Consequences of a flood in Kristianstad, Sweden : a GIS-based analysis of impacts on important societal functions

Sammanfattning: According to a recent report from the Swedish Civil Contingencies Agency, the city of Kristianstad is considered as one of the most vulnerable in Sweden regarding consequences of a flood. Being protected by a barrier system, a failure would most likely have serious impact on the city. As parts of the city are situated below sea level, a heavy rainfall may cause considerable consequences since there is no natural outlet and all water has to be pumped out. To quantify the consequences, the master thesis “Consequences of a flood in Kristianstad, Sweden”, focuses on important societal functions and the impacts to individual objects at different water levels. A disastrous consequence has been defined for 125 important societal objects in the city, which relates to a water level where the activities at the object must stop due to security, accessibility or other reasons. Consequences of a water level at elevations from -2.4 m up to +4.0 m with 0.1 m steps have been investigated and related to characteristic discharge in the river Helge å, as well as to characteristic sea water levels in the Baltic Sea. The objects chosen are all situated within the +4.0 m flood area and are identified by using the priority classes 0-4 of the Styrel project, a plan that regulates disconnection of electrical power in case of transient power shortage. Two key figures are used to quantify the impacts on the city; the number of affected objects related to number of total objects, and affected objects providing service to a main part of the population related to total number of objects of this category. Four scenarios have been studied that would reflect a 100-year event; three with high discharge in the river Helge å and a barrier failure, a fourth scenario with a heavy rainfall. A consequence of a west barrier failure is that 16% of the objects with important societal function would have to close. This includes 27% of the objects providing service to a main part of the population. The figures for a Hammarslund barrier failure is 59% and 45% respectively, and for a simultaneous failure of the two barriers 70% and 58% respectively. A 100-year precipitation would affect 32% of the objects, including 12% of the objects providing service to a main part of the population. The most vulnerable object category at a 100-year event is retirement homes, while freshwater boreholes belong to the least vulnerable. In case of a 100-year precipitation, the hospital administration is found to be in special need of protection.