In case of flood, Hamburg has created its modern “Harbor City” on dwelling mounds
Flooding is one of the effects of climate change we can notice in different European cities already. For example, Stockholm is coping with this major problem as Sweden consists of many rivers and is surrounded by the ocean. In Germany, Hamburg is an example where city planners built the so called “Hafen City” (Harbor City) on dwelling mounds, 8 meters above the water level.
Adaptations to the flooding risks are necessary in many European cities, basically everywhere people live, work, and trade close to the water. As the water level will increase in the following years, ongoing urbanization requires rebuilding methods now.
Flood defence has different solutions, depending on individual cases. In some parts there can be made dunes, soil structures like dikes or dams, in others specific water retaining structures like cofferdams, gravity walls, sheet pile walls, etc. or engineering works like luices, locks, cut-offs, storm surge barriers, pumping stations, and so on.
HAMBURG’S BILLION-PROJECT “ELPHI” IS "ON THE WATER"
Hamburg’s Harbor City with its recently opened Elbphilharmonie (called “Elphi”) is an extension of the old “Speicherstadt”, the warehouse district, where in former times coffee and spices where traded. Now, in the Harbor City there are companies, modern gastronomy and a waterside promenade. The water-arms that flow through it make the charm of the district. The different “quarters” are set up some meters above the sea level; underground carpark are built under flood protection. Because Hamburg has learned from its history.
In 1962 a huge storm tide from the North Sea surprised the city, destroyed 60,000 houses and killed about 315 people. The water reached a 5,7m above NN, the highest level ever registered. After this catastrophe additional flood protection measures and emergency plans have been carried out: Dikes were shortened and strengthened, leaving river arms and bays detached from the sea. The design water retaining height was raised up to 6,7m, so a following storm in 1976 could not damage the dikes heavily. Still, the harbor area was vulnerable. In 2000 a flood protection construction program was started and the “Harbor City” was developed, where the existing dikes offered the new district no protection.
The solution was elevating the buildings on plinths made of mounds, connecting the Harbor City with bridges and streets to the old town, also above the flood-line, at least 7,5m above NN. All buildings stand on artificial bases, 8m above sea level. The perimeter is on the sides exposed to wind, such as the southern sides of Strandkai and Überseequartier. The interior of flood-secure plinths provides huge space for underground car parks, so that almost all stationary traffic can be accommodated. The Harbor City can continue to function virtually without restriction even during a flood and despite its “island” situation.
SAFE FOR THE MOST EXTREME FLOODING
In cases of high water, underground parking garage entrances close their flood gates, windows are able to withstand high water pressures and steel bulkheads prevent eventual damage on the glass windows by floating debris. Living is not allowed on the ground floors, they are only used for restaurants and offices. The apartment blocks have different access levels in order to cope with varying water levels around the blocks. There are also escape routes on different heights to guarantee a safe evacuation if needed. That means, that in case of storm tide or flooding, citizens are safe up to 7,5m. Over that edge Hamburg's citizens get warned by firecrackers. Authorities assume a very low probability for that case.