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December 2013 Issue

Novel Approach to Tsunami, Flooding Barriers
Hans J. Scheel

So far, protection walls, i.e., breakwaters, have been erected along coastlines in attempts to protect cities, harbors and nuclear power stations against tsunamis and flooding. Furthermore, meteorological services and expensive warning systems have been established to give notices for populations to escape to higher ground in the event of such natural disasters.

Even with such common preventive measures in place, the March 2011 tsunami that occurred in Honshu, Japan, killed at least 20,000 people and caused the Fukushima nuclear power plant accident, with after effects still affecting the local community. The tsunami also hit Sendai, Japan, where Tohoku University is based.

Tsunami waves from earthquakes and landslides typically have an amplitude of 30-to-100-centimeters height in the ocean at a typical depth of 4 kilometers. Only when these waves approach decreasing water depth as they near the shore do the catastrophic tsunami waves several meters high form, with wave height being further multiplied by the funnel effect of bays.

Tsunami waves reached 38 meters in the Kamaishi Bay in Japan during the March 2011 incident, destroyed the world’s deepest breakwater and parts of the harbor and the city, and killed more than 1,000 people. Such devastation was unable to be prevented by conventional measures.

In contrast to establishing breakwaters along the coast, a novel approach is to reflect the tsunami pressure waves before the catastrophic high waves are formed using offshore barriers made of steel fences and rocks. This approach is based on the high velocity, c, of tsunami waves in the ocean at 700 to 800 kilometers per hour being reduced by decreasing water depth as the waves come nearer to shore. The product of amplitude (wave height), A, squared times velocity is constant: A2 x c = constant. This explains the sudden increase of tsunami waves near the coast. Thus, a deep, vertical, stable barrier in the ocean located on the continental shelf at a water depth between 30 and 500 meters (preferably at 200 meters depth) will reflect the fast tsunami pressure waves.

The building of such walls by conventional technology and the use of concrete is complex and expensive and does not give absolute protection, as was evident with the Kamaishi breakwater, the damaged remainder of which can be seen in Google Earth.

The novel barrier concept is based on high-strength steel fences, which are stabilized with rocks deposited from top, with one of three different methods. The first method involves a steel fence with horizontal anchors that is lowered from rolls on pontoons into the sea. Simultaneously, rocks are inserted to fix the anchors and, thus, the fence in order to form a stable barrier extending several meters above sea level. On top, a thick concrete wall with a hanging, inclined surge stopper is set up to protect the service road along the barrier, as well as the coast, from flooding.

A second method consists of two parallel fences with distance holders, with rocks inserted from above into the gap between these two fences. The fences are interconnected and form a horizontal barrier, for example, of 800 kilometers length to protect the coast of Honshu.

The third method uses long gabions, or steel-fence baskets filled with rocks, which are lowered into the sea to form a long, stable barrier. In this case, a more expensive steel fence is required compared to the other two methods described above.

Steel that is resistant to corrosion from saltwater is essential. All metal components of the barrier should have the same composition, for example, stainless steel T316, in order to prevent electrocorrosion in the ocean. This steel may be further protected by coatings of elastic PVC or polyamide polymer, or by a concrete covering.

A U.S. patent application, 13/861,608, dated April 12, 2013, and international patent applications, WIPO PCT/IB2013/055276, dated June 27, 2013, and WIPO PCT/IB2013/059511, dated October 21, 2013, are pending for this new approach to tsunami and flood barriers.

Initial cost calculations have been done, with the resulting estimate being approximately $11 million for 1 kilometer of a 30-meter-deep barrier, 5.6 meters wide and extending 3 meters above sea level, including the concrete road on top with concrete walls and surge stopper. These calculations were prepared using Internet data from U.S. companies and information from Geobrugg AG, a company based in Romanshorn, Switzerland, about stainless-steel fences. Erecting these barriers to natural disasters could save lives and prevent catastrophic damages.

If the U.S., Japan and other governments begin large-scale efforts to protect their coasts from tsunamis and flooding by applying this more efficient barrier technology, these projects would stimulate national industries and job growth.

The costs of such substantial undertakings can partially be offset by land reclamation between the barriers and the coasts, by using tidal energy from turbines located inside the barriers to generate renewable electricity, or by using these areas as seawater reservoirs for large-scale fish farming.

In addition to guarding against tsunamis and flooding, this new type of barrier could also bring about ecological benefits. Coastlines and beaches, as well as flora and fauna, can gain protection against oil spill catastrophes and against tar originating from the cleaning procedures of ships. Furthermore, coastal erosion can be prevented by such tsunami barriers.

Hans J. Scheel, retired from the Swiss Federal Institute of Technology, started Scheel Consulting and was visiting professor/invited scholar at Osaka and Tohoku universities in Japan and at Shandong University in China. He has a chemical background and has solved crystal growth and epitaxy problems, authored 120 technical publications and patents, and co-authored and edited seven books in the field.


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