It is expected that precipitation will occur increasingly in extreme heavy showers, especially in summer. This causes more often water annoyance in urban areas (Fig. 7.3).

The capacity of the urban water system is mostly not prepared to discharge extreme amounts of rainwater. Beside that, space in the public space is limited. Cities on sandy soils do have the ability to infiltrate large amounts of water and solve the water-problems, but lower areas do not have these opportunities, due to the wetter and less impervious clay and peat soils. In these areas spatial solutions

Fig. 7.2 Living and economy in Groningen, based on relief (Source: Roggema et al., 2007)

need to be found to store rainwater. In more dense urban areas with a lack of public space it might be necessary to demolish small parts of the existing city. The concept that has been developed for Delfzijl (Klap, 2007), where parts of the existing city were kept free for natural processes of sea, water and nature (Fig. 7.4) is as inspiring as unusable. Cities in a shrinking situation may see this as an option, but in growing cities this kind of solution is hard to realise. There, the solution needs to be found in an increased flexibility in the urban water system (Fig. 7.5). The public space needs to have a dual function: in normal circumstances it functions as park or green space, but during extreme wet periods the same space is used as storage basin. However, this offers chances to design a dynamic city image and special buildings (Fig. 7.6).

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