Alternative protection3 April 2008
A flexible semi-mobile flood protection system has been developed to address failings in traditional flood protection measures such as high costs, low strength, water leakage and slow deployment
There are many alternatives to sandbags on the market, and undoubtedly with the recent flooding witnessed in the UK, Europe and the US, countless more are on the way. One such alternative is AquaFence – a semi-mobile flood protection system that has been in development since 1997 and in full production since 2005.
The system has been developed over a ten-year period to ensure its suitability for use in a live flood situation. The system is a replacement for the traditional sandbag wall that is used for flood protection the world over, and has the possibilities to improve reaction time and effectiveness in most situations where property is threatened by flood water.
Although sandbags are the most common form of flood protection, they are notoriously time and manpower intensive to set-up – on average a ten-man team can take up to 72 hours to erect a 100m sandbag wall. In known flooding areas, this can often mean that hundreds of workers and volunteers are required to spend days preparing for a coming flood. Testing has, however, confirmed that an AquaFence flood wall of 100m length can actually be set up by ten men in one hour. One such area where hundreds of people were needed to prepare for regular local flooding is Mount Vernon in Washington, US. When the Skagit river threatens the Mount Vernon Downtown district, it takes hundreds of volunteers and city workers 12 to 15 hours to set up a sandbag wall. AquaFence needs just a small team of workers to set-up flood defence in about a third of the time.
Mount Vernon’s state-of-the-art AquaFence flood fighting arsenal was shown to the rest of the country after the town took delivery of its AquaFence system in September. At a demonstration held on 24 September, the entire system was installed in just four hours, with a team of 16 people. The AquaFence flood wall was erected along Mount Vernon’s Main Street, stretching from Division St. to Kincaid St., a total of 460m in length.
This particular installation was used to train the local authority workers on exactly how to use AquaFence. A key aspect of the system is its ease of use but Mount Vernon was keen to ensure its staff could harness the set-up time of AquaFence the moment it is needed in a live flood situation. The reaction to AquaFence at Mount Vernon was positive and the company’s US division, based in Lynwood, Washington, is expecting to see more towns show an interest in the system as a result of the demonstration.
One AquaFence element actually replaces approximately 900 sandbags. The short set-up time of AquaFence is achieved through this, and the all-in-one design of the AquaFence sections (elements). Each 200cm wide and 120cm high (as standard, other heights available) element is self-contained, with everything needed to erect it attached, ensuring that parts aren’t lost during storage, transport or deployment during bad weather.
Each AquaFence element consists of two boards of marine grade plywood in compact flat packs. A standard AquaFence element is 2m long and constructed to tolerate water heights from 60cm to 120cm, although custom elements are made to order.
Once an element is hand-lifted into place, it is a case of raising the vertical section, which forms the wall, and clipping four securing poles into place. The next element is then attached and a highly durable, PVC section that is impervious to water ensures complete integrity at the join. This method also enables a 5° angle to be implemented (vertical and horizontal), which allows an AquaFence flood barrier to follow an uneven course and to lessen the requirement for specially designed elements.
When flood water arrives, the downward pressure of the water on the bottom section of the element provides strength and stability ensuring that the AquaFence elements stay in place. This new concept in flood protection has been developed to ensure high integrity throughout an AquaFence installation, which is fortified by a specially developed seal that mitigates water ingress between AquaFence elements and the ground. In areas where there is a risk of heavy floating debris, a specially designed debris shield can be fitted, which uses the flood water itself as a protective cushion.
AquaFence is available as a mobile version for hard ground installation. The semi-mobile solution for soft-ground installation requires the use of a pre-fabricated concrete base. AquaFence engineers can work with customers and contractors during the assembly of the base which, due to its small size, is low-cost, inconspicuous and unobtrusive, allowing clear passage for pedestrians and vehicles when not in use. AquaFence can be used without this foundation but it is recommended to use it for known flooding hotspots.
On average, a 200cm wide, 120cm high sandbag wall costs the same as an identical sized AquaFence element. However, AquaFence can be used over and over, whereas sandbags may be used only once – they may become contaminated during flooding and are thus classed as hazardous waste and have to be disposed of as such, which is an expensive and time-consuming process.
AquaFence in action
AquaFence is already used at several locations throughout Europe and is currently undergoing certification to the FM Global standard in Hamburg. Norwegian insurance company Gjensidige has purchased AquaFence and installed it outside a division of the Norwegian State broadcasting company NRK. NRK’s offices are situated on the Myren estate near the river Aker in Oslo, Norway. Gjensidige decided to buy the AquaFence solution after a series of episodes where the river Aker broke its banks and water penetrated the neighbouring building complex.
Another Norwegian customer is the Skedsmo Kommune, close to Lillestrøm in Norway. In cooperation with NVE (the Norwegian Water Resources and Energy Directorate) Skedsmo has chosen AquaFence for protection from floods and high waters on the river Øyern. When the dike was built around the city, it was lowered in places to keep the view. In order to do this, NVE demanded that alternative protection was made available, leading to the deployment of AquaFence at a 140m section in front of Dynea Factory.
AquaFence has local offices in Rakkestad in Norway, Düsseldorf in Germany, and Washington, US. The company has also opened new offices in Stockholm in Sweden and in Warwickshire, UK. AquaFence UK will act as a central point of contact for AquaFence customers to address their local flooding issues.
The AquaFence UK office joined forces with AquaFence A/S to demonstrate AquaFence at the Tees Barrage during September, October and November 2007. A single AquaFence element was placed directly in front of the Bear Trap water gate to demonstrate the kind of pressure that AquaFence is able to cope with and also a longer section running parallel to the water flow, protecting two islands from the water. As the water rushed by, the AquaFence elements mitigated any water ingress into the protected area.
AquaFence is the brainchild of Thor Olav Rørheim. Since 1997, he has worked on development and improvement of flood protection systems in cooperation with the Norwegian University of Life Sciences (UMB) and Innovation Norway – with additional support from the Norwegian Water Resources and Energy Directorate (NVE). This venture led to the establishment of AquaFence in 1999.