Möglichkeiten und Grenzen einer Mitbenutzung von Verkehrsflächen zum Überflutungsschutz bei Starkregenereignissen

摘要

The wasterwater collection system in Germany has recently had consistent problems in handling stormwater events. Taking the impacts of climate change into account increased rainstorm events are expected in the near future. These rainfalls will become more severe, especially those of short duration. Meanwhile the percentage of hardened and built up area in cities is currently still growing. It is therefore very likely that cities will face an increase of sewer overflow and flooding of streets which can cause severe damages. Rainwater is traditionally being drained through an extensive underground sewer system. These systems are usually designed for defined return periods of precipitation according to the type of urban area they are situated in. With climate change these periods are changing and the stormwater runoff is increasing. Therefore suitable solutions have to be developed in order to reduce the risks of flooding. As the provision of additional retention volume within the system is both inefficient and too expensive new innovative approaches in stormwater management become necessary. A currently much discussed approach to prevent or at least to reduce flooding problems in cities is the creation of multifunctional areas. In this concept, urban spaces like streets, parking lots, green areas, sport fields or playgrounds are temporarily used to collect and to retain rainwater peaks. Most of the year the public spaces are dry and during that time they fulfill their regular and primary function. In the rare case of a stormwater event they are temporarily used for storing or transporting rainwater in order to prevent damages. The intention of this approach is not only to create a sustainable stormwater management strategy for the city but at the same to improve the quality of the urban living environment and of public spaces. The development of a single urban area as a public space and for water collection at the same time can generate synergies and result in financial benefits. The doctoral thesis focuses on the potentials and on the limits of a multifunctional use of urban streets and squares for stormwater-management. Amongst traffic planners there are still some concerns whether a multifunctional design of streets is compatible with the traffic-related requirements that they need to meet, such as e.g. safety and accessibility. The thesis examines to what extent these concerns are justified and shows how they can be dealt with. By developing guidelines for an integrated planning approach and by drafting transferable principles for a water sensitive road design it gives practical advice of how to successfully implement the multifunctional use of roads. Beyond that possible ways of financing multifunctional urban design are being illustrated and evaluated. The ideas of a watersensitive street design were applied to a selected street in the city of Hamburg. The implementation of the concept to a case study proves that a multifunctional approach in road design can give a substantial contribution to urban stormwater management. On the other hand it also makes clear that the use of streets and squares for the retention and transportation of runoff peaks is not capable of solving the flooding problem on its own but that it has to go hand in hand with other measures of rainwater management.