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Flooding in Hamburg

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Aerial view of Hafen City, Hamburg

Aerial view of Hafen City, Hamburg.  No flood barriers here.

There was a flood in Hamburg while I was there, on November 30. Hamburg has a unique strategy to deal with floods, and it’s pretty interesting.

Floods are actually common here. They usually result from a storm surge in the North Sea; during a storm sturge, the sea level on the coast rises quickly, and the waters of the river Elbe have nowhere to go but to flood the city.

Hamburg is not the only city vulnerable to storm surges, of course. Most cities, greater Vancouver included, rely on a network of dikes to hold back the waters. Hamburg has its own dikes, but it also uses a unique strategy: it lets the water flood parts of the city. This gives more room for the waters, and as a result the height of the flood crest is not as high.

But doesn’t that cause a lot of damage? Not really; that’s the beauty of the strategy.

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Hafen City flooded in 2013. Ooops, forgot the car.

First, there are rural areas around the city where low-lying areas are meant to be flooded. On the island of Wilhelmsburg, for instance, a natural wetland park has been preserved, but there is also an area where a main dike was moved inland so as to create an area that where flood waters can enter. This is a large area where a huge volume of flood water can spread out, which lowers the height of the flood. But when the area is not flooded, it is a low-lying meadow that is used to graze sheep or cows. This, of course, benefits the city since the island faces downtown across the river.

 

This strategy of giving a river room to expand – so-called building with nature – is not unique to Hamburg, of course, though the extent to which it is applied is remarkable. But what makes Hamburg unique is a decision to apply this strategy to some of the built-up core of the city.

Flood-proof store at pier level

Flood-proof store at pier level

Hafen City is the new urban development that faces downtown across a series of canals that used to be the old port. Already half completed, the 2.4 square kilometer site has already nearly 2000 inhabitants and over fifty buildings, all showcases of energy-efficient architecture. And Hafen City is built to get flooded; in contrast to downtown, there are no dikes to protect it. When you walk along the canals in this new district, you quickly notice that much of the city is at different levels: there are streets and walkways at the old level of the piers, there are streets built higher, and then there are elevated walkaways above that still.

You also notice that the shops and cafes at pier level have doors and windows that look like they are bomb-proof. In fact, they are built to withstand a flood, one of as much as three meters above the lower street level. Most of the stores, businesses, and appartments are built on the higher level, though. A lot of what is at ground floors in many buildings is considered floodable: indoor parking lots, some storage, that sort of thing. Even if the waters rise by a full story, as they did in 2007, life and business goes on. Urban planner Thorsten Gödtel stayed dry throughout the worse of that flood:

Sitting in a café, Gödtel felt as safe as if he were peering into an aquarium, even though silty water swirled halfway up the restaurant’s extra-thick windows, inches from his aquiline nose. He left the restaurant on an elevated roadway, keeping his feet dry.

Even if the waters rise three meters above the street, these Hafen City  appartments stay dry.

Even if the waters rise three meters above the street, these Hafen City appartments stay dry.

The same approach is now used in the much older shoreline of Sankt Pauli. The famous fish market is located at pier level, which is floodable (and was indeed flooded on November 30). Merchants know to pack their wares to higher land; some of the more permanent fixtures, such as restaurants, now have sturdy flood-proof doors and windows. There always seems to be someone who does get the notice, though; every time there is a good flood, photographers come down in droves to film the cars whose owners forgot that they had parked at pier level, now flooded if not floating. Nothing is ever completely fool proof.

Further up-river, the fancy shoreline properties of Övelgönne are all lined up with dikes. These dikes are not particularly high, about waist level, so they do not impede the views. Breaking the continuity of the dike are flood proof doors here and there. These are kept open for access to the beach and pedestrian path, but can be closed during high waters. These work, most of the time, because they are built on a lower, broader dike; the houses are already sitting much above river level. Otherwise, the site is quite similar to Crescent Beach in Surrey, Ambleside in West Vancouver, or Locarno in Vancouver.

Are these places in Metro Vancouver vulnerable to storm surges? Absolutely, they are. Sand bags are used during king tides in Vancouver; the Crescent Beach dike is undersized, and water seeps under it at high waters. The estimated bill to shore up the dikes is $9.4 billion (yes, with a b).

This will be a hard pill to swallow. Hamburg, along with many European cities, is still building its system, and it’s costly, but at least a lot of work has already been done. We have our work cut out for us; the longer we wait, the more expensive it’s going to be.

Detail of a flood gate at  Övelgönne

Detail of a flood gate at Övelgönne

Walking along the dike in Övelgönne.  A bit like Locarno or Crescent Beach.

Walking along the dike in Övelgönne. A bit like Locarno or Crescent Beach.

 

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Written by enviropaul

February 1, 2016 at 4:55 pm

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