Urban drainage systems

March 2020: Current urban drainage systems are at risk of system failure due to climate change induced rising frequencies of extreme weather. Experts recommend augmenting current capacities using hydraulic distribution systems (e.g. relief tunnels, storage units) and combining them with green infrastructures.

Information

Extreme weather can place pressures on urban drainage systems and cause wide-scale flooding. A new study simulates ‘stress tests’ on urban drainage systems in light of changing rainfall patterns and speed of snow melts due to climate change. The study finds low resilience amongst current systems and frequently predicts overloading and structural failure. Such failure risks can lead to breaks in the system or acute blockages that lead to flooding. This becomes increasingly concerning as frequencies of climate change induced extreme weather increase. The authors warn that frequent flooding due to systems failure could negatively impact water quality of surrounding lakes, rivers, and streams, and lead to biodiversity loss in aquatic habitats. It further increases risks to public health due to potential spread of disease in flood water.

Implications and opportunities

The study finds that not many urban drainage systems are built for the changing conditions of climate change and associated extreme weather conditions. To improve the resilience of current systems, it is recommended that systems improvement is combined with green infrastructure designs. Systems improvement could include investment decisions of malfunction costs and costs of flooding in comparison to investment costs into resilient systems. In addition, municipalities could bypass lines and apply appropriate combinations of relief tunnels, storage units or other distributed hydraulic structures to augment drainage system capacities in a resilient manner. Further, the introduction of green infrastructure such as rain barrels, green roofs, rain gardens, or on-site water treatments could alleviate pressures on drainage systems.

Limitations

Urban drainage systems are location specific and follow local government guidance. As such, all recommendations require careful adaptation to local geographic and policy contexts prior to their application.

Sources

Ando, A. W., et.al. (2019). Willingness-to-volunteer and stability of preferences between cities: Estimating the benefits of stormwater management. Journal of Environmental Economics and Management, 102274. doi:10.1016/j.jeem.2019.102274

Mohammadiun, S., et.al. (2019). Effects of bottleneck blockage on the resilience of an urban stormwater drainage system. Hydrological Sciences Journal. doi:10.1080/02626667.2019.1690657