Alternative to dikes strengthens country's defenses against flooding

The Netherlands, a country with only half its land exceeding 1 meter above sea level, will strengthen weak links along its northwestern coastal area by 2016 with an innovative "sand solution".

The solution is to be a defense against the impact of major storms as it creates more space for nature and recreation, according to Dutch officials.

Most of the 10 weak links where waves are particularly powerful have already been reinforced, and the work on the remaining locations is in full swing, Roeland Hillen, an official of the water authority, said on Tuesday at a construction site along the Hondsbossche and Pettermer Seawall in NorthHoll and province.

"By the beginning of 2016, all the weak links will have been strengthened, and the Dutch coast will be protected against flooding for the next 50 years," said Hillen, managing director of the flood protection program, part of the Rijkswaterstaat, a mission that manages the Nether-lands' main network of high-ways and waterways.

Along the centuries-old sea wall, a 12-meter-high sand dune is being erected with a particular type of sand extracted from the sea. Between the dike and the newly created dune is a small valley.

Dozens of meters farther into the sea, a smaller dune, also made of sand, is taking shape. Extracted by dredging vessels offshore not far from the site, the sand is transported through pipes onto the shore and pumped to designated locations.

For Luc Kohsiek, chairman of the regional water authority, Hollands Noorderk wartier, this "sand solution", which is in line with the Dutch history of "taking land from the sea", is a more flexible concept compared with traditional engineering projects.

"If you rebuild the dike, it will cost as much as the sand here. Suppose that within 50 years sea level rises, you have to increase the height of the dike again. That's not flexible. But with sand, if the sand erodes, we hire a couple of ships; within a month, all the sand is here again," Kohsiek said.

The Hondsbossche dike, made entirely of sand before the 14th century, was rebuilt in 1873 with heavy blocks of basalt reinforcing its seaward side. From 1977 to 1981, it had grown to a height of 11.5 meters above sea level as required by the Delta Plan, the Netherlands' national coastal defense initiative launched after the catastrophic 1953 floods that killed more than 1,800 people.

Under the current strengthening plan, "we bring the sand here and nature will rebuild it in its own way," Kohsiek said. "By doing this, the defense (against the rising sea) will be as strong as possible," he said. "But if you have only a pile of sand, no one will come here. That's why we have also designed in the southern part a big inner lake for recreation."

At the southern end of the dune, where construction work is almost finished, is a huge pond on the sand bed. Around it, a patch of newly planted grass sways - the only visible man-made signature.

The dune begins there, curving into a 200-to 300-meter-wide beach and spreading naturally into the sea.

"To build the new stretch of dunes and beaches, no fewer than 35 million cubic meters of sand are needed. Up until now, 27 million cubic meters have been pumped to their designed locations," project manager Dirk Bakker said.

(China Daily 11/06/2014 page11)