Storm surge barriers The European experience

The notion of storm surge barriers is not unique to New York - they are being tried in a number of other locations.

Thames River Barrier, London

London has been periodically flooded since records began back in 1099, with water levels reaching as high as 2.38 m (7.8 ft). In 1953, a particularly disastrous flood occurred in which the tide rose by 2 m (6.5 feet) above its predicted normal level, 300 people drowned and about 65,000 hectares (160,000 acres) near the mouth of the Thames River were covered with seawater.

The Thames River barrier has been constructed to protect London. It is located on the Woolwich Reach, 14 km east of London Bridge. Construction commenced in 1974 and the barrier was opened in 1984. As shown in Figure 9.7, it spans the 520 m river width with four large navigation openings and six smaller flood control openings. Four main rotatable (about a horizontal axis) gates, 61 m wide, span the main navigation channels. Their design is based on Tainter gates (referred to as 'rising sector gates'), steel structures with a radius of curvature of 12 m (66 ft). The gates are hollow so that water can drain into and out of them as they are closed and opened. They are designed to be stored underwater when the gates are open, flush with the sill depth of 9 m (30 ft), so that there is unlimited overhead clearance for ships. There are also four 30 m gates, which, being normally stored in the overhead position, are called falling radial gates. The 9 piers on which the gates are mounted occupy 17 per cent of the span. As shown in Figure 9.8, each of the main gates can be raised to an overhead position for maintenance. They can also be partially opened near the river bottom to the

Figure 9.7 Thames River barrier with the gates partially open in the undershot position for flushing away accumulated sediments

Source: http://alumweb.mit.edu/clubs/uk/Events/Barrier.jpg.

Downriver

Downriver

Downriver

Figure 9.8 Various positions of the Tainter gates in the Thames River barrier

Source: Holloway et al, 1978.

Figure 9.8 Various positions of the Tainter gates in the Thames River barrier

Source: Holloway et al, 1978.

undershot position to use river currents to scour out any accumulated sediment. The Thames Barrier was given an attractive architectural appearance, which has helped to make it something of a tourist attraction.

The Thames Barrier is the world's second largest movable flood barrier (the largest is the Oosterscheldekering in The Netherlands). It is designed to withstand a 1000-year return flood with a very low upstream water level (Clark and Tappin, 1978). When conditions indicate that a tidal surge is building downstream to a dangerous level, an early warning is sounded that is normally several hours in advance of the order to close the barrier. In certain circumstances, however, the warning time could be as short as one hour. Therefore, the machinery is designed to close each gate in 15 minutes and the complete barrier within 30 minutes (Fairweather and Kirton, 1978).

Since 1982, the Thames Barrier has been closed over 100 times. The barrier now has to be closed as often as 12 times a year, compared to 4 or 5 times when first commissioned. This has recently led the Greater London Authority to reexamine the revised estimates of global warming and the effects of climate change that the city is likely to experience in the next century and to consider whether the barriers need to be strengthened or rebuilt entirely. In 2005, a suggestion that it might become necessary to supersede the Thames Barrier with a much more ambitious 16 km (10 miles) long barrier across the Thames Estuary from Sheerness in Kent to Southend in Essex was made public.

Delta Project, The Netherlands

A series of flood protection barriers and seawalls known as the Delta Project were built in The Netherlands after more than 1800 people were drowned during the same 1953 North Sea storm that ravaged southeast England. Work began soon after and finished in 1997 with the completion of the storm surge barrier across the 360 m wide Nieuwe Waterweg (see Figure 9.9). This barrier has two hinged, floating Tainter gates that are swung out to meet each other, then filled with seawater and dropped onto a supporting sill before an impending North Sea storm makes landfall. It protects greater Rotterdam's 1 million inhabitants and seaport from flooding.

The barrier was designed to be capable of withstanding forces and actions that have a probability of occurring once in every 4000 years (a 5.3 m surge plus another 4.5 m wave run-up at the present stand of MSL). The design life of the barrier is 200 years (Ypey, 1982).

Figure 9.9 The Netherlands' Nieuwe Waterweg (New Waterway) storm surge barriers, spanning the 360 m width of the river, were opened in 1997

Source: http://images.encarta.msn.com/xrefmedia/sharemed/targets/images/pho/t902/T902 898A.jpg.

Figure 9.10 A second example of Dutch engineering is the Eastern Scheldt barrier, completed in 1986

Note: Stretched over a width of 3 km, 66 piers are built on 45 m centers with 40m wide gates. The height of the gates is 6-12 m. This barrier, built across the Scheldt estuary does not allow the passage of ships.

Source: www.safetyengineering.nl/servic6.jpg.

To build a second storm surge barrier across the mouth of the Eastern Scheldt estuary was enormously difficult (see Figure 9.10). The tidal volume at the mouth is over 109 m3 during ebb or flood tide; the main channels are almost 40 m deep. Over 0.5 x 106 m3 of prefabricated pre-stressed concrete were needed, and 11 specialized ships had to be designed and built to assist in the construction.

Venice Lagoon, Italy

Venice suffers from chronic flooding that now threatens the integrity of many of its historic structures. After several decades of controversy, the installation of 79 storm surge barriers across the 3 inlets (Lido, Malamocco and Chiiogia) of the Venice Lagoon was finally approved in 2002; construction began shortly thereafter. So-called Project Moses follows a novel design of three groups of submerged, hinged gates, as sketched in Figure 9.11. The idea of a barrier first arose in 1966, after the disastrous 2 m flood that brought thousands of volunteers to Venice to help to save priceless art treasures. The cost of Moses has nearly doubled since it was approved (see www.veniceinperil.org/news_articles/newsarticles1.htm).

In the face of an approaching storm, air will be pumped into the hollow caissons, normally lying flat on the floors of the three inlet channels, to allow them to rotate up to and penetrate the surface (see www.smit.com/sitefactor/public/ downloads/pdf/Marine%20Projects/Venice%20flood%20barrier.pdf). The sum of the three barrier widths is 1600 m. The individual gates measure about 30 m high, 20 m wide and 4—5 m thick. The barriers are expected to cost between US$3-4 billion and the target completion date is 2011.

Figure 9.11 After decades of controversy, a decision was made by the Italian government in 2002 to construct three inflatable storm surge barriers across the entrances of the lagoon separating the city of Venice from the Adriatic Sea

Source: www.veniceinperil.org/images/Moses-Barrier.jpg.

St Petersburg, Russia

The city of St Petersburg, with 5 million residents, is located on the delta of the Niva River at the eastern end of the Gulf of Finland of the Baltic Sea. The city floods regularly, often once a year, and has suffered from floods with surges greater than 1.6 m about 300 times in recorded history, including 3 catastrophic floods in 1777 (3.2 m), 1824 (4.2 m) and 1924 (3.8 m). Begun in the Soviet era but never completed, the project was resurrected in 2002 and is presently under final construction. The barrier is 25 km long and is composed of 11 earth and rock dam sections, six water exchange sluice gates and two navigation passages, the larger of which is 940 m in width.

A sketch of the project including the six sluice gates, shipping entrance/barrier and the elevated city ring road extension is shown in Figure 9.12 (Plate 14). Of all the European examples, St Petersburg's pertinent characteristics are most similar to those of New York: a large city of great commercial and cultural significance, built on a flood plain delta with gentle topography at the mouth of a navigable river (third largest in Europe) with strong seasonal flow variations, and with an indented or semi-enclosed coastline susceptible to surge amplification.

Figure 9.12 Sketch of the storm surge barrier and seawall system that is presently under construction to protect the city of St Petersburg, Russia (see Plate 14 for color version)

Source: www.oceansatlas.org/unatlas/-ATLAS-/IMAGES/HIGH/i24l-1 .jpg.

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