When flooding strikes, water levels can change drastically in just hours or even minutes. Given this volatility, you might wonder: does the information we use to map flood hazards change constantly as well?
What are flood hazard studies?
Flood hazard studies are long-term planning tools. They synthesize a lot of different information to help us forecast how the landscape around water bodies may be impacted by flooding, and assist surrounding communities with appropriate development.
Hazard studies use water level data that has a 1% chance of occurring annually (that’s why you might have heard a lot recently about “one in 100 year flooding).
Hazard studies are location specific. They focus on a single river, but may also include data on smaller rivers within the area being studied.
Flood hazard studies and river forecasting – what’s the relationship?
Our river forecasters use current water level data from monitoring stations to forecast rising and falling river levels. In contrast, flood hazard studies incorporate data about both a river and the surrounding topography.
Flood hazard studies and river forecasting work together to help us determine flood risk. Whereas forecasting helps us anticipate potential water levels, flood hazard studies help us anticipate the effect a flood might have on flood hazard areas of the surrounding landscape.
Water levels change all the time, and river forecast information is updated continuously. But because topographical information tends to remain pretty constant, flood hazard studies are relevant for long periods of time – there’s typically no need to update them unless the river or the landscape surrounding it changes significantly.
Of course, such change is possible. One major reason for this is new development around water bodies. If a new bridge is built to cross a river, for example, this might have an impact on the area’s flood hazard map. In a case like this, ESRD would be alerted of the changing conditions, and part or all of the hazard study area would be reviewed as necessary.
We’ve been producing flood hazard studies in Alberta since the 1970s – but many of the studies we currently use were produced in the 1990s as part of the Canada-Alberta Flood Damage Reduction Program. To supplement these studies, ESRD continues to produce studies through our Flood Hazard Identification Program. All of our studies are searchable by community, stream, and basin.
What happens now?
After a major flood, the province collects extensive information about the extent of the flood in order to evaluate flood hazard studies that have been impacted. We want our evaluation to reflect the best possible understanding of what has happened – ground and aerial surveys, river flow information, and other data may all be used to enhance this understanding. This process helps us learn from what has happened – so that we can be as ready for the future as possible.