Flood protection for future storm surges

In the night of Feb­ru­ary 17, 1962, a severe storm surge was announced for the North Sea coast. How­ev­er, there was no talk of any dan­ger to Ham­burg. So the cit­i­zens of the Hanseat­ic city were com­plete­ly unpre­pared when the Elbe washed the mass­es of water into the city. Many dikes broke and the south of Ham­burg sank in the flood. That night, 315 peo­ple died, thou­sands were left home­less or even lost every­thing they owned.

Employ­ees of the Ham­burg Uni­ver­si­ty of Tech­nol­o­gy were also direct­ly affect­ed: “My father was train­ing with the Ger­man Armed Forces in Ham­burg in Feb­ru­ary 1962. He and his com­rades were deployed to fish the numer­ous dead out of the water with a boat. He report­ed that they fas­tened the dead along­side their boats and brought them ashore. Rel­a­tives who saw their fam­i­ly mem­bers tied up like this col­lapsed by the dozen.”

Modern dike construction followed

Hur­ri­cane Vincinette swept across the coun­try that night, bring­ing dis­as­ter with unprece­dent­ed storm surge lev­els. In more than 60 places, the dikes could not with­stand the mass­es of water. Although the breach­es were sub­se­quent­ly closed again, one thing was clear: the city of Ham­burg need­ed a com­plete­ly new flood pro­tec­tion con­cept. It quick­ly became clear that it was not pos­si­ble to repair and raise the dikes. As a result, around 100 kilo­me­ters of com­plete­ly new pro­tec­tive struc­tures were built with a height of at least 7.20 meters above sea level.

Equipped for the future?

Pro­fes­sor Peter Fröh­le at the Tech­ni­cal Uni­ver­si­ty of Ham­burg is study­ing the con­se­quences of glob­al warm­ing and its influ­ence on the Elbe from a hydraulic engi­neer­ing per­spec­tive. The head of the Insti­tute of Hydraulic Engi­neer­ing answers ques­tions about how well equipped Ham­burg will be in terms of flood pro­tec­tion in the future:

Will we have to expect more frequent storm surges in Hamburg in the future?

Yes. As a result of cli­mate change and the asso­ci­at­ed rise in sea lev­el, storm surges will be even high­er in the future, giv­en the same storm inten­si­ty. Water lev­els that used to occur once every hun­dred years will then also come upon us much more fre­quent­ly, for exam­ple every five years. In addi­tion, storms may become even more intense as a result of cli­mate change, which would then fur­ther increase the frequency.

What impact would a storm surge have on Hamburg today?

The flood pro­tec­tion sys­tems are very safe in Ham­burg and also along the entire North Sea coast, which was most recent­ly evi­dent in Decem­ber 2013. Dur­ing storm Xaver, water lev­els occurred in Ham­burg that were almost half a meter high­er than in 1962. In Ham­burg and on the North Sea coast, the flood pro­tec­tion sys­tem func­tioned prac­ti­cal­ly smooth­ly, so no seri­ous dam­age occurred. In the mean­time, flood pro­tec­tion has become even bet­ter. Unfor­tu­nate­ly, how­ev­er, there is still no one hun­dred per­cent pro­tec­tion against nat­ur­al disasters.

How high can the water rise before it’s “land under” again, and how can better forecasting methods help?

In the cur­rent con­struc­tion pro­gram of the Free and Hanseat­ic City of Ham­burg, it is planned to expand dikes and flood pro­tec­tion facil­i­ties to a height of at least 8.30 meters above sea lev­el. If a water lev­el does sig­nif­i­cant­ly exceed the eight-meter mark, fore­cast­ing meth­ods are the basis for warn­ing the pop­u­la­tion. A good fore­cast is also impor­tant for the author­i­ties’ oper­a­tional plan­ning, so that they can then close mobile flood pro­tec­tion facil­i­ties, such as storm surge gates and bar­rages, and pre­pare and coor­di­nate dike defense. The more pre­cise and ear­li­er the fore­casts arrive, the sim­pler and eas­i­er it is to pre­pare for a storm surge. In Ham­burg, the Storm Surge Warn­ing Ser­vice is respon­si­ble for this.

What measures besides higher dikes has flood protection developed in the past, and what specifically are you researching?

In addi­tion to dikes and flood pro­tec­tion walls, there are a vari­ety of con­cepts to pro­tect against flood­ing. These range from adapt­ed con­struc­tion meth­ods and the cre­ation of space for the water to dams or bar­rages designed to pre­vent the inflow of a flood wave. At the TU Ham­burg, we are look­ing into the future of flood pro­tec­tion on the Tidal Elbe against the back­ground of cli­mate change. To this end, we iden­ti­fy and ana­lyze con­ceiv­able options for future flood pro­tec­tion and eval­u­ate them from a hydraulic engi­neer­ing, water man­age­ment, eco­log­i­cal and eco­nom­ic per­spec­tive. In addi­tion to changes in tidal con­di­tions, cur­rents and water lev­els, we must also con­sid­er con­se­quences for flo­ra and fau­na as well as for nav­i­ga­tion and oth­er uses. Our results will then be used to derive options for action in the future.