Frequently Asked Questions - Advisories and Warnings
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Q.
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What causes flooding in Alberta?
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A.
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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.
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Q.
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What does the phrase "advisories and warnings" mean?
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A.
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The phrase "advisories and warnings" refers to the types of notices
that advise, watch for, or warn of future (hours to days) abnormally high water levels.
The following advisories and warnings issued by the
Flow Forecasting Team are ranked from lowest to highest in terms of risk to life and severity
of property damage:
The following advisories are issued by
River Engineering and Water Monitoring of Regional Services Northern Region when streams and
rivers are ice covered:
Advisories only are issued during ice conditions due to the
unpredictability of
water levels when streams and rivers are ice covered.
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Q.
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What does a Spring Runoff Advisory mean?
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A.
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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.
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Q.
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What does a High Streamflow Advisory mean?
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A.
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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.
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Q.
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What does a Flood Watch mean?
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A.
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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.
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Q.
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What does a Flood Warning mean?
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A.
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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.
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Q.
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What does an Ice Jam Advisory mean?
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A.
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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.
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Q.
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What is the significance of a River Breakup Advisory?
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A.
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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.
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