Cost-benefit analysis of improving flood protection in Tübingen-Lustnau

The task of this study was to examine the extent to which the construction of a flood retention basin in the Goldersbach valley in Tübingen makes economic sense. Against this background, the cost-benefit effects of several project alternatives and the following zero variant were examined:

• Zero variant: No implementation of flood protection measures.
• Project variant 1: Construction of a flood protection advance warning system to extend the advance warning time.
• Project variant 2: Construction of a flood protection advance warning system and construction of a flood retention basin.
• Project variant 3: In contrast to project variant 2, supplementary implementation of private property protection measures.

For the underlying project duration, the occurrence of flood events of varying frequency and intensity was assumed, the damage impact of which can be reduced by the existence of project-induced advance warning times or the availability of a flood retention basin. However, the corresponding “reduced damage costs” must be compared with the associated project costs (construction and operating costs of the flood protection facilities).

First of all, the damage costs were estimated for the zero variant, using cost estimates from previous flood events that occurred under the “without flood protection” regime. The damage costs of the zero variant then served as reference damage costs for the various project variants. This resulted in the “avoided damage costs” due to flood protection as the gross benefit from the individual project alternatives. These were then compared with the project costs incurred for the individual project alternatives and the corresponding net benefits were determined. From this, it was then possible to derive statements about the economic benefits of the individual project alternatives. As part of a sensitivity analysis, the underlying assumptions were also varied and their impact on the cost-benefit levels determined.