Dredging: Methods and Their Impacts
What is dredging?
In only a few words dredging is excavating in a body of water rather than on dry land. For centuries, dredging has been a reliable method to maintain and improve waterways by moving materials to enhance navigation in harbors and rivers. More recently, remediation dredging has been coined to define cases where dredging is doing more than just facilitating navigation.
Remediation dredging is the act of removing material from the bottom of aquatic environments.
Dredging methods can be categorized into two primary types: hydraulic dredging and mechanical dredging. Each method has its unique advantages and challenges, which we'll explore in detail.
Hydraulic Dredging
Hydraulic dredging is primarily conducted using a floating barge equipped with a submerged suction head. This head agitates the sediment on the channel floor and utilizes a series of hoses to pump the resulting slurry—a mixture of water and sediment—through the system to a designated disposal site through a series of pipes. An analogy could be drinking a milkshake through a straw.
Key Characteristics of Hydraulic Dredging:
- Cumbersome Logistics: This method relies on setting up a network of suction pipes, that convey the slurped up slurry away from the dredged site for disposal. These pipes need to extend from the suction head doing the work all the way to a large location to settle out water from the soils. These pipes can easily extend miles for miles, making logistics complex, especially on an island.
- Lack of Precision: This method operates like a vacuum, indiscriminately sucking up everything in its path. Heavier materials can be left behind and lighter particles from outside the suction head can be swept in. As a result, there is less control over exactly what materials are being removed. This may lead to environmental concerns.
- Messy Operations: The mixing of solids and water is the defining element of this method. The “mixed up” solids or slurry can complicate disposal and lead to challenges in managing the environmental impact at the disposal site. This is because the runny slurry is more difficult to handle, and the “mixed up” water adds volume to the excavated material in need of disposal.
C-HAWQ’s Impact on Marco Island
Dredging the canals is the only way to remove the contaminated sediment. Marco Island originally received a proposal of $189 million to hydraulically dredge the canals. This high cost is due to the large operation hydraulic dredging entails. It comes with disruption of roads and waterways from the miles of pipes stretching the entire distance sediment slurry is transported for separating and disposal. The C-HAWQ Initiative is proposing a mechanical dredging solution due to its flexibility, efficiency, and lower environmental footprint. This solution will cost significantly less, will not impede water or roadways, and will have the most effective results. As we strive to maintain and restore our waterways, understanding the differences and implications of each dredging method becomes increasingly important for the restoration of Marco’s waterways.
It Implements similar processes used for maintaining navigation channels, while additionally enhancing flood control, and improving aquatic habitats’ health. The Marco Island waterways are under increased stress from recreation, runoff, and natural disasters. Dredging will improve the water quality in Marco Island but, different dredging methods can be used, so the question of how to dredge is more important than ever.
Mechanical Dredging
Mechanical dredging, on the other hand, involves the use of machinery—such as backhoes or excavators—that utilize buckets or claws to scoop sediment directly from the bottom of the waterway. Mechanical dredging is preferred in smaller areas that require more precision and minimize the resuspension of contaminants. To continue the analogy above, this is like scooping a thick milkshake with a spoon.
Key Characteristics of Mechanical Dredging:
- Increased Accuracy: With advancements in 3D positioning systems, operators can closely monitor how deep they are digging and where they have already excavated, allowing for a more controlled dredging process. The materials excavated are mixed with the water far less and are more contained within the bucket doing the work.
- Cleaner Process: Since mechanical dredging does not mix up the excavated materials and water nearly as much as hydraulic dredging it does not produce a slurry. This minimizes the environmental mess associated with hydraulic methods. This results in less impact on surrounding ecosystems.
Efficiency in Confined Spaces: Mechanical dredging is often more efficient as it does not require extensive piping systems, making it well-suited for narrow or confined areas. Another great environmental benefit resulting from the lack of piping is the ability to better contain the excavation area being worked in. The actions taken to contain the work site, in conjunction with other pollution-limiting precautions, are collectively referred to as Best Management Practices (BMPs). BMPs are critical in protecting the environments being benefited by remediation dredging while the hard work is performed. They will need to be the subject of a future blog post.
Types of Dredging Methods
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