In the last 30 years London has had five severe flooding occurrences (March 1977, September 1986, July 2000, April and December 2008). Climate modelling based on more up-to-date rainfall events and patterns suggests that the City of London can expect to experience more frequent and severe precipitation events in the future which may seriously impact various public infrastructures.
Current infrastructure was designed and constructed on the basis of standards and codes that were developed decades ago. These standards and codes were based on historic climate and design storms which are no longer representative of the current rainfall patterns. With the changes in these rainfall events and climate patterns, some infrastructure may no longer have the capacity to handle the new rainfall events.
The main objectives of Water Resources Management include ensuring the safety of people and property, maintaining functionality of open watercourses, streams and rivers and contribute towards the health and protection of the City's eco/environmental systems. London's municipal infrastructure, which is in place today and planned for the foreseeable future, reflect these objectives with respect to managing urban stormwater runoff.
Design criteria and stormwater pipe and overland flow channel sizing generally include approved design standards for rain storms of a specified return period. Pipes are generally designed to convey the minor runoff (5 year rainfall) and overland routes are designed to provide conveyance for the major runoff that cannot be accommodated in the pipe system.
Generally, increased runoff volumes and flows resulting from changes in land use are managed by:
- The implementation of quality, erosion, and quantity/flood control Stormwater Management (SWM) Facilities within or at the downstream end of the storm sewer networks; and
- Explicit consideration of a major system to convey flows which exceed the capacity of the minor system (pipes and facilities). Specified return periods were typically 2 to 10 years for the minor system and 2 to 5 years for the major system.
In February 2007, the Department of Civil and Environmental Engineering of UWO completed a study related to the Assessment of Risk and Vulnerability to Changing Climatic Conditions within the Thames River Watershed (Study #1). This study was prepared by Dr. Slobodan Simonovic and Predrag Prodanovic. The conclusions of this study identified that:
"Climate change is expected to intensify flooding in the basin, thus bringing flows in higher magnitude with more frequent occurrence. Such conditions may demand additional investments in flood management infrastructure and may require complete revision of budgets for flood management and yearly maintenance. It may even require retrofitting and replacing current (or even building additional) flood management infrastructure. Engineering design standards in light of changed climatic conditions may also need revision.”