island has a high flood risk due to frequent earthquakes and tropical storms. Many of the rivers in Taiwan have strong upstream erosion, and this causes a heavy accumulation of materials downstream.
In densely populated Taiwan, dredging is part of the river management methods used by the Water Resources Agency (WRA). As part of a strategy to protect lives and property, the WRA uses dredging to maintain stable flow paths. Rivers in Taiwan are also dredged so the gravel and sand removed can be used for construction and other purposes.
Dredging for Coastal Protection
Two dredging strategies to protect coastal lands from flooding are nourishment and channel deepening.
Beach nourishment is a strategy that involves adding sediment to beaches to mitigate ongoing erosion. While this does not address the root cause of erosion, it can help to prevent it. This strategy typically involves dredging sand and other materials from the water and redistributing it to broaden the beach. This strategy must be ongoing to keep a coast protected from destructive storm surges.
Dredging for coastal protection does not just occur along the ocean coastline. In 2021, New York Governor Kathy Hochul announced the completion of a $15 million dredging product designed to repair and restore lands along Lake Ontario and the Saint Lawrence River. This dredging was part of a much larger project across New York State. According to a press release from the governor’s office, more than 75% of the materials dredged were reused for beach nourishment, general fill, and other purposes.
Reservoir Dredging and Watershed Management
In addition to providing water for large populations, reservoirs also serve as a habitat and food source for fish, frogs, and other wildlife living in the area.
Contemporary reservoirs are meticulously constructed and engineered to withstand the formidable forces of nature. Nevertheless, they remain vulnerable to the detrimental impacts of deforestation and natural erosion. These occurrences can introduce sediment, debris, salt, and even refuse into the reservoir, leading to a substantial accumulation of these materials, and adversely impacting the water supply and the surrounding ecosystem.
Dredging is a highly effective strategy to remove reservoir deposits created by natural or manmade forces. Dredging has also been used to increase the storage capacity of a reservoir.
Dredging Challenges and Environmental Considerations
Like many other activities involving changing the natural environment, dredging has been scrutinized. Naturally, the increasing awareness of the adverse consequences of dredging has prompted demands for its responsible and conscientious execution.
When executed incorrectly, dredging can severely harm an underwater ecosystem, affecting the immediate dredging location and areas downstream.
Marine life is particularly susceptible to these repercussions, as they rely on their surroundings for habitat and sustenance.
Substantial alterations to the riverbed or sea floor can disrupt crucial areas used for spawning and shelter. For instance, removing gravel can harm Atlantic salmon, European bullhead, brown trout, and other fish species' spawning grounds. Moreover, the changes induced by dredging can disrupt the development of eggs and embryos, which are intricately influenced by temperature and water quality factors.
Dredging also stirs up silt that can remain suspended in water for long periods. This can lower oxygen levels and stir up harmful chemicals. Additionally, materials removed by dredging can be challenging to dispose of, particularly when those materials include garbage and contaminants.
The impacts of dredging are not just restricted to marine environments. Floodplains are an essential part of ecosystems and maintaining biodiversity, and dredging can negatively impact the natural dynamics of floodplains and the animal populations that live there.
While dredging can provide positive impacts, these negative impacts are driving the push for greater sustainability.
Innovative Dredging Technologies
Technology continues to disrupt dredging and waterway management, just like every other industry. Many innovative dredging technologies have been focused on greater precision and efficiency.
One recent innovation involves using multi-beam sonar to allow an operator to see underwater infrastructure during dredging. In turgid water, this innovation allows an operator to see around a dredge to position it as accurately as possible. This innovation is particularly useful when dredging reservoirs, around dams, and inside marinas, where there is typically significant infrastructure underwater. Images created by the system are stored in a database for analysis, documentation, and planning.
Another area of innovation focuses on low-cost methods for removing fine sediment. Hydrosuction is a technique involving sending water into the bottom sediment to create a slurry so that it can be siphoned away.
Water injection dredge
Water injection dredge is another innovation that involves pumping water into bottom side movements at high volumes and low pressure. This creates a bottom layer with a higher density than the surrounding water that can be transported by gravity downslope to deeper waters. This can be a more cost-effective way of removing fine sediments without traditional dredging equipment. This technique also requires less labor, but only under the right conditions.
Community Engagement and Government Initiatives
Given the benefits, costs, and impacts of dredging, several government programs and initiatives exist for oversight and community engagement.
In the US, the federal National Dredging Team is an interagency group focused on ensuring dredging occurs promptly and cost-effectively. The government group focuses on environmental protection and restoration.
A key focus of the team is implementing a national dredging policy designed for regional and national consistency around dredging issues. This policy would also address conflict resolution and create a forum for engagement between key stakeholders and government agencies.
Other key focuses of the dredging team include:
- Managing dredged material
- Increasing public education around the issue of dredging
- Maintaining a forum for conflict resolution
What Does the Future Hold for Dredging to Reduce Flooding
In conclusion, flooding, one of the most destructive natural disasters, poses significant threats to human lives, property, and public services. Its extensive economic and human toll is a pressing global concern.
Climate change and changes in land use are set to exacerbate the risks of flooding, making the need for effective mitigation measures more critical than ever.
Dredging, a well-established technique with various applications in river management, coastal protection, and reservoir maintenance, can play a crucial role in flood prevention when used with comprehensive strategies. However, its potential adverse environmental impacts, such as disrupting marine ecosystems and affecting floodplains, call for responsible and conscientious execution.
Advances in dredging technology are improving precision and efficiency, while government initiatives and community engagement are essential in ensuring that dredging is carried out in a balanced and environmentally responsible manner. The evolving field of dredging is vital in mitigating the destructive effects of flooding in an ever-changing world.
Read More: Sustainable Dredging Practices: Minimizing Environmental Footprints
References and Further Reading
Western Dredging Association. (2021, April). Reservoir Dredging: A Practical Overview. WEDA. Available at: https://www.westerndredging.org/phocadownload/Workgroups/Reservoir_Dredging
Environment Agency. (2021, December 23). Floods and Dredging: Explaining the Environment Agency's Approach. Available at: https://environmentagency.blog.gov.uk/2021/12/23/floods-and-dredging/
New York State Governor's Office. (2021, December 30). Governor Hochul announces completion of Phase II of State's $15 million regional dredging project. [Press release]. Available at : https://www.governor.ny.gov/news/governor-hochul-announces-completion-phase-ii-states-15-million-regional-dredging-project
United States Environmental Protection Agency. (Retrieved 2023, October 16). National Dredging Team. Available at: https://www.epa.gov/ocean-dumping/national-dredging-team