What beats sandbags the best?

Sandbags are the traditional form of emergency dikes, said Professor Bas Jonkman at the Flood Proof Holland event. Although the method of laying sandbags is tried and tested, there is a growing need for alternatives that are faster, and that require less manpower while being at least as reliable.

The testing ground for flood defences, located just south of the campus, features dams around the low-lying land, water reservoirs, and locks that can be opened to simulate flooding. The scale is somewhere between a hydraulic engineering laboratory and the full-scale reality. On the day of the event, there are people in army uniforms, researchers, inventors and students in shorts from high schools.

Four alternatives

Four alternatives are to be tested against a traditional wall of sandbags. The alternatives will be judged on speed of deployment, reliability, and scalability. The teams laying the sandbags are rated on cooperation, team spirit and, of course, how long their dams resist the rising water.

After the inevitable failure of the sandbag dam, the water flows on to one of the four innovative dams, which then, hopefully, will stop the flood. All four alternatives use water to stop the water.

Despite its light appearance, the tube barrier stems the flood very well. Inventor Robert Alt says he was inspired by a plastic pool that proved impossible to move once it contained a tiny level of water. For the tube barrier to remain in place it’s essential that water flows over the floor mat instead of under it. The mat is therefore fixed to the pavement and is weighed down with metal strips. Once the mat is in place the barrier fills with water and will stop the flood. One sixty-five centimetre thick unit weighs sixty-five kilogrammes and it can block ten metres in length. The units are attached with zippers and Velcro mats.

The mobile dike (mobieledijk.nl) consists of a long water-filled body, covered with a coarse net for strengthening and a tough orange vinyl cover. The manufacturer claims laying the mobile dike is 90 times faster than sandbags.

Once deployed, the Slamdam looks like a giant hippo. People seems to enjoy leaning into the massive yet yielding black softness of this tough waterbag. “It just feels sturdy,” says Anna van de Hadelkamp, one of the firm’s representatives. She explains that the Slamdam is made of rubber with polyester strengthening. The units are five metres long and should have a two centimetre overlap when placed. Once filled with water, the hydrostatic pressure will seal adjacent bags. The hippo-like bags need no anchoring – they’re simply impossible to tip over.

Finally there is the box barrier. The stackable yellow boxes are connected by black watertight wedges, covered with lids to keep the shape and filled with water. The system is compact: a forty foot container can store 400 metres of box barriers. Three men can dam 100 metres in one hour, say the representatives Bas Reedijk and Marcel Plug. Another bonus feature they mention is that their system is vandalism-proof. “You cannot stab it with a knife.”