The short answer is that Maritime Dredging is needed as often as it is required. We’re going to drill down a bit into exactly what that means, and how to figure that out, but every dredging project is different. There are different inflows, different dredging requirements, and different budget considerations that will determine the dredging frequency that is required for your project. This is what makes hiring a dredging consultant so important.
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The reason it’s so hard to determine the exact dredging frequency, or dredging cycle, is that every climate, body of water, and water use is very different. Take the Chesapeake Bay region, for example, you’ll see official dredging cycle estimates ranging from 2 years, to 200 years depending on the type of use, and the required level of dredging.
That report also points out a range of dredging and the frequency required for each project. The Broad Creek navigation channel has an estimate of 5 years for high bound dredging, and 20 years for low bound dredging – with the “most probable” dredging cycle falling somewhere in the middle at 10 years.
The reason for the range of years really has to do with costs. The high bound dredging cycle is expected to carry an annual cost of 401 k, versus the low bound annual cost of just 34k. The most probably dredging cycle of 10 years carries an annual cost of around 108k. It’s a good balance between annual cost, and when dredging will be absolutely required.
In the Gulf region, dredging of shipping channels is required every couple of years. Without dredging, shipping traffic wouldn’t be able to safely pass through the region.
Determining Your Dredging Frequency
The number one factor in determining your dredging schedule is the reason that you’re dredging. If you’re dredging because you need an absolute minimum depth for ships, then your frequency will be fairly regular and determined by that cycle. If you’re dredging just to create a healthier and deeper body of water, to remove contaminants, or to restore fish habitat, your schedule may not be as rigid.
Determining your dredging frequency requires looking at several factors:
- Depth Required – What depth do you need to maintain? This would be the absolute minimum depth that you will allow the body of water to reach. You’ll want to factor in a safety buffer if the depth is mission critical, like for navigation routes or ports and harbors.
- Dredging Depth – How deep can you dredge? If you can only dredge a few feet versus a few dozen feet, this will determine how often you’ll need to dredge the same area. Obviously, 2 feet will fill up much quicker than 20 feet and will need to be dredged more often.
- Inflow Considerations – How quickly do silt and debris fill in the body of water? Although dredging is often measured in cubic yards, we’ll simplify this a bit. If you have a 10-foot lake that you’re dredging to 25 feet, (assuming 10 feet is the minimum depth) you can allow 15 feet of silt and debris before dredging is required again. If you lose 1 foot of depth per year, that gives you a 15-year cycle. However, if you lose 5 feet per year, you’re now on a 3-year cycle.
Overdredging to Reduce Frequency
One method that is employed by the military is to overdredge certain areas to reduce the dredging frequency.
A dredging practice widely used by the Corps’ Coastal District offices in maintaining navigation projects is that of overdredging, often referred to as advance maintenance dredging. The Corps currently uses overdredging to maintain 300 estuarine and coastal navigation projects. Overdredging, or advance maintenance, can either be in the form of overdepth or overwidth dredging.
Dredging can be disruptive, so the ability to lengthen the frequency of dredging can be very beneficial to regions that require dredging every couple of years. By simply digging deeper and wider than what is normally required, it will take longer for the area to fill in to the minimum required depths.
There is a larger cost associated with overdredging, but this is usually offset by the reduced frequency.
It also may not be possible to overdredge in your area. It really depends on the regulations that you’re working with. Sometimes only minimal dredging is allowed to take place, which will also increase the frequency of your dredging project.
Reputable Dredging Companies
It’s important to hire a company that will be able to guide you through the process and offer a frequency that fits your budget – and gets the job done. There’s nothing worse than having to dredge a body of water only to find out it needs to be done again much quicker than anticipated because the company didn’t estimate properly
Find an experienced company that offers premier dredging services that will be able to lean on past projects to help you properly estimate dredging frequency.
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