Abstract
Pluvial flooding already challenges the capacity of drainage and sewerage system in urban areas in Scandinavia. For system owners this requires a stricter prioritization when improving the systems. Experts seem to agree that a regime shift from improving old combined sewers by piped solutions to more sustainable drainage systems (SuDS), must take place. In this paper results from an investigation amongst the largest cities in Norway, Denmark and Sweden concerning drivers and preferred methods for improving the old system are presented. The results indicate that Norway ranks flood prevention lower than the other Scandinavian countries. During the last decades, Norwegian authorities have had a strong focus on pollution from wastewater treatment plants (WWTP). The attention to drainage and sewerage system regarding flooding, water leaks, infiltration or pollution has been neglected. Renewal or rate of investment in relation to existing drainage and sewerage system is easy to register, and provides a measure of the activity. In order to optimize flood prevention, and may be promoting the use of SuDS, the cities should be required to measure the efficiency, either by monitoring or modeling the impact of stormwater to the system. Lack of such requirements from Norwegian authorities seem to be a plausible explanation to why Norwegian cities are less focused on flood prevention compared to Swedish and Danish cities.
Highlights
In a period with changing climate, impacts on both precipitation patterns and urban drainage will occur [1]
Sustainable Urban Drainage Systems (SuDS) like ponds, open ditches, green roofs, etc. are in many countries made for stormwater treatment
This study primarily investigates how cities were dealing with flood prevention
Summary
In a period with changing climate, impacts on both precipitation patterns and urban drainage will occur [1]. Increasing total rainfall and rainfall intensity will result in a greater load on the drainage and sewerage systems. These important infrastructure systems were designed and built years ago, and increased precipitation was not part of the design criteria. In urban areas in Scandinavia the authorities only to a small extent have required stormwater treatment, and. Extreme rainfall events in Norway are expected to increase slightly up to 2025, and sharply towards 2050 [23]. A comparison of extreme rainfall events with 24 hour durations from the past 100 years [26], show only small variations between the Scandinavian countries regardless of the return period and season. Only small differences are found when comparing specific measurements from the capitals of each country
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