With floodwaters continuing to rise in height and frequency, the world is searching for the ultimate in flood protection.
Sandbags have always been the first thought at the very mention of the word “flood” images on the television and in newspapers around the world bear witness to the all encompassing flood protection properties of the sandbag as our saviour as waters rise around our properties or critical infrastructure. Images of armies of volunteers and military, shovelling sand into burlap bags or the issuing of them to householders to protect their property are a part of our flood consciousness.
The humble sandbag has been with us since the late 18th century starting life as field fortifications for the military because burlap and sand (or soil) were cheap and readily available not to mention the accessibility of available manpower for filling these defence systems. The basic science behind the effectiveness of a sandbag in a blast mitigation scenario is that the sand slows down the velocity of the bullet to the point that it is either completely stopped or slowed to such a speed that it will not cause serious injuries. The sand also absorbs any shards or projectiles from ricochet. It is the friction created by moving soil or sand grains that creates multiple tiny air bubbles which dissipates s the effect of an explosive blast or bullet.
But the sandbag does have its downsides; According to the UK Environment Agency it will generally take 2 people 1 hour to fill 12 sandbags, they can be difficult to handle, laying them can be very time-consuming, sacking material is biodegradable and will perish if left in place for a long time.
In 2007 the British Army had a requirement for a non-metallic berm wall to provide ballistic protection for ammunition storage areas in Afghanistan. UK based J&S Franklin Ltd teamed with Terram Ltd to develop a non-metallic berm wall, which led to the manufacture of a range of force protection products, called DefenCell.
DefenCell enables force protection walls to be built very rapidly in operational conditions using the latest technical high performance geotextile fabrics from Terram combined with new construction techniques and bonded together in various configurations to produce a series of adjoined cells, known as geocells. These can be filled with locally available fill materials (sand or soil or crushed rock) to produce structures of various sizes and shapes providing structural strength and integrity.
The cellular concept was well established in the construction industry, primarily for ground stabilisation and slope reinforcement, however by increasing the size and height of the cells as well as adding a unique interlock system between multiple layers J&S Franklin were able to significantly enhance the capabilities, providing a product that are protecting several critical infrastructure sites in the UK, and are in operational deployment in Afghanistan, Chad and several US Bases.
With DefenCell basically being an upgraded, improved, modernised sandbag, and having had such great success in a Force Protection role, it made sense to test its functionality in a wide range of applications, including flood protection.
Some 10 years ago, Congress tasked the U.S. Army Engineer Research and Development Centre (ERDC) to “devise real-world testing procedures” for “promising alternative flood-fighting technologies” Through the General Investigation Research and Development Program, ERDC conducted research and developed a laboratory procedure for the prototype testing of temporary barrier-type flood-fighting structures intended to increase levels of protection during floods.
Manufacturers of “Flood Fighting Technologies” were invited to bring their product to the test facility in Vicksburg, USA, together with all equipment and supplies required to erect their product prior to testing, using their own staff or ERDC personnel (after suitable training from the manufacturer) to construct the barrier ready to test in a flood scenario.
The DefenCell Flood Barriers are supplied in 5m long sections, 0.50m high. The sections are held open using a simple aluminium frame and filled with locally available materials (earth, sand, crushed rock etc). The frame is then removed to the next section and installation continues. Depending on the application, an impermeable sheet is placed on the front side of the barrier to reduce any water penetration.
The US Army Corps of Engineers (USACE) have been at the prime provider of flood protection in the US and their Engineer Research and Development Center (ERDC) on the Mississippi has been at the forefront of testing innovative new products against their benchmark assessments of sandbags for flood barriers. The DefenCell cellular system was tested successfully by ERDC and added to their range of approved products.
In 2010 the DefenCell DC2 Lightweight Non-metallic Barrier, passed the strict testing procedure and appeared in the list of flood protection products approved by the US Army Corp of Engineering.
In May 2011 a DefenCell DC2 Flood Wall System was deployed in Smithland Kentucky, USA, to save the town from an imminent record flood surge caused from snow melts from the northern areas together with torrential rainfall. A town of just 400 people, it was estimated that they had just 75 hours to prepare for a record surge in river levels, and protect itself from the Ohio River.
“Based on (calculation) and communication with EOC (Louisville District Emergency Operations Center), we determined there was insufficient time to fill and place sandbags, and that the DefenCell Wall System was the best choice to stay in front of the rising water,” geotechnical engineer Steven Shifflett said.
Within 24 hours of receiving a call, DefenCell delivered three miles of Flood Wall units that, once installed, would provide almost four feet of additional flood protection barrier to a key stretch of the levee in Smithland. Within an hour of delivery to Smithland, small volunteer teams formed from local citizens, city employees, National Guard support, and even inmates from nearby correctional facilities were able to start placing, connecting and filling, the DefenCell Flood Wall systems, and within the first three hours they achieved an installation rate of 20+ units per hour. In this short period they installed the equivalent to over 22,000 sandbags.
The end result was more than 10,500 linear feet of Flood Walls, consisting of over 700 units stacked two units high, stretching over one mile in length using more than 4,700 tons of sand contained in the geotextile system.
The speed height and depth of this installation would not have been possible using traditional sandbags.
The DefenCell barriers remained solid throughout the surge and the town was saved from flooding.
“If it wasn’t for the geo-textile flood barriers (DefenCell) two thirds of Smithland – including the Country Seat – would be under water right now, “ said Brent Stringer, Livingston County Management Officer. “Not only has the product exceeded our expectations but also the expectations of the Army Corps of Engineers.” He continued, “The geotextile flood walls performed way above my expectations in flood control as well as time taken to set up. My future flood response plans will look different now.”
To put this product in a direct comparison with a sand bag – The smallest DefenCell product is the DefenCell Ranger – It is equivalent to 40 sandbags, and yet can be filled by 2 people in less than 10 minutes.