Scenarios Research on Urban Inundation Management in Riverine Combined Sewer Districts

Owing to rapid population growth and climate change, urban inundation management is pushing urban drainage systems to have more variety and resilience. Urban inundation management measures should take various forms to deal with all types of situation and to improve resilience. Deep-tunnel and pipe network improvements are common measures in riverine combined sewer districts. Research on the effects of deep-tunnel and pipe network improvement is presented for a case study of a typical riverine combined sewer district with a hydrodynamic model that integrated Storm Water Management Model and Shallow Water Model. The results demonstrate that the numerical model can reproduce well the historical rainfall-induced inundations after calibration and validation. Three designed rainfalls with different return periods were set as inputs for the model. An analysis of the model results shows that inundation inducements can be divided into two categories, insufficient drainage capacity of the local pipe system and backwater effect of the downstream channel. Deep-tunnel construction can only mitigate the inundations caused by the backwater effect of downstream channel while pipes network improvement can mitigate the local inundations caused by insufficient sewer pipe capacity. Moreover, pipe network improvement can also increase the inundation risks of downstream areas, which emphasizes the importance of source controls of rainwater and capacity of downstream pump station. It also suggests that a combination of green and gray infrastructures into a "hybrid" control system is a more reliable approach to inundation management. The results can help deeply research the urban inundation management measures and provide insights to engineers and governments for urban design planning and maintenance.