Particularly in the winter half-year, stormy weather may cause water levels to quickly rise over the banks of the river Elbe and the canals, which could completely wreck a car. Therefore, in the event of a flood warning (see the official descriptions listed below), promptly bring yourself and your car to “the safe side” behind the dike line. Should the bulkheads of the bridges at the Speicherstadt historical warehouse district have already been closed, drive to the higher parts of the HafenCity, where your car will also be safe. The values listed below have been added for clarity: The average plinth height in the Speicherstadt is almost 7 metres above standard elevation zero, while the street is between 4.50 and 5.50 metres.
Before a flash flood, the city’s population is warned through the firing of blanks, radio announcements and eventually also siren alarms and local loudspeaker announcements. Flood warnings are issued when the water level exceeds the standard elevation zero (Normalnull or NN) or the Mean High Water (MHW). The height of the flood and the expected time of occurrence are calculated and issued by WADI and the BSH, Hamburg’s flood protection service.
Approximately eight hours before the expected rise in water level, blank rounds are fired from the firing bases at Ernst-August-Schleuse, Teufelsbrück, Maakenwerder Höft, Hafentor and Stadtdeich. The warning consists of two consecutive blanks fired rapidly. This warning means that the expected rise in water level will exceed 4.50 m above standard zero (NN), which is more than 1.50 m above Mean High Water (MHW). Flash flood warnings for the City and Port of Hamburg are issued when the water level is expected to rise 4.50 m above NN (the normal water level at high tide is approximately 2.00 m above NN).
Most radio broadcasters (for example NDR, RSH) regularly announce water level forecasts. Transmission times vary for each broadcaster. Should the city be threatened by a flash flood with a water level of at least 5.00 m above NN, all radio broadcasters will start transmitting the warnings of the Hamburg Department of the Interior in regular intervals approximately nine hours before the flood. In extreme cases, warnings may also contain orders to evacuate areas under particular danger.
Additionally, sirens will be used in serious cases in the areas threatened by flooding (one minute wailing sound). This means that citizens should turn on radio devices and pay attention to the announcements.
Should water threaten to overflow or break dikes, the district offices will also deploy loudspeaker vans to the endangered areas and may eventually issue orders for evacuation. Information on this is provided by the Hamburg Port Authority (HPA), Neuer Wandrahm 2–6, 20457 Hamburg, telephone +49-40-42847-2887. In cooperation with the local district offices in Hamburg-Mitte, Altona, Bergedorf and Harburg, the Department of the Interior has published a free leaflet for the population living on the flood plains of the river Elbe. These are issued to over 109,000 households every year and inform residents on proper behaviour in the event of flooding. Additionally, the Department of the Interior/Civil Protection has made the latest leaflet available for download as a PDF document.