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==Pluvial (Surface) flooding==  

==Pluvial (Surface) flooding==  

Pluvial flooding occurs when larger storms exceed the capacity of the urban drainage system to convey water, resulting in flooding of some low-lying areas. This may result in traffic interruption, economic loss, infrastructure damage, basement flooding and other undesirable consequences. As the climate changes, the incidence of extreme weather events in Ontario is expected to increase, causing  urban drainage system capacity to be exceeded more frequently. This will be particularly severe in older areas where the minor system was not designed to today’s standards and/or major system pathways have been altered or do not exist.

Pluvial flooding occurs when larger storms exceed the capacity of the urban drainage system to convey water, resulting in flooding of some low-lying areas. This may result in traffic interruption, economic loss, infrastructure damage, basement flooding and other undesirable consequences. As the climate changes, the incidence of extreme weather events in Ontario is expected to increase, causing  urban drainage system capacity to be exceeded more frequently. This will be particularly severe in older areas where the minor system was not designed to today’s standards and/or major drainage system pathways have been altered or do not exist.

LIDs are well suited to address localized flooding because they can be shoehorned into smaller areas that may have increased flood risk.  Runoff reduction and temporary detention are the primary means by which LIDs can reduce flooding at the scale of urban drainage systems.  Kim & Han (2008)<ref>Kim, Y., & Han, M. (2008). Rainwater storage tank as a remedy for a local urban flood control. Water Science and Technology: Water Supply, 8(1), 31-36.</ref> and Han & Mun (2011)<ref>Han, M. Y., & Mun, J. S. (2011). Operational data of the Star City rainwater harvesting system and its role as a climate change adaptation and a social influence. Water Science and Technology, 63(12), 2796-2801.</ref> conducted studies in Seoul, South Korea, to assess the extent to which the installation of  rainwater harvesting cisterns could help mitigate existing urban flooding problems without expanding the capacity of the existing urban drainage system.  System operational data showed that 29 mm of rainwater storage per square meter of impervious area (3000 m³ cistern in this instance) provided sufficient storage for a one in 50 year period storm without the need to upgrade downstream sewers designed to 10 year storm capacity.  Stormwater chambers, infiltration chambers, bioretention and other LID systems designed with large volumes of temporary storage could have similar benefits, while also reducing runoff volumes and providing other co-benefits (see section below on ‘designing for flood resilience’).

LIDs are well suited to address localized flooding because they can be shoehorned into smaller areas that may have increased flood risk.  Runoff reduction and temporary detention are the primary means by which LIDs can reduce flooding at the scale of urban drainage systems.  Kim & Han (2008)<ref>Kim, Y., & Han, M. (2008). Rainwater storage tank as a remedy for a local urban flood control. Water Science and Technology: Water Supply, 8(1), 31-36.</ref> and Han & Mun (2011)<ref>Han, M. Y., & Mun, J. S. (2011). Operational data of the Star City rainwater harvesting system and its role as a climate change adaptation and a social influence. Water Science and Technology, 63(12), 2796-2801.</ref> conducted studies in Seoul, South Korea, to assess the extent to which the installation of  rainwater harvesting cisterns could help mitigate existing urban flooding problems without expanding the capacity of the existing urban drainage system.  System operational data showed that 29 mm of rainwater storage per square meter of impervious area (3000 m³ cistern in this instance) provided sufficient storage for a one in 50 year period storm without the need to upgrade downstream sewers designed to 10 year storm capacity.  Stormwater chambers, infiltration chambers, bioretention and other LID systems designed with large volumes of temporary storage could have similar benefits, while also reducing runoff volumes and providing other co-benefits (see section below on ‘designing for flood resilience’).

==Riverine Flooding==

==Riverine Flooding==