Impacts of climate change on urban drainage systems – a case study in Fredrikstad, Norway

Abstract

Norway has frequently encountered flood damage in urban areas during recent years. In this paper the authors, taking Veumdalen catchment in Fredrikstad as an example, simulated the possible consequences in the sewer system, in the present, predicted and artificial climate scenarios. Indicators that describe (1) surface flooding, (2) surcharging sewers, (3) basement flooding and (4) combined sewer overflow (CSO) are defined to represent the adverse effects of climate change. It is concluded from the annual-based simulation that the total volume of water spilling from the flooding manholes will increase 2–4-times the increase in precipitation, and the total CSO will increase 1.5–3-times as much as the increase in precipitation. The simulation results also show that the number of flooding manholes and number of surcharging sewers may change dramatically and irregularly with a slight change of precipitation, and vary with events and durations.

Keywords:

• climate change
• combined sewer overflow (CSO)
• flooding
• surcharging sewers
• urban drainage systems

Acknowledgements

The Research Council of Norway and the Department of Mathematical and Technology, University of Life Science, have co-financed the research project: The impact of climate change on flood damage in cities and the increase of pollution discharged from sewerage systems, and optimal measures to reduce the adverse impact. We thank Karin Anja Arnesen at the water and wastewater section in Fredrikstad municipality for providing the relevant information for the case study.

Notes

1. Norwegian guideline for stormwater management (Lindholm et al. 2005, Fredrikstad 2007a) requires that private house owners have responsibility to build their basement floors 0.9 m above the top of the municipal drainage in order to avoid frequent basement flooding. We therefore use 0.9 m as a critical level to assess the risk of basement flooding.