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During the Red River flood in the spring of 1997, many communities
lying along the waterway were both surprised and outraged by
the destruction of the bulging river. Despite major flood-control
measures taken in the past, overflowing water managed to cover
202,500 hectares, or about five percent of Manitoba's farmland.
And as a result, about 28,000 Manitobans were evacuated and overall
damages were pegged at more than $150 million. Despite the seemingly
unexpected nature of the disaster, the geologic record shows
clearly that floods have been occurring as long as rain has been
falling, and so geologists tend to view floods as normal and
expected events.
Two of the most common landforms resulting from these normal
and expected events are natural levees and floodplains. During
a flood, as sediment-laden water flows out of the completely
submerged channel, the depth, velocity and turbulence of the
water decrease abruptly at the channel margins, where the coarsest
part of the suspended load is deposited to form a natural levee.
Farther away, finer silt
and clay settle out across the stream's floodplain, a relatively
flat region of valley floor that is periodically inundated by
floodwater.
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| Pale blue shows the Red River's
floodplain and marks the 2,000 square kilometres of the river
valley that was underwater during the 1997 flood. The thin blue
line is the seemingly minute riverbed itself. (Modified from
original map by Steven Fick/Canadian Geographic, July/August
'97) |
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