There are three causes of flooding in Alberta.
Snowmelt for plains and mountains: Snow on the plains usually melts and runs off during the March to April period. Excessive, rapid melting may flood smaller streams and rivers having their headwaters in the plains areas. Mountain snowmelt usually occurs during the May to July period. While mountain snowmelt may result in localized flooding, snowmelt by itself is generally not sufficient to cause flooding in major mountain fed streams unless accompanied by rainfall.
Rainfall: Rainfall affects big and small watercourses in Alberta. Flooding along major mountain-fed rivers (such as the Oldman and Bow Rivers) is caused by heavy rainfall, or heavy rainfall during mountain snowmelt.
Ice Jams: Ice Jams can occur anytime during the winter, although freeze-up or break-up are the most usual times. They can be initiated when the ice cover breaks up into floes and moves downstream. A jam occurs when the ice floes accumulate at a location and partially or completely block the channel. The ice blockage restricts the flow in the river, causing water levels to increase. In some cases the water levels can increase enough to cause flooding along the jam. Ice jams tend to form repeatedly at certain locations.
Alberta Environment monitors weather patterns, precipitation and provincial water levels and flows. The Environmental Monitoring and Evaluation Branch provides a comprehensive series of public advisories about potential flooding. These include river stage-up advisories, ice-jam warnings, high stream flow advisories, flood watches and flood warnings. These warnings are posted on the Alberta Environment website.
Spring Runoff Advisory
A Spring Runoff Advisory means that stream levels are rising or expected to rise due to snowmelt and no major flooding is expected. Minor flooding in low-lying areas is possible. Anyone situated close to the streams affected (property owners and the general public) is advised to be cautious of rising levels.
High Streamflow Advisory
A High Streamflow Advisory means that stream levels are rising or expected to rise rapidly and no major flooding is expected. Minor flooding in low-lying areas is possible. Anyone situated close to the streams affected (campers, fishermen, boaters and the general public) is advised to be cautious of the rising levels.
A Flood Watch means that stream levels are rising and will approach or may exceed bankfull. Flooding of areas adjacent to these streams may occur. Anyone situated close to the streams is advised to take appropriate precautionary measures.
A Flood Warning means that rising river levels will result in flooding of areas adjacent to the streams affected. Anyone situated close to the river should take appropriate measures to avoid flood damage.
River Breakup Advisory
A River Breakup Advisory is usually issued with the onset of warmer Spring temperatures and implies that ice breakup may result in the formation of ice jams. The location and occurrence of ice jams, and possible associated flooding, are very unpredictable. Local authorities and residents are advised to monitor the ice covers and water levels in the rivers in their communities particularly in areas where spring ice jams have been a problem in the past.
Ice Jam Advisory
An Ice Jam Advisory means that ice jams have been reported in a river or stream. The potential exists for sudden increases in river levels both upstream and downstream of the ice jam. Changes in water levels can occur upstream of the jam as water collects behind the jam. If the jam releases suddenly, a surge of water could be sent downstream. Local authorities and residents are advised to monitor the ice covers and water levels in the rivers in their communities particularly in areas where ice jams have been a problem in the past.
Protecting Your Home
If a flood watch/warning is issued, take the following steps to reduce your risk of damage or loss:
• Know where to obtain sandbags, plywood, plastic sheeting and lumber to protect your house.
• Remove any household effects you can. If this is not possible, move possessions from the basement to an upper floor.
• Seal hazardous materials such as weed killers and insecticides in plastic garbage bags and move them into safe storage or dispose of them safely.
• At the first warning of flooding, and if it is safe to do so, turn off electrical power and leave it off.