Feature: Dutch turn dikes into innovative sites to fight floods

Multifunctional, technology enhanced and innovative water defence levees figure prominently in the largest ever dike reinforcement program undertaken in the Netherlands, adding new impetus to the low-lying country's millennium long fight against flooding.

"With sea levels climbing and climate change expected to boost storm frequency and intensity in the Northern Sea and increase discharges in the rivers reinforcing and making the dike system much safer has become an absolute necessity," Richard Jorissen, director of the flood protection program at the Dutch national and regional water authorities, told Xinhua in an interview.

Dutch dikes are subject to strict safety criteria requiring that almost one third (1,100 km) of the prime dikes and 256 locks and pumps undergo reinforcement. As of 2017 the safety criteria will become even stricter to reflect the increased population and values protected by the dikes.

In response to changing social, urban and economic needs the main players involved, Rijkswaterstaat and regional water boards, sought to augment the 300 repair projects with new functions, while combining innovative and cost-effective approaches.

"Our endeavour is not just to repair infrastructure. We aim at adding new dimensions to the dikes and combine them with coastal, urban, agricultural, spatial and high technology developments," explained the Dutch engineer in charge of a proposed 7.4-billion-euro (about 8 billion U.S. dollars) package of flood-protection upgrades until 2028.

MULTIFUNCTIONAL DIKES

Integrating various functions, whether recreational, urban or public, into dike reinforcement are already in the pipeline.

One such example, with plans expected to finalise later this year, involves flood protection combined with creating new agricultural land in the north of the Netherlands off the city of Groningen, an area vulnerable to flooding not only because of adverse weather conditions, but also due to earthquakes caused by gas extraction.

"To reinforce the existing coastal dike we are planning to build a new secondary levee and use the land for suitable to salt water cultivations," explained the program director.

A 5-km long and 1.5-km wide chunk of land stretching between the two dikes will be divided in two areas, allowing sea water to bring in silt and raise the soil level on the one, while the other half will be used for cultivations of suitable crops, such as cockles and samphires.

"New dike development could also be combined with housing or recreational functions," said the expert in hydraulic engineering, "ensuring that dikes continue to be part of the Dutch life as has been the case for centuries."

The Netherlands is divided and ringed by the world's most extensive dike network of over 22,500 km.

"There are dikes practically everywhere. In the cities, along the rivers and the coasts, concealed under cycling and walking paths, roads and dunes," said Jorissen, who has participated over the past 10 years in some of the largest infrastructure and hydraulic projects in his country.

In the coastal area near the seaside town of Katwijk in the northern outskirts of The Hague the new dike-in-a-dune construction became a "multi-dike" when combined with an adjacent parking space.

"The project involved creating a dike within a dune to secure the area against flooding and meeting the requirements for a car park, while retaining the passage between the beach and the village," said Jorissen.

The Wakkere Dijk in Munnikenland, situated in the heart of the Netherlands between river Waal and Maas, serves as a flood evacuation area for large livestock and a strand is being constructed as a recreational observation point.

Also in the tourist town of Dalfsen along river Vecht in the east of the country a dike has been integrated in a housing and shopping development.

Dikes have been for over 1,000 years an intrinsic part of flood safety in the Netherlands.

Today nine million Dutch, more than half the population, live at areas in risk of flooding as one forth of the country lies below sea level. Even after the construction of the high technology enhanced delta works and dams, following the big flood of 1953, which left unprecedented damage and 1,836 casualties, dikes still remain significant pillars of the country's flood protection system.

Together with creating additional room for the rivers and continuously nourishing the sandy shores and dunes Rijkswaterstaat and regional water authorities deliver the required safety measures.

The Dutch invest over 1 billion euros a year in water safety, while water management, including delta and water technology, is the second largest economic sector after agriculture, providing 80,000 jobs and annual turnover of 17.5 billion euros.

CLIMATE AND MOBILE DIKES

Along with more functions the Dutch water and local authorities aim at combining the dike upgrades with new technology, while preserving cultural and historic sites.

One such example is the so-called Climate Dike, a levee 100 times stronger than a normal one, which can also serve as foundation for homes in the small town of Streefkerk, 20 km east of Rotterdam in the south of the country.

The dike constructed near the town's marina along the river Lek is an example of the Dutch high-tech engineering prowess as large concrete piles are placed vertically 25 meters below the soil level to help raise its height by around 1,5 meters compared to average dikes, which are between 7 and 9 metres high.

"By lying in the heart of the village the new construction has provided an opportunity for urban redesigning," said Jorissen.

Economic return might prove crucial in this high tech solution, which costs almost three times (20-25 million euros per km) more than an average dike (around 9 million euros per km).

At the forefront of the new flood-control program also lie new generation mobile defences, such as the dike at the historical centre of the village Spakenburg, situated in a former shallow inlet of the North Sea, which was flooded 100 years ago. The dike, a 335-meter barrier made of a mixture of steel and plastic in U shape, rises automatically as the water level rises.

"It allows for almost immediate protection, which is needed as the village is vulnerable to flooding caused by strong winds, which hit fast, leaving practically no time for preparations," explained Jorissen. At a cost of 6 million euros the longest mobile dam in the world can protect Spakenburg in just three hours after warning.

NATURAL MATERIALS

In addition the new program aims at minimizing environmental impacts and using natural materials, especially in protecting dikes from erosion. New materials, such as geo-textiles are used to prevent erosion as they allow the water to go through, but keep the sand in place.

More specifically the Dutch were the first in the world to construct a vertical geotextile screen following two different high technology methods in the berm of the river levee along the Nederrijn, near Opheusden town to prevent piping. Piping occurs in case of abnormally high water levels and water seeps under the levee and starts to carry sand.

Moreover, the technology allows placing the screen with precision making it suitable for use in densely populated areas where the screen has to be placed next to houses and roads.

Another intriguing process strengthens dikes with layers of coarse sand, while vertical digging pulls iron or sand "curtains" inside the dikes to protect them from erosion.

"To add reinforcements within the heart of the dike innovation is crucial," pointed out Jorissen, who has also worked on flood protection projects in various countries, including China, the United States and Poland.

Besides harnessing nature's power to protect their vulnerable nation, the Dutch export their high-tech engineering prowess worldwide.

With the world market, currently valued at 500 billion euros annually, predicted to grow extensively in the next years, countries, such as China, Brazil, Germany, Saudi Arabia, Indonesia as well as the United States, and Britain, top the Dutch water management agenda for cooperation. (1 euro = 1.08 U.S. dollars) Endit