The capacity of grey infrastructure in urban flood management: A comprehensive analysis of grey infrastructure and the green-grey approach

Urban inundation management should take various forms to deal with different flood situations, rapid popula-tion growth, and climate change. Research on the advantages and disadvantages of grey infrastructure, such as deep tunnels and pipe networks, is necessary to apply hybrid green-grey infrastructure scientifically and effi-ciently. A novel urban flood model was applied in a highly urbanized region to evaluate the grey infrastructure. Green-grey approaches were also compared. The results showed that deep tunnels decreased the peak flood volume and shortened the time of peak flow. Pipe network improvements decreased the peak flood volume but did not affect the time of peak flow. However, the deep tunnels could not mitigate local inundations caused by insufficient sewer pipe capacity, whereas pipe network improvements could not mitigate inundations caused by backwater flooding. Moreover, pipe network improvements tended to generate new downstream inundation hot-spots. Green-grey infrastructures performed better than grey infrastructures for urban flood reduction. A hybrid green-grey approach was recommended. Suitable combinations of green-grey infrastructures improve the sta-bility and effectiveness of urban flood management.