A flume at Deltares' Delft facility in the Netherlands opened in early October. The facility is designed to help the country adapt to rising sea levels and extreme weather events by enabling researchers to test full-size structures against battering waves.

The Delta Flume, as it is named, is capable of creating some of the world's largest man-made wave patterns, enabling coastal engineers to test the performance of dikes and other structures in waves that measure up to 4.5 m high.

"Both [climate change and rising land values] will require costly improvements of sea defenses, but the money should be spent wisely, [on] those locations that need it the most," says Marcel R. A. van Gent, head of the coastal structures and waves department at Deltares, an applied water and subsurface research institute. Van Gent wrote in response to questions posed by Civil Engineering online.

(Watch a video animation of the test facility.)

Inaugural wave breaks in front of a reviewing stand. Image source: DeltaresInaugural wave breaks in front of a reviewing stand. Image source: DeltaresAssessing which flood defenses have the greatest need for improvement requires more information about their existing strength and how their designs can be optimized than existing test facilities were able to provide, says van Gent.

"On top of that, one of the research topics that has hardly been addressed so far is how much time does it take between initial damage to a dike until actual breaching of a dike occurs," van Gent says. "It is important to know how many hours after initial damage of a dike we have left before flooding would actually occur."

(Watch this video from the BBC on final tests at the facility prior to its opening.)

While many materials and structures can be tested using scale models, there are certain processes that cannot be scaled down and tested in that way, the company says. This includes the behavior of sand, clay, grass and such natural construction materials as brushwood. Some flow characteristics inside sea defenses are also difficult to test at smaller scales, van Gent says.

The flume allows prototypes to be tested and assessed. The flume measures 300 m in length and has a width of 5 m. It comprises a 42 m long wave generator and two concrete trough sections built to different depths: a 183 m long, 9.5 m deep section and a 75 m long, 7 m deep section. The design provides room for testing at the 9.5 m depth and also provides a transition zone that will enable the simulation of foreshores, areas that remain under water at high tide but above water at low tide. The flume replaces a smaller, 240 m long, 5 m wide, and 7 m high version that operated under the same name on the site for 34 years.

The flume is built on a 3 m thick reinforced-concrete base plate atop 800 piles. Its sides are made of reinforced concrete and measure between 1.5 and 2 m thick depending on the location along its length.

The facility uses freshwater at all times because of the toll that salt water would have both on the concrete and the flume's surrounding environment as it splashes out of the trough. The differences in behavior between salt water and freshwater are minor and easily calculable, van Gent says.

Specifications

Wave flume

Overall length approximately 291m

Width: 5 m

Depth: 9.5 m

Wave generator

Full stroke: 7 m

“Dry-back”, piston-type wave board drive (cradle, 4 pistons)

Second-order wave steering system

Active Reflection Compensation

Installed electric power for wave generation: 1.9 MW

Wave machine design and supplier MTS (USA)

Wave characteristics

Maximum height (regular) H max, r: 3.3 m

Maximum wave height H = 4.5 m

Maximum significant wave height H m0: 2.2 m

Wave peak period (H m0 = 2.2 m): 5.7 s < Tp < 13.4 s

Wave period 1 s < T < 20 s.

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