HafenCity Hamburg: living on a dike. (Photo: Luidger, Wikicommons)
Increasing rainfall levels will force most Dutch riverside cities to augment their flood defences. Why not improve the urban quality at the same time, asks PhD student Bianca Stalenberg.
Urban flood defences in the Netherlands are a shared concern between the water board, which is primarily responsible for safety, and the municipality, which is also interested in the social and economic viability of riverfront and hinterland areas. In her thesis, ‘Design of floodproof urban riverfronts’, PhD student Bianca Stalenberg, of the faculty of Civil Engineering and Geosciences, attempts to bridge the often opposing views of flood safety and urban quality by presenting examples of flood defences that improve the urban life quality instead of hampering it. Which moreover is a topical issue, since precipitation is expected to increase over the next century, as will the discharge of the main rivers. The worst case scenario for the Rhine river, for example, forecasts an increase in flood levels of one to three meters for several cities.
So what are the best practices thus far? Stalenberg mentions HafenCity, in Hamburg, Germany, where new residential and office blocks built on the existing quays also improved the flood defence. Every ground floor located below the level of nine metres above the German water level standard, has a waterproof construction: windows are built to withstand high water pressure, and steel shutters are provided to protect the windows against the impact of floating debris. No living areas are allowed on the ground floors – just car parks, restaurants and offices.
In more general terms, an adaptable flood defence (AFD), as Stalenberg proposes, is an integrated multifunctional structure that is not only capable of withstanding the highest of flood levels, but also incorporates promenades, houses, shops and offices, as well as parking places and roads. The whole structure has been designed to minimise the impact of high waters on urban life, even in the face of meteorological or economic changes.
Design options depend on the type of riverfront (varying from harbour, car park and historic buildings to skyscrapers) and on the flood retaining structures, such as dikes, quays or flood defence gates.
To come up with the best design for a specific situation, Stalenberg has assembled eleven different types of riverfronts and ten types of flood defences (including the adaptable one) into an Urban Flood Protection Matrix tool. This template allows the municipality and the water board to evaluate appropriate options.
Stalenberg’s PhD supervisor, professor Han Vrijling, sees a lot of public interest in multifunctional flood defences, but reticence among administrative bodies. “Various institutions have their own planning and legislations”, Vrijling says. “Initiating a combined project will almost inevitably lead to extra delays, which tends to cause most administrators to shy away.” Nevertheless the first pragmatic and small-scale combinations have been built.
Bianca Stalenberg will defend her PhD thesis on 8 September 2010 at 12:30 in the Aula.
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