Air Bubble Curtains with Bubble Tubing®
Air Bubble Curtains also known as Bubble Barriers
Air bubble curtains made with Bubble Tubing® have an enormous potential that warrants further research, toward the protection of marine mammals, maritime environments, and those who work or find recreation in the ocean.
Air Bubble Curtains are also known under several other names: Air barrier, air curtain, bubble barrier, bubble curtain, pneumatic barrier, pneumatic boom, barrier of air bubbles, curtain of air bubbles, air bubble curtains, bubble wall, bubble screen.
How do Bubble Curtains function?
The interest in bubble curtains and the effect of air bubbles in water was studied in detail during the Second World War in order to block sound waves created by submarines. It has also been demonstrated that air bubbles in water reduce the rate of sound wave dispersion and disrupt the propagation of energy densities that would normally be observed. The effectiveness of bubble curtains depends mainly on the frequency of the waves, the volume of air injected, the size of the bubbles, the number of air diffuser lines used and the distance between the bubbles emanating from the air diffuser lines.
The operating principle of a curtain of bubbles consists in creating a wall more or less dense, a flexible bubble barrier that rises continuously from the bottom of the water to the surface.
This wall of air bubbles is created using a properly adapted compressor and capable of operating continuously according to the estimated air volume. These bubble curtains serve as a buffer zone to reduce the impact of shock waves, sound waves and frequencies of these shock events dispersing in water from a source (e.g. sea bed pile driving). The injected air flow must be large enough to form a very dense and efficient bubble curtain. Depending on the project, we regularly suggest the installation of double or triple bubble curtains to maximize the amount of bubbles present. In the case of a double or triple curtain, the lines of Bubble Tubing® diffusers are installed parallel to one another at a distance specific to each project. The reasoning is that each layer of bubble tubing contributes to the reduction of the total impact, so by incorporating several layers it is possible to increase protection in the aquatic environment.
Independent studies are underway to determine the specific capacity of the Bubble Tubing®. The market for noise attenuation and environmental protection by two-phase barriers is certainly evolving.
What are the various functions of Bubble Curtains?
Mitigate damage in marine environments from noise and the effect of blasting due to mining, drilling, seismic surveys and underwater pile driving.
Used as underwater noise attenuation systems, air bubble curtains use air to reduce the effects of shock waves from underwater explosions. Weighted Bubble Tubing installed on the sea floor in a marine application attenuates the propagation of sound waves and the effect of undersea blast shock and pile driving that can harm marine life. Applications for bubble curtains are numerous.
Marine pile driving at large construction sites produces considerable noise and high pressure underwater. These conditions can be lethal to fish and can harm marine mammals. In an effort to reduce sub aquatic sounds generated by work sites, projects now employ air bubble curtains. These air bubble curtains provide an effective barrier to sound propagating through water, because of the difference in density between air and water.
Multi lines of air bubble curtains can increase efficiency of the attenuating effects of the bubbles. A series of Bubble Tubing® rings around the pile generates denser bubble curtains. Bubble Curtains are a potential strategy as a mitigation measure to address acoustic impacts to marine mammals in the new NOAA Ocean Noise Strategy Roadmap.
Common sources of high pressure noise at sea:
Demining operations and underwater blasting
Drilling for the installation of offshore wind turbines
Retraction of marine structures
Oil prospecting operations (seismic)
Military activity using seismic or sonar equipment
Port and coastal development
Protecting marine mammals from offshore oil platforms and wind power farm construction and continuous operation vibrations and noise (machinery and engine noise)
Offshore drilling and oil exploration in maritime environments and their effect on the ecosystem are of great concern. Noise mitigation technology to reduce underwater sound coming from marine construction, oil exploration as well as continuous noise coming from offshore oil extraction and wind power companies operations are required.
In the ocean, whales and other marine mammals use gentle sound pulses to communicate about feeding, mating, and to keep their groups together. But as we increasingly probe the ocean, the loud sounds of exploration, development, and construction send powerful waves that can confuse, disorient and harm these marine mammals.
Reducing underwater sounds is an important goal. Air bubble curtains offer a promising means of lessening the impact of aggressive sound on marine mammals by confining and reducing sound intensity and the speed over which the sound waves travel.
Surrounding active undersea operations with walls of bubbles will alter the shape of the noise waves. When a pressure wave hits an air bubble, it will compress the bubble, and then it will expand again, so energy is lost. Sound travels faster through water than air but will slow down if it hits air bubbles.
It was established that a continuous sound or an impulsive sound greater than 160 decibels could disturb the behavior of marine mammals. Even constant noise, coming from oil exploration and extraction is different from the staccato bursts emitted by driving piles, engines and machinery on board ships.
Air bubbles are then a means of reducing the sound transmitted from stationary sources. By surrounding a rig or ship with bubbles of air the amount of noise can be reduced and dispersed.
Containing oil spills within a given area
Another main concern over offshore drilling and oil exploration is oil spill containment. Oil spills related to maritime and inland waterway transport is also a risk.
Air Bubble curtains can act as a containment measure in the case of an oil spill in calm waters, e.g. for protecting harbors, marinas or seaports and shorelines.
A bubble air barrier installation consists of submerged, perforated tubing from which compressed air is released. The result is a rising curtain of bubbles which produces an up-swelling on the water surface above the tubing. The up-swelling produces a raised surface behind which the floating oil molecules can be trapped. The air barrier (air curtain) represents an alternate method of containing or confining spilled oils within a given area, allowing time for implantation of decontamination methods.
Fish guiding and containment systems in waterways such as rivers
There is an increasing demand for marine life conservation worldwide. Submerged air bubble curtains not only reduce the sound, but create a linear screen that can protect, deflect, herd & guide specific fish species away from the pile, water intakes, hydroelectric dams or contaminated areas.
In Denmark, RS Coast Care has tested Air Bubble Curtains with our Bubble Tubing® to protect beaches, harbors and coastlines against seaweed, algae, jellyfish and other floating debris.
More and more companies specialize in the development of barrier protection systems for small fish such as salmon smelts that migrate between rivers and the sea.
These companies contact us to obtain our Bubble Tubing® to integrate in their existing guiding systems that function with various components. Bubble Tubing® creates a bubble curtain deterring fish from swimming past the bubble wall. By installing Bubble Tubing® in a strategic location of a dam, a hydrant or other engineering structure, we can redirect fish to ladders specially designed for them. Other components such as strobe lights and sounds at low frequencies can be added to redirect the fish to safe places or prevent them from passing into water intakes that can be fatal to the fish.
As seen on the video below, air bubble curtains made of Bubble Tubing® are already in use as fish screening systems to stop jellyfish from entering and blocking water intake pipes in the United Kingdom.
Motion control and direction of floating debris
Hotel chains and other tourism businesses living along coastal regions are faced with a growing problem of seaweed called Sargassum. The seaweed is pushed by waves on the beaches and accumulates sometimes up to 9 feet thick! The daily costs associated to the machinery and the employees required for to the collection of these seaweeds is staggering. The growing presence of Sargassum (and indeed many other species of aquatic plants or algae) in the sea is due to the increase of nutrients in the water, increase in temperature and sea currents and winds. The tourism industry is affected by this problem in areas such as the island of Saint-Martin, Guadeloupe, Mexico and Martinique. Other debris may be found floating on the water surface such as bottles, plastic bags and micro plastics. Installing bubble curtains can be a solution to contain these floating debris and algae for easier retrieval before they arrive on the coasts. Bubble curtains can prevent floating debris from entering channels or create a current that can repel algae and debris to a less sensitive area.
Silt barrier and turbidity curtains to contain sediments in suspension
Bubble curtains also meet the requirement for containing silt and turbidity for in-situ work where sediment containment barriers are mandatory. When working in a stream, river or lake, marine construction and dredging companies are required to install a physical curtain called a floating turbidity barrier.
These barriers do not allow free passage for boats and work equipment. Whereas a bubble curtain does both: it allows movement of boats and equipment over the barrier while retaining sediment and other suspended matter. In this case, a bubble curtain installed from the stream, river or lake bed will mitigate the migration of silt and other suspended sediments through the water column.
Our Bubble Tubing® has proven to be very effective as a silt barrier and turbidity curtain during these applications. Also, in this article, research is currently underway to validate the effectiveness of bubble curtains in altering stream dynamics. Water currents in the outer curves of riverbeds are slower allowing for sediment deposition and accumulation. Over time, a sand bank can be created, making shipping impossible without dredging under certain circumstances. By installing a bubble curtain in this outer curve, this creates a sufficient current to prevent sediment buildup.
These are a few of the applications for Bubble Curtains. We look forward to working closely with engineers, scientists and water managers to find bubble curtain applications to protect wildlife and the environment so projects can move forward in an environmentally responsible manner.
Who may need to create a bubble barrier?
Demand for bubble curtains is booming. Who are our customers:
Acoustic reduction specialists
Oil platform managers
Companies specializing in dredging
Marine construction companies
Hydroelectric dam managers
Companies specializing in fish barriers
Environmental engineering firms
Cities to recover waste in canals and rivers
Floating waste recovery companies
Environmental groups and citizen associations
Bubble Tubing® is available in ½, ¾, 1 and 1 ¼” I.D. , in weighted or non-weighted formats. It is also available with 100’ already mounted on a stainless steel diffuser, the OctoAir-10 industrial grade diffuser.