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Choosing a cofferdam system is about more than keeping water out of a work area. The right system must fit the site conditions, provide a safe and reliable dry work zone, stay within the project’s budget and schedule, and be practical to install and remove.
Those requirements can vary considerably from one project to another. A bridge repair in a shallow stream presents different challenges than utility work along a shoreline or construction in deeper water. Soil conditions, water depth, available space, environmental restrictions, and equipment access can all affect which temporary water-control method makes the most sense.
Contractors generally have several options, including sheet pile cofferdams, earthen berms, sandbags, and water-inflated cofferdams. Knowing where each system works best helps project teams choose a solution before work begins.
Start With the Conditions at the Site
There is no single cofferdam system that is ideal for every project. Selection should begin with the physical and operational conditions contractors will face in the field.
Water depth is one of the first considerations. The barrier must handle the expected water level while maintaining adequate freeboard above the surface. Current velocity, changing water levels, and sediment conditions can also affect stability and performance.
The bottom of the waterway matters, too. Rocky, uneven, or debris-filled surfaces can make some systems more difficult to install, while soft sediment can affect how other barriers are anchored or supported.
Contractors should also consider how much room is available. Some systems require heavy equipment, large staging areas, or significant excavation, while others can operate within a relatively small footprint.
Other questions include:
- How long will the cofferdam need to remain in place?
- How quickly must the work area be isolated and dewatered?
- Is heavy equipment able to reach the installation area?
- Are there vibration, noise, or environmental disturbance concerns?
- Will the system need to be moved and reused elsewhere on the project?
- How difficult will removal and site restoration be once the work is complete?
Those factors can quickly narrow the available options.
Sheet Pile Cofferdams
Steel sheet piling is one of the most established methods of creating a temporary water barrier. Interlocking steel sheets are driven into the ground to form an enclosure around the work area.
Sheet piles can provide a strong barrier and are often used for deeper excavations, bridge foundations, marine construction, and projects where significant structural support is required.
Their strength, however, comes with installation requirements that may not suit every site. Sheet piles generally require pile-driving or vibratory equipment as well as sufficient access for cranes and other heavy machinery.
Driving steel sheets into the subsurface can also generate vibration and noise. Those impacts may be important considerations when work is being performed near buildings, utilities, environmentally sensitive areas, or populated neighborhoods.
Removal can require much of the same equipment and access considerations as installation.
For projects where structural strength and depth are the primary concerns, sheet piling may be appropriate. For shallower temporary water-control work, contractors may find that the installation requirements outweigh the benefits.
Earthen Berms
Earthen berms create temporary barriers using soil, rock, or other fill material placed across or around the work zone.
One advantage is the use of relatively familiar construction methods and equipment. Where suitable material is readily available, and the project has enough room, an earthen berm can provide an effective temporary barrier.
A berm generally requires considerably more space than a vertical or inflatable barrier because the material must be placed on slopes capable of remaining stable. That can be difficult in narrow waterways or locations where maintaining water flow around the work area is important.
Earthen systems can also create additional environmental considerations. Placing and removing fill may disturb the waterway bottom and surrounding terrain, and contractors must manage erosion and sediment during both construction and removal.
The material also must go somewhere when the project is finished, potentially adding hauling, disposal, and restoration costs.
Sandbag Cofferdams
Sandbags remain one of the simplest temporary water-control methods and can be useful for small, shallow, or short-duration projects.
They require relatively little specialized equipment, and individual bags can be placed by hand in areas where machinery has limited access.
Their simplicity can become a disadvantage as the project gets larger.
Building a substantial barrier requires filling, transporting, and placing many bags. Labor requirements can increase quickly, especially when the cofferdam must cover a long distance or withstand greater water depth.
Removal presents the same problem in reverse. Every bag must be removed from the work area, and damaged bags or loose fill can create cleanup concerns.
Sandbags may therefore make sense for small-scale work but become less practical as project size and water-control requirements increase.
Water-Inflated Cofferdams
Water-inflated cofferdams take a different approach. The system uses durable interconnected tubes filled with water to create the weight and stability necessary to hold back the surrounding water.
HSI’s Aqua-Barrier® is designed to use the water already available at the project site. Once positioned, the barrier is filled with water, creating a temporary isolation system without requiring pile driving or large quantities of soil or sand.
Because the system rests on the surface rather than being driven into the subsurface, installation can reduce the need to disturb the waterway bottom. It can also eliminate the vibration associated with driven sheet piling.
Water-inflated systems can also be drained, removed, and reused. For contractors performing multiple phases of work — such as successive bridge pier repairs or utility installations — the same barrier may be repositioned as the project progresses.
Aqua-Barrier systems are available at heights ranging from approximately 2 to 8 feet and can be configured for different site conditions. The appropriate size depends on water depth, sediment depth, and the amount of freeboard required above the anticipated water level.
Compare the Full Project Cost
Material price alone does not tell the full story when comparing cofferdam systems.
A lower-cost barrier can become more expensive if it requires additional labor, heavy equipment, imported material, disposal, or lengthy installation and removal.
Project teams should evaluate the entire temporary water-control process, including:
- Mobilization and equipment
- Materials
- Labor
- Installation time
- Dewatering requirements
- Environmental controls
- Maintenance during construction
- Removal
- Disposal
- Site restoration
- Potential reuse
Schedule is also directly related to cost. A system that can be installed and removed more quickly may reduce equipment rental, labor, and downtime even when its initial material cost is higher.
For contractors using cofferdams regularly, reuse can further change the calculation. A reusable system spreads its acquisition cost across multiple projects instead of treating the barrier as a single-use expense.
Consider the Available Footprint
Space can be one of the most overlooked factors in cofferdam selection. Contractors need room for workers, pumps, excavation equipment, materials, and the actual construction activity taking place inside the dewatered area. A system with a large footprint can reduce usable workspace or obstruct more of the waterway than anticipated.
Installation and Removal Matter
Removal is an important part of system selection for temporary work. Sheet piles may require heavy equipment for both driving and extraction. Earthen berms require excavation and removal of the fill. Sandbag systems require crews to retrieve potentially hundreds or thousands of individual bags.
A water-inflated cofferdam can instead be drained after the work is complete. Once the water is removed, crews can clean, fold, and transport the barrier for storage or another installation.
For projects with tight schedules or multiple construction phases, the ability to install, remove, and relocate a temporary barrier can be an important operational advantage.
Choosing the Right Cofferdam System
Cofferdam selection should begin well before crews arrive at the water’s edge. The right choice still depends on engineering requirements and site-specific conditions. A system that performs well on one project may not be suitable for another.
Water depth, current, soil conditions, site access, available workspace, project duration, and environmental requirements all influence which system best balances performance and constructability.
Sheet piling can provide the structural capacity required for demanding or deep-water applications. Earthen berms may work where space and fill material are readily available. Sandbags can remain practical for small jobs.
For projects requiring temporary water isolation without pile driving or large quantities of imported material, a reusable water-inflated cofferdam can provide another option.
HSI’s Aqua-Barrier system is designed to create a temporary dry work area using water from the project site while reducing the equipment, material handling, and site disturbance associated with some conventional cofferdam methods.
Project teams should evaluate the entire installation — not just the barrier itself — before making a final selection. Matching the cofferdam system to the site’s conditions can reduce installation challenges, control costs, and help crews spend more of the project schedule completing the work the cofferdam was installed to make possible.
For help determining whether an Aqua-Barrier system fits the conditions of an upcoming project, contact HSI Services to discuss water depth, site dimensions, access, and other project requirements.