Changes

==Riverine Flooding==

==Riverine Flooding==

Urbanization increases impervious surfaces and the increased impervious surface will result in an increase in runoff, as a result the flows exceed the capacity of the receiving downstream section of river and this may cause flooding.

Riverine flooding occurs when rivers and streams exceed the capacity of their channels to convey flows, resulting in water overtopping the banks and flowing into adjacent areas.  In urban areas, this typically occurs where there has been an increase in upstream impervious cover that is not adequately mitigated by stormwater management practices.

''“Hydrological changes associated with urbanisation are increased storm runoff volumes and peak flows (Qp), faster flow velocities and shorter time of concentrations. A reduction in infiltration generally leads to less groundwater recharge and baseflow.The flashy response results in tremendous stresses for the urban stream and downstream receiving areas (Walsh et al., 2005)."''

''“Hydrological changes associated with urbanisation are increased storm runoff volumes and peak flows (Qp), faster flow velocities and shorter time of concentrations. A reduction in infiltration generally leads to less groundwater recharge and baseflow.The flashy response results in tremendous stresses for the urban stream and downstream receiving areas (Walsh et al., 2005)."''

[[File:2022-01-18-severe-weather-2021-21-billion-damage-image2.jpeg|thumb|700px|''“In today's world of extreme weather events, the new normal for yearly insured catastrophic losses in Canada has become $2 billion, most of it due to water-related damage. Compare this to the period between 1983 and 2008, when Canadian insurers averaged only $422 million a year in severe weather-related losses (IBC, 2022)"''<ref>Insurance Bureau of Canada (IBC). 2022. Severe Weather in 2021 Caused $2.1 Billion in Insured Damage." News & Insights. Accessed: https://www.ibc.ca/news-insights/news/severe-weather-in-2021-caused-2-1-billion-in-insured-damage</ref>.]]

 

 

Catastrophic losses from flooding have been steadily rising in Canada over the last two decades. The most common stormwater practices for mitigating riverine flooding are wet ponds and dry ponds, typically located at the end of the urban drainage system near streams.  LIDs are traditionally designed to manage more frequent and lower magnitude rain events. However, as mentioned above, larger storm chambers, trenches and even bioretention can be designed with large temporary storage volumes to provide flood control functions similar to wet or dry ponds.

In order to protect downstream properties from flood increases due to upstream development, CVC and TRCA have established flood control targets (2012 Stormwater Management Criteria Document) for future SWM planning through the process of updating of  Hydrologic Studies and Subwatershed-level Stormwater Management Studies that  characterize flood flow rates, define the location and extent of Flood Damage Centers and assess the potential impact of further urbanization.

In order to protect downstream properties from flood increases due to upstream development, CVC and TRCA have established flood control targets (2012 Stormwater Management Criteria Document) for future SWM planning through the process of updating of  Hydrologic Studies and Subwatershed-level Stormwater Management Studies that  characterize flood flow rates, define the location and extent of Flood Damage Centers and assess the potential impact of further urbanization.